CISE Seminars

Nanostructures are often distinguished by their large surface-to-volume ratios that, upon integration into devices, can lead to a high density of nanoscale interfaces. The impact of these interfaces on device function is, in many cases, not yet well understood. In this talk, I will describe recent theoretical efforts, using first-principles density functional theory and many-body perturbation theory, towards fundamental understanding of interfacial electronic structure –and its relationship to measured transport and spectroscopy –at nanoscale metal-organic and organic-organic interfaces.
Examples to be discussed are the conductance of amine- and pyridine-linked molecular junctions; chemical contributions to surface-enhanced Raman scattering for benzene thiol on gold; and preliminary work on charge separation and optical absorption processes for covalently-joined donor-acceptor organic systems.

This talk discusses the use of inelastic x-ray scattering to probe the momentum and energy dependence of the excitation spectrum of high temperature superconductors. The technique is introduced and two examples are discussed; measurements of two magnon scattering in the La2-xSrxCuO4 high-Tc cuprate and measurements of phonons in an iron-pnictide, SmFeAsO1-xFx. In this latter example, we find anomalous behavior in certain phonons as a function of doping and speculate that

this is a signature of unusual electron-phonon coupling in these materials. I conclude with a brief discussion of the future with the construction of a new synchrotron, NSLS-II at Brookhaven.

I will present results obtained at NRL on the formation and use of wafer-scale films of graphene for sensor, microelectromechanical and radio-frequency device applications. We have investigated graphene formed by thermal decomposition of SiC, transferred films of CVD-grown graphene and spin-on films of chemically modified graphene. Our initial device results are encouraging and indicate that graphene has a promising future for both electronics and sensor applications.

Electron tunneling is a powerful quantitative probe of the excitation spectrum of superconductors.  The scanning tunneling microscope (STM) is a convenient tool for measuring the tunneling spectrum at different spots on a superconducting sample, thus probing the spatial variations of the excitation spectrum. Such measurements have been used on the high-temperature superconducting cuprates, giving us an atomic scale view of the excitation spectrum. I will describe STM experiments performed as a function of temperature on samples of the cuprate BSCCO, with the aim of understanding how superconductivity develops in the material as it is cooled down from the “normal” state. By directly measuring the spectrum at different locations in space and at different temperatures, we come to the conclusion that superconductivity develops in a spatially inhomogeneous fashion in this compound. A detailed study of the shape of the spectrum as a function of doping and temperature gives us insight into the nature of the energy gap seen in the spectrum.

Innovation and commercialization of technology are essential to the U.S. economy and becoming increasingly the domain of start-up companies rather than large corporations. Dr. Smoliar will discuss trends and opportunities for entrepreneurs in the context of her own experience commercializing fiber lasers at Mobius Photonics, a company she founded in 2005 in Silicon Valley.

Organic semiconductors promise to deliver new versatile electronic devices, with various functionalities, by combining diversity, flexibility, and light weight with the ease of processing and low cost. Small molecule organic semiconductors, such as pentacene and rubrene, are particularly attractive because they exhibit high electronic mobility. But they have poor solubility, which is a serious limitation for their use in cost-effective applications. Different routes are proposed in chemically-tailoring the molecular structure to increase solubility and achieve ease of processing, while maintaining or improving the device performance.

We report on growth, structure and properties of a variety of soluble organic semiconductors in the class of functionalized pentacenes and anthradithiophenes. We demonstrate that the performance of organic thin film transistors (OTFTs) is dominated by the complex microstructure of the organic film (crystal orientation, grain-boundaries, amorphous domains), which in turn is dictated by the chemical structure and processing. 2,8-difluoro-5,11-bis(triethylsilylethynyl) anthradithiophene (diF-TESADT) [1] is particularly attractive. Thin film transistors of this material are interesting given the unique film forming properties. We present a simple method to induce enhanced grain growth and improved device performance in solution-processed TFTs by room-temperature chemical modification of the source-drain contacts [2]. The film microstructure obtained by manipulation of chemical interactions and surface energies, at the nanoscale level, offers good test-structures for studies of the effect of the grain size and grain distribution on the charge transport. In parallel with films, we investigate single crystals that can serve as model systems allowing the study of intrinsic properties [3]. For this material, the mobility of the organic TFTs reaches values 0.5 cm2/Vs, and can be as high as 6 cm2/Vs in single crystal devices. Furthermore, we present evidence that the 1/f flicker noise is sensitive to structural changes in the transistor channel, and can be a diagnostic tool for the quality of the devices.
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References:
1. Subramanian, S.; Park, S. K.; Parkin, S. R.; Podzorov, V.; Jackson, T. N.; Anthony, J. E. J. Am. Chem. Soc. 2008, 130, 2706.
2. Gundlach, D. J.; Royer, J. E.; Park, S. K.; Subramanian, S.; Jurchescu, O. D.; Hamadani, B. H.; Moad, A. J.; Kline, R. J.; Teague, L. C.; Kirillov, O.; Richter, C. A.; Kushmerick, J. G.; Richter, L. J.; Parkin, S. R.; Jackson, T. N.; Anthony, J. E. Nature Mater. 2008, 6, 216.
3. Jurchescu O. D., Subramanian S., Kline R. J., Anthony J. E, Jackson T. N., Gundlach D. J., Chem. Mater. 2008 20, 6733.

In most of passive and active devices, charge carriers flow through a bulk wire or sometimes near its surfaces/interfaces. In a one dimensional nanodevice, the transport property may be quite different from bulk devices. We have studied model one-dimensional devices, such as carbon nanotube, Si nanowire and graphene. We have tried to understand the geometric and electronic structures or the transport properties of these nanowires using scanning tunneling microscope (STM), atomic force microscope (AFM), scanning Kelvin probe microscope, electrostatic force microscope (EFM) and scanning gate microscopes (SGM). We begin to learn many new physics, such as 1) different screening behavior in 1-D, 2) deviation from a Fermi liquid, 3) different defect bands from those in the 3-D counter parts, and 4) size effect in superconducting nanodot.

The enigma of the hydrophobic force has for decades captured the imagination of scientists. The seventy years old idea by Frank and Evans that the hydrophobic effect was mainly due to some kind of "iceberg" formation around a hydrophobic solute stimulated countless experiments and molecular dynamics simulations.
This is not surprising because a better understanding of hydrophobic interactions is extremely important as hydrophobic effects determine to a large extent protein structural dynamics and functioning in their natural environment.

Here we present results of ultrafast two-dimensional infrared spectroscopy experiments on the OH-stretch vibrational mode of water molecules near hydrophobic groups. Our experiments demonstrate that the hydrophobic groups induce a dramatic slowing down of the hydrogen-bond dynamics of the solvating water molecules. This change in dynamics perfectly correlates with a considerable decrease of the orientational mobility of the water molecules.
Our
findings suggest the hydrogen-bond network around hydrophobic groups is not more rigid as compared to the bulk, but that the hydrogen bond dynamics in the two cases are very different.

Recent advents in nano-lithography and self-assembly techniques have extended the scope and definition of artificial dielectric structures. One opts to integrate structures with long-range order and whose properties are controlled at the nano-scale. We will follow the subject through examples: carbon nanotubes, self-assembled array of holes and, Oh Yeh, graphene.

Conjugated molecules and oligomers have attracted large attention in the last years due to their interesting electronic and transport properties. The interaction of these molecules with metallic surfaces is attractive both for the properties of the metal-organic interface and for the possibility of tuning the crystal structure of the films using the surface as a template.

In the present work we focus on an ab initio investigation based on density functional theory of pentacene adsorbed on Copper surface. We also compare with the case of the DPDI molecule adsorbed on the same substrate. We address structural and electronic properties, and we relate our results to experimental data, STM, XSW, and angle resolved photoemission spectroscopy in particular.

Our theoretical findings show a flat adsorption geometry for both pentacene and DPDI molecules. For what concerns the electronic structure, a strong rehybridization of the molecular electron states is found in the range of the occupied p states. These results lead to an interpretation of the adsorption mechanism of pentacene in terms of a coupling intermediate between the physi- and the chemi-sorption regimes.

One-dimensional quantum conductors have always captured the imagination of physicists. While a strictly one-dimensional material mostly remains a theoretical construct, a vast number of materials can be viewed as macroscopic ensembles of weakly-coupled quantum chains, making them interesting test cases for theoretical models and even some practical applications in nanotechnology. I will discuss the electronic properties of some quasi one-dimensional electronic materials grown on Si surfaces. Highlights include the self-assembly of indium atoms on Si(111) into a weakly-coupled two-dimensional array of parallel atom wires [1], and the formation of highly uniform YSi2 nanowires on Si(100) [2]. The silicide nanowires exhibit electronic properties reminiscent of a multichannel one-dimensional conductor. These include the stepwise increase of the tunnel current as a function of tip bias in scanning tunneling microscopy and the appearance of a fluctuating charge-density-wave instability at low temperature, opening up a small band gap. The indium wires also undergo an insulator-metal transition. Here, we show that although these electronic instabilities arise from the low dimensional nature of these materials, they should not be attributed to Fermi surface nesting or the traditional Peierls instability. Instead, the insulator-metal transition arises from dynamical fluctuations that are driven by lattice entropy, which is more consistent with an order-disorder transition. In the final part of my talk, I will describe recent efforts in my group to utilize some of these nanowires in a nanoscale Coulter counter for the electrical read out of base pair sequences in DNA molecules.

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[1] “Mechanism of the band gap opening across the order-disorder transition of Si(111)4x1-In,” C. Gonzalez, J.D. Guo, J. Ortega, F. Flores, and H.H. Weitering, Phys. Rev. Lett. 2009 (in press).

[2] “Charge order fluctuations in one-dimensional silicides,” C. Zeng, P.R.C. Kent, T.-H. Kim, A.P. Li, and H. H. Weitering, Nature Materials 7, 539-542 (2008)

A fascinating prospect in molecular electronics is to use molecular switches in transport devices. Here, we present the results of our research on photochromically switchable diarylethenes. In solution, these molecules can be reversibly transformed from a conjugated, ‘on’-state to a cross-conjugated, ‘off’-state, by using light of the proper wave lengths (‘on’ to ‘off’:   550 nm; vice versa:   330 nm). Once connected to gold, this situation may change. In fact, ‘first generation’, diarylethene molecules attached to gold can only be switched in one direction. We attribute this to the strong coupling of these molecules to the metal. By chemically modifying the molecule, such that it couples more weakly to the electrodes, reversible switching has indeed been obtained.
We will present a novel molecular device, which consists of a network of gold nanoparticles, connected by ‘second generation’ photochromic switches. Using visible light and UV light, we can control its conductance. Optical spectroscopy, revealing subsequent shifts of the Au surface plasmon, demonstrates molecular switching independently. Due to the network structure, these devices are relatively stable (~ day) at room temperature.

Semiconducting, insulating, and metallic nanoparticles have attracted considerable interest recently due to their size-dependent, quantum confinement characteristics, which make them attractive for a broad platform of optical, magnetic, and electronic devices. Proposed commercial applications include solid state lighting devices, magnetic recording media, and ultra-light video displays.

For nanoparticles to be employed in an array of commercial and industrial applications, a technique for the facile, rapid, and site-selective assembly of homogeneous, densely packed, defect-free thin films must be realized. The most widely used methods for casting nanoparticle (NP) constituents into densely packed, thermally stable films, such as evaporation-driven self assembly and Langmuir-Blodgett casting, have some recognized limitations, including the inability to achieve both large-scale ordering of the nanoparticles as well as robust chemical and structural properties. NP deposition schemes also require an understanding of both the NP dynamics in solution and the interactions that govern nanoparticle-substrate and nanoparticle-nanoparticle binding. Further, these procedures require knowledge of the intrinsic and collective properties of NPs that arise from of electrostatic, magnetic, and fluctuating electric dipole effects. The organization and stability of colloidal NP assemblies are markedly affected by the surface charge state of the constituents. Although much research has been done on the assembly of nanoparticles with a distribution of surface charge states, little has been done on the assembly of like-charged nanoparticles. In this case, repulsive Coulomb interactions, as well as van der Waals, dipole-dipole, and steric interactions govern the types of assemblies that can form. The only nanoparticle deposition scheme that considers the primary physical characteristics of the NPs in the film formation and incorporates the most favorable attributes of NP deposition is electrophoretic deposition.

Progress in the electrophoretic deposition of nanoparticles and other nanoscale materials will be the emphasis of this presentation. Highlighted discoveries include the fabrication of free-standing nanoparticle thin films, comprised solely of electrophoretically deposited nanoparticles.

The research of my group interfaces with chemistry, physics, materials science, and biological and medical science. We are interested in solid state and soft biological materials that have well-defined atomic structures. Our work is in the areas of materials chemistry, solid state chemistry and physics, scanning probe microscopy, molecular electronics, novel chemical and biochemical sensors and nanomaterial based biological transporters and carriers for drug, DNA and protein delivery and novel therapeutics applications of nanomaterials. Specific projects include, (1) Nanotube synthesis including self-oriented multi-walled carbon nanotube arrays [Fan et al., Science, 1999], highly quality single-walled carbon nanotubes (SWNTs) by chemical vapor deposition (CVD) and their patterned growth on substrates [Kong et al., Nature, 1998; Soh et al., Appl. Phys. Lett., 1999;] and single particle patterning for nanotube growth [Javey et al., 2005, JACS]. (2) Fundamental electrical and electromechanical Properties of Nanotubes [Tombler, Nature, 2000; Cao, PRL, 2003 & 2004; Kong, PRL, 2001]. (3) Suspended nanotube synthesis and quantum transport [Cassell, JACS, 1999; Franklin, 2000; Cao, PRL, 2004]. (3) Nanotube Molecular Sensors and Biosensors. We are exploring nanotubes as novel electronic sensors for gases and biomolecules in solutions [Kong et al., Science, 2000; Chen, PNAS, 2003; Chen, JACS, 2004]. (3) Molecular electronics with ultrahigh performance [A. Javey et al., Nature Materials, 2002; A. Javey, Nature, 2003]. (4) Organic Electronics with Quasi 1D Electrodes [Qi, JACS, 2004]. (5) Intracellular Molecular Transporters and Near Infrared Nano-Therapy. We showed recently that nanotubes are transporters capable of shuttling various cargos (e.g. proteins and SiRNA) across cell membranes [Kam, JACS, 2004&2005]. We also developed a method to destruct cancer cells selectively by using nanotubes and near-infrared light [Kam, PNAS, 2005]. This is an exciting new area in nanobiotechnology in our group with many exciting opportunities ahead. (6) Germanium Nanowires. We are exploring novel synthesis, characterization and applications of semiconducting nanowires [Wang, Angew. Chemie, 2002 *2005; JACS, 2004&2005].

LOCATION: Brian Bent Memorial Lecture Hall, Room 209 Havemeyer Hall

The formation of barriers to charge transfer at semiconductor interfaces has been a focus of considerable research for over fifty years. While early work centered on the intrinsic physical properties of the semiconductor, ultrahigh vacuum surface studies revealed the importance of extrinsic, interface-specific effects in understanding the systematic behavior of these Schottky barriers. Without intervening adsorbate layers, chemical reactions and interdiffusion can occur, even near room temperature, which alter the interface region, introducing new phases, crystal defects, and localized electronic states. With the advent of surface science, new methods have emerged to predict and control Schottky barriers at the nanoscale.

Metal nanoparticles and carbon nanotubes are used in a variety of catalytic systems for energy conversion and production, including photoelectrochemical cells, fuel cells, and batteries. Understanding their structure and catalytic properties is essential for improving their performance and integrating them in devices for applications. Although their structures can be studied down to atomic resolution, their catalytic activities have been mainly studied at the ensemble level, obtaining averaged properties. Ensemble-averaged study is fundamentally inadequate for nanoparticles and carbon nanotubes, however, as they are intrinsically heterogeneous -- Nanoparticles have structural dispersions and carbon nanotubes have various chirality. Here I report our efforts in using single-molecule fluorescence imaging to study the catalytic properties of metal nanoparticles and single-walled carbon nanotubes (SWNTs) at the single-particle/single-tube level. Specifically, I will describe: (1) Imaging catalysis of individual metal nanoparticles at the single-particle single-turnover resolution in real time under ambient conditions (2) Imaging electrocatalysis of SWNTs at the single-reactive-site, single-reaction resolution.

The dramatic improvements in the microelectronic industry are the result of aggressive scaling of devices. This is followed by necessary changes in the materials used. Thus, recently two major parallel efforts can be observed:
1) Replacement of the traditional SiO2 gate dielectric by new high-k materials. High-k dielectrics will enable maintaining the same gate capacitance, while increasing film thickness, thus suppressing the tunneling current through the gate.
2) Replacement of the traditional doped poly-Si electrode by a metallic gate. This effort results from the fact that with dimensions shrink the poly-Si gate suffers from problems of poly depletion and high gate resistance. These problems are alleviated when a metal is used as the gate electrode.

We are studying metal/high-k interfaces for advanced microelectronic devices. Various materials such as HfO2, Gd2O3 and Al2O3 are explored as gate dielectrics, and the interface between these oxides and various metals is studied. The research ai

ms at understanding the correlation between material properties (e.g. interface composition, structure and chemical bonding) and electrical properties of metal/high-k stacks. In particular, we are interested in understanding the effect of various properties on the effective workfunction at the interface with the aim of tuning the Fermi-level position at metal/high-k interfaces.

Time-resolved studies using 100-fs laser pulses generate CN radicals photolytically in solution and probe their subsequent reaction with solvent molecules by monitoring both radical loss and product formation. The experiments use both single wavelength and broadband detection to follow the CN reactants by transient electronic spectroscopy at 400 nm and to monitor the HCN products by transient vibrational spectroscopy near 3.07 m. The observation that CN disappears more slowly than HCN appears shows that the two processes are decoupled kinetically and suggests that the CN radicals rapidly form two different types of complexes that have different reactivities. Electronic structure calculations find two bound complexes between CN and a typical solvent molecule (CH2Cl2) that are consistent with this picture. The more weakly bound complex is linear with CN bound to an H atom through the N atom and is primarily responsible for the rapid HCN signal rise. The more strongly bound complex has a structure in which the CN bridges Cl and H atoms of the solvent and is primarily responsible for the more slowly decaying CN signal. These complexes form the basis for examining CN radical reactivity with seven different chlorinated solvents, where both linear and bridging CN-solvent complexes tend to react more slowly with solvents with more Cl substituents. This result also appears when examining CN reactivity with a group of 16 different alkane, alcohol, and chloroalkane solutes in CH2Cl2. For chloroalkane solutes, increasing the Cl atom content of the solute decreases the reaction rate, in keeping with previous observations for the reactions of Cl in liquids.

It is demonstrated that the zero-dimensional character of the silicon atom dangling bond (DB) state allows controlled formation and occupation of a new form of quantum dot assemblies - at room temperature. Coulomb repulsion causes DBs separated by less than ~2 nm to experience reduced localized charge. The unoccupied states so created allow a previously unobserved electron tunnel-coupling of DBs, evidenced by a pronounced change in the time-averaged view recorded by scanning tunneling microscopy. It is shown that fabrication geometry determines net electron occupation and tunnel-coupling strength within multi-DB ensembles and moreover that electrostatic separation of degenerate states allows controlled electron occupation within an ensemble.

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Reference: Controlled Coupling and Occupation of Silicon Atomic Quantum Dots at Room Temperature, M Baseer Haider, M. Baseer Haider, Jason L Pitters, Gino A. DiLabio, Lucian Livadaru, Josh Y Mutus and Robert A. Wolkow, Physical Review Letters 102, 046805, 2009

DNA is well-known as the genetic material of living organisms. Its most prominent feature is that it contains information that enables it to replicate itself. This information is contained in the well-known Watson-Crick base pairing interactions, adenine with thymine and guanine with cytosine. The double helical structure that results from this complementarity has become a cultural icon of our era. To produce species more diverse than the DNA double helix, we use the notion of reciprocal exchange, which leads to branched molecules. The topologies of these species are readily programmed through sequence selection; in many cases, it is also possible to program their structures. Branched species can be connected to one another using the same interactions that genetic engineers use to produce their constructs, cohesion by molecules tailed in complementary single-stranded overhangs, known as 'sticky ends.' Such sticky-ended cohesion is used to produce N-connected objects and lattices.

Structural DNA nanotechnology is based on using stable branched DNA motifs, like the 4-arm Holliday junction, or related structures, such as double crossover (DX), triple crossover (TX), and paranemic crossover (PX) motifs. We have been working since the early 1980's to combine these DNA motifs to produce target species. From branched junctions, we have used ligation to construct DNA stick-polyhedra and topological targets, such as Borromean rings. Branched junctions with up to 12 arms have been produced. We have also built DNA nanotubes with lateral interactions.

Nanorobotics is a key area of application. PX DNA has been used to produce a robust 2-state sequence-dependent device that changes states by varied hybridization topology. We have used this device to make a translational device that prototypes the simplest features of the ribosome. We have built a cassette that incorporates this device into a 2D array to control a robot arm; we have also used two opposed cassettes to capture patterning molecules. Bipedal walkers have also been built. In addition, we have also built a robust 3-state device.

A central goal of DNA nanotechnology is the self-assembly of periodic matter. We have constructed 2-dimensional DNA arrays from many different motifs. We can produce specific designed patterns visible in the AFM. We can change the patterns by changing the components, and by modification after assembly. Recently, we have used DNA scaffolding to organize active DNA components, as well as other materials. Active DNA components include DNAzymes and DNA nanomechanical devices; both are active when incorporated in 2D DNA lattices. We have used pairs of PX-based devices to capture a variety of different targets. Multi-tile DNA arrays have also been used to organize gold nanoparticles in specific arrangements. Recently, we have self-assembled a 3D crystalline array and have solved its crystal structure.

Techniques for crystallization of silicon has been of significant interest mainly for large area displays, integration of high performance circuitry on glass and potential solar cell applications. Electrical annealing of poly-crystalline or nano-crystalline silicon is one of the potential approaches for crystallization.

Short duration large amplitude electrical stresses result in melting of Si µ-wires and growth from melt takes place after the stress. The electrical current density can reach up to ~ 100 MA/cm2 during this process. These extreme current densities has lead to observation of asymmetric melting, attributed to significant electron-phonon scattering. This thermoelectric effect, phonon-drag, is a component of Thomson effect which is related to more commonly known Peltier and Seebeck effects.

We will be sharing some of our recent findings on crystallization, phase-change oscillations and thermoelectrics based on simple experiments on nano-crystalline silicon micro/nano-wires and do a brief overview of thermoelectrics.

In order to realize hydrogen as a future energy carrier we need to address scientific challenges related to the development of efficient hydrogen production from renewable energy sources, safe and efficient hydrogen storage and significant improvements in fuel cell catalysis in order to lower the expensive Pt loading. I will demonstrate how we have use x-rays to address fundamental interactions at interfaces related to the oxygen reduction reaction on Pt and to bring an understanding to the contributing factors to the increased activity for a new class of dealloyed Pt-Cu catalysts. I will also demonstrate, based on photoelectron spectroscopy measurements, that we can hydrogenate carbon nanotubes to nearly 100% using an atomic hydrogen source and that Pt catalysts can assists in the hydrogenation using molecular hydrogen.

The prediction of structure is a key problem in computational materials science that forms the platform on which rational materials design can be performed. For many materials chemistries standard computational quantum mechanics is highly accurate in selecting the true ground state of a system from a small set of candidate structures, though notable exceptions exist. Finding ground states by traditional optimization methods on quantum mechanical energy models is difficult due to the complexity and high dimensionality of the coordinate space. An unusual, but efficient solution to this problem can be obtained by merging ideas from heuristic approaches and ab initio methods: In the same way that scientist build empirical rules by observation of experimental trends, we have developed machine learning approaches that extract knowledge from a large set of experimental information and a database of over 15,000 first principles computations, and used these to rapidly direct accurate quantum mechanical techniques to the lowest energy crystal structure of a material. Knowledge is captured in a Bayesian probability network that relates the probability to find particular crystal structure at a given composition to structure and energy information at other compositions. We show that this approach is highly efficient in finding the ground states of binary metallic alloys and can be easily generalized to more complex systems. Using this approach we have already identified more than 200 new compounds, including several new Li battery materials, as well as a novel radiation detector.

Covering less than 2% of the dry land in the United States with only moderately efficient solar cells can produce enough electricity to satisfy the national demand for energy. Unfortunately, despite the 30-40% annual growth of the photovoltaic (PV) industry, to date the sum total area of solar cells produced and installed worldwide is 3 orders of magnitude smaller. Furthermore, current manufacturing methods do not scale up sufficiently quickly to fulfill the demand in the next several decades. This talk will outline properties of conjugated organic-based compounds, organic PV device architectures, and device physics that potentially enable scalable, cost-effective solar energy harvesting. Additionally, the talk will touch upon novel organic light emitting devices showing significant promise for efficient, yet cost-effective solid state lighting. Time permitting, novel sensors enabled by uniquely nano-structured organic semiconductor devices will be described.

Standard semiconductor lasers operate in a limited wavelength range, below about 4 microns. Quantum cascade lasers (QCLs) that operate in the mid-IR and far-IR have important applications to medicine, environmental sensing, and national security. While short pulse lasers (~100 fs) are available for standard semiconductor lasers, that is not the case for QCLs. Standard passive modelocking is hard to do in QCLs because of their long coherence times and short gain recovery times. We propose a fundamentally different approach, based on the self-induced-transparency
(SIT) effect, that turns these weaknesses into strengths. Solitons, modelocking, and SIT are all reviewed at the beginning of the talk.

We present high resolution x-ray diffraction measurements on antiferromagnetic Chromium, which is known to exhibit strong coupling phenomena despite the familiar weak-coupling density wave ground state. We directly measure the spin- and charge-density wave order parameters as the magnetism is suppressed with applied pressure using diamond anvil cell techniques at the Advanced Photon Source. In the low pressure regime, the BCS-like ground state is manifest in the decades-long exponential suppression of the order parameters, while at high pressure this weak-coupling behavior is cut off by a quantum phase transition. We identify quantum confinement as the physics driving the exponential suppression of the antiferromagnetic phase. We find that Cr is unique among stoichiometric itinerant magnets studied to date insofar as the quantum phase transition is continuous in nature, allowing experimental access to the naked quantum singularity where the competition between the destabilized density wave and more strongly coupled ground states is most intense. Our results inform the growing body of evidence that weak- and strong-coupling phenomena indeed coexist in many solid state systems, such as continuously tuneable charge density waves in manganites, unconventional superconductivity in spin density wave Bechgaard salts, and charge density wave characteristics of the checkerboard order in the high-Tc cuprates.

Thermal effects are ubiquitous to biological processes. Microelectromechanical systems (MEMS) technology allows the integration of sensitive thermal detection and efficient thermal control with fluidic manipulation, thereby enabling the interrogation of biomolecules in controlled microscale environments unattainable with conventional technologies. This presentation will highlight our research in applying MEMS technology to thermally based biomolecular characterization and manipulation.
We will discuss the application of MEMS technology to thermodynamic characterization of biomolecules, focusing on a miniaturized differential scanning calorimeter. The device consists of a pair of freestanding microfluidic chambers integrated with thermal sensing and control elements. Minute differential heat between the sample and buffer contained in the chambers is measured to assess the biochemical reaction, potentially with orders-of-magnitude smaller sample consumption when compared with conventional instruments. We will also present an investigation of microfluidic platforms for manipulating biomolecules using synthetic and bio-polymers that undergo strong temperature-induced, reversible conformational changes. For example, aptamers, or oligonucleotides with sequence-dependent shape to bind specifically to other molecules, can potentially enable efficient microsystems for analyte extraction. This is demonstrated by capture and concentration of small-molecule analytes by aptamer-functionalized microbeads in a microfluidic chamber, analyte release and device regeneration by thermally induced, reversible breakage of analyte-aptamer binding, and label-free detection of the released analyte by mass spectrometry.

Pattern-imprinting’ involves the conversion of physisorbed molecules to chemisorbed, in localized reaction. This study represents, therefore, an extension of the laboratory’s interest in reaction dynamics, made possible by Scanning Tunneling Microscopy. Patterns which can readily be self-assembled, it will be shown, include nano-corrals and switches.

Manipulation of matter on the scale of atoms and molecules is an essential part of realizing the potential that nanotechnology has to offer. In this talk I will describe a method to nanosculpt matter by controllably exposing it to an intense and highly focused beam of electrons. Electron irradiation can be used to controllably displace or ablate regions of the material, such as thin metal films and graphene sheets, with nearly atomic resolution. I will discuss the impact of this work in nanoelectronics and molecular translocation studies through nanopore-based transistors.

The development of practical optoelectronic and photonic devices

demands accurate characterization of the optical properties of

materials. Some of these materials include zinc oxide (ZnO) and

strontium titanate (STO) thin films. Spectroscopic reflectometry (SR)

and spectroscopic ellipsometry (SE) are uniquely powerful tools for

accurately characterizing the optical properties, structure and

thicknesses of thin films. Combining both techniques in one

measurement offers many advantages, not the least of which is reduced

systematic errors from the simultaneous analysis of multiple data

sets.



The use of SR and SE concurrently (SRSE) to successfully develop

optical models, and determine the variation in refractive index, n and

extinction coefficient, k above and below the band edge of ZnO, for

thin films deposited on silicon and platinum substrates at various

deposition temperatures will be discussed. For the first time, a

graded index layer is used to model the surface roughness layers to

give more accurate fits to the data on Pt substrates.



Also, the development of an optical model based on reflectometry

data, for STO films deposited on silicon and platinum at various

substrate temperatures will be discussed. The analysis reveals an

index gradient in STO deposited on silicon and no interface layer as

reported in other publications.

Transistor scaling to smaller dimensions has been replaced with equivalent scaling. Improvements in transistor performance are now achieved using new materials and processes. The introduction of new materials such as high ?
dielectrics and metal gate materials has replaced traditional silicon dioxide and doped polysilicon gates. Advances in ellipsometry not only enable thickness determination, they also allow observation of defect states in the interface and high ?. Mobility improvement is achieved through a variety of processes that stress the transistor channel. Optical measurements can be used to measure the change in band structure in silicon. New fully depleted silicon on insulator wafers are predicted to be critical to future transistor technology.
Characterization of thin SOI materials has proven that optical measurements are sensitive to the existence of quantum confinement or quantum size effects (QSE). The first step in identifying changes in optical properties, especially the dielectric function, is demonstrating that the data is not due to other phenomena such as stress. We show that the blue shift E1 critical point of thin silicon on insulator films is not due to stress. This blue shift is attributed to quantum confinement. We also discuss why energy shifts in E1 smaller than KT can be observed optically. This talk will overview these recent advances in optical measurements.

Over the last decade much progress has been made in understanding the electronic properties of individual small molecules. We have used electromigration to produce three-terminal devices in which the nanoscale gap between source and drain electrodes is bridged by, ideally, a single molecule. These single-molecule transistors

(SMTs) can be useful tools for studying physics and physical chemistry at the molecular scale. I will present recent results in two areas. We have used SMTs as model systems to study the Kondo effect, a classic piece of strong electron correlation physics.

We find that Kondo physics in SMTs has systematic differences from that observed in semiconductor quantum dots, and most recently we have extended these investigations to examine universal scaling in the nonequilibrium Kondo regime. Secondly, we have found that the electrode structures used in SMTs are tremendous plasmonic optical antennas, leading to very large surface-enhanced Raman scattering (SERS) from the junction. We have very strong evidence that we are able to observe single-molecule Raman emission simultaneously with conductance measurements. Such measurements open many exciting possibilities for future studies.

According to a recent report by the Department of Energy, “world demand for energy is projected to more than double by 2050 and to more than triple by the end of the century.” Thus, the development of alternative energy sources is now recognized by government, society and the global community as an urgent need. Sunlight is the most abundant source of energy on Earth and, if harvested efficiently and economically, can address the energy demands in the future. Organic solar cells potentially offer a low cost, large area, flexible, light-weight, clean, and quiet alternative energy source for indoor and outdoor applications. Our research in this area focuses on controlling material processing conditions and designing/synthesizing materials having a broad absorption spectrum and high charge carrier mobility. In parallel with materials synthesis and processing, we have developed characterization techniques to probe film morphology, to image the donor-acceptor networks laterally and vertically, to assign phase domains to the donor and the acceptor components, and to study nanoscale charge transport in polymer solar cells. Another problem related to energy issue addressed in our group is to understand and control the charge injection mechanism in organic light emitting diodes, which find applications in lighting and display technologies. The ability to control the charge injection leads to devices that operate at lower bias and are therefore more power efficient. From an overall perspective, these studies tackle fundamental critical problems associated with emerging organic semiconductor based technologies that generate energy and that contribute to energy conservation.

Incorporation of biomolecules into nano-object design provides a unique opportunity to establish highly selective and reversible interactions between the components of nanosystems, the property previously intrinsic only to biological matter. Utilization of this approach is appealing for development of novel strategies for the assembly of complex nanosystems, metamaterials and nano-medical applications. Our work explores how DNA and proteins can be engaged in addressable interactions of inorganic nano-components, and how morphology of self-organized structures can be regulated. By tailoring interplay of specific recognition interactions and non-specific physical effects we have demonstrated an ability to control assembly kinetics, clustering, and phase formation of DNA-capped nanoparticles on surfaces and in bulk. The design principles and experimental illustrations of building static and reconfigurable well-defined biomimmetic nano-systems, the progress in understanding their elastic properties and application for label-free biomolecular detection will be discussed.

Detecting spin resonance (the q = 0 magnon mode) in

correlated magnetic systems has a long tradition, starting with works by

Kittel, Richards and Tinkham in the 50's. The development of high field

magnets and broad-band far infrared spectroscopic techniques opened new

ways for studying materials with exotic magnetic order. The magnetic

field dependence of the resonance can be used to explore the interaction

between the spins and the interaction between the spins and the crystal

lattice. Results on the triangular spin system NaNiO_2, the helimagnet

LiCu_2O_2, the canted antiferromagnet LaMnO_3, and other materials will

be discussed in detail.

Can we design, build and operate nanometer-scale logic circuits that perform conventional binary computation using only the spin degree of freedom? I will review progress towards this goal, highlighting the development of spin excitation spectroscopy to measure g-values, exchange energies, anisotropy energies and spin configurations of assemblies of magnetic atoms on surfaces.

The first part of the talk is dedicated to the oriented growth of KNbO3 nanowires by hydrothermal synthesis. Alkali niobate materials are believed to be the best candidates for replacing Pb containing piezoelectric materials. Furthermore, they are foreseen for photocatalytic production of H2 from water splitting. Therefore, the preparation of large arrays of oriented KNbO3 nanowires would drive the development of novel generation of devices.



The second part of the talk deals with the newly discovered chemical mechanism in the synthesis of of Carbon Nanotubes (CNTs). Mixing C2H2 and CO2 in an equimolar proportion (C2H2/CO2 =1) provides outstanding kinetics characteristics of the reaction, leading to a large-scale production of carbon nanotubes free of amorphous carbon. The equimolar C2H2-CO2 reaction allows CNTs growth at temperatures well below 500°C without any arduous pre-activation of the catalyst, on numerous functional materials like oxides, nitrides, carbides or metals. It is an attractive synthesis pathway for the direct integration of CNTs into devices which do not support the traditional high temperature synthesis of CNTs.

The integration of ferroelectric oxides into microelectronic devices requires a better understanding of stress and size effects onto ferroelectric properties of epitaxial thin films and superlattices which are generally imposed by the underlying substrate due to misfits in their lattice parameters and their thermal expansion coefficients. We have utilized polarized micro-Raman spectroscopy to investigate such stress effects in epitaxially grown BT, ST, and BST thin films and their superlattices with different periodicities as a function of temperature. The structure - property correlations will be discussed in comparison with the bulk, thin film, and nano-crystalline forms of these materials
In the second part of the talk we will discuss Magnetoelectric (ME) multiferroics with coexistence of the electric and the magnetic order parameters in the same phase. Such materials exhibit the phenomenon called the ME effect; i.e. magnetization induced by an electric field and electric polarization by a magnetic field.

This seminar is hosted by the Chemical Engineering Department, Prof. McNeill and co-hosted by NSEC.

TBA

We developed new generalized synthetic procedures to produce uniform-sized nanocrystals of many transition metals and their oxides without a size selection process (see Review in Angew. Chem. Int. Ed. 2007, 46, 4630). The synthesized nanocrystals include metals (Fe, Cr, Cu, Ni, and Pd), and metal oxides (-Fe2O3, Fe3O4, CoFe2O4, MnFe2O4, NiO, and MnO) and MnS). We report the ultra-large-scale (10s of grams) synthesis of monodisperse nanocrystals of magnetite and MnO from the thermolysis of metal-oleate complexes (Nature Mater. 2004, 3, 891). We synthesized uniform-sized nanocrystals of various oxides of ZnO, TiO2, CeO2, Sm2O3 and FeOOH via non-hydrolytic sol-gel reactions. We developed a new T1 MRI contrast agent using biocompatible manganese oxide (MnO) nanoparticles (Angew. Chem. 2007, 5397), exhibiting detailed anatomic structures of mouse brain. We reported on the fabrication of monodisperse nanoparticles embedded in uniform pore-sized mesoporous silica spheres (J. Am. Chem. Soc 2006, 128, 688; Angew. Chem. 2008) and PLGA polymers (Adv. Mater. 2008, 20, 478) for simultaneous MRI, fluorescence imaging, and drug delivery. We fabricated magnetic gold nanoshells consisting of gold nanoshells (for NIR photothermal therapy) that are embedded with Fe3O4 nanoparticles (for MRI contrasting agent), and conjugated them with cancer targeting agent (Angew. Chem. 2006, 45, 7754). We synthesized hollow magnetite nanocapsules and used them for both the MRI contrast agent and magnetic guided drug delivery vehicle (Nature Mater. 2008, 7, 242).

Recent studies in the field of carbon based materials: graphenes and nanotubes, revealed their superior electronic properties that outperform many of semiconductor analogs. To become practical for mass production carbon devices must though overcome a number of difficulties, of a technical rather than fundamental nature. This allows one to hope that it is a matter of time, and there is no a principal physical limitation restricting the field. This talk, thus, focuses on the novel physics and unexpected functionalities of nanotube (NT) materials with low-dimensionality.
In the talk a single aspect of the NT physics will be highlighted: the charge scattering and related effects caused by the hetero-interface of the NT material with the technologically important Si-based substrate. Less commonly studied mechanisms, such as remote Coulomb impurity and surface polariton scattering, will be detailed and applied to single-tube field-effect devices as well as NT array thin-film transistors.

A combined experimental and computational study of a series of substituted pentacenes including halogenated, phenylated, silylethynylated and thiolated derivatives will be presented. Experimental studies include the synthesis and characterization of six new and six known pentacene derivatives and a kinetic study of each derivative under identical photo-oxidative conditions. Structures, HOMO-LUMO energies and associated gaps were calculated at the B3LYP/6-311+G**//PM3 level while optical and electrochemical HOMO-LUMO gaps were measured experimentally. The combined results provide for the first time a quantitative assessment of HOMO-LUMO gaps and photo-oxidative resistances for a large series of pentacene derivatives as a function of substituents. With this substituent effect data in place, it is now possible to rationally design larger, photo-oxidatively persistent acenes. Two new persistent heptacene derivatives will be described and progress towards the preparation of persistent nonacenes will be discussed.



Because acenes and cyclacenes map directly onto zig-zag carbon nanotubes, they can be considered precursors to semi-conducting single walled nanotubular compounds (SWNCs). We are interested in exploring this approach as a means to prepare a library of uniform SWNCs. Experimentally, a highly diastereoselective Diels-Alder chemistry involving fullerenes has been demonstrated. Its potential utility to convert large acenes into cyclacenes will be discussed. Computationally, it will be shown that the electronic properties of SWNCs prepared by tethering cyclacene compounds vary as function of the tether.



Finally, a recently discovered chemistry for the hydrogenation of nanostructured carbons will be discussed. Fullerenes, SWNTs, MWNTs and graphite have all been successfully functionalized.

As micro and nanoscale electronic and optical devices make advances in speed, functionality and integration, demands on their fabrication processes and equipment continue to accelerate. Recently, there also has been an increasing impact of fabrication technologies in large-area microelectronics, displays, microsystems and biomolecular structures. These technologies enable the micro/nanostructuring of a variety of organic and inorganic materials, developing new synthesis techniques, and producing structures and devices previously deemed unfeasible. To facilitate these explorations, processing techniques and multifunctional systems are desired that can handle various substrate materials and geometries, including large areas, flexible sheets and nonplanar surfaces. We review advances in micro/nanolithography, photoablation and other technologies developed for these applications, distinguishing their requirements from those of established semiconductor fabrication technologies.

The design and preparation of nano-bioelectronic systems such as molecular electronic devices or biosensors often requires both, a tailored nanostructure patterning and the control over a functional molecular coating on the supporting inorganic substrate.

I will report on our recent investigations in these two areas: 1) For a possible “hybrid” integration of molecular electronic devices into current microelectronic circuitry the fabrication of well-defined nanoscale contacts on the same semiconductor wafer using only existing process technology will be advantageous. We investigated the fabrication of such “on-chip” nanogap electrode devices with predetermined electrode separation down to below 10 nm based on silicon-on-insulator and GaAs/AlGaAs heterostructure substrates. Using these devices we studied the electronic transport properties of 8.5 nm long conjugated molecular wires and molecule-nanoparticle hybrid systems. 2) Monolayers of DNA tethered to gold surfaces within electrolyte solution can be electrically manipulated due to their negative charge. We have been able to induce the switching of entire DNA layers between a ‘lying’ and a ‘standing’ conformation. Here, the dynamics of single and double stranded DNA exhibits pronounced differences which originate from their dissimilar mechanical properties, suggesting a novel scheme in label-free biosensing.

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References: 1) Luber et al., Small (2007); Strobel et al., Nanotechnology (2007)

2) Rant et al., Biophys. J. (2006); Rant et al., PNAS (2007)

We study electrical transport through single molecules in vacuum using

mechanically controllable break

junctions. By repeatedly breaking and fusing the lithographically

structured gold contacts we acquire

low-bias conductance histograms and IV characteristics of molecular

model systems with different

anchoring groups. We find that the presence of single-molecule

signatures in these measurements

critically depends on the surface density of molecules at the contact.

It can be controlled by choosing

suitable experimental parameters for different temperatures. Breaking

histograms of hexanedithiol and -

diamine junctions reveal conductance values that are in agreement with

literature data. Benzenedithiol

and –diamine, however, do not exhibit clear peaks in conductance

histograms. We attribute this

shortcoming to a large variability in possible junction geometries.

Using a new Fullerene-based

anchoring for the benzene molecules we are able to obtain reproducible

conductance data.

Hosted by Prof. Venkataraman

Electron spins trapped in solid-state systems exhibit strong hyperfine interactions with a nuclear spin reservoir, which is normally fluctuating and randomly oriented. As this represents a fundamental decoherence mechanism for the electron spin [1], several theoretical scenarios to suppress this effect in optically active semiconductor quantum dots (QDs) have been proposed [2,3]. However, implementation of these proposals requires a deeper understanding of the properties of the mesoscopic QD nuclear spin ensemble and of the possibilities of manipulating the nuclear spins.

For that purpose, we use optical preparation and detection of the spin and energy of QD electrons to manipulate and measure the average nuclear spin polarization (NSP) in a single, self-assembled QD [4]. Our experiments show that the transfer of spin information between the electron and the nuclei is strongly dependant on the degree of the nuclear spin polarization itself. This feedback of nuclear spin polarization on the electrons in form of an effective magnetic field makes the coupled electron-nuclear spin system behave in a highly nonlinear way [5]. I will present experimental evidence for these nonlinearities and discuss recent time resolved studies of NSP which show that a QD electron can also be very efficient in destroying an established QD NSP [6].

Moreover, due to the nonlinear behavior of the coupled electron-nuclear spin system, this nuclear spin decay can have interesting non-exponential characteristics in the presence of external magnetic fields. I will discuss how a systematic study of the dynamics of NSP in external magnetic fields could give a more detailed picture of the mechanisms causing QD nuclear spin depolarization and what role nuclear quadrupolar interactions might play for the QD nuclear spin ensemble.

Ultimately, further understanding of these subtle interactions could enable us to improve the decoherence time of the electron spin.

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[1] A. V. Khaetskii et al., Phys. Rev. Lett. 88, 186802 (2002).

[2] A. Imamoglu et al., Phys. Rev. Lett. 91, 17402 (2003).

[3] G. Giedke et al., Phys. Rev.A 74, 32316 (2006).

[4] C.W. Lai et al., Phys. Rev. Lett. 96, 167403 (2006).

[5] P. Maletinsky et al., Phys. Rev. B 75, 35409 (2007).

[6] P. Maletinsky et al., Phys. Rev. Lett. 99, 056804 (2007).

Freely suspended SiNx membranes are structurally robust, highly insulating, and transparent to high-energy electrons. As a result, they can serve as a platform for electronic device development with the important feature of being compatible with transmission electron microscopy (TEM). The use of these membrane-based devices for correlating charge transport in CdSe and PbSe nanocrystal arrays with their detailed structural information revealed by TEM analysis will be discussed. Electron transparency also translates to the near complete elimination of the resolution limiting “proximity effect” from electron beam lithography. By exploiting this resolution enhancing feature on SiNx membranes, it is possible to directly write pairs of electrodes separated by nanometers, so called “nanogaps.” I will discuss the application of nanogaps to measurements of single/few-nanocrystals and their relation to information provided by TEM imaging. In addition to providing imaging capability, the TEM can play an active role in device development. I will discuss “nanosculpting,” a new technique for fabricating nanostructures by controllably exposing materials to an intense electron beam in a TEM. The effect of electron irradiation can be used to displace or eliminate regions of the material with resolution on the scale of tens of atoms per exposure. By exploiting this behavior, unique new nanostructures can be made whose properties may offer new insights into the nature of mesoscopics.

I have started my sabbatical stay at the Columbia Nanocenter. In order to introduce myself I will give a short summary of my activity in Lausanne on carbon based nanostructures, mainly carbon nanotubes, but I will touch few issues related to peapods and graphene. I will discuss growth, defects, mechanical and magnetic properties and some possible applications of carbon nanotubes.

Electron spins trapped in solid-state systems exhibit strong hyperfine interactions with a nuclear spin reservoir, which is normally fluctuating and randomly oriented. As this represents a fundamental decoherence mechanism for the electron spin [1], several theoretical scenarios to suppress this effect in optically active semiconductor quantum dots (QDs) have been proposed [2,3]. However, implementation of these proposals requires a deeper understanding of the properties of the mesoscopic QD nuclear spin ensemble and of the possibilities of manipulating the nuclear spins.

For that purpose, we use optical preparation and detection of the spin and energy of QD electrons to manipulate and measure the average nuclear spin polarization (NSP) in a single, self-assembled QD [4]. Our experiments show that the transfer of spin information between the electron and the nuclei is strongly dependant on the degree of the nuclear spin polarization itself. This feedback of nuclear spin polarization on the electrons in form of an effective magnetic field makes the coupled electron-nuclear spin system behave in a highly nonlinear way [5]. I will present experimental evidence for these nonlinearities and discuss recent time resolved studies of NSP which show that a QD electron can also be very efficient in destroying an established QD NSP [6].

Moreover, due to the nonlinear behavior of the coupled electron-nuclear spin system, this nuclear spin decay can have interesting non-exponential characteristics in the presence of external magnetic fields. I will discuss how a systematic study of the dynamics of NSP in external magnetic fields could give a more detailed picture of the mechanisms causing QD nuclear spin depolarization and what role nuclear quadrupolar interactions might play for the QD nuclear spin ensemble.

Ultimately, further understanding of these subtle interactions could enable us to improve the decoherence time of the electron spin.

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[1] A. V. Khaetskii et al., Phys. Rev. Lett. 88, 186802 (2002).

[2] A. Imamoglu et al., Phys. Rev. Lett. 91, 17402 (2003).

[3] G. Giedke et al., Phys. Rev.A 74, 32316 (2006).

[4] C.W. Lai et al., Phys. Rev. Lett. 96, 167403 (2006).

[5] P. Maletinsky et al., Phys. Rev. B 75, 35409 (2007).

[6] P. Maletinsky et al., Phys. Rev. Lett. 99, 056804 (2007).

We report on infrared spectroscopy of charge dynamics in monolayer

graphene. IR reflectance and transmission measurements were performed on

graphene transistors as a function of gate voltage. From these data, we

obtained the optical conductivity of graphene at various carrier

densities. The dominant feature of the optical conductivity is an

interband transition with the onset at twice the Fermi energy, which

evolves systematically with gate voltage. Similar behavior was observed

with the Fermi level on either side of the Dirac point. We will compare

these results with theoretical predictions and discuss several new aspects

of the charge dynamics in graphene uncovered by this work.

Nearly twenty years since the first discovery of the even denominator fractional quantum Hall effect (FQHE), a complete understanding of the the nu=5/2 state continues to be among the most exciting problems in semiconductor physics. It is widely believed that this exotic state of matter is described by the Moore-Read “Pfaffian” wavefunction, resulting from a BCS-like pairing of composite fermions. In recent years this wavefunction has received special interest owing to its non-abelian quantum statistics which underlies a new paradigm for topological (fault tolerant) quantum computation. In spite of several important theoretical advancements however, an unequivocal experimental verification of the Moore-Read description is still missing. While recent experimental studies have measured the fractional charge [1] and tunneling spectroscopy [2] predicted by the Moore-Read description, continued efforts to experimentally confirm the spin polarization state at nu=5/2 remain unsuccessful.
In this talk I will review past and recent studies of the 5/2 and discuss our efforts to better understand the full nature of this enigmatic state using both traditional low-noise transport measurements and novel experimental approaches. Recent results of our examination of the 5/2 state in a never-before observed low field regime [3] will be presented including the unexpected contrasting behaviour of the 5/2 and neighbouring odd-denominator FQHE states under application of a parallel field [4].

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[1] M. Dolev et al, Nature, 452, 829 (2008)
[2] I.P. Radu et al, Science, 320, 899 (2008)
[3] C.R. Dean et al, PRL, 100, 146803 (2008)
[4] C.R. Dean et al, submitted to PRL (May, 2008)

Understanding the details of molecular conduction is paramount for the rational design of photovoltaics, sensors and molecule based electronics, whose function is dictated or enhanced by the use of molecular assemblies to modulate charge transport. To enable the design and implementation of such systems, key aspects that need to be addressed are: 1) how molecular connectivity and local molecular interactions (i.e. environment) can be used to influence electron transport behavior and 2) how spatial confinement influences the assembly of molecules on surfaces in nanoscopic junctions, and ultimately their electrical response. In order to address these questions, we are exploring a set of well defined measurement platforms in which the organization of molecular assemblies within nanoscopic electrical junctions and their behavior (i.e. chemical and/or conformational changes) while under bias are being examined. In this work, combined STM and inelastic tunneling spectroscopy (IETS) measurements, using crossed-wire junctions, have been used to investigate the transport properties of isolated porphyrins and aggregates assembled on Au surfaces. Interestingly, the transport properties of single molecules vary significantly from that of their corresponding aggregates. These large aggregates of ca. 5 - 10 nm in dimension show a clear bias dependent switching behavior and are found to exhibit Coulomb blockade. In addition to these studies, we also working to implement a key metrology need to follow the properties of molecules within the buried interfaces formed by nanoscopic electrical junctions via a combined nanolithography/confocal Raman/conducting probe AFM platform. Our progress on the development of these measurements will also be described.

The interaction of light with magnetic matter is well known: magneto optical Faraday or Kerr effects are frequently used to probe the magnetic state of materials. or manipulate the polarisation of light .
The inverse effects are less known but certainly as fascinating: with light one can manipulate matter, for example orient their spins. Using femtosecond laser pulses we have recently demonstrated that one can thus generate ultrashort and very strong (~Tesla?s) magnetic field pulses that provide unprecedented means for the generation, manipulation and coherent control of magnetic order on very short time scales.
In this talk the basic ideas will be discussed and illustrated with recent results.
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A.V.Kimel, A.Kirilyuk, P.A.Usachev, R.V.Pisarev, A.M.Balbashov and Th.Rasing,Ultrafast nonthermal control of magnetization by instantaneous photomagnetic pulses, Nature 435 (2005), 655-657
C.D.Stanciu, F.Hansteen, A.V.Kimel, A.Kirilyuk, A.Tsukamoto, A.Itoh and Th.Rasing, All-optical Magnetic Recording with Circularly polarized Light, Phys.Rev.Lett.99, 047601 (2007)
Demonstration of compact all-optical recording of magnetic bits by femtosecond laser pulses. This was achieved by scanning a circularly polarized laser beam across the sample and simultaneously modulating the polarization of the beam between left and right circular. White and black areas correspond to ?up? and ?down? magnetic domains, respectively.

TBA

TBA

Nonlinear optics is used to study oligonucleotides at aqueous/solid interfaces for the first time. The experiments avoid the use of labels and DNA modification other than surface attachment and are broadly applicable for investigating DNA during its interaction with biological targets as well as charged biopolymers in general. Detailed thermodynamic state information for interfacial DNA single strands, namely, the interfacial charge density, the interfacial potential, and the change in the interfacial energy density, is obtained. Complementary polarization-resolved resonantly enhanced second harmonic and vibrational sum frequency generation spectra of glass surfaces functionalized with single-stranded and duplex DNA oligonucleotides are also presented. These spectra yield detailed conformational information of surface-bound oligonucleotides, including the chirality of the stereogenic centers and the chirality of the supramolecular duplex structure. The implications for predicting and controlling macromolecular interactions, improving biodiagnostics, and understanding life processes are discussed.

With today?s electronics approaching its scaling limit, a new emphasis has been placed on looking for new materials which can provide better electronic properties than silicon. It is extremely important to develop a thorough understanding of these new materials and take advantages of them in the device design. In my presentation, I will discuss two nano-materials ? carbon nanotubes and graphene.

Carbon nanotubes have been shown to have outstanding electronic properties mainly owing to their dimensionality. I will present details on the fabrication and measurement of a gate-all-around carbon nanotube transistor ? an ultimate device design which takes advantage of the smallness of this class of materials. Challenges in material complexity and device fabrication will be discussed. In a tube FET, the nanotube itself is left undoped to prevent dopant fluctuations related changes of the device characteristics. In the second part of my presentation, I will present an in depth study of the impact of different work function metal gates on the performance of individual nanotube FETs, nano-inverters and ultimately an entire nano-circuit ? a ring oscillator.

Graphene has been a rapid rising star in the scientific community in the past two years. As the basic building block for carbon nanotubes, graphene shares many common physical properties and is attractive for electronic applications because of the possibility of large scale film growth and implementation. I will discuss devices fabricated from single layer graphene and elucidate on our current understanding and the required studies planned to achieve better device performance in future nano-electronic applications.

Fast dephasing of electron spins in an ensemble of quantum dots is detrimental for applications in quantum-information processing. We show that dephasing can be overcome by using a periodic train of light pulses to synchronize the phases of the precessing spins, and demonstrate this effect in an ensemble of singly charged (In,Ga)As/GaAs quantum dots [1]. We first discuss the physical mechanism of this synchronization in a quantum-dot ensemble [2, 3]. A periodic train of circularly polarized light pulses from a mode-locked laser synchronizes the precession of the spins to the laser repetition rate, transferring the mode-locking into the spin system. The mode-locking technique allows us to measure the single-spin coherence time to be 3 microseconds [1], which is four orders of magnitude longer than the ensemble dephasing time of 400 picoseconds. The technique also offers the possibility of achieving all-optical coherent manipulation of spin ensembles, in which electron spins can be clocked by two trains of pump pulses with a fixed temporal delay. After this pulse sequence, the quantum-dot ensemble shows multiple bursts of Faraday rotation signals, whose repetition period agrees well with developed theory. The nuclei in these experiments act constructively, leading to the nuclear-induced frequency-focusing effect, which moves the electron-spin precession into dephasing-free subspace [4]. This effect has the potential for focusing all precession frequencies of the quantum-dot ensemble to a single precession mode.
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[1] A. Greilich, D. R. Yakovlev, A. Shabaev, Al. L. Efros, I. A. Yugova, R. Oulton, V. Stavarache, D. Reuter, A. Wieck, and M. Bayer, Science 313, 341 (2006).
[2] A. Greilich, R. Oulton, E. A. Zhukov, . A. Yugova, D. R. Yakovlev, M. Bayer, A. Shabaev, Al. L. Efros, I. A. Merkulov, V. Stavarache, D. Reuter, and A. Wieck, Phys.Rev. Lett., 96, 227401 (2006).
[3] A. Shabaev, Al. L. Efros, D. Gammon, and I. A. Merkulov, Phys. Rev. B 68, 201305(R) (2003).
[4] A. Greilich, A. Shabaev, D. R. Yakovlev, Al. L. Efros, I. A. Yugova, D. Reuter, A. D. Wieck, and M. Bayer, Science 317, 1896 (2007).

Carbon nanotubes are clean systems for studying physical phenomena in one dimension (1D). Electrons in 1D at high density are known to form a Luttinger liquid. However, at low density and in the absence of disorder, the ground state is predicted to be a 1D Wigner crystal - an electron solid dominated by inter-electron Coulomb repulsion. I will describe our recent experiments with ultra-clean semiconducting carbon nanotubes in the few-electron regime. Using low-temperature Coulomb blockade spectroscopy in a magnetic field, we map out the exchange coupling as a function of electron (or hole) number [1] and find excellent agreement with a Wigner crystal model.

At high electric fields, these suspended nanotube devices show striking negative differential conductance - a phenomenon attributed to non-equilibrium phonons. We obtain the first direct evidence of such "hot" phonons [2] using spatially-resolved Raman spectroscopy in conjunction with electrical transport. We directly observe the parabolic temperature profile expected for Joule heating in 1D; surprisingly, short (~2 micron) devices show no heating profile even at very high bias (1.5 V). These measurements reveal the mechanisms of hot-phonon decay, thermalization and thermal transport in carbon nanotubes [3].
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[1] V. V. Deshpande and M. Bockrath, Nature Physics (2008). Available online at doi:10.1038/nphys895 [2] A. W. Bushmaker, V. V. Deshpande et al, Nano Letters 7, 3618 (2007) [3] V. V. Deshpande et al, Submitted

Our understanding of energy transfer and -dissipation in carbon nanotubes (CNTs) is essential to an assessment of their potential use for electronic and optical applications. Here I will concentrate on discussing our current understanding of radiative and non-radiative processes in semiconducting CNTs and CNT aggregates. Specifically we explore the ultrafast dynamics of different excitons in these one-dimensional systems using a variety of linear and non-linear optical probes. I will discuss the role of phonons, defects and metallic tubes for non-radiative decay and photoluminescence quantum yields in semiconducting CNTs which today can exceed 3%, up from less than 0.1% reported previously. This, in combination with recent progress in the preparation of structurally sorted samples, quiet literally provides CNTs with a brighter future for use in optical and optoelectronic applications.

Anyone who ever took an electronics laboratory class is familiar with the fundamental passive circuit elements: resistor R, capacitor C, and inductor L. However, in 1971 Leon Chua proposed from symmetry arguments that there should be a fourth fundamental element, which he called a memristor M (an acronym for memory resistor). Although he showed that such an element had many interesting and valuable circuit properties, until now no one has presented a useful physical model nor example of a memristor. I will show using a simple analytical example that memristance arises naturally in nanoscale systems for which solid-state electronic and ionic transport are coupled under an external bias voltage; it is essentially an electrochemical device. I will describe the mechanism of memristance in titanium dioxide crosspoint switches built in our laboratory, and show some of the interesting applications these devices have.

The Center for Functional Nanomaterials (CFN) at Brookhaven National Laboratory is a science-based user facility funded by the U.S. Department of Energy and devoted to nanotechnology research addressing challenges in energy security. We envision the CFN becoming an enabling resource for advanced materials research in the northeastern United States, offering a broad portfolio of scientific capabilities through an active user program. I will present an overview of the CFN and the user facilities that are accessible without cost via a peer-reviewed proposal process.

Nanometer-scale self-assembly has applications in both today?s and future technology. As examples of the possibilities, I will present ongoing research efforts investigating the use of self-assembled polymer films as high-resolution patterning materials for high-performance semiconductor devices. The discussion will highlight both the promise and versatility as well as limitations and challenges still to be addressed. I will also discuss our nascent CFN program in nanostructured photovoltaic materials and devices.

TBA

The ultimate success of nanotechnology scale-up and commercialization will depend on our ability to understand and manage environmental health and safety issues. A major challenge for nanomaterial EHS research is the sheer number of new nanomaterials under development coupled with the many ways in which a given nanomaterial can be formulated through surface functionalization, coating, doping, or incorporation into composites. How can small, innovation-based companies move forward in this atmosphere of uncertainty before the health risks of their products, if any, can be properly identified and quantified? This talk describes strategies for nanomaterial synthesis, fabrication, and processing that can be employed in the near term to reduce health risks to workers and technology end-users. In addition classical engineering controls such as particulate air filters and fume hoods, the manufacturing processes themselves can often be designed for improved product safety using toxicological information already available for nanomaterials or conventional analogs. This talk will give examples where adverse biological responses to nanomaterials are actually due to impurities or degradation products. Examples will be given of new purification protocols designed for detoxification and of antioxidant surfactants for ?green? processing in aqueous phases. Further progress in this field will require continued close collaboration between the nanomanufacturing and health sciences.

This presentation will describe the synthesis of inorganic nanocrystals and their covalent functionalization with organic molecules. Specifically, the preparation and anticancer activity of taxol-coated gold nanoparticles with a well-defined number of drug molecules will be discussed. In another example, one-dimensional core-shell structures are synthesized via covalent attachment of polymer chains to thiol-functionalized gold nanorods. The presence of the polymer shell renders metallic nanocrystals (MW?108 g/mol) soluble in many organic solvents. When chloroform solutions of hybrid gold nanorods are dried on solid substrates, the nanocrystals undergo spontaneous self-organization into ring-like arrays. Our investigation revealed that the rings of rods are templated by later
microdroplets that condense from the air due to evaporative cooling of organic solvents. The size of rings can be controlled if monodisperse water droplets are used as soft templates. This method is highly versatile and can be used for the preparation of ring-like assemblies of inorganic nanocrystals regardless of their size, shape, and chemical composition.

Nanomaterials are predicted to outperform currently available thermoelectric materials in terms of the efficiency of conversion of heat into electricity, with major potential applications in power generation and harvesting of waste heat. I will introduce basic concepts for how to use nanostructuring to control phonon and electron flow in thermoelectric devices.

Our own projects focus on proof-of-principle experiments to demonstrate Carnot efficiency in thermoelectric energy conversion using III-V, heterostructure nanowires at low temperatures. I will discuss these experiments, including novel methods to measure a temperature differential across a quantum dot embedded into a single-crystalline nanowire.

TBA

I will give an overview of our recent exeperiments on spin injection, spin transport, and spin precession in single graphene layer based field effect transistors.

After an introduction into the physics of spin transport I will discuss how we fabricated our devices, where ferromagnetic electrodes are used as spin injectors and detectors. I will discuss:

a) spin injection and detection using a non-local four terminal measurement technique

b) the observation of spin transport with a typical spin relaxation length of 1.5 to 2 micrometer

c) the observation of Hanle type spin precession

d) the observation of anisotropic spin relaxation

e) the effect of carrier drift on the spin transport

f) our recent experiments on spin transport in graphene nanoribbons

TBA

TBA

Graphene, a single atom-thick sheet of graphite, is a zero-gap semiconductor with an unusual linear dispersion relation (analogous to the Dirac equation for massless relativistic particles) and a density of states that vanishes at a singular point. Graphene is an exciting new condensed matter system, both for the opportunity to observe the physics associated with massless Dirac Fermions in the laboratory, and because of materials parameters which make it attractive for technological applications. However, in the few years since the experimental realization of graphene, progress toward cleaner (higher mobility) samples has largely stalled. I will discuss experiments performed on atomically-clean graphene on SiO2[1] in ultra-high vacuum to determine the intrinsic and extrinsic limits of mobility in graphene[2,3], which point out both the promise of the material as well as the technological challenges that lie ahead in realizing better graphene samples. Intrinsic scattering by the acoustic phonons of graphene[3] limits the room-temperature mobility to 2 x 105 cm2/Vs at a carrier density of 1012 cm-2, higher than any known material. However, extrinsic scattering due to charged impurities in the substrate[2] and substrate polar optical phonons[3] currently impose much more severe limits on the mobility, pointing out the importance of substrate engineering for improving graphene devices[4].
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[1] ?Atomic Structure of Graphene on SiO2,? Masa Ishigami, J. H. Chen, W. G. Cullen, M. S. Fuhrer, and E. D. Williams, Nano Letters 7, 1643 (2007).
[2] ?Charged Impurity Scattering in Graphene,? J. H. Chen, C. Jang, M. S. Fuhrer, E. D. Williams, and M. Ishigami, to appear in Nature Physics, arXiv:0708.2408.
[3] ?Intrinsic and Extrinsic Performance Limits of Graphene Devices on SiO2,? J. H. Chen, C. Jang, S. Xiao, M. Ishigami, M. S. Fuhrer, arXiv:0711.3646.
[4] ?Printed Graphene Circuits,? Jian-Hao Chen, Masa Ishigami, Chaun Jang, Daniel R. Hines, Michael S. Fuhrer, and Ellen D. Williams, Advanced Materials 19, 3623 (2007).

Among the challenges for application of organic semiconductor (OSC)-based devices are voltage reduction, enabling of complementary logic, and increased response speed. A further goal is to employ these devices to conserve or capture energy. New materials that we are developing for these purposes include electron transporting semiconductors requiring minimal gate dielectric films, highly polarizable and chargeable solution-deposited gate dielectrics, and chemically sensitive heterostructures just a few monolayers thick. We will specifically describe organic and polymer chemistry that has resulted in new naphthalenetetracarboxylic diimide and oxadiazole-containing n-OSCs for transistors, diodes, and solar cells, processes for layered ionic "conductors" that have very high capacitance as gate dielectrics in transistor circuits, and hydroxylated p-OSCs with selective responses to vapors of national security interest. N-channel transistors were made with semiconductor mobilities >0.2 cm2/Vs and turnon voltages <1 V. Detection of 100 ppb of a model phosphonate ester vapor with response times of tens of seconds was achieved. Diodes with >10 MHz response speeds and photovoltages approaching 1 V were demonstrated. Incorporation of these devices into energy harvesting and multifunctional circuit architectures will be discussed.

Materials chemistry has provided the foundation for fabrication processes that allow for circuit elements that are 1000 times smaller than the diameter of a human hair. On a technical level, implementation of new concepts and inventions into innovative technologies needs an integrated, collaborative, multidisciplinary team oriented research/development effort in order to rapidly capitalize on research insights, coupled with an understanding of market needs. This presentation will focus on the development of polymer materials technologies for both passive and active electronic applications.

The 2007 Nobel Prize in physics was awarded to Albert Fert and Peter Grunberg for their discovery of the Giant Magnetoresistive effect (GMR). In a period of about ten years, the path from basic science to industrial production of hundreds of millions of devices for a worldwide consumer market was successfully completed. The application of GMR devices in hard disk read heads is often considered to be one of the first large scale applications of nanotechnology. Jacques Kools, principal of KoolerHeadz, a boutique consultancy firm serving the nanotech and nanomanufacturing industries, will present a perspective on the industrialization of GMR as a chain of multidisciplinary phases, where each phase is dominated by particular disciplines: basic solid state physics, materials science, device physics and process integration, and finally manufacturing technology. From this analysis we can glean important lessons for future nanotech applications:
? Why did this application succeed in making it to the marketplace while others failed?
o When and how did we know this was going to work?
o What "fundamental limits" were circumvented through a paradigm shift?
o What types of resources were deployed and how much?
? What were the roles of different players?
o academia vs. industry
o equipment vs. device industry
? Who turned this innovation into a successful business?


Seats will be limited, so please RSVP by replying to this message or send an email to stvhelp@columbia.edu if you plan to attend. Faculty, post-docs, graduate students are encouraged to attend.
Host: Dan Abraham, x14138. Please contact Dan if you would like to schedule time with Dr. Kools.

The fuel cell is a thermodynamically and practically efficient device that directly converts chemical energy to electrical energy. Of central interest to the realization of the "hydrogen economy" has been the proton exchange membrane (PEM) fuel cell, which is fed by a fuel of hydrogen that is broken into protons and electrons at a catalytic electrode, and then recombined with oxygen at a second catalytic electrode to form water. Nearly exclusively, the catalysts for PEM fuel cells are based nanoparticles supported on carbon. These work great, in the sense that the highest power densities are generated using such materials, but there is room for significant improvement. High performances generally are associated with intolerable levels of expensive Pt catalysts, nanoparticles tend to agglomerate over time losing active surface area, and the catalysts are sensitive to "poisoning" by nearly unavoidable fuel and atmospheric contaminants.

In this presentation, I will discuss our research into using an alternative approach to make fuel cell electrocatalysts by employing chemical dealloying to selectively remove one component of a multicomponent alloy and form a three-dimensionally nanoporous (np) metal. In the form of ultra-thin foils, dealloyed nanoporous metals hold promise to address many of the concerns associated with nanoparticles catalysts. Specifically, we will talk about mechanisms of coarsening (and avoiding coarsening) in np metals, functionalizing np metals into ultra-low precious metal content catalysts, the mechanical properties of np metals, and the unique catalytic behavior of np metals. All these scientific issues will be presented in the context of engineering actual working fuel cells using nanoporous metal catalyst electrodes, and the successes we have had in quickly improving their performance to levels approaching state-of-the-art nanoparticle-based devices.

There are many examples in Biology where functional specificity is coded on the sequence and structure of closely related members of a single protein family. For example, different Hox proteins assign morphological identities along the anterior posterior axis of vertebrates and invertebrates based on their ability to distinguish among very similar DNA sequences. Cadherins are cells adhesion proteins that, despite remarkably similar sequences and structures, recognize each other in such a way that they produce highly specific cell-cell adhesion when presented on apposing cell surfaces. The molecular basis of these phenomena will be discussed based both on computational and theoretical analyses of three-dimensional molecular structures and on in-vitro and in-vivo assays of molecular and cellular function.

The talk will present our efforts to produce ultracold, tightly bound molecules from atomic gases. These heteronuclear molecules have a permanent electric dipole moment, and will allow creation of ultracold matter with unexplored dipolar interactions, as well as play a role in quantum computation. We have successfully produced loosely bound fermionic KRb molecules using a scattering resonance known as a Feshbach resonance. Near this resonance, we have studied the inelastic decay of molecules due to collisions with different atomic partners. Quantum statistics plays an important role in the inelastic molecular loss rates. Suppressing this loss is key to creating deeply bound molecules starting from the Feshbach molecules. The scheme for the final step of the process, transferring the Feshbach molecules to tightly bound molecules using optical two-photon techniques, will be discussed.

Prof. Edwin C. Kan

Silicon Nanoelectronics: from Flash Memory to Beyond

The talk will start from the scaling theory of Flash memory and how heterogeneous material design with 3D electrostatics considerations can push the present operational principles to optimize the device density and characteristics. Design will highlight how to maintain the retention time requirements while reducing the program/erase time and voltage aw well as increasing endurance. From the design principles learned, we will then investigate further material integration issues, including nanotube/nanowire and graphene, for implementing switches and memories beyond the present CMOS technology road map up to the 22nm node.

Prof. Farhan Rana

Probing the Ultrafast Optical and Terahertz Dynamics of Electrons and Holes in Graphene

Using ultrafast optical pump-probe techniques we study the intraband and interband relaxation dynamics of carriers in epitaxial graphene. Our results indicate a fast 70-120 fs relaxation component which is attributed to carrier-carrier intraband scattering and a slow 1-2 ps component which is attributed to carrier-phonon scattering. We also measure the optical properties of epitaxial graphene all the way from the visible to the terahertz frequency range. In the near-IR to mid-IR range the optical conductivity of graphene is dominated by interband processes and is very well described by the value pi*e*e/2h. In the terahertz range, the optical conductivity is described by intraband processes and allows one to measure the plasmon dispersion and extract the carrier densities and the carrier momentum relaxation times. In the visible frequency range, we see a deviation of the optical conductivity from the value pi*e*e/2h.
We also discuss the possibility of a bandgap in epitaxial graphene and its signatures in the measured data. The talk will also discuss the device applications of graphene in ultrafast optical devices and in terahertz plasmon oscillators.

*** Please note room change***

Today?s emerging nano technology based on molecular device and biological science demands appropriate tools for chemically investigating a specific part with nanometer scale spatial resolution in ambient condition. Electron microscopy fits very well in the spatial resolution aspect, but they hardly provide any molecular information and strictly require a high vacuum condition. Scanning Probe Microscopy, such as STM and AFM, also provides nanometer scale spatial resolution but only with very limited molecular information due to their inherent imaging mechanism: tunneling and force interaction between molecule and tip. Laser spectroscopic information in nanometer scale would be most desirable because of its inherent capability to give a wealth of information on the chemical bonding and functional groups. Since the diffraction limit does not allow us to focus light to dimensions smaller than roughly half a wavelength, traditionally it was not possible to interact selectively with nanoscale features.

In this talk, recent effort and development in molecular nano analysis in ambient condition to overcome the diffraction limit as well as current limitations of AFM by combining AFM with Raman spectroscopy will be presented. Additionally, recent data probing before-and-after of single-wire reaction on the side wall of Single-walled Carbon Nanotube (SWNT) will be presented.

Historically, most of the interesting material discoveries occured accidentally, and were followed later by "basic research". At present, quantitative Quantum Mechanical understanding exists for at least some material properties. Yet, the tradition has been to first assume/determine the system of interest,and then calculate its specific properties. This raises the question: Could one reverse the process, and start by first stating a desired, target material property and then search theoretically for the atomic configuration or structure that has this target property? This "Inverse Band Structure"(IBS)approach involves combining insights from biologically-inspired Evolutionary Approaches with Quantum-Mechanics, permitting search of astronomic spaces of possible atomic configurations. I will illustrate IBS for identifying Nano-structures with target optical properties; semiconductors with given Curie temperature and discuss future prospects for design of the recently discovered "carrier multiplication" in quantum-dots (getting two electron-hole pairs for the price of one photon).

Nanoentities are usually suspended in a liquid to avoid adherence to solid surfaces by the van der Waals forces. Once suspended, however, the nanoentities are in the realm of extremely small Reynolds number (Re) of only 10-5 (Re = 106 for a human swimmer) where viscous drag force overwhelms. Controlled manipulation of nanoentities requires suitable external forces of precise magnitude and direction that can be administered remotely and accurately in a liquid. Here we describe the controlled manipulation of nanowires, including motion and orientation, using electrophoretic (EP) and dielectrophoretic (DEP) forces via electric potentials applied to patterned electrodes. Suitably charged nanowires can be manipulated to follow any prescribed trajectory by the voltages. Nanowires can be compelled to execute controlled linear motion with speeds of 500 ?m/sec and rotation motion with rates of 104 rpm, with relevance to MEMS devices. Since nanowires, especially multi-segmented nanowires, can be functionalized for chemical and biological purposes, the manipulation of nanowires is also relevant to biomedical applications.

Interfaces and surfaces play a key role in modern electronics and optoelectronics. The function of many devices is generated by the interfaces between conventional semiconductors, such as silicon or GaAs. The electronic properties of bulk semiconductors themselves are by far not as useful or spectacular.

In contrast to standard semiconductors, many materials with complex electronic systems, such as superconductors, magnets or multiferroics already show in the bulk intriguing functional electronic properties. At interfaces involving such materials, the complex electronic interactions of the bulk can cause unique effects. The electron systems can be drastically altered; new electronic phases may occur, often with dramatic consequences for the electronic properties of the materials (see, e.g. [1,2])

In the presentation I will provide an overview of the startling phenomena taking place at the interfaces between complex electronic systems and discuss how fundamental questions bear a direct impact on applications.

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[1] S. Thiel et al., Science 313, 1942 (2006)

[2] N. Reyren et al., Science 317, 1196 (2007)

Recent experiments by the U.C. Berkeley group [1] have explored the dynamics of helium-four superflow through an array of several thousand nanosized apertures. These experiments have found that, as the temperature is lowered, phase-slippage in the apertures changes its character, from synchronous to asynchronous. I shall describe a model of superflow through arrays of nanosize apertures which aims to account for these findings [2]. It has two basic ingredients: (a) disorder, associated with each aperture having its own random critical velocity; and (b) effective inter-aperture coupling, mediated through the bulk superfluid. It predicts that synchronicity of the phase-slips is lost at lower temperatures, due to an effective broadening of the distribution of the critical velocities. It also predicts that, as the disorder becomes weak, there is a nonequilibrium phase transition to a regime in which the inter-aperture couplings induce macroscopic, synchronous, system-wide phase-slip avalanche events. If time permits, I shall touch on some of the many connections between avalanche phenomena in superfluid helium and those arising in other settings, such as magnetism, charge-density wave materials, and seismology.

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[1] Y. Sato, E. Hoskinson and R. E. Packard, Transition from synchronous to asynchronous superfluid phase slippage in an aperture array, Phys. Rev. B 74, 144502 (2006).

[2] D. Pekker, R. Barankov and P.M. Goldbart, Phase-slip avalanches in the superflow of helium-four through arrays of nanosize apertures, Phys. Rev. Lett. 98, 175301 (2007).

By investigating the clustering patterns of CdSe/Au nanoparticle mixture on TEM grids after solvent evaporation, the formation process of CdSe/Au binary nanoparticle superlattices was studied. 1-dodecanethiol was found to be critical in making the superlattices. The role that the thiol played was investigated under various concentrations. Large areas of superlattices were formed from CdSe/Au nanoparticle pairs of different size ratios. The effect of nanoparticle size ratio on superlattice symmetry was discussed.

We have elaborated a method for measuring the elastic moduli of individual nanostructures like carbon nanotubes, molybdenum disulfide nanotubes, inorganic nanowires, and their nanometer-sized bundles. It was found that the elastic coefficients strongly depend on the production method of these nanostructures and in some cases one can improve their Young?s/shear moduli by various manipulations. This method has been successively applied for measuring the elastic response of cytoskeleton protein polymers.

The nanoscale world is not a scaled-down version of the macroscopic world. Nanoscale structures have special properties by virtue of their smallness alone, which include quantum confinement, high surface-to-volume ratio and susceptibility to fluctuations. By virtue of their size, nano-scale structures serve as a ?poster-child? for experimental demonstration of the effect, where fluctuations involve an increasing fraction of a system as system size decreases. How fluctuations will affect and be handled in developing nanoscale electronic devices is an interesting challenge.

Here I will demonstrate how combining the tools of statistical mechanics with direct imaging at the atomic scale using scanned probe and other surface imaging techniques allows the effects of fluctuations to be observed and quantified 5, 6. Two examples relevant to nanoelectronics will be presented. First the effect of fluctuations at the interface between two materials, as in a nanoelectronic contact, will be illustrated for a metal/molecule system. Second the interaction of current with structural fluctuations on the surface of a conductor will be demonstrated. Both cases will be discussed in terms of their potential impact on nanoelectronic transport characteristics.

What happens once you've submitted a manuscript to Physical Review Letters? How are referees chosen for your paper? What factors play a role when the editor makes a decision on the disposition of your paper? How does the editorial office work? How is PRL performing in the new millennium? How is your university and country performing in the last few years? And what turbulent developments are there in the world of publishing scientific material?

These and other questions will be discussed in a presentation about facts, style, statistics, history, referees, authors and 'hot' papers, which will culminate in a lively debate about the imminent changes in the landscape of scientific publishing.

Near-field effects can lead to dramatic enhancement in radiative transfer, especially when electromagnetic surface waves are involved. Though near-field effects due to surface waves have been a topic of great theoretical scrutiny over the last decade, experimental investigation is limited to a few cases - primarily because of the difficulty in achieving parallel surfaces. I will present results from our modeling of near-field radiative transfer which makes it possible to investigate radiative transfer between a microsphere and a flat plate or two microspheres. Using a technique similar to the measurement of "force-distance curves" with an AFM, we have successfully measured near-field radiative heat transfer enhancement between a sphere and a flat surface. The details of the technique will be discussed.

Jingqin Cui
Department of Chemical Engineering, City College of New York

?Mechanistic Study of Asymmetric Silver Electroless Deposition on Templated Polystyrene Spheres?

The control of the surface morphology of a metal deposit plays an important role in (i) tuning the signal in surface-enhanced Raman scattering studies, (ii) assembly of patchy particles, and (iii) catalysis. Recently, we developed a novel templating procedure to manufacture surface-anisotropic, silver-modified polystyrene spheres via electroless silver deposition. Our data indicated that the silver deposition process might be diffusion-controlled due to the observed dependence of the amount of silver deposited on the stirring rate. Here we report on the effect of reaction conditions on the morphology of the silver deposit.

Xiaoding Wei
Department of Mechanical Engineering, Columbia University

?High Strength and Plastic Strain Recovery of Nanocrystalline Cu Films?

Submicron thick Cu films with average grain size of about 40 nm were fabricated and mechanical properties of those films were tested by Plane-strain Bulge Test. The nanocrystalline Cu shows much higher strength than the coarse-grained counterpart. Characteristic deformation mechanisms, such as grain boundary sliding and grain rotation were observed. More importantly, behavior of ?plastic strain recovery? was found on the nanocrystalline Cu films.

Light interacting with a metal surface can excite both single particle and collective (plasmon) excitations. Nonlinear photoelectron emission spectroscopy and microscopy allow us to study the light-surface interaction with energy, momentum, spin, and spatial resolution. First I will show several examples how a study of single particle excitation provides information on the band structure, photoemission dynamics, and adsorbate excitations on single crystalline metal surfaces. Next I will present the recent results on ultrafast photoemission electron microscopy of surface plasmon excitation, interference and focusing in nanostructured Ag films.

An overview will be given of experimental progress in demonstrating silicon-based quantum computing at the few qubit level, in which the qubits are comprised of engineered single phosphorus atoms embedded in the silicon host, with information encoded onto the electron spin state of these atoms.

The experimental work will be discussed in the context of a bi-linear MOS architecture compatible with scale-up and fault-tolerant operation involving fast, coherent transport of spin qubits around the chip. The presentation will also touch on interfacing CMOS control electronics to the qubit arrays.

A short video will be shown, which provides an accurate visualisation of what the silicon quantum computer would ?look like? in operation.

Since 2000, the Australian Centre for Quantum Computer Technology has published more that 600 papers related to its dual research focus of silicon and optical quantum computing ? see www.qcaustralia.org for a full listing.

The major mathematical problem of the analysis of crystallographic preferred orientation (?texture analysis?) is the inversion of experimental ?pole figures?, i.e. sampled spherical distributions of crystallographic axes (PDFs) defined on S2, into an orientation density function (ODF) defined on SO(3). The relationship of an ODF and its corresponding PDFs is basically modelled by a Radon transform. However, in contrast to the inverse Radon problem the PDF?to?ODF inversion problem does not possess a unique solution, but additional modelling assumptions are required. Canonical modelling assumptions seem to include the non?negativity of both orientation and pole density functions as well as their smoothness implied by the characterization of the range of the Radon transform. Due to a novel method of PDF?to?ODF inversion applying radial basis functions and an implementation employing fast Fourier transform algorithms we get rid of obsolete restrictions such as seriously bounded series expansion degree, seriously bounded total number of components, regular spherical grid of measurements on the pole sphere, weak to moderate textures, large cpu times etc. Since it is now possible to process intensity data arbitrarily scattered on the pole sphere and successively compute numerical approximations of an ODF explaining the data while they are being measured, we suggest a new experimental strategy, which depends on the texture being measured itself. In particular we suggest an adaptive successive refinement of an initial coarse uniform grid to a locally refined grid where the progressive refinement corresponds to the pattern of preferred crystallographic orientation. At each level of refinement an ODF is computed, and the refinement is terminated if some stopping rule is accomplished. The advantage of this strategy is that it either largely decreases the measuring time or makes best use of the available measuring time. It is especially well suited to capture, represent and analyse extremely sharp textures as in technical single crystals.

A great deal of interest has emerged in the use of organic semiconductors for photodetecting applications, particularly for mechanically flexible photodetector applications. We have been pursuing an architecture for photodetectors which uses submicron phase engineered crystalline organic photoconductor particles in place of traditional organic thin film heterojunctions. Moving to this material system affords significant advantages in performance and processability, which will be presented, including wider spectral range, increased air stability, and printing-compatible deposition techniques.

A number of devices will be presented, including a 4x4 active matrix imager with organic semiconductor frontplane and backplanes. Some of the challenges in device integration and processing, including forming contacts, material deposition, and self absorption will also be discussed. A wish list for future materials development will also be discussed.

The excellent properties of single-walled carbon nanotubes (SWNT) and
graphene sheets create opportunities for their use in various areas of
electronics. In these cases, aligned arrays of pristine SWNTs and
rationally synthesized graphene-like materials provide thin film
semiconductors for scalable circuit integration. This talk describes (1)
methods for growing aligned arrays of SWNTs, (2) approaches to make
multilayer, superstructures of these arrays, and (3) chemical techniques for
producing conjugated carbon monolayers in flat sheets and 3D layouts.
Transistors and circuits formed of these materials illustrate some of the
electrical, mechanical and optical properties that can be achieved.

Excitonic effects in ideal 1D systems are known to show very peculiar features. However, the occurrence of such effects in real systems is far from being obvious. Besides, the relevance of Coulomb interactions can strongly depend on the specific system. We present the main characteristics of optical excitations in semiconductor nanotubes, as obtained from accurate ab-initio many-body calculations, and compare them with other quasi-one-dimensional semiconducting systems. Our theoretical approach, which includes both self-energy corrections and excitonic effects through the GW BSE formalism, can provide a deep understanding of excited-state properties. In all the studied cases, excitonic effects play a crucial role, with tightly bound excitons dominating the spectra. Within the same formalism, we first compute two-photon absorption spectra, achieving excellent agreement with recent experiments. Moreover, a complete symmetry analysis of the excitonic states is carried out, fundamental for understanding the luminescence features observed in experiments.

Billions of dollars/euros are being invested in "clean-coal" technologies (CCT) to produce "green energy" (electricity, synthetic natural gas, and synthetic liquid fuels), with near-zero GHG (greenhouse gases, i.e., CO2) emissions. Why the strong interest in coal gasification, a core CCT technology? What is the status of development and commercialization (thermal vs. chemical cracking)? Are CCTs including CO2 capture and sequestration effective and economically viable vis-a-vis alternative and renewable energy source?

TBA
*Please note time and venue change for this seminar.

Nanoparticle Phase Stability and Catalysis

This talk will consist of two parts. In the first part, the synthesis and characterization of xHfO2-(1-x)ZrO2 nanoparticles (x = 0 to 1) prepared by aqueous co-precipitation will be discussed. Both precursor concentration and annealing environment are used to control the structure and morphology of the resulting crystalline nanoparticles. In the second part, a new water-gas shift catalyst composed of Cu and CeO2 will be described. This material exhibits an interesting microstructure and has shown high activity for this reaction which produces hydrogen (CO+H2O?CO2 + H2).

Incorporation of custom-design nanomaterial into photonic devices and systems enables the realization of optical functionalities favorably controlled with external optical and electrical effects. In my research group, we work on the development of new nanophotonic hybrid devices and systems that consist of multiple combinations of nanostructures (epitaxially grown, chemically synthesized, deposited, etc.) for the applications of light generation, displays, modulation, sensing, imaging, alternative energy, and communications in a wide spectral range from the ultraviolet to the visible.

In this talk, we will present the device conception, design, modeling, fabrication, experimental characterization, and theoretical analysis of examples of our hybrid nanophotonic systems that incorporate different types of functional nanomaterial including GaN/InGaN and AlGaN/GaN quantum structures, CdSe, CdSe/ZnS and CdS nanocyrstals and nanorods, Au-Ag nanoparticles, and TiO2?ZnO nanoparticles. Among these examples are our hybrid white light sources for solid state lighting with tunable light properties; our localized plasmon-coupled nanocrystal emitters for controlled modification of spontaneous emission; our nanocrystal hybridized scintillators for enhanced photodetection and photovoltaics in UV; and our visible (blue) and UV quantum electroabsorption modulators for optical clock injection directly into silicon microelectronics and secure no-line-of-sight communication.

Muon spin relaxation (MuSR) is a powerful method in detecting static and dynamic magnetic behaviors near the phase boundary.
By MuSR measurments, we showed that quantum phase transitions in itinerant magnets MnSi (via pressure tuning) and
(Sr,Ca)RuO3 (via Sr/Ca substitution) are associated with phase separation and complete suppression of critical dynamic behavior [1].
MuSR results in HTSC systems [2,3] also indicate phase separation between nonmagnetic/superconducting and magnetic/non-superconducting volumes near the spin-charge stripe state. Similar phase separation between antiferromagnetic phase and non-magnetic spin gap state has been found in frustrated square lattice J1/J2 [4] and Kagome lattice spin systems [5]. After reviewing these results and relevant phase diagrams in heavy-fermion systems, we consider if the behaviors associated with first-order transition, phase separation, and discontinuous changes are generic to quantum phase transitions.

[1] Y.J. Uemura et al., Nature Physics 3 (2007) 29.
[2] A.T. Savici et al., Phys. Rev. B66 (2002) 014524.
[3] K.M. Kojima et al., Physica B326 (2003) 316.
[4] H. Kageyama, Y.J. Uemura et al, unpublished results [5] P. Mendels et al., Phys. Rev. Lett. 98 (2007) 077204.

Search for topologically non-trivial states of matter has become a prime goal for condensed matter physics. Recently, a new class of topological insulators has been proposed. These topological insulators have an insulating gap in the bulk, but have topologically protected edge states due to the time reversal symmetry. In two dimensions the edge states give rise to the quantum spin Hall (QSH) effect, in the absence of any external magnetic field. We show that the QSH state can be realized in HgTe/CdTe semiconductor quantum wells. By varying the thickness of the quantum well, the electronic state changes at a critical thickness. This is a topological quantum phase transition between a conventional insulating phase and a phase exhibiting the QSH effect with a single pair of helical edge states. This theoretical proposal has been tested in a recent experiment carried out at University of Wuerzburg, and the distinct signatures of the QSH state have been experimentally observed.
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[1] Bernevig, Hughes and Zhang, Science, 314, 1757, (2006)
[2] Koenig et al, Science, to be published.

Organic semiconducting materials are now being considered as the active materials in displays, electronic circuits, solar cells, chemical and biological sensors, actuators, lasers, memory elements and fuel cells. The flexibility of their molecular design and synthesis makes it possible to fine-tune the physical properties and material structure of organic solids to meet the requirements of technologically significant applications.
I will present our recent work on new organic semiconducting materials and dielectrics. I will also cover some work towards rational design of organic semiconductor materials by understanding effects of molecular structure and surface properties on molecular orientation, crystalline packing and film morphology.

Given that about 90 percent of the world?s power is generated by thermal means, any cost-effective method to increase efficiency and/or extract work from heat lost to the environment could have significant impact on energy conservation and, thereby, reductions of CO2 emissions. Direct thermal to electrical energy conversion using solid-state thermoelectric devices is attractive because such devices contain no moving parts, are environmentally benign, and can operate under small temperature differences. Thermoelectric materials are ranked by a figure of merit, ZT, which is defined as ZT = S2o T/k, where S is the thermopower or Seebeck coefficient, o; is the electrical conductivity, k is the thermal conductivity, and T is the absolute temperature. For the performance of thermoelectric devices to be about 30 percent of the Carnot limit and, thereby, comparable to their macroscopic gas or vapor-based counterparts, one must develop materials with ZT > 3. Five decades of research on bulk semiconductors has increased room-temperature ZT only marginally, from about 0.6 to 1. While each property in ZT can be individually increased by several orders of magnitude, the challenge in increasing ZT lies in the fact that S, o, and k are interdependent ? changing one alters the others, making optimization extremely difficult. Recent research on nanostructured materials has led to sharp increases in ZT, although the fundamental reasons of why and how nanostructuring helps are not completely understood. In this talk, I will report some of our group?s work on electron and phonon transport in nanostructured materials that have uncovered some of the underlying reasons. Based on this we have created a set of criteria for designing nanostructured thermoelectric materials, which have led to three new classes of materials: (i) molecular heterostructures; (ii) complex oxides; (iii) bulk nanostructured semiconductors. The talk will provide a background of the field and explore new directions of research.

The electronic properties of amorphous thin films are of great interest due to their application in devices such as light emitting devices, solar cells, photodetectors, and lasers. Compared to conventional crystalline materials, amorphous thin films have the potential to enable entirely new functionality, larger areas, higher efficiencies, flexible substrates, and inexpensive fabrication. In this talk I focus on organic materials, where continued device optimization increasingly requires a deep understanding of the physics of the underlying electronic processes. I employ microscopic models of polaron and exciton processes to calculate macroscale phenomena in amorphous small molecular weight organic thin films using Monte Carlo (MC) simulations comprising a new simulation tool called the Organic and Nano-Electronics Simulator, or ONESim. The principle results reported here: (1) the identification of significant errors in existing models of molecular energy level disorder in polarizible media; (2) a rigorously self-consistent quantitative fit of our exciton diffusion model to experimental data for a small molecular weight amorphous organic solid; and, (3) the first MC simulations of equilibrium polaron mobilities in amorphous organic solids as a function of both field and carrier concentration. I will also describe recent results adapting ONESim to the student of quantum dot (QD) devices, such QDLEDs.

Most of the new technological development depends on advances in materials science. The synthesis of new materials is based on the fact that most properties of solids depend on their atomic structure, chemical composition and site of solids, if the size is comparable to the interatomic spacing. Nowadays nanocrystalline materials form a new class of disordered solids, typically having average grain sizes of a few nm and can exhibit photonic, electronic and mechanical properties that are very different from those of conventional crystalline materials.
At the time the most active fields of research and developments of nanostructured materials in Laboratory of High Tech Materials are focusing in bulk metallic glasses reinforced by nanocrystals, photoluminescent nanocrystals of Si in matrix of amorphous SiO and non-magnetic hexagonal nanocrystalline Ni films grown by radio frequency magnetron sputtering.
Metallic glassy alloys exhibit superplastic behaviour in the supercooled liquid state due to viscous flow which allows them to be molded in any desirable shape. Nanocrystals reinforced bulk metallic glasses represent a big step in the ever-constant endeavour of synthesis and optimization of new high ? tech materials. We focus on Pd ? based and Zr ? based examples of metallic glasses reinforced by nanocrystals prepared by conventional liquid quenching and also by high energy repeated deformation processing via mechanical alloying.
Samples prepared in large quantities by thermal decomposition of SiO at temperatures above 850 0C exhibit strong photoluminescence, at room temperature, in the near infrared and at energies higher than the band gab of bulk silicon, as a result of excitonic recombination under quantum confinement conditions.
We demonstrated that it is possible to produce single-phase hcp Ni films stable at RT, regardless of the kind of substrate and the film thickness, via radio frequency magnetron sputtering by selecting properly the Ar pressure. The prepared hcp Ni films are not ferromagnetic down to 4.2 K.


References

1) C. Politis, W. L. Johnson; Preparation of Amorphous Ti1-xCux (0.10 < x < 0.87) by Mechanical Alloying; Appl. Phys. 60, 1147 (1986).
2) V. Kapaklis, P. Schweiss, C. Politis: Bulk Amorphous and Nanocrystalline Reinforced Pd- Based Alloys: Formation, Structural, Thermal and Elastic Properties; Adv. Eng. Mat. 7, 123 (2005).
3) V. Kapaklis, C. Politis, P. Poulopoulos, P. Schweiss; Photoluminescence from silicon nanoparticles prepared from bulk amorphous silicon monoxide by the disproportionation reaction; Appl. Phys. Lett. 87,123114 (2005).
4) P. Poulopoulos, V. Kapaklis, C. Politis, P. Schweiss and D. Fuchs: Non-Magnetic Hexagonal Ni Films Grown by Radio Frequency Magnetron Sputtering; 6, 3876 (2006)

Silicon Complementary Metal Oxide Semiconductor (CMOS) technology is perhaps the most astounding technologies of the present time. Driven by aggressive scaling, the technological innovations and advances in design and manufacturing have postponed the ?end? of CMOS. The next 10 to 15 years, every effort will be done to push CMOS toward its ultimate limits. What lies beyond?

Conventional top down approach and the bottom up nanotechnology inspired by chemistry, physics and biology appear to be converging. Although these and other technological innovations are very promising, their near term success in industry mainly depends on their compatibility with standard CMOS processing.

Collaboration between experts of different disciplines is the key to extend the CMOS era and to be prepared for the post-CMOS era. Nanotechnology education and research must encourage cross fertilization of different ideas and approaches to realize novel IC technologies with potential advantages in cost, performance and functionality. The talk will discuss how innovative activities of NSEC and MRSEC at Columbia University and availability of robust CMOS platform and education at Rochester Institute of Technology together may lead to immense opportunities.

(1) The use of a very thin gate dielectric based on a self assembled monolayer (SAM) has been found to improve the performance of individual semiconducting single-walled carbon nanotube FETs. (2) We have investigated organic n-channel TFTs based on a series of cyanoperylene diimide derivatives. (3) Novel organic charge-transfer salts based on the Cu-dichloro-dicyano-benzoquinone complex that exhibit reversible non-volatile resistive memory switching phenomena are presented.

Nanotube-bundle based thin-film transistors (NTB-TFTs) have been explored in recent years to improve the performance of flexible electronics (e.g. displays, e-paper, large-area sensors, flexible antennae, etc.) to address the medium-to-high performance applications in the 10-100 MHz range. These transistors are made from composites consisting of carbon nanotubes (CNTs) or silicon nanowires dispersed randomly in plastic or glass substrates. Most of the reported work on NTB-TFTs has concentrated on device fabrication and processing, but little is understood about the fundamental physics that govern device operation and scaling. Problems which could limit the ultimate performance of these devices include the presence of metallic tubes, hysteresis due to charge injection, and unacceptably high power dissipation in high frequency applications. Furthermore, since the composite is made from low thermal conductivity plastics and organics, self-heating is expected to become a severe bottleneck to performance.
In the present talk, a theoretical and computational basis is developed for electro-thermal transport in nanotube composites for TFT applications. The analysis uses concepts from heterogeneous percolation theory, heat-transport physics and device physics. A finite volume method for computing electrical and thermal transport in random CNT-network composites is developed. The effect of the geometrical /statistical properties of the tube network, contamination by metallic tubes, and the influence of interfacial resistance parameters on the electrical and thermal characteristics of the device are presented. Percolation effects on thermal transport and the limits of the traditional effective medium theory are discussed. Finally, investigation of the thermal transport between two contacting nanotubes using the molecular dynamics simulations is discussed.

Shengguo Jia
MRSEC, Dept. of Applied Physics and Applied Math

Mechanism of the Electrophoretic Deposition of CdSe Nanocrystal Films
The charge on nanocrystals is not only used to stabilize the colloidal systems but also to assemble these materials into novel films and superlattices. Here, we propose a model for the charging of colloidal CdSe nanocrystals in non-aqueous solvents involving the dissociation of ligand molecules from specific surface sites. We also develop a mechanistic model to explain the electrophoretic deposition of nanocrystal films based on electrophoretic mobility measurements, photoluminescence from nanocrystal solutions and films, and observations from deposition experiments. Even though equally thick nanocrystal films are obtained on both negative and positive electrodes, the numbers of positive and negative nanocrystals are not equal in solution. After appropriate reprecipitation cycles, the surface ligands on colloidal CdSe nanocrystals are partially removed, giving rise to unpassivated surface sites that may enable the nanocrystals to better ?stick? to electrodes during electrophoretic deposition. Thus, the surface charge of the nanocrystals is very significantly influenced by the presence of coordinating ligands. The factor limiting the maximum thickness achievable by electrophoretic deposition is thought to be the concentration of the minority charged nanocrystals (negatively charged nanocrystals in our experiments).

Chul-Ho Lee
Thermoelectric Transport in 1-D Semiconducting Nanostructures

One-dimensional (1-D) nanostructures, including nanowires, nanorods and carbon nanotubes (CNTs), have attracted significant attention as building blocks for nanoscale electronics, optoelectronics and sensors. Although the understanding of the electronic properties of these nanostructures is necessary for these potential applications, it is difficult to find the reliable techniques for investigating them. Thermoelectric power (TEP) measurements can be a powerful tool for further understanding of the electronic properties since TEP is the most sensitive quantity to any change of an electronic band structure. In this presentation, we report on in-situ TEP measurements of individual 1-D semiconducting nanostructures (including ZnO nanorods and GaN nanowire) using a microfabricated heater and thermometers. Reasonable estimates of the carrier concentration are made using the temperature dependence of the TEP. Furthermore, the changes of conductance as a function of applied gate voltage can be correlated to TEP with the semiclassical Mott relation.

1) National CRI Center for Semiconductor Nanorods and Department of Materials Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang, Gyeongbuk 790-784, Republic of Korea

In this talk I will discuss 2 problems related to the electronic structure and coherent transport properties of graphene ribbons. The

first is the relation between gate potential and induced density both in graphene and graphene ribbons. I show that, on top of the classical

electrostatic contribution, the quantum contribution to the capacitance in 2D graphene yields direct information about the slope of the Dirac bands. In the case of graphene ribbons, numerical self-consistent calculations show the dependence of the capacitance on the graphene width. The second problem is coherent transport accross a constriction in graphene ribbons. The influence of edge type, shape, and dimensions of the constriction on the ballistic conductance is analyzed [2,3]. I will discuss also a possible all-carbon device whose conductance is not determined by the metallic contact [3], and possible quantum-dot like states in graphene constrictions [2].




_____________________

[1] J. Fern?ndez-Rossier, J. J. Palacios, L. Brey, cond-mat/0702473, accepted in PRB [2] F. Mu?oz-Rojas, D. Jacob, J. Fern?ndez-Rossier, J. J. Palacios, Phys. Rev. B *74*, 195417 (2006)

[3] F. Mu?oz-Rojas, J. Fern?ndez-Rossier, J. J. Palacios, in preparation

In principle, time-dependent current density functional theory (TDCDFT) allows for exact calculations of the transport properties of single molecules. In practice, one is forced to make approximations to the exchange-correlation functional employed, and the computationally less costly ground-state DFT in a local approximation (LDA/GGA) is used. This introduces several errors that can lead to an overestimation of the calculated current by one to three orders of magnitude. We will discuss the origin and scope of these errors. Special focus will be given on the effects of a smooth functional without derivative discontinuity on the transport properties and Coulomb Blockade effects. We will also present ideas how quantitative results can be obtained with the available techniques. E.g., we perform model calculations for a diode type molecule, which exhibits a structure of a double quantum dot and which has been investigated experimentally.

Michael Tambasco:

"Modeling the Role of Ligands in Controlling the Sizes, Shapes and Supramolecular Ordering of Quantum Dots"

The density of electronic states controls many physical properties of a quantum dot and can be tuned by altering the dot's size, shape, or composition. In colloidal methods, ligands are used to control quantum dot size, shape, and polydispersity; however, there exists no a-priori means of describing specific conditions that will optimize the synthesis procedure. We apply a mean field theory to study the role of ligands in quantum dot synthesis. We examine the effects of ligand concentration on thermodynamic and structural properties, and compare our results with available data.

Millicent Smith:

"Structural Properties of Nanosized Barium Titanate"

We have investigated the structural and phase transition properties of various sizes of nanocrystalline barium titanate (BaTiO3) using XRD, pair distribution function (PDF), and Raman spectroscopy. Temperature-dependent Raman spectroscopy and XRD measurements indicate that the phase transition is diffuse in temperature, in opposition to the sharp transition that occurs in the bulk and is predicted by Landau theory. We also report PDF measurements showing an increasing amount of apical Ti-O bond distortion with decreasing particle size. We believe that these distortions have a higher degree of directional disorder in small particles than in larger particles, accounting for the decreased c/a ratio in the small particles.

Carbon nanostructures are attractive for spin polarized electronics due to low spin orbit coupling which should lead to long spin coherence times. In this talk, I will introduce spin polarized electronics and current applications in magnetic recording and memory. These are based primarily on spin polarized transport in metals and tunnel junctions. More recently, investigation of spin polarized transport has been performed in new materials systems such as carbon nanotubes. I will discuss our research on spin in carbon nanotubes (CNT) and mesoscopic graphite flakes. We observe magnetoresistance in CNT and graphite spin valves, which is a signature of spin polarized transport. We are now working to achieve spin transport in single layer graphene. Finally, I will discuss our efforts to develop molecular beam epitaxy growth of graphene layers on insulating substrates, including the challenges for both solid source and gas source growth. This project is in the early stages, but I will talk about our approach and some preliminary findings.

Daohua Song:

"Probing ferroelectricity in nanoscale materials"

Abstract: Second harmonic generation (SHG) is performed on single BaTi2O5 nanowires (NWs). It is found that SHG provides a simple but effective approach for distinguishing crystallographic orientations of individual NW. The spontaneous polarization is found to be along the NW axis. By examining the temperature dependence of the SHG signal, we observed a 2nd order ferro-para phase transition. The Curie temperature Tc is determined to be around 290 0C in comparison to the bulk value 430 0C. Possible reasons for this phenomenon will be discussed. It is the first time that SHG has been successfully applied to study the phase transition to the level of a single NW.


Sioan Zohar:

"Magnetic resonance in Fe2O3 nanoparticle arrays."

Bernard-Duraffourg?s condition for semiconductor laser action requires that emission exceed absorption at laser wavelengths. Thus, strong self-absorption at luminescent wavelengths in direct bandgap semiconductors limits the performance of conventional semiconductor-lasers and optical-amplifiers. Here we demonstrate novel self-assembled nanoscale deep-centers in GaAs having dramatically lower self-absorption and higher Einstein B coefficients than band-to-band transitions. Our GaAs deep-level material is shown to be unique among important III-V-semiconductors at the 1.3-1.5?m wavelengths in achieving transparency at near-zero injection, because of insignificant self-absorption (3.6 cm-1, instead of the 104 cm-1 in typical direct-bandgap semiconductors) at luminescent-wavelengths. We created this materials property by engineering a Franck-Condon shift of the absorption spectra away from the luminescence spectra, thus making the Bernard-Duraffourg condition easier to satisfy. This Franck-Condon shift could become an important paradigm for semiconductor lasers with near-zero threshold. Additionally, our novel GaAs deep-centers exhibit an Einstein B-coefficient (a fundamental materials property, which limits the attainable device efficiency-bandwidth product) eight times that of typical direct-bandgap semiconductors. We discuss the thermodynamics of formation of the self-assembled nanoscale deep-centers.
In related work, we used an analytic continuation of the energy-bands in a k.p method to derive simple analytic wavefunctions and optical selection-rules for nanoscale deep-centers in terms of simple materials parameters (e.g., Kane dipole). A large number of semiconductors can be modeled this way. In our work on distributed-Bragg-reflectors (DBRs), we used an exact treatment of Maxwell's equations to derive generalized form and structure factors for impedance and reflection from periodic layers having arbitrary index profile. Significant differences from kinematic X-ray diffraction theory are seen.

Spin based electronics, commonly referred to as "spintronics", seeks to expand the functionalities of microelectronic devices by introducing the ability to manipulate the carrier's spin, in addition to or instead of its charge. Key steps in spintronic devices include the injection, manipulation and detection of the carrier's spin. Spin valves and magnetic tunnel junction devices, which are metal based spintronic devices, have already found important applications in high capacity hard disk drive read heads and have potential for high performance non-volatile solid state memories. However, spin manipulation must be introduced into mainstream semiconductor devices in order to realize the full potential of this field.
One vital step towards the realization of this goal is the development of magnetic semiconductors, which can be built into existing device structures. Most magnetic semiconductors however, are complex structures, which cannot readily be introduced as a part of existing devices. This has been the motivation for development of dilute magnetic semiconductors.

Dilute magnetic semiconductors (DMS) are semiconductors in which a fraction of the cations are substitutionally replaced by magnetic ions. The exchange interaction between the spin of the dopant atoms and the carriers in the semiconductor host is expected to bring about global ferromagnetic order in the entire lattice in these materials. The search for novel DMS candidates has been driven by two cardinal requirements - a material system with well-developed growth technology, and a high Curie temperature. Several theories have offered explanations as to the origin of ferromagnetism in DMS, and have predicted high curie temperatures in transition metal doped III-V nitrides and II-VI oxides.

In this work, we have investigated the growth and characteristics of one such promising candidate, transition-metal doped InN. InN films were deposited on c-sapphire substrates by molecular beam epitaxy, employing GaN underlayers to reduce the lattice mismatch between the film and substrate.
Room temperature photoluminescence experiments revealed a bandgap of about
0.8 eV in InN, which is typical for crystalline films. The films were doped with up to 6% Cr with no noticeable trace of crystalline secondary phases detected by X-ray diffraction. However, Mn-doping led to segregation of manganese nitride. Hall effect measurements revealed n-type behavior in both undoped as well as Cr-doped films. Cr-doped InN exhibited magnetic hysteresis, with a small remanence and coercivity up to room temperature.
X-ray magnetic circular dichroism experiments revealed dichroism at the Cr L-edge, confirming that the Cr in the matrix was magnetically active. While long-range magnetic order was observed well above room temperature in this material, deeper probing of the magnetic behavior revealed metastability.
The origin of magnetic behavior in Cr-doped InN is discussed in the context of bound magnetic polaron formation, as well as the role of impurity bands in mediating magnetic order.

Using the ?next-generation? molecular beam epitaxy system, we have reproducibly synthesized thin films of LaSrCuO, BiSrCaCuO and BaKBiO with rms surface roughness in the range 0.2-0.5 nm. This technology has enabled fabrication of precise and uniform multilayers and superlattices, some of which contain barriers or high-Tc superconductor (HTS) layers that are just one-unit-cell thick and yet have no pinholes over macroscopic areas.1 In turn, such heterostructures enable novel experiments that probe into the basic physics of HTS. For example, we have established that HTS and anti-ferromagnetic order phase-separate on ?ngstrom scale,2 while the pseudo-gap state apparently mixes with HTS on an anomalously large length scale (?Giant Proximity Effect?).3

In this talk, I will review of our most recent experiments on such films and superlattices, including XRD, AFM, angle-resolved TOF-SARS, high-resolution TEM, transport, resonant X-ray scattering and, for the first time, ultrafast photo-induced RHEED.4 The results include atomic-layer synthesis of ?artificial? (metastable) superconductors with high-Tc (above liquid nitrogen temperature), a discovery of interface HTS, and an unambiguous demonstration of strong coupling of in-plane charge excitations to out-of-plane lattice vibrations.

The p-n junction diode is the basis for nearly all-modern semiconductor electronics, and is useful for characterizing fundamental properties of semiconductors. Here, I will describe the formation of ideal-carbon nanotube p-n diodes along individual single-walled carbon nanotubes (SWNTs). As a model system, these diodes are used to examine the interplay between transport and optical properties in quasi 1D semiconductors. I will show that many-body effects, in particular doping induced band-gap renormalization and excitonic effects, strongly dominate the transport and optical properties due to strong confinement.

Understanding collective dynamics in the presence of disorder has been of long standing interest in magnets from iron to high temperature superconductors. Here we present the first direct measurements of fluctuations in the nanoscale spin- and charge-density wave superstructure associated with weakly pinned antiferromagnetic domains in elemental Chromium. The technique used is X-ray Photon Correlation Spectroscopy, where coherent x-ray diffraction produces a speckle pattern that serves as a ?fingerprint? of a particular magnetic domain configuration. We measure the temporal evolution of the patterns, which corresponds to domain walls advancing and retreating over micron distances. While the domain wall motion is thermally activated at temperatures above 100K, it is not so at lower temperatures, and indeed has a rate which saturates at a finite value ? consistent with quantum fluctuations - on cooling below 40K. We discuss a model in which the tunneling degree of freedom, which involves rotating the Fermi surface by 90 degrees, can be considered a spherical, nanoscopic ?quantum? rotor in a potential with minimum along the cubic directions. We will also show that the dynamics of magnetic domains in chromium is a special case of the more general class of problems of dynamics in disordered systems that include everything from glassy behavior and ?jamming? in gels to earthquakes. Unique to the antiferromagnetic system, however, is that quantum tunneling can provide an additional channel for relaxation.

Nanotechnology in the environment. Applications of nanotechnology to environmental problems, particularly water purification, will be discussed. Both new separation systems which use magnetic nanoparticles as well as photo-oxidative remediation using nanoscale carbons, are possible technologies for this area. While these systems are being developed and tested under real world conditions, it is also essential to understand their environmental impacts and take steps early in the development process to minimize those impacts.

The trends towards ultimate miniaturization in semiconductor technology and the fabrication challenges in nanotechnology call for new approaches and materials which enable the fabrication of nanometer sized structures. One of the most widely used technologies to generate such patterns is electron beam lithography where an electron beam with a potentially sub-nanometer diameter is scanned over the substrate coated with a polymeric resist layer. The smallest obtainable structure size not only depends on the beam diameter but also on the resist resolution, determined to a large extent by its building blocks. Therefore research and development in the field of nonpolymeric high resolution electron beam resists is of high interest. It has been shown that calixarene derivatives used as negative tone electron beam resists have the potential to pattern down to the 10 nm regime an below.

On the one hand we are looking for ways to reduce the required electron dose which is almost three orders of magnitude higher for calixarene derivatives compared to commercial polymeric resist materials. Optimum processing conditions for Hydrogen-Silsesquioxane is another focus of studies.

Applications ranging from single electron transistors to

The Constitution states that the purpose of the patent system is to ?Promote the progress of the useful arts?. There is a wide range of views as to whether that purpose is being realized with the operation of the patent system today ? from the pharmacological industry that supports it, to many computer scientists who are against it. In this presentation, we will delve into patents to understand how they are meant to operate, and will then discuss whether or not the system is accomplishing its constitutional mandate. Along the way, we will discuss patent claims, patent litigation, and the current backlog in the Patent Office. You will come away with a fairly sophisticated understanding of how you can use the patent system to your advantage.

We studied the adsorption of organic molecules, growth behavior, and physical properties on silver, gold, and HOPG surfaces by using ultra-high-vacuum low-temperature scanning tunneling microscopes. Combined with low energy electron diffraction and first-principles density functional theory calculations, we tried to understand the self-assembly mechanism of molecular structures, and then to find the key parameters which can modulate their structures for obtaining functional molecular thin films. The following three factors are found to be useful for the modulation. 1) The electric filed can induce molecular structural transition due to the molecular polarity, which is helpful for designing functional molecules of electronic devices. 2) The alkyl chains of quinacridone derivatives (QA) determine the orientation of molecular overlayers on an Ag(110) substrate. The interaction of QA and the Ag substrate is primarily due to chemical bonding of oxygen to specific positions at the silver substrate, determining the molecular orientation and preferred adsorption site. However, the intermolecular arrangement can be adjusted via the length of attached alkyl chains. We are able to fabricate uniform QA films with very well controlled physical properties. 3) By thermal and chemical control, we are able to self-assemble three dimensional molecular nanostructures, e.g. ordered PTCDA structures exclusively on flat Ag(111) facets, or DMe-DCNQI structures exclusively on stepped Ag(221) facets. It is demonstrated that bonding, the key factor for selectivity, occurs via the end-atoms, while the molecule?s mid-region arches away from the substrate. Theoretical results obtained by high-level theoretic calculations are consistent with the experimental observations.

DNA is considered as one of the attractive candidates for molecular electronics. It was studied in many ways including: electrical transport, atomic force microscopy (AFM) and scanning tunneling microscopy (STM). The results of various measurements of charge transport in DNA seem inconsistent. A deeper look into the experiments can offer a general understanding of the reports and ways to optimize the conductivity in DNA.

We attach short (26 bp) DNA molecules to a gold surface at one end and to a gold nanoparticle on the other end. Upon approaching and contacting the gold particle with a conductive AFM tip with a controlled applied force, we can measure current-voltage curves through the double-stranded DNA molecule. Our measurements show relatively high currents (200 nA@2 V). We report a comprehensive set of control experiments that support these results. Further, we compare the electrical conductivity of monolayers of: ssDNA, dsDNA and dsDNA with thiols in the upper end. The results call for faster conduction mechanism than those suggested to account for the solution chemistry experiments.

One of the attractive DNA derivatives for nanoelectronics is G4-DNA, a molecules composed of consecutive guanine tetrads. I will present clear polarizability measurements in this molecule. In addition, I will also report STM spectroscopy of single poly(G)-poly(C) DNA molecules and universal scaling behavior observed in these spectra.

It is widely recognized that the types of grain boundaries in a material and the manner in which they are connected affect a wide range of properties and, ultimately, a material's performance and lifetime. Understanding causal structure/property relationships relies on accurate descriptions of the grain boundary network, which is structurally complex. To distinguish one grain boundary from another, it is necessary to characterize five independent parameters. Furthermore, the different types of grain boundaries are connected in non-random configurations. To capture this complexity, we have developed techniques to measure the five-dimensional grain boundary character distribution (the relative areas of different boundary types, distinguished by lattice misorientation and grain boundary plane orientation). Based on observations in a range of metals and ceramics (Al, grain boundary engineered Ni, Cu, and ??-brass, Fe-1%Si, WC, MgO, SrTiO3, TiO2, MgAl2O4, and Al2O3), we are beginning to understand how the grain boundary character distribution evolves with time and is influenced by impurities and processing conditions. One general observation that will be described in this talk is that grains within polycrystals have preferred habit planes that correspond to the same low energy, low index planes that dominate the external growth forms and equilibrium shapes of isolated crystals of the same phase. A second topic will be the probable existence of a steady state grain boundary character distribution that is correlated to grain boundary energies and is established in the early stages of growth. A theory for the development of steady state, characteristic grain boundary character distributions will be described.

Organic and Polymer materials have been utilized both as active and passive materials for nanotechnology. This talk details the investigation of dendrimer based precursor polymers that have been used to prepare ultrathin films or nano-objects. Compared to their linear polymer analogs, these materials have interesting generation dependent properties and processability. The formation of hybrid organic-inorganic nanoparticles results in interesting energy transfer and electron transport properties.

In a climate of intense economic competition, leading microprocessor manufacturers currently strive to double integration density roughly every two years. At this frenetic pace, dimensional tolerances are no longer scaling with dimensions, contributing to growing variability in the properties of nominally identical devices. Innovations in device and circuit co-design are combating this problem to some extent, but economic limits on allowable power dissipation are now severely limiting clock speeds. Even technological optimists are beginning to doubt that planar silicon CMOS technology can be extended much beyond the 22 nm lithography generation. Still, there are some reasons to believe that integration densities will continue to increase and clock speeds will climb again. New non-volatile memory devices, currently poised to enter the market, may ultimately be scalable to dimensions of 10 nm and smaller. Field effect transistors based on semiconductor nanowires or carbon nanotubes offer the prospect of similar lithographic dimensions. Finally, the Nanoelectronics Research Initiative is funding university research aimed at device concepts that can greatly exceed the ultimate capabilities of the field effect transistor. I argue that such devices will have to be implemented in a (nearly) energy-conserving logic. Simple arguments suggest that some physical systems and device concepts may be much better suited than others for such a technology.

We discuss the Feshbach shape resonance in the exchange-like interband pairing term as the possible mechanism for high Tc. It occurs in multiband superconductivity as a resonance in the configuration interaction between different pairing channels in different subbands. ARPES of cuprates show the coexistence of two different subbands at the Fermi level due to nanoscale phase separation forming a superlattice of quantum stripes. In the superlattices the different spatial location and disparity of the wavefunction symmetry of the two components make possible the interband exchange pairing. The shape resonance occurs at dimensional electronic topological transitions. The high Tc maximum is reached at the Feshbach shape resonance for the 1D to 2D electronic topological transion (1D/2D ETT) in the electronic spectrum in the superlattice of quantum stripes. A BCS to BOSE-like transition occurs going from 2D to 1D side of the ETT. We report the evidence for Feshbach shape resonance in electron doped MgB(2), a multiband superconductor in the clean limit that provides the simplest high Tc (40K) superconducting system (HTcS) playing the role of atomic hydrogen for HTcS. The exchange pairing at the 2D to 3D Lifshitz electronic topological transition (2D/3D ETT) is shown to be the key term controlling the increase of the critical temperature from 0.3K to 40K as confirmed by recent Raman data.

We explore functional nanoelectronics that is complementary to silicon electronics. Single electron devices, quantum computing devices, spintronic devices and Tera-herz devices are the subjects of our interests, where an electron spin, a nuclear spin and an exciton etc. may be controlled at single particle levels. To realize these devices at nanoscale dimensions, we not only use conventional semiconductor materials, but also use carbon nanotubes and molecular materials that have extremely small dimensions, fabricated with conventional lithography technique. New physics or new functionalities that appear in the nanoscale devices are also our interest.

A liquid flow-cell was recently developed by NIST in conjunction with the synchrotron-based ultra-small-angle x-ray scattering (USAXS) facility at Sector 33 (now at 32) of the Advanced Photon Source (APS) near Chicago. Taking full advantage of the high brilliance and wavelength tunability of the 3rd generation synchrotron source, and the ability to "probe" nanometer-to-micrometer scale structures in a wide range of materials, attainable with the Bonse-Hart Si crystal optics, the flow-cell offers exceptional capabilities for the analysis of complex solution-mediated systems. The flow-cell apparatus was designed to enable quantitative studies of the synthesis, dispersion and processing of solution phase nanomaterials. On-going studies include characterization of DNA-wrapped and surfactant stabilized carbon nanotube dispersion and extensional alignment in suspensions, colloidal interactions, and characterization of gold nanoshells and nanowires. In the present talk, I will summarize results obtained from studies of the precipitation and growth of nanocrystalline ceria via a soft-chemistry route in aqueous media. This work was carried out in collaboration with Columbia University researchers and APS/UNICAT scientists. Measurements were performed over a temperature range from 20 to 35 ?C for reaction times of up to 12 hr. Previously published TEM results (Zhang, et al., J. App. Phys. 95 4319-4326, 2004) indicate that ceria particles are single crystals with narrow size distributions. The growth process is believed to occur in two steps: an initial nucleation event followed by a slow and continuous growth at the particle surface without further nucleation. USAXS results have suggested a more subtle growth mechanism may be involved, with two ?feature? populations that persist throughout the post-nucleation phase. One population remains dimensionally stable with respect to size, while the other continues to grow over time. We will present scattering data and modeling results that yield feature volume size distributions, mean and median sizes for each population, population surface areas, volume fractions and number distributions, as a function of both reaction time and temperature. Efforts are now focused on understanding the relationship between these populations and their role in the growth process itself.

Silver and gold nanoparticles have intense colors due to collective excitations of conduction electrons, so-called plasmon excitation. The wavelength of this excitation varies with particle size and shape, such that it is possible to make nanoparticles having any color in the visible spectrum. In the last few years there has been interest in using these properties, as well as the chemical properties of silver and gold, to make sensors for biomolecules. This talk will describe the particles, and methods for sensing, with emphasis on the use of theory and computational modeling to determine scattering and extinction properties as a function of nanoparticle structure. Two kinds of theory are used: continuum electrodynamics and time dependent density function theory. Each theory has a range of applicability, but there is enough overlap that one can use theory as a quantitative tool both for the interpretation of experiments, and for prediction of new phenomena.

Semimetallic bismuth (Bi) has been extensively investigated over the last decade since it exhibits very intriguing transport properties due to their highly anisotropic Fermi surface, low carrier concentration, long carrier mean free path l, and small effective carrier mass m*. In particular, the great interest in Bi nanowires lies in the development of nanowire fabrication methods and the opportunity for exploring novel low-dimensional phenomena. In the present work, we report a novel method to grow high-quality, single-crystalline Bi nanowires and magneto-transport properties of an individual Bi nanowire. Bi thin films were grown on a thermally oxidized Si substrate in a radio frequency (rf)-sputtering system with a Bi target of 99.9%. The deposition of Bi was carried out in a vacuum chamber with a base pressure of 5.0 ? 10-7 Torr. Rf power of 100 W and an Ar working pressure were utilized, yielding a growth rate of 27.5 &#8491;/sec. For growth of the Bi nanowires, the sputtered-Bi thin films were transferred to a furnace for heat treatment at 270 &#730;C for 10 hours. A combination of electron-beam lithography and a lift-off process was utilized to fabricate an individual Bi nanowire device. Interestingly, after heat treatment at 270 &#730;C for 10 hours, uniform and straight Bi nanowires with high aspect ratios were found to be extruded from the surface of the as-grown films. The growth of Bi nanowires on the films is attributable to the relaxation of stress, originating from a thermal expansion mismatch between the film and the substrate. This mismatch is due to the large difference in the coefficient of thermal expansion of Bi (13.4 ? 10-6/&#8451;) and Si (3.0 ? 10-6/&#8451;). The grains of a Bi film grown at 100 W (27.5 &#8491;/sec) and annealed at 270 &#730;C was found to have preferred orientation, i.e., (003) and (006). Under compressive stress, the flow of Bi atoms to the preferred orientations is substantial so that the grains having the preferred orientation play a role as seeds for the growth of Bi nanowires. The correlations between the thickness and mean grain size of the Bi films deposited at 100W rf power has been investigated. The diameter of the Bi nanowires was found to decrease in proportion to the thickness and the grain size of the films, indicating that the diameter of the Bi nanowires can be controlled by manipulating the thickness of as-grown films. The largest magnetoresistance (MR) reported in the literatures for an individual 400-nm-diameter Bi nanowire, 2496 % at T = 110 K and 286 % at T = 300 K were obtained, indicating the longest mean free path (l) and relaxation time (&#964;). Our results demonstrate that high-quality, single-crystalline Bi nanowires can be grown by the stress-induced method, providing motivation for exploring underlying physics in single-crystalline Bi nanowires, e.g., the magneto-transport and thermoelectric properties.

DNA bases and amino acids as well as their solvated clusters and larger assemblies were studied in the gas phase, in solution, and at the single molecule level in frequency and time domains. Four topics will be presented: (1) The electronic spectrum of adenine and the lifetime of its first excited state were studied from the perspective of the photostability of nucleobases; (2) Photophysical and chemical properties of jet-cooled L-phenylalanine (Phe) were also studied and found to be very much dependent on its molecular conformations. An unusual charge distribution was discovered in Phe+ radical cation that was also correlated strongly with the conformation; (3) An ultrafast chemical reaction involving the DNA base thymine was studied in the gas phase and in solution respectively by the pump-probe technique of transient ionization and transient stimulated Raman spectroscopy, the latter of which allows one to observe molecular vibrations in real time in the limit of the Uncertainty Principle; (4) Finally, a special type of single molecule FRET spectroscopy is to be presented in the form of a newly-developed three-color alternate laser excitation scheme with its application to the folding kinetics of DNAzyme in in vitro solution.

SEMINAR CANCELLED

The electron transport properties of hybrid ferromagnet-normal metal structures such as
multilayers and spin valves depend on the relative orientation of the magnetization direction of the ferromagnetic elements. Whereas the contrast in the resistance for parallel and antiparallel magnetizations, the so-called giant magnetoresistance, is relatively well understood for quite some time, a coherent picture for non-collinear magnetoelectronic circuits has evolved only recently. We discuss here such a theory for electron charge and spin transport with general magnetization directions. Many phenomena, such as current-induced spin-transfer torque, spin pumping, and enhancement of the Gilbert damping constant, can be understood and predicted for different material combinations.

Metal nanoparticles play a significant and well-developed role in the vapor-liquid-solid (VLS) synthesis of a variety of nanostructures, including semiconductor nanowires. For example, it is well-known that the minimum nanowire diameter resulting from axial growth is influenced by the nanoparticle diameter, thereby enabling diameter-selective control of nanowires. The metal nanoparticle-catalyzed VLS synthesis route is applied to the controlled synthesis of tapered Si and Ge nanowires of different polymorphs [1], and of tapered nano-helices. A key feature is that metal eutectic droplets exhibit unexpected and dynamic behavior during VLS growth [2], enabling possibilities for additional control of shape, as well as of the location of additional nucleation and growth. Among the possible mechanisms by which the evolution and transport of the metal catalyst mass occurs is an electrostatic charge-induced dissociation of the droplets. These taper angle-controlled semiconducting nanostructures possess unexpected structural and remarkable optical scattering properties [3].

[1] L. Cao, L. Laim, C. Ni, B. Nabet and J. E. Spanier, J. Amer. Chem. Soc. Communications 127, 13782-3 (2005).
[2] L. Cao, B. Garipcan, J. S. Atchison, C. Ni, B. Nabet and J. E. Spanier, Nano Lett. 6, 1852-7 (2006).
[3] L. Cao, B. Nabet and J. E. Spanier, Phys. Rev. Lett., 96 157402 (2006).

As electronic devices shrink to the nanometer scale, the relative importance of individual chemical bonds becomes larger and larger. Carbon nanotubes represent an extreme limit of this rule, as the modification of a single lattice site can dramatically change chemical activity and electronic properties. This presentation will focus on single-site experimentation in which we find, create, and alter point defects in single-walled nanotubes. Due to the correspondence between chemical and electronic properties, changes in device conductance reveal these chemical processes happening in real-time and allow the sidewall to be deterministically broken, reformed, and conjugated to target species. We routinely functionalize pristine, defect-free nanotubes at one, two, or more sites, and have demonstrated three-terminal devices in which a single-molecule attachment controls the electronic response.

Recent progress in nanotechnology has yielded new device components with unprecedented capabilities. However, the small size of these building blocks makes it difficult to position them into functional assemblies using existing patterning techniques. As one solution to this problem, we have converted the protein shells of two viruses into scaffolds that can position nanoscale objects with excellent spatial resolution. In one case, this strategy has been used to synthesize arrays of fluorescent molecules, providing efficient mimics of the light harvesting system present in photosynthetic organisms. In a second research area, well-defined core/shell materials have been prepared for applications in diagnostic imaging. The cornerstone of these efforts has been a series of new synthetic reactions that can modify biomolecules with high site-selectivity and yield. This presentation will focus on the development of these methods and the applications of the new materials that have been built through their use.

Dynamic characteristics of organic thin film transistors (OTFTs) are one of the important topics from both standpoints of fundamental physics and device application, although there have been few works on this subject. Transient phenomena caused by step gate voltage and complex impedance were investigated for the pentacene and C_60 thin film transistors. Equivalent circuit models were proposed for the analysis of the results. Two decay components in transient current was observed which corresponds to charge injection and some kinds of relaxation process. From the complex impedance analysis, on the other hand, the effect of contact resistance and grain boundary was discussed. The present results suggest the importance of interfaces in the device for the dynamic operation. That is, a field effect mobility is not necessarily a unique parameter to determine the FET characteristics from a viewpoint of high speed performance.

Understanding and predicting the properties of quantum many-particle systems remain a theoretical and computational challenge. In materials simulations, the standard model is an independent-electron approach in the framework of density-functional theory. In systems where the effects of particle interaction are strong, this approach is often inadequate. Several alternatives are being pursued. Among these, we have been developing a non-perturbative Monte Carlo approach using auxiliary fields. Our approach takes the form of a linear superposition of independent-particle calculations in fluctuating external fields. The different field configurations are "entangled" by random walks. An approximate solution is formulated to control the sign problem. I will discuss progress and prospects in the development and application of this approach. Results will be presented on lattice models for ultracold atomic gases, and on electronic structure computations in molecular systems and bulk materials.

Novel methods are described for producing polymer-free carbon nanotube yarns and transparent sheets, together with their properties and applications as multifunctional materials. The yarns are strong, highly resistant to creep and to knot or abrasion-induced failure and provide a giant tunable Poisson?s ratio for stretch in the fiber direction. The nanotube sheets have higher gravimetric strength than the strongest steel sheet or the polymers used for ultralight air vehicles and proposed for solar sails. Applications evaluations are described for artificial muscles, thermal and light harvesting, energy storage, field-emission electron sources, electrically conducting appliqu?s, three types of lamps, displays, and sensors.

R.H. Baughman, M. Zhang, S. Fang, A. A. Zakhidov, M. Kozlov, S. B. Lee, A. E. Aliev (University of Texas at Dallas), and K. R. Atkinson (CSIRO Textile & Fibre Technology, Belmont, Victoria, Australia)

Graphene, a single layer of carbon atoms arranged in a simple honeycomb lattice, is the building block of graphite, fullerenes, and carbon nanotubes and has fascinating electronic properties. Of fundamental interest is the effectively massless, relativistic character of its charge carriers. This arises as a result of its unique electronic structure, characterized by conical valence and conduction bands that meet at a single point in momentum space (at the Dirac crossing energy). Of practical interest is the fact that its carrier motion is ballistic at room temperature, making graphene potentially useful for ultrasmall, ultrafast computing devices. I will describe the synthesis of graphene thin films (from one to four layers) grown on insulating silicon carbide wafers and report the evolution of their electronic band structure using angle-resolved photoemission spectroscopy (ARPES). For monolayer graphene, we can determine the electronic spectral function, which encodes the many-body interactions amongst the quasiparticles in the system-namely the charge and vibrational excitations. Our measurements show that the bands around the Dirac crossing point are heavily renormalized by electron-electron, electron-plasmon, and electron-phonon coupling, showing that these interactions must be considered on an equal footing in attempts to understand the quasiparticle dynamics in graphene and related systems. For bilayer graphene, I will describe the electronic band structure as a function of doping. By selectively adjusting the carrier concentration in each layer, changes in the layer-dependent Coulomb potential lead to a control of the gap between valence and conduction bands. This control over the band structure suggests potential application of bilayer graphene to switching functions in atomic-scale electronic devices.

[1] Bostwick, A., Ohta, T., Seyller, T., Horn, K. & Rotenberg, E. Quasiparticle Dynamics in Graphene. Nature Physics, in press.
[2] Ohta, T., Bostwick, A., Seyller, T., Horn, K. & Rotenberg, E. Controlling the Electronic Structure of Bilayer Graphene. Science 313, 951-954 (2006).

Graphene, a single layer of carbon atoms arranged in a simple honeycomb lattice, is the building block of graphite, fullerenes, and carbon nanotubes and has fascinating electronic properties. Of fundamental interest is the effectively massless, relativistic character of its charge carriers. This arises as a result of its unique electronic structure, characterized by conical valence and conduction bands that meet at a single point in momentum space (at the Dirac crossing energy). Of practical interest is the fact that its carrier motion is ballistic at room temperature, making graphene potentially useful for ultrasmall, ultrafast computing devices. I will describe the synthesis of graphene thin films (from one to four layers) grown on insulating silicon carbide wafers and report the evolution of their electronic band structure using angle-resolved photoemission spectroscopy (ARPES). For monolayer graphene, we can determine the electronic spectral function, which encodes the many-body interactions amongst the quasiparticles in the system-namely the charge and vibrational excitations. Our measurements show that the bands around the Dirac crossing point are heavily renormalized by electron-electron, electron-plasmon, and electron-phonon coupling, showing that these interactions must be considered on an equal footing in attempts to understand the quasiparticle dynamics in graphene and related systems. For bilayer graphene, I will describe the electronic band structure as a function of doping. By selectively adjusting the carrier concentration in each layer, changes in the layer-dependent Coulomb potential lead to a control of the gap between valence and conduction bands. This control over the band structure suggests potential application of bilayer graphene to switching functions in atomic-scale electronic devices.

To describe conduction through a single molecule requires combining accurate chemical information with a suitable transport model. A standard approach is to find the transmission of single-particle states described by density functional theory using a local exchange correlation (xc) functional. We have used this approach to study the possibility of organometallic spintronics in molecules containing two cobaltocene moieties. To test and extend the standard methodology, we construct new xc potentials based on the optimized effective potential (OEP) approach and calculate electron transmission through two atomic chain systems, one with charge transfer and one without. For systems that may have charge transfer, the presence or absence of self-interaction error plays a key role. We find that the OEP approach changes the LUMO state and the HOMO-LUMO gap, thereby dramatically altering the calculated molecular conductance.

In conventional superconductors, the appearance of an energy gap in the electronic spectrum indicates pairing of electrons into Cooper pairs and a simultaneous transition into a macroscopic superconducting state. In contrast, in the underdoped high temperature superconductors, an energy gap is already present in the normal state. An understanding of this normal state gap or ?pseudogap? has proven elusive, because its ground state electronic structure was unknown. Here, we present the first studies of electronic structure in La2-xBaxCuO4, a unique system where the superconductivity is strongly suppressed and static spin and charge orders or ?stripes? develop near a doping level of x=1/8. Using angle resolved photoemission we detect an energy gap at the Fermi surface that vanishes only at four nodal points and has a momentum dependence consistent with d-wave symmetry. And in tunneling spectroscopy, we find that the density of states DOS(E)&#61621;|E|, with zero-DOS falling exactly at the Fermi energy. In theory, an energy gap due to d-wave electron pairing interactions has such a structure. Remarkably, this gap persists and has the maximal magnitude at x=1/8, precisely where superconductivity vanishes. Thus, the non-superconducting La1.875Ba0.125CuO4 exhibits an electronic ?pseudogap? consistent with a phase incoherent d-wave superconductor whose Cooper pairs are localized into spin/charge ordered structures - ?stripes?.

We use total internal reflection fluorescence microscopy (TIRFM) to directly visualize single proteins as they interact with individual molecule of DNA, and we are specifically interested in proteins that are involved in the repair of damaged DNA. For these studies we have developed new technologies that rely upon fluid lipid bilayers and microscale diffusion barriers to organize DNA molecules into defined "curtains" on the surface of a flow chamber. This "highthroughput" single-molecule approach allows us to visualize hundreds of individual DNA molecules in a single experiment and track the behavior of potentially thousands of individual proteins.

This talk will address 2 basic problems plaguing our world?s society: 1) abundant cheap clean primary energy and 2) related to it: the freshwater problem (because that also needs energy). The solution is seen in a massive development of solar energy with all its possibilities: solar thermal energy, solar electricity, biomass, wind and some less known possibilities like updraft towers, tidal power, floating turbines etc. Information of all these forms of primary energies will be supplied, in particular: their present contribution, energy harvest factors, energy payback times, costs and their possible contribution to our energy needs over the next few decades. The role of nuclear energy will also be briefly discussed in particular with respect to its social implications. The talk will not be strictly technical but is intended to be rather informative to a general audience.

Organisms have been making exquisite inorganic materials for over 500 million years. Although these materials have many desired physical properties such as strength, regularity, and environmental benign processing, the types of materials that organisms have evolved to work with are limited. However, there are many properties of living systems that could be potentially harnessed by researches to make advanced technologies that are smarter, more adaptable, and that are synthesized to be compatible with the environment. One approach to designing future technologies which have some of the properties that living organisms use so well, is to evolve organisms to work with a more diverse set of building blocks. These materials could be designed to address many scientific and technological problems in electronics, military, medicine, and energy applications. An example is a virus enabled lithium ion rechargeable battery we recently built that has many improved properties over conventional batteries. This talk will address conditions under which organism first evolved to make materials and scientific approaches to move beyond naturally evolved materials to genetically imprint advanced technologies.

The amazing advancements achieved to date in Si complementary metal-oxide-silicon (CMOS) technology have come primarily from scaling, i.e., from reducing the critical dimensions of the transistors. Because it is becoming increasingly difficult to further reduce critical dimensions such as the gate oxide thickness, alternative methods of improving transistor performance are also being employed. One important approach is to increase the electron and hole mobility in the transistors, by using strained Si for the electrically active region of the transistors, for example. A serious limitation of strained structures is the introduction of misfit dislocations that reduce the strain and also make the material unsuitable for device applications. This presentation will focus on research to understand dislocation nucleation mechanisms in epitaxial SiGe/Si structures and to fabricate defect-free strained Si structures for CMOS applications.

Nanoporous materials have many potential applications due to their very high surface area to volume ratio. Nanoporous gold is of particular interest because of its resistance to corrosion as well as the ability to tailor the gold surface to be sensitive to various chemical and biological species. Nanoporous gold can be synthesized by subjecting a homogeneous solid solution alloy of gold and silver to a process known as dealloying, during which the silver is selectively removed from the alloy. This is commonly accomplished by immersion of the alloy into nitric or perchloric acid. In the process, the surface diffusion of the gold component is significantly enhanced which enables the remaining gold to adopt the form of a open nanoporous network of voids. The connecting ligaments and cell sizes are of the order of 10 nm to 100 nm in size depending upon processing parameters. The ratio of the volume of gold to the overall volume is between 25% and 35%. Nanoporous gold has been synthesized in bulk form, and more recently in thin film form. In this talk, we will discuss experiments in which nanoporous gold films have been synthesized with two different methods. The mechanical properties and robustness of nanoporous gold films will be examined. In addition, results in which nanoporous gold is incorporated with homogeneous gold films to make nanostructured freestanding thin films will be discussed. Finally, an array of potential applications for nanoporous gold films and nanostructures constructed from them will be explored.

Advanced materials, utilizing nanostructures to provide new materials properties and opportunities for the independent control of materials structures and properties, offer new promise for addressing some of the grand energy challenges facing our future. This talk will review opportunities opened up at the nanoscale, with materials of reduced dimensionality and enhanced surface-to-volume ratio. Some examples of research accomplishments and opportunities at the nanoscale will be described. Special attention will be given to the potential of advanced materials and nanoscience to have an impact on addressing grand energy challenges for the 21st century and beyond.

Mildred Dresselhaus is an Institute Professor of Electrical Engineering and Physics at MIT. Prof Dresselhaus is a native of the Bronx, New York City, where she attended the NY City public schools through junior high, completing high school at Hunter College High School in NYC. She began her higher education at Hunter College in NYC and received a Fulbright Fellowship to attend the Cavendish Laboratory, Cambridge University (1951-52). Prof Dresselhaus received her master's degree at Radcliffe College (1953) and her Ph.D. at the University of Chicago (1958).

Prof Dresselhaus has served as President of the American Association for the Advancement of Science, Treasurer of the US National Academy of Sciences, President of the American Physical Society and is currently Chair of the Governing Board of the American Institute of Physics. She is a member of the US National Academy of Engineering, as well as of the Engineering Sciences Section of the National Academy of Sciences, the American Philosophical Society, and a Fellow of the American Academy of Arts and Sciences, the American Physical Society, the IEEE, the Materials Research Society, the Society of Women Engineers, the American Association for the Advancement of Science, and American Carbon Society. She has received numerous awards, including the US National Medal of Science and 19 honorary doctorates worldwide. She served as the Director of the Office of Science at the US Department of Energy in 2000?2001. She is the co-author of four books on carbon science. Her research interests are in electronic materials, particularly in nanoscience and nanotechnology, with special regard to carbon related materials, novel forms of carbon, including fullerenes, carbon nanotubes, porous carbons, activated carbons and carbon aerogels, as well as other nanostructures, such as bismuth nanowires and the use of nanostructures in low dimensional thermoelectricity. She recently headed a national Department of Energy Study on "Basic Research Needs for the Hydrogen Economy," including hydrogen production, storage, and use.

The basics of glass science (structure, formation, thermodynamic stability, relaxation and atomic transport) as they apply to metallic alloys are reviewed. The essential phenomenololgy of mechanical behavior is presented: stiffness, homogeneous deformation (creep), inhomogeneous deformation (shear bands), and fracture (ductile and brittle). All of these phenomena can be understood based on ordering and disordering processes on the atomic scale. Experiments on colloidal glasses allow a direct look at the atomic scale mechanisms.

Biography
Frans Spaepen is the John C. and Helen F. Franklin Professor of Applied Physics at Harvard University Division of Engineering and Applied Sciences. 1971 received undergraduate degree in Metallurgical Engineering at the University of Leuven; and in 1975 received Ph.D. in Applied Physics from Harvard University. He joined the faculty of DEAS in 1977. From 1990 through 1998 he was Director of the Harvard Materials Research Laboratory/MRSEC. His research interests span a wide range of experimental and theoretical topics in materials science, such as amorphous metals and semiconductors (viscosity, diffusion, mechanical properties), the structure and thermodynamics of interfaces (crystal/melt, amorphous/crystalline semiconductors, grain boundaries), mechanical properties of thin films, and the perfection of silicon crystals for metrological applications. He is a Fellow of the American Physical Society (Chairman, Division of Materials Physics, 1992), a Fellow of TMS-AIME, a Foreign Member of the Vlaamse Academie voor Wetenschappen en Kunsten, and a member of ASM, and the Materials Research Society (Councillor: 1986-89; 1990-93; Chairman, Program Committee, 1993-2000). In 1988 he was Chairman of the Gordon Research Conference on Physical Metallurgy, and in 1990 he co-chaired the Fall Meeting of the MRS in Boston. He is co-editor of Solid State Physics, Principal editor of the Journal of Materials Research, and an editorial board member of a number of materials science journals.

Conformable phase masks and transparent photopolymers provide the basis for a simple optical technique that can form complex, but well defined three dimensional (3D) nanostructures in a single exposure step. This talk describes the method, presents and range of examples of its ability to form 3D nanostructures including free standing particles with controlled shapes) and rigorous coupled-wave analysis of the
associated optics. Single step, large area 3D pattern definition, sub-wavelength resolution and experimental simplicity represent features that make this method attractive for applications in photonics, biotechnology and other areas. We provide examples in passive mixers in microfluidics, bandgap structures in photonics, and reservoir targets in shockless laser compression.

Seokwoo Jeon was born in Seoul, Korea in 1975. He received his B.S. degree in 2000 and his Master degree with Professor Shinhoo Kang from Seoul National University in 2003 after one year exchange graduate student with Professor Paul V. Braun at University of Illinois at Urbana-Champaign UIUC). He is currently pursuing his Ph.D. degree in Materials Science and Engineering at UIUC under the guidance of Professor John A. Rogers. His research interests include softlithography, 3D nanopatterning, microfluidic systems, and optically functional materials & devices.

Single-walled carbon nanotubes (SWNTs) are attracting researchers from many fields due to their unique properties. This type of materials possesses electronic band structures that are tunable by their diameter and chirality. In this presentation, carbon feeding rate is shown to be related with the diameter distributions of SWNTs produced by chemical vapor deposition method. Detailed analysis reveals that conditioned activations of nucleating nanoparticles, together with the traditional VLS mechanism, determines the growth of SWNTs in a CVD process.
Two types of electronic devices, polymer electrolyte-gated field effect transistors and Schottky diodes from asymmetric metal-SWNT contracts, were fabricated to explore possible devices applications of those SWNTs synthesized on Si/SiO2 substrates.

Colloidal semiconductor nanocrystals can be produced nowadays in a variety of sizes, shapes and compositions. Due to their flexible surface chemistry, colloidal nanocrystals are also very attractive objects for use as building blocks in different functional structures within the bottom-up self-assembly approaches. In this presentation, we touch three different topics related to semiconductor nanocrystal assemblies and physics, as outlined in the title. We start with discussion of energy transfer in multilayer structures comprising luminescent CdTe nanocrystals, which are constructed in an energy gap gradient manner, and report on a highly efficient funneling of excitation energy from layers comprising smaller nanocrystals towards the layer with the largest nanocrystals. Further on, we show that nanocrystals of CdSe, CdTe or InP can very effectively photosensitize needle-like fullerene microcrystals that act as photoconductors, and discuss this in terms of a ?photodoping? effect based on the charge separation. Finally, we present single particle photoluminescence spectroscopy data on the ?nanocrystals of mixed dimensionality?, consisting of spherical CdSe cores surrounded by elongated CdS shells. The Stark effect is in particular pronounced in these nanorod-like particles, and we demonstrate this by direct manipulation of the excited state of the nanorods using strong external electric fields. In the hybrid structures of CdSe/CdS nanorods and organic dye molecules, electrical control of energy transfer is possible, which can lead to realization of a single molecule field effect switch.

Since the discovery of their electroluminescent properties, conjugated polymers have been extensively investigated as active materials in light-emitting diodes (LEDs). They can also serve as the semiconducting layer in organic field-effect transistors (FETs) where they show good charge transport characteristics. Ambipolar light-emitting field-effect transistors combine the emission properties of polymer LEDs with the switching behaviour of FETs in a planar structure. Light emission due to the recombination of holes and electrons can then be directly observed within the transistor channel. The position of the narrow emission zone is controlled by the applied voltages and can be varied throughout the entire channel. This vividly visualizes simultaneous hole and electron accumulation in ambipolar FETs and furthermore could enable novel integrated electro-optical devices. This presentation will introduce the prerequisites to achieve ambipolar transport and light emission in polymer field-effect transistors, demonstrate examples for different semiconducting polymers and transistor geometries and show how they can be used to study charge transport and recombination in conjugated polymers.

Surface treatments of nanocrystal surfaces can strongly affect their light emission properties but normally have little effect on the optical absorption of the nanocrystals. Cyanide, which binds strongly to both Cd and S(e)? in CdS(e) nanocrystals, is shown to increase the bandgap (blueshift the absorption spectrum) of aggregated nanocrystalline films by up to 0.3 eV, the shift being larger for small crystal size. This is explained by further localization of electrons in the nanocrystals by the negative cyanide. The effect is reversible: the original spectrum is recovered if the cyanide is rinsed off or oxidized. Freshly deposited films, of crystal size &#61603; 4 nm, undergo a small red-shift (due to electron overlap between neighbouring crystals) upon drying due mainly to capillary forces compacting the films. Subsequent cyanide treatment electronically decouples neighbouring crystals.

An important frontier in nanocrystal synthesis is the growth of composites of different materials in the same nanostructure as means of increasing functionality. One particularly interesting combination of materials is that of a metal and semiconductor in the same nanoparticle where metal tips can provide anchor points for electrical connections and for self assembly. We developed the growth of metal (Au) tips on the apexes of semiconductor (CdSe) rods, forming 'nano-dumbbells' (NDB's), via a simple chemical reaction . From the viewpoint of self-assembly they are equivalent to bi-functional molecules such as the di-thiols manifesting two sided chemical connectivity and the use of the tips for assembly is demonstrated. We also found that by increasing the concentration of gold in the reaction, rods with a metal tip on one side are formed . This process occurs by a unique ripening process as substantiated by experimental work and model calculations. The process leads to a transition from two to one sided growth. Such systems manifest a unique model for a metal-semiconductor nanoscale junction. A fundamental and intriguing problem associated with such systems is the mechanical and electronic properties of the metal-SC nanojunctions. The electronic properties of metal-semiconductor nanojunctions were investigated by scanning tunneling spectroscopy of the gold-tipped CdSe rods and by electrostatic force microscopy. In STS sub-gap states at the metal-semiconductor interface were observed , while in EFM we see evidence for charge separation at the metal-semiconductor interface.

1. T Mokari, E Rothenberg, I Popov, U Banin, Science 304, 1787 (2004)
2. T Mokari, CG Sztrum, A Salant, E Rabani and U Banin, Nature Materials 4, 855 (2005)
3. D Steiner, T Mokari, U Banin, O Millo, Physical Review Letters 95, 056805 (2005)

The electronic structure of materials in the proximity of the Fermi level largely determines gross properties such as electric and thermal conductivity, magnetism, strongly-correlated effects, etc. We tend to create nanometer scaled materials with novel properties, particularly by seeking the possibilities to tailor their electronic structure around the Fermi level. The key in achieving this goal is in the preparation of well defined low-dimensional structures. For the preparation of new complex structures we explore two distinct possibilities. The first one regards the use of a transition metal as a substrate for the growth of noble metal layers. The system of our choice is Ag/V(100). Vanadium has hybridization gaps with respect to silver and grants for the quantization of electronic states in the overlayer. The particularity of this system is extremely good epitaxy and uniformity of the silver in the limit of the thinnest films, down to the atomic level. This leads to well defined quantized states and novel silver properties, e.g. pronounced electron-electron and electron-phonon correlations, which are to a certain extent limited due to the finite interaction with substrate electronic states. A quite different approach regards the use of an ultra thin insulating layer which largely decouples interactions between adsorbate and the metallic part of the substrate. The system we use is Al2O3/Ni3Al(111). This alumina film is characterized by a high degree of perfection due to its commensurate structure with respect to Ni3Al(111), and consequently hundreds of nanometers large domains. It has a very complex structure which is not yet fully understood. More interestingly, this surface can be used as a template to grow ordered hexagonal arrays of metal clusters. The 4.16 nm superstructure of the alumina film directly accounts for the typical periodicities found in the arrays. We report on our recent investigation of possible arraying effects for magnetic iron clusters and large copper-phthalocyanine molecules. The distinct nature of the two investigated systems requires the use of two different, though complementary, experimental techniques. The first one is high-resolution angle-resolved photoelectron spectroscopy which is mainly used in the Ag/V(100) studies. The other one is low-temperature scanning tunneling microscopy and spectroscopy which is used in the adsorbate/Al2O3/Ni3Al(111) studies. Both techniques are exploited at their current limits in order to reveal fine details in the unique electronic structure of the investigated systems.
Short biography: Received Ph.D. degree in Physics from Zagreb University in 2003. During the Ph.D. studies main interests were focused to the lifetime issues in low dimensional structures studied by high-resolution ARPES. 2003 postdoc at the University of Bonn, Institute of Physical Chemistry. Areas of interest shifted to low-temperature STM and advanced metallic, molecular and hybrid nano-structures. In 2005 awarded the Alexander von Humboldt fellowship.

Cryogenic temperatures and a UHV environment provide the conditions for stable STM operation, facilitating high resolution imaging, local spectroscopy, and single atom / molecule manipulation. Combination of these experimental capabilities was utilized to study the interaction of adsorbates with oxygen vacancies on TiO2(110). This type of point defect is common for reducible transition metal oxides and greatly influences their surface chemistry. Since their unexpected catalytic activity was discovered, Au-nanoparticles on TiO2(110) have received considerable attention. Deposition of Au at low temperature inhibits thermally activated diffusion and aggregation, thus leads to adsorption of single Au-atoms. Two different distinctive adsorption sites have been identified through STM imaging and manipulation: Au-atoms either adsorb on bridge sites between five-fold coordinated Ti atoms or in oxygen vacancies, i.e. substituting the missing bridging oxygen atom. Moreover, another characteristic property of oxygen vacancies on TiO2(110) was revealed: When a porphyrin derivative is laterally manipulated to the vicinity of an oxygen vacancy, the peak-position of molecular orbital related resonances in dI/dV spectra shifts to lower energies. This behaviour is consistent with a positive charge localized at the vacancy sites.

I will describe two separate theoretical studies of the role played by metallic contacts in determining the low-bias transport properties of metal-molecule junctions. Recent break-junction experiments have reported the conductance of H2 molecular junctions drops by more than a factor of two when Pt contacts were simply replaced with Pd. We are able to explain these results surprisingly well by directly computing the conductance of H2 with Pt and Pd metallic contacts using an ab initio scattering state approach based on density functional theory. Surface polarization of the metallic electrode affects the energetic position of the frontier orbitals relative to the contact Fermi level. We study a model metal-molecule contact, benzene physisorbed on graphite. The benzene HOMO-LUMO gap, computed using the GW approximation for the electron self-energy, is substantially altered from its gas phase value, as well as differing from the results of DFT calculations. A model calculation illustrates the impact of this polarization for other conjugated molecules.

Biographical Sketch: Jeffrey B. Neaton received his Ph.D. in Physics from Cornell University in 2000, under the guidance of Neil W. Ashcroft. After a three-year stint as a departmental postdoc in the Department of Physics and Astronomy at Rutgers University, he joined the Molecular Foundry at Lawrence Berkeley National Laboratory in 2003, first as a postdoc under Steven G. Louie and eventually as permanent staff. He is presently acting lead scientist of the Foundry?s Theory group. His current research interests center on computational nanoscience, in particular the development and application of methods for calculating the structural, spectroscopic, and transport properties of inorganic and molecular nanostructures, particularly at interfaces. Present areas of interest include the electronic properties of the metal-organic interface, hybrid silicon-organic interfaces, and single-molecule junctions; self-assembly; nanoparticle superlattices; ultrathin epitaxial films of transition metal oxides, such as ferroelectrics and multiferroics; and structural and electronic phases of light elements under pressure.

TBA

Ever since the invention of the scanning tunneling microscope, the growing versatility of scanning probe microscopy (SPM) has been rich with examples of technological innovations driving scientific progress. This presentation will highlight advanced imaging modes and other new capabilities opened up with the recent introduction of new controller architectures and scanner geometries by the SPM market leader. Imaging modes expanding realspace nanoscale characterization beyond topography have played an important role in the expansion of SPM applications. While phase imaging has become a standard tool for nanoscale mechanical characterization, the combination of force feedback with electrical measurements has allowed SPM to play an important role in the characterization of nanoscale electrical devices. Examples of new capabilities that will be discussed include harmonic imaging and high-speed data capture, giving access to realtime cantilever dynamics and allowing the deconvolution of material properties contributing to probe sample interactions. Electrical imaging modes and associated single-point spectroscopies have been augmented through the combination with a novel feedback mechanism and low-noise position sensors, expanding opportunities for electrical characterization of delicate samples such as thin polymer films and loosely bound carbon nanotubes.

Advanced techniques in nanoscience now enable the creation and measurement of ultrasmall mechanical devices. These nanoelectromechanical systems (NEMS) offer unprecedented opportunities for sensing and quantum measurements. I will describe several specific applications of NEMS that we are currently pursuing: vacuum-based force sensing, single-molecule mass spectrometry, fluid-based biochemical force assays for single-molecule molecular recognition, and number-state measurements of single quantum jumps in a NEMS device at ultralow temperatures.

The first two applications employ ultraminiature mechanical devices that offer sensitivity down to the single-molecule limit. Their reduced size yields extremely high fundamental vibrational frequencies while simultaneously preserving very high mechanical responsivity. For vacuum-based applications this powerful combination of attributes translates directly in to high force and mass sensitivity ? in the near future we should attain the zeptonewton force regime and single Dalton (1 amu) mass levels, respectively. In fluidic media, even though the high quality factors attainable in vacuum become precipitously damped, the small device size and high compliance still yields response below the piconewton level ? roughly the force required to break individual hydrogen bonds within a macromolecule. Finally, single-quantum experiments involve ultrasensitive measurements on high frequency devices while avoiding linear coupling ? a novel class of measurements anticipated years ago, but not yet realized with mechanical systems.

We introduce Photothermal Heterodyne Imaging, allowing the optical detection and absorption spectroscopy of individual nano-objects. Surface Plasmon Resonance spectra of individual gold nanoparticles as small as 5nm are recorded. Intrinsic size effects are unambiguously observed and analyzed within the frame of Mie theory. Photothermal detection and spectroscopy of individual CdSe nanocrystals in the multiexcitonic regime are performed. The origin of the photothermal signal is discussed. For a same nanocrystal, absorption and luminescence spectra are confronted.

Jason received his BS in Materials Science & Engineering from MIT in 1998 and his MS in Materials Science from Stanford in 2000, and then went on to work at E Ink Corp in Cambridge, MA as a lead technology developer focusing on commercialization of the world?s first electronic ink display. He is currently in the final year of his PhD in the Department of Physics at Cambridge University working for Prof Henning Sirringhaus on organic transistors. He is interested in advancing novel technologies in fields such as alternative energy.

For years, nanotechnology has promised many exciting scientific advances for the future, and the first products containing engineered nanoparticles and nanotubes are starting to reach the consumer markets. From an industry perspective, the novel physical and chemical properties that nanoscale materials promise to deliver must be integrated into new products, either by improving existing products or by enabling novel business opportunities. This talk will give a broad overview of some programs within DuPont that are utilizing nanoengineered materials with a focus on aerosol nanoparticle synthesis as a method to create a wide variety of nanoparticles will well-controlled properties and chemistries. Through aerosol synthesis, very specific nanoparticle properties, including morphology, crystallinity, and particle size distribution can be achieved through appropriate reactor design, instrumentation, and process parameter control.

Over the past several years, organic field-effect transistors (FETs) and their integrated circuits have attracted considerable attention since organic FETs possess attributes that complement silicon-based LSI devices. Organic FETs can be manufactured on plastic films at low (ambient) temperatures by printing processes; therefore, they are thin, lightweight, mechanically flexible, and potentially inexpensive to manufacture. Recent studies of organic FETs are driven by flexible displays and radio frequency identification (RFID) tags. As the third application, we have proposed and demonstrated flexible, large-area sensors and actuators in which organic FET active matrices are used for data readout from area-type sensors or to drive large-area actuators. In this talk, I report recent progress, issues, and future prospects of organic FET-based flexible, large-area sensors and actuators. The first example of large-area sensors is an electronic artificial skin (e-skin). Among area sensors, sensing of a touch is important for robots in the next generation. An artificial skin integrating pressure sensors and peripheral electronics using organic FETs is fabricated for the first time based on the scalable circuit concept. In particular, moving images of pressure have been taken by a flexible active matrix with organic transistors whose mobility reaches as high as 1.4 cm2/Vs. The transistor is electrically functional even when it is wrapped around a cylindrical bar with a 0.5 mm radius. Then, I report on a large-area, flexible, and lightweight sheet image scanner on a plastic film integrating high-quality organic field-effect transistors (FETs) and organic photodiodes. Organic photodetectors distinguish between black and white from the difference of reflectivity between black and white parts on paper. The sheet has no optical or mechanical parts and therefore very thin and lightweight. Organic FETs are also suitable for applications to large-area actuators. We have fabricated a novel, flexible, lightweight sheet-type Braille display that is fabricated on a plastic film for the first time by integrating high-quality organic FETs with plastic actuators. A small hemisphere that projects upwards from the rubber-like surface of the display is attached to the tip of each rectangular actuator.

Takao Someya received the Ph.D. degree in electrical engineering from the University of Tokyo, Japan, in 1997. From 2001 to 2003, he worked on organic electronics in the Nanocenter (NSEC) of Columbia University and Bell Labs as a Visiting Scholar. Since 2003, he has been an Associate Professor of the Department of Applied Physics, University of Tokyo. His current research focus is on organic transistors, flexible electronics, plastic circuits, and molecular scale electronics. He is an IEEE/EDS Distinguished Lecturer since 2004 and a recipient of 2004 IEEE/ISSCC Takuo Sugano Award. Since 2003, the number of press coverage has been more than 200, which include BBC, The Washington Post, The Economist, Scientific American, and National Geographic Magazine. His ?large-area sensor array? electronic thin film was featured in Time Magazine as one of its ?Best Inventions of 2005? in its November 21st issue.

Highly correlated electron systems are of considerable interest, particularly in the design, discovery and growth of novel bulk materials. One of the primary driving forces of basic research in the physics of new materials is the synthesis of these materials in single crystalline form. Our interests lie in studying and understanding the structure-property relationships in novel ternary intermetallics synthesized by metallic flux-growth methods. This talk will highlight the synthesis, structures and physical properties of ternary lanthanide ? transition metal ? main group element intermetallics (Ln ? T ? X), where T = Co, Rh, Ir, Ni, Pd, and Pt, and X = Ga, In, Sb and Sn. Several phases will be discussed, including LnnTIn3n+2 (n = 1, 2, ), CePdGa6, Ce2PdGa12, Ce2PdGa10, LnNiSb3, LnNi1-xSb2 (x ~ 0.4), and Ln3Co4Sn13.

III-V semiconductor nanostructures have the potential to revolutionize a variety of technologies such as optoelectronics, field emission and high temperature sensing. Presently, it appears that the selective area or templated growth method is perhaps one of the more promising avenues for fabrication of tailored and highly confined semiconductor nanostructures. Templated growth of semiconductor nanostructures, which involves epitaxial growth through a selective mask, allows for precise control over quantum dot size, shape, spacing and uniformity, and could potentially mitigate the nonradiative defects associated with the direct writing techniques [1,2]. Selective growth of III-V semiconductor structures, particularly gallium arsenide and gallium nitride, using a dielectric mask with micron size openings has been extensively reported in the literature. In comparison, there appears to be only few reports on the selective growth of III-V nano-structures inside sub-100 nm SiO2 windows. Here, we report on the templated growth of III/V nanostructures inside sub-20 nm SiO2 windows using molecular beam epitaxy (MBE).

This work has been accomplished in collaboration with K. Conway, L. Denault, D. Hays, C. Keimel R. Klinger, S. Krishna, K. Krishnan, F. Sharifi, A. Stintz and S.T. Taylor.

Our research group at NIST is developing spin torque nano-oscillators (STNOs) as microwave microwave sources and mixers. STNOs employ lithographically defined point contacts with a 40 nm diameter to inject high density current into magnetic multilayers. Current-driven transfer of angular momentum between the magnetic layers in such a structure results in spontaneous precession of the magnetization once the current density exceeds the stability threshold. The magnetization precession generates microwave electrical signals as a result of giant magnetoresistance that occurs in such magnetic multilayer structures. Devices exhibit high Q-factors in excess of 10,000 at 25 GHz. They are tunable by varying both applied magnetic field and dc current. STNOs are essentially a nano-scale magnetic analog to voltage-controlled oscillators (VCOs). We have demonstrated much of the functionality associated with VCOs using STNOs, including frequency modulation [1] and injection locking [2]. Most recently, we have shown that two STNOs can be mutually phase locked to each other, thereby resulting in a coherent increase in output power [3]. I will describe the basic principle of STNO operation, including a review of the fundamentals of spin dynamics in ferromagnetic systems. I will then review the subject of injection locking, which is a universal property of regenerative oscillators that employ a negative-loss element to compensate for internal losses of the oscillator. Finally, I will show how current injection locking and mutual phase locking of STNOs are further examples of the injection locking principle.

[1] M.R. Pufall, W.H. Rippard, S. Kaka et al., Applied Physics Letters *86* (8), 082506 (2005).
[2] W.H. Rippard, M.R. Pufall, S. Kaka et al., Physical Review Letters *95* (6), 067203 (2005).
[3] S. Kaka, M.R. Pufall, W.H. Rippard et al., Nature *437*, 389 (2005).

Non-lithographic fabrications of devices such as electronics and sensor have been studied extensively by assembling nanometer-sized building blocks into the device configurations. While various nanocomponents have been applied as building blocks to construct nanodevices, the more reproducible methods to assemble them onto precise positions are desirable. We have been fabricating peptide-based nanotubes (antibody) and functionalizing them with various recognition components (antigen), and our strategy is to use those functionalized peptide nanotubes, which can recognize and selectively bind a well-defined region on patterned substrates, as building blocks to assemble three-dimensional nanoscale architectures at uniquely defined positions and then decorate the nanotubes with various materials such as metals and quantum dots for electronics and sensor applications. We have been functionalizing assembled nanotubes by metal and semiconductor nanocrystals for photonics, electronics, and sensor applications. Recently, we have synthesized nanotubes with certain peptide sequences that can selectively grow specific nanocrystals on nanotubes via biomineralization. By changing the peptide conformation on the nanotubes by pH, the nanocrystal size and shape were controlled. The Zn finger peptides could also affect nucleations of ZnS nanocrystals by their unfolding conformations and the resulting phases of ZnS nanocrystals were controlled to be the wurtzite structure although zinc blende is the stable structure for ZnS at room temperature. These sequence peptide-incorporated nanotubes are expected to become conductivity-tunable building blocks for nanodevices by controlling the size, the shape, and the phase of coated nanocrystals. For material synthesis, we used ring-shaped peptide assemblies as templates to produce various nanometer-sized crystals inside the cavities. These nano-rings mimic the Nature to grow crystals at room temperature, which need high temperature to grow by other synthetic methods. This approach can be applied to grow various exotic nanocrystals at room temperature, which is extremely important in industrial applications.

Nanotechnology focuses on small scale effects. Energy is a global issue. Despite such disparities, there is a growing awareness that nanoscience and nanotechnology can have a profound impact on energy generation, storage, and utilization by exploiting the significant differences of energy states and transport between nanostructures and macrostructures. In this talk, I will begin with a few examples regarding the exploitation of nanoscale effects for solar energy conversion, hydrogen storage, and will move on to the exploration of size effects for thermoelectric energy conversion. We will show that by exploring the interface scattering of electrons and phonons, the thermoelectric figure of merit can be improved in nanocomposites. Recent work on characterization of thermoelectric properties of individual nanowires and nanotubes will also be discussed.

Dr. Gang Chen received his Ph.D. from UC Berkeley in 1993. He taught at Duke University (1993-1997), UCLA (1997-2001) and is currently a professor at MIT. His research interests are on nanoscale transport phenomena, particularly thermal energy transport, and their applications in energy and information technologies. He is a recipient of the NSF Young Investigator Award and a Guggenheim Fellowship. He serves on the editorial board of four journals covering heat transfer and nanotechnology, and chairs the advisory board of ASME Nanotechnology Institute.

Shape memory alloys (such as NiTi) have fascinated scientists for their ability to ?remember? their original shape when heated. This change is base on a martensitic phase transformation from one crystal structure to another. Their thin-film embodiment has drawn much attention because of their potential use as actuation materials in microelectromechanical systems (MEMS). NiTi thin films are commonly sputtered in an amorphous form and require a high-temperature crystallization step to create their crystalline (actuating) form. The crystallization process is driven by nucleation and growth and is highly dependant on temperature. We have studied the crystallization process using in situ heating transmission electron microscopy methods. This talk will present our observations and a quantitative description of the crystallization kinetics using the Johnson-Mehl-Avrami-Kolmogorov (JMAK) theory. Our approach of coupling our experimental observations with the JMAK theory has rendered us able to predict the microstructure (particularly, the average grain size) over a broad range of temperatures. It has been found that the resulting microstructures control the martensitic transformation behavior and the films associated actuation properties. Such insights can contribute to the development of materials with optimal (actuation) properties.

Ainissa G. Ramirez, Ph.D. is an Assistant Professor of Mechanical Engineering at Yale University. Her work focuses on the development of thin film NiTi shape memory alloys for microelectromechanical systems (MEMS). Dr. Ramirez received her training in materials science and engineering at Brown University (Sc.B.) and Stanford University (Ph.D.). She worked as a member of technical staff at Bell Laboratories, Lucent Technologies in Murray Hill, NJ for 4 years before joining the faculty at Yale in 2003. She has been awarded MIT?s TR100 Young Innovators Award, the Sloan Research Fellowship, and the NSF CAREER award. She has written over 25 technical articles and holds 6 patents. Dr. Ramirez is also a leader in science education and serves as an advisor to the Liberty Science Center (Jersey City, NJ) and the Exploratorium (San Francisco, CA). At Yale, she is the director of the award-winning science lecture series for children called, Science Saturdays. She sits on the board of directors for the Connecticut Academy for Education.

Nanomaterials are of strong interest for both fundamental and technological reasons. At the fundamental level, nanomaterials possess novel physical and chemical properties that differ from those of isolated atoms or molecules and bulk matter due to quantum confinement effects and exceedingly larger surface area relative to volume. These novel properties are highly promising for applications in emerging technologies such as nanoelectronics, nanophotonics, non-linear optics, miniaturized sensors and imaging devices, solar cells, and detectors. Semiconductor nanoparticles have been studied extensively because of their potential application in electronic devices and the opportunity they offer to study the effects of quantum confinement. A unique subset of semiconductor nanoparticles is doped semiconductor nanoparticles. We have recently studied several doped semiconductor nanoparticle systems with the goal to understand the relation between their optical properties and the structure of the host nanoparticles as well as that of the dopant. In the case of Mn2+-doped ZnSe nanoparticles, we have found that the location of the Mn2+ significantly influences its optical emission properties. This understanding is important for designing new nanophotonics materials. We have also investigated the bioconjugation of silica-coated CdSe quantum dots to IgG proteins for potential applications in cancer biomarker detection and have found that the silica coating significantly enhance the stability of the CdSe quantum dots in buffer solutions based on photoluminescence properties. Metal nanoparticles have also attracted considerable attention due to their interesting properties and potential applications. We have studied the optical and structural properties of different metal nanostructures including aggregates, nanorods, and nanoshells with the goal to optimize their SERS (surface-enhanced Raman scattering) activities. For example, we have very recently demonstrated SERS from single, hollow gold nanostructures. Exceptional sample homogeneity leads to a nearly tenfold increase in signal consistency over standard silver substrates. SERS offers a unique combination of molecular specificity and extremely high sensitivity that few other analytical techniques can offer. SERS based on metal nanoparticles, in conjunction with photoluminescence from semiconductor quantum dots, have been exploited for detection of cancer biomarkers.

Recent experiments by Kim and Chan, and very recently Reppy and coworkers, have seen signs of superfluidity within samples of solid helium-4. This raises a number of interesting questions: Can superfluidity exist within the equilibrium ground state of solid helium? What properties must a quantum solid have to be also superfluid? A normal solid is a self-assembled Mott insulator, while a supersolid is self-doped so it has carriers that can Bose condense. The measured supersolidity may alternatively be due to extended defects in a not-fully-annealled normal solid: a dislocation line can be a superfluid wire, while a grain boundary can be superfluid "film".

In this seminar, I will present our recent work on the growth and electrochemical properties of single crystalline vanadium pentoxide (V2O5) nanorod, amorphous V2O5 nanotube, and Ni-V2O5 nanocable arrays. Vanadium pentoxide nanorod arrays were grown by electrochemical deposition, surface condensation induced by a pH change, and sol electrophoretic deposition. Uniformly sized vanadium oxide nanorods with a length of about 10.m and diameters of 100 or 200 nm were grown over large area with near unidirectional alignment. TEM micrographs and electron diffraction patterns of V2O5 nanorods clearly show the single-crystalline nature of nanorods from all three growth routes with a growth direction of [010]. Electrochemical analysis revealed that nanorod array electrodes possess significantly improved storage capacity and charge/discharge rate approximately 5 times higher applicable current density than that of sol-gel derived films. V2O5 coated Ni nanorods arrays were grown by template-based electrochemical deposition of Ni, followed by electrophoretic deposition of V2O5 layer. Each Ni core nanorod is covered completely and uniformly by V2O5 shell of average thickness of about 40nm. The current density and Li+ insertion capacity of Ni-V2O5 nanocable array electrodes possess approximately 10 times larger capacitance than single crystal V2O5 nanorod arrays and 40 times larger than sol-gel derived polycrystalline V2O5 films. The most significant improvement in the electrochemical supercapacitor performance based on Ni-V2O5 nanocable arrays is on the simultaneous enhancement of specific power and specific energy with the enhancement easily above one order of magnitude. Further improvement in energy storage density and cyclic fatigue resistance with carefully designed doping and amorphotization will also be briefly discussed.

Considerable attention has been devoted to developing an understanding of the mechanisms that dominate electrical transport in metal-molecule-metal junctions comprised of single and small ensembles of molecules. In this talk, we will present an overview of recent research on the electrical and spectroscopic characterization of molecular junctions inserted along the length of sub-40-nm diameter Au and Pd metal nanowires (i.e., in-wire junctions) fabricated by template-directed synthesis. In particular, we will show results that investigate the relationship between the temperature dependent (10 ?V 300 K) current-voltage (I-V) characteristics and the vibrational spectra measured by inelastic electron tunneling (IET) spectroscopy for candidate molecular wires and bistable switching molecules. The two types of molecular wire junctions that were studied incorporate a self assembled monolayer of dithiolated oligo (phenylene-ethynylene) (OPE) molecules and their -NO2 derivatives. The I-V of these junctions are stable and reproducible between +/-1V. Temperature independent I-V are measured for both types of junctions, which is indicative of coherent tunneling transport. Moreover, strong vibrations associated with ??(18b) and ??(19a) ring modes were observed in both junctions. In contrast, measurements of molecular junctions that incorporate SAMs based on aniline derivatives show reproducible bistable switching with an on-off ratio of >10:1 at 1V. Differences are observed in the vibrational spectra that depend on the state of the junction.

Theresa S. Mayer received the B.S. degree in Electrical Engineering from Virginia Tech in 1988, and the M.S. and Ph.D. degrees in Electrical Engineering from Purdue University in 1989 and 1993. In 1994, she joined the Department of Electrical Engineering at Penn State University-University Park, where she is a Professor. Her research interests are in semiconductor and molecular device fabrication, integration, and characterization. Her research activities have included investigating high-speed III-V electronic devices, metallodielectric frequency selective surfaces, heterogeneous integration of micro- and nanometer-scale devices, molecular electronic devices, and nanosensor transducer arrays. Prof. Mayer was a Kodak Fellow (1990-1993) and the recipient of a National Science Foundation CAREER Award (1995), and a Penn State Engineering Society Outstanding Teaching Award (2000). She currently serves the general chair of the IEEE Device Research Conference and the chair of the Gordon Research Conference on the Chemistry and Physics of Nanostructure Fabrication.

A systematic procedure is developed to evaluate the density of planar defects together with dislocations and crystallite or subgrain size by X-ray line profile analysis in fcc crystals. Powder diffraction patterns are numerically calculated by using the DIFFaX software for intrinsic and extrinsic stacking faults, and twin boundaries for the first 15 Bragg reflections up to 20 % fault density. It is found that the Bragg reflections consist of five sub-reflection types categorized by specific selection rules for the hkl indices in accordance with the theory of Warren. It is shown that the profiles of the sub-reflections are Lorentzian type functions. About 15.000 sub-reflections are evaluated for their FWHM and their positions relative to the exact Bragg angle. These values are parametrized as a function of the density and type of planar faults. A whole profile fitting procedure, previously worked out for determining the dislocation structure and crystallite size distributions, is extended for planar fault by including these data into the software. The method is applied to evaluate twin densities in nanocrystalline and submicron grain size copper specimens. It is found that twinning becomes substantial under a crytical crystallite or subgrain size of about 40 nm, in accordance with other observations.

Although the methods and tools for research are the same in academia and industry, the goals, funding, and external forces are quite different. These differences will be highlighted through the description of the R&D process leading to several start-up company products over the past 20 years. These products include microplate readers, biosensor based systems, and microfluidic (lab-on-a-chip) systems. In most cases the fundamental research discovery that leads to a product concept is just the tip of the iceberg with respect to the series of inventions and engineering efforts necessary to bring the product to the market. The same process undoubtedly will apply to nanotechnology products as well.

This talk deals with research toward information processing by assemblies molecular components arranged in locally coupled arrays. I will discuss our recent work on <br>1) self-assembly of 2D nanocomponent arrays by in situ hybridization to DNA scaffolding, <br>2) the electrical behavior of alkanethiol//oligo(phenylene-ethynylene) bilayer molecular junctions, and <br>3) information processing by nonlinear phase dynamics in locally connected arrays. This work represents a paradigm shift that could lead to computers with high-level capabilities far beyond those of conventional systems.

The challenge of defining semiconductor integrated circuit elements at sub-100 nanometer dimensions has created opportunities for alternative patterning approaches. One attractive non-traditional approach utilizes the phenomenon of self assembly. Under suitable conditions, certain materials self organize into patterns offering promise for enabling further advances in semiconductor microelectronics. Diblock copolymers are particularly attractive for this application because – like photoresist materials used for lithography – they can act as sacrificial templates for patterning integrated circuit elements. We have successfully integrated a polymer self assembly process into our 200mm semiconductor fabrication facility. Self assembly has applications in both today’s and future microelectronics, and materials integration is the critical first step for adoption into high-performance semiconductor technology. We will describe key applications of self assembly in high-performance semiconductor device fabrication, including its use in on-chip decoupling capacitors, nanocrystal FLASH memories, and multi-nanowire field-effect transistors. The discussion will highlight both the promise and versatility of this technique, as well as some limitations and challenges still to be addressed.

Atomically uniform films of Ag and Pb have been successfully grown on several substrates (Fe, Si, and Ge). The potential barrier at the interface confines the electrons in a film to form quantum well states. The resulting electronic structure of the film is substantially different from the bulk counterpart, and the physical properties of the film can vary significantly as a function of film thickness. These variations generally follow a damped oscillatory behavior, and the underlying physics is similar to the shell effect associated with the periodic property variations of elements in the period table. This talk discusses the basic electronic structure of thin metal films as measured by angle-resolved photoemission and the connections to physical properties including the surface energy, thermal stability, work function, electron-phonon coupling, etc. Quantum size effects can also affect morphological evolution during film growth and heat treatment. X-ray diffraction studies show that the observed development of nanoscale features can be related to the energetics of the system.

Bio information:

EDUCATION
University of California at Berkeley (1973-1978), Ph.D. Physics.
National Taiwan University (1967-1971), B.S. Physics.

EMPLOYMENT
Associate Director (1999-), Head, Solid State Sciences and Materials Chemistry Program (1991-), Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign.
Professor (1988-), Associate Professor (1984-1988), Assistant Professor (1980-1984), Department of Physics, University of Illinois at Urbana-Champaign.
Postdoctoral Research Associate, IBM T. J. Watson Research Center (1978-1980).

The cytoskeleton inside cells provides the necessary mechanical stability of a cell and is essential in the mechanotransduction between cell nucleus and membrane. It comprises an interpenetrated network of three types of filamentous networks. Several of these filamentous networks, such as F-actin, exhibit strain stiffening: the stiffness increases with deformation. Until recently, the leading explanation was that stiffening is an entropic effect related to stretching-out of individual thermally-undulating filaments. I will present numerical simulations of networks, however, that demonstrate the limited validity of the assumptions involved. In effect, our calculations indicate that strain stiffening is a consequence of the network structure rather than the response of filaments.

Ultraprecision finishing of the II-VI semiconductors, some of which have applications in infrared optics (CdS, ZnSe) and as potential substrates for short wavelength light emitters (ZnO, ZnSe), poses particular challenges due to the unique chemical and structural properties of these materials. Studies on their surface finishing have demonstrated the achievement of superior surface finish and form accuracy. However, subsurface lattice disorder introduced by the process is known to persist and may pose severe limitations on both surface performance and, for substrate applications, suitability for subsequent epitaxial growth. Two investigations of the near surface changes caused by surface preparation are presented. The first focuses on the use of Rutherford backscattering in the channeling configuration to study the nature, extent and distribution of subsurface damage in finely finished bulk single crystals of CdS, ZnSe and ZnO. In the second study, nanoindentation is used to investigate near surface changes caused by surface preparation. The resulting mechanical behavior of ZnO prepared by chemomechanical polishing, mechanical polishing and chemical etching is presented. In particular, the effect of surface condition on the critical load for the onset of plastic deformation is examined.

Don A. Lucca is currently Regents Professor and Tom J. Cunningham Chair in the School of Mechanical and Aerospace Engineering and a member of the faculty of the School of International Studies at Oklahoma State University. He also holds the position of Guest Scientist in the Center for Integrated Nanotechnologies Group (MST-CINT) in the Materials Science and Technology Division at Los Alamos National Laboratory. He received a BS degree from Cornell, MSE from Princeton, and PhD from Rensselaer Polytechnic Institute all in Mechanical Engineering. He is a Fellow of the Society of Manufacturing Engineers, has received the Alexander von Humboldt Research Award for Senior Scientists, and holds an honorary doctorate from Universit?t Bremen. His current research is directed towards developing basic understanding of the mechanics and physics which govern microscale and nanoscale fabrication processes used to create ultraprecision surfaces and thin films, and to investigating the mechanical, chemical, electrical and photonic nature of the surfaces which result.

Nature produces a wide variety of exquisite mineralized tissues fulfilling diverse functions, and often from simple inorganic salts. Organisms exercise a level of molecular control over the physico-chemical properties of inorganic crystals that is unparalleled in today's technology. This reflects directly or indirectly the controlling activity of biological organic surfaces that are involved in the formation of these materials. In our bio-inspired approach to the synthesis of inorganic crystals, we design nano/micropatterned organic surfaces to orchestrate inorganic crystallization. This approach made it possible to achieve a remarkable level of control over various aspects of the crystal nucleation and growth, including the precise localization of particles, nucleation density, crystal sizes, morphology, crystallographic orientation, arbitrary shapes, microstructure, stability and architecture. The mechanisms of molecular recognition at the organic/inorganic interface will be discussed.

Particulate flows are applicable to a wide-range of engineering problems spanning the tribology, nanomanufacturing, and granular flow arenas. They are used to planarize nanoscale devices on silicon wafers during the semiconductor integrated circuit (IC) manufacturing process and the fabrication of next-generation data storage. They have also been explored as dry alternative lubricants for high-speed applications in both powder and granular forms. The first segment of this presentation will focus on work conducted in chemical mechanical polishing (CMP). CMP is one of the processes involved in the manufacturing of semiconductor ICs, where slurry with nano-size particles is sheared between a silicon wafer and a polymeric pad. In this reverse-tribology problem, the slurry (?wet? particulate flow) wears the thin film layers on the wafer surface. Consequently, the ultra-thin layers are polished and planarized. The slurry is a complex mixture of Newtonian fluid and nanoparticle abrasives, which makes the CMP problem continuously unpredictable. This talk will explain how we are attempting to solve this multi-physics, multi-scale problem with modeling and experiments. The second segment of the presentation will showcase work that has been done with dense ?dry? particulates in sliding contacts, namely powder lubricants and granular materials. These particulate flows have been proposed as alternative lubricants to oils, which are unable to sustain loads at very high temperatures. The Particle Flow & Tribology Laboratory is also currently developing the first ?granular journal bearing? to study the hydrodynamic behavior of granular flows in rough and loaded rolling contacts. This instrument will be valuable for studying granular materials behavior for the development of next-generation planetary rover technology for Martian exploration.
Biography
C. Fred Higgs, III received his B.S. in mechanical engineering from Tennessee State University. He received his M.S. and Ph.D. in mechanical engineering at Rensselaer Polytechnic Institute (RPI). Prior to coming to Carnegie Mellon University, he completed his post-doctorate at the Georgia Institute of Technology in the Woodruff School of Mechanical Engineering. He has authored or co-authored over 25 archival papers and has been an invited speaker at numerous international conferences, including the Materials Research Society (MRS) CMP Symposium, the International VLSI/ULSI Multilevel Interconnection Conference (VMIC), the International Multi-level Interconnect Conference (IMIC), and most recently, the 2006 MRS Symposium: "Nanostructured and Patterned Materials for Information Storage?. An assistant professor in the mechanical engineering department at Carnegie Mellon, he has recently been appointed an Associate Editor of the STLE Tribology Transactions Journal. Dr. Higgs is a professor in the ?Alfred P. Sloan PhD Program?, which supports professors and their students at select institutions who are recognized as magnets and mentors to minority PhD students in engineering and science.

Electron-electron and electron-phonon interactions can lead to unexpected properties in one-dimensional properties that are different than in three-dimensions. In the present study we explore a promising candidate system of "wires" that approach the one-dimensional limit: self-assembled atomic chains on stepped silicon surfaces. Using angle-resolved photoemission and scanning tunneling microscopy we probe the momentum resolved and spatially resolved electronic structures of Si(553)-Au atomic chains. Our findings show geometry plays a key role in the electronic structure demonstrating: (1) the one-dimensional nature of the Fermi surfaces of self-assembled atomic chains [1], (2)the small but measurable two-dimensional coupling that varies with the spacing between chains [2], (3) the formation of quantized resonances in finite chain segments [3], and (4) how electronic effects can influence the length distribution of atomic chains. Such geometrical effects will play a key role in determining the low-temperature properties, such as recently observed charge density wave phases.

[1] J.N. Crain, A. Kirakosian, K.N. Altmann, C. Bromberger, S.C. Erwin, J.L. McChesney, J.L. Lin, and F.J. Himpsel, Phys. Rev. Lett., 90, 176805 (2003).
[2] J.N. Crain, J.L. McChesney, F. Zheng, M.C. Gallagher, P.C. Snijders, M. Bissen, C. Gundelach, S.C. Erwin, and F.J. Himpsel, Phys. Rev. B, 69, 125401 (2004).
[3] J.N. Crain and D.T. Pierce, Science, 307, 703 (2005).

I will present a comprehensive study of shot noise in multiple-barrier resonant-tunneling devices such as double-barrier resonant-tunneling diode (DBRTD), triple-barrier resonant-tunneling diode (TBRTD) and superlattice photodiode (SPD). Shot noise measurement, in combination with the conductance, is a useful tool to elucidate the transport mechanism in mesoscopic devices. The shot noise in DBRTDs is reduced over the Poissonian value 2eI in the positive differential conductance region and is enhanced over 2eI in the negative differential conductance region. Two completely different tunneling mechanism such as coherent tunneling and sequential tunneling both can successfully explain the quasi-triangular shape of the I-V curve and the noise structure in DBRTDs. Can shot noise distinguish between coherent tunneling and sequential tunneling? To address this question experimentally, we have done a systematic study of the shot-noise in TBRTDs in which we have varied the width of the potential barrier between the wells, from the isolated-well to the strongly-coupled-well limits. Along the way, we have found that there are quantitative differences between the behavior of the shot noise in TBRTDs and that observed in DBRTDs. Those differences highlight the limitations of semi-classical calculation that fails to explain them. Superlattice photodiode is a multiple-barrier system, where the carrier electrons are injected by optical excitation and the transport mechanism can be changed by using external electric field. At very low fields, transport occurs via superlattice minibands, as in a mesoscopic metal in the diffusive regime, whereas at very high fields electrons hop, tunneling through individual barriers. We have found experimentally that shot noise approaches the value same as the shot noise in metallic diffusive conductors when the quantum wells are strongly coupled and approaches Poissonain value when the coupling is weak or a strong external electric field is applied. Although the result is consistent with the existing theories for one-dimensional multiple-barrier devices, the theories cannot account for the dependence of the noise on the superlattice parameters we have observed.

Near-field microwave radiation from a circular loop antenna is coupled into the scanning tunneling microscope (STM) junction, and the resultant microwave rectification current (MRC) is employed to investigate nanoscale physical phenomena. The STM tunneling junction has the intrinsic current-voltage (I-V) nonlinearity originating from the density of states (DOS) and the tunneling probability; thus the tunneling current at microwave frequency is rectified. The MRC is modulated electrically by RF switch for lock-in detection, and the recorded spectra confirm the d2I/dV2 dependence. The coupled microwave amplitude is calibrated from the numerical analyses of the spectra. This observation naturally raises the possibility of inelastic electron tunneling spectroscopy (IETS) implementation, and it is shown that the nanoscale magnetic domains and the isotope shift of the single-molecule vibrational energy can be resolved by MRC spectroscopy and microscopy. Acetylene (C2H2) and its isotope (C2D2) are clearly resolved by MRC vibrational spectroscopy and microscopy. The antiferromagnetic domains of the Cr(001) surface are also resolved with spin-polarized tip and the MRC technique. Therefore, STM-IETS and the spin-polarized STM (SP-STM) are demonstrated by this novel approach using MRC. Further research using MRC will reveal its potential for the study of various nanoscale phenomena. References
Spectroscopy and Microscopy of Spin-Sensitive Rectification Current Induced by Microwave Radiation: Joonhee Lee, Xiuwen Tu, and Wilson Ho, Nano. Lett. 5, 2613 (2005).
Atomic-scale Rectification at Microwave Frequency: X. W. Tu, J. H. Lee and W. Ho, J. Chem. Phys. 124, 021105 (2006).

Semiconductor nanowires and nanorods have attracted increasing interest due to their novel physical properties and diversity for potential electronic and photonic device applications. For the nanomaterials preparation, a catalyst-assisted vapor-liquid-solid (VLS) method has widely been used since this technique offers an easy and simple method for the synthesis of many kinds of semiconductor nanowires including Si, GaAs, ZnO, and GaN. Alternatively, our group developed catalyst-free metal-organic chemical vapor deposition of ZnO nanorods in order to minimize both incorporation of unintentional impurity and formation of a mixed interfacial layer, i.e., by utilizing direct adsorption of atoms on the top surface of nanorods. In this presentation, I will discuss characteristics of ZnO nanorods grown by catalyst-free metal-organic chemical vapor deposition, and their nanorod heterostructures and device applications. First of all, the catalyst-free method excludes possible incorporation of metal impurities which may occur in the catalyst-assisted VLS methods, which enables to minimize unintentional impurity incorporation and offer high purity nanorods. As evidence of the high purity ZnO nanorod growth using the catalyst-free method, free exciton emission peaks was observed in PL spectra of ZnO nanorods measured even at low temperatures below 15 K. With precise thickness control down to the monolayer level, compositionally modulated nanorod quantum structures can be readily designed within individual nanorods. Moreover, ZnO nanorods grown by this method are aligned vertically and exhibit uniform thickness and length distributions, highly appropriate for a direct integration of incorporating 1D nanorod on a device platform to fabricate a unique vertical devices and device arrays. Finally, I briefly describe our recent activities on ZnO nanorod device fabrication and evaluation, including nanorod light emitting devices, field-effect transistors (FETs), Schottky diodes, and logic circuits.

Since their discovery in 1991 carbon nanotubes (CNTs) have attracted a great deal of attention because of their remarkable mechanical and electronic properties. At low temperatures, electronic transport through CNTs exhibits a wealth of quantum and mesoscopic phenomena, including charge quantization, finite size and many-body effects, which makes them an interesting system for quantum dot (QD) studies, in many aspects complementary to QDs in semiconductor heterostructures. In this talk I will review the basic electronic properties of CNTs and discuss our recent low temperature experiments on single CNT QDs, which show the wide range of physics regimes attainable with this system: from ambipolar single quantum dots in strong Coulomb blockade to quantum supercurrent transistors in the open QD regime.

References:
P. Jarillo-Herrero et al. Nature 429, 389 (2004)
P. Jarillo-Herrero et al. Nature 434, 484 (2005)
P. Jarillo-Herrero et al. PRL 94, 156802 (2005)

The myriad phase transitions found in the manganites are classic examples of the effects of coupled degrees of freedom in strongly correlated materials. In this talk, I will focus on one particular phase which emphasizes this point: the orbitally and magnetically ordered ground state in insulating, half-doped manganites. "Orbital order" describes a phase transition in which the population of a particular valence electron spatial wave function on an ionic site is correlated throughout the lattice. In the case of manganites, the ionic sites of interest are the Mn ions and their strongly correlated 3d valence electrons. Since the overlap between adjacent Mn orbitals dictates their magnetic interaction, orbital ordering of the Mn sites functions as a precursor to the magnetic ground state -- or at least, this has been the picture for 50 years! The challenge to testing this picture has been the absence of a probe that can directly observe the orbital order: after all, this requires a probe which can see that the shape of the electron cloud around one Mn site is different from its neighbor's. I will explain how resonant x-ray diffraction provides such a probe and how this technique permits a unique and direct comparison of orbital and spin correlations in half-doped manganites. I will also discuss new results from coherent x-ray resonant diffraction measurements, which may be used to image the orbital order domains and probe their dynamics.

The determination of the structure and electronic properties of organic thin films grown on inorganic substrates is highly relevant for the application of these systems in organic electronic devices. Likewise the interaction of biomolecules with inorganic materials has recently attracted a lot of interest with the aim of determining the characteristics of bio-active surfaces for biotechnological applications. In these films, characterized by a large number of degrees of freedom, structure, morphology and electronic properties are strongly interrelated and often depend critically from the growth conditions and therefore should be possibly studied in situ and in the same experimental system. With the aim of reaching a better understanding of the above-mentioned film properties and of related effects like molecule substrate bond formation, charge transfer processes at the interface and in the films, our group studies the growth of organic thin films by means of various experimental techniques mostly using synchrotron radiation; our experimental apparatus combines structural techniques like Grazing Incidence X-ray Diffraction (GIXD) and He Atom Scattering (HAS) with spectroscopic techniques like High resolution X-ray Photoemission spectroscopy (HRXPS), X-ray Absorption Spectroscopy (XAS) and most importantly Resonant Photoemission (RESPES). Example of phenomena like substrate induced modification of the electronic states of the organic molecules at the interface, film induced structural rearrangements of the substrate and electron charge transfer processes will be presented referring to thin films of large planar molecules like Cu-phthalocyanine, PTCDA but also small biomolecules like L-cysteine.

The adsorption and self-organization of copper(II) octaethyl porphyrin (CuOEP) has been studied in detail on heterogeneous surfaces by STM, LEED and UPS. Ultrathin NaCl films have been grown on Cu(111), Ag(111) and Ag(001) and for submonolayer coverage the formation of NaCl islands 1 to 3 ML thick coexisting with clean metal regions is observed. CuOEP molecules have been deposited on the so prepared heterogeneous salt-metal surfaces. STM reveals that the molecules self organize in ordered monolayers on the bare metal areas as well as on the NaCl islands. Series of STM observations performed by increasing the CuOEP coverage reveal that the molecule-substrate interaction can be tuned in a discrete manner by controlling the number of NaCl layers. In particular the adsorption energy of CuOEP decreases by introducing an insulator layer and by increasing its thickness. Such a dependence of the adsorption energy on the NaCl thickness can be explained in the frame of van der Waals theory. On the other hand, for CuOEP directly adsorbed on metals, UPS measurements show that a charge transfer from the adsorbate to the substrate occurs. The comparison of UPS and STM measurements with DFT calculations shows that on all the three metal substrates the CuOEP-metal binding is mainly of ionic nature and no chemisorption occurs.

This talk focuses on how the shape of nanostructures can control light on the nanometer scale. Two different systems will be discussed: (i)nanofabricated metallic films of nanohole arrays and (ii) chemically synthesized semiconducting nanocrystals. We will describe an innovative fabrication scheme for preparing large-area, free-standing films of nanoscale holes. These metallic films exhibit enhanced transmission with spectra characteristic of interacting holes. When investigated in the near-field, these films support surface plasmon polariton standing wave patterns whose wavelength and polarization can be controlled. Also, we will discuss how nano- and microcrystals of tin sulfide can have optical properties dramatically different from bulk, but whose properties can be attributed to a different crystal structure and not quantum size effects.

Following our work on a triple quantum dot single-electron rectifier, we report recent measurements on three quantum dots coupled in a ring geometry. The quantum dots are fabricated in a GaAs/AlGaAs heterostructure containing a two-dimensional electron gas using lithographically patterned gates and an etched trench in the center of the ring. By only energizing certain gates, this device allows us to study electron transport through a single dot, a double dot, or a triple dot ring. We can determine the absolute number of electrons in a quantum dot using a nearby charge sensor and find that we are able to tune a single dot to the one and two electron regime. We find several sharp peaks in the differential conductance, occurring at both zero and finite source-drain bias, for the one and two electron quantum dot. At zero source-drain bias, the temperature and magnetic field dependence of the conductance is consistent with a standard Kondo resonance. We attribute the peaks at finite-bias to a Kondo effect through excited states of the quantum dot.

I will discuss electrical transport between half-metallic manganite electrodes connected by native domain walls and, more exotically, carbon nanotubes. Manganites are mixed-valent oxides of manganese that display interesting physical properties such as ?electronic? phase separation, and metallic phases with almost fully spin polarised conduction electrons.

Native domain walls. In a phase separated thin film manganite device, magnetic domain walls can be created in ferromagnetic percolating pathways. The magnetoresistance of these devices was tested in different geometries, yielding qualitatively different results. Moreover, the changes in resistance-area product are large enough to suggest that the domain walls display mesoscopic phase separation at the wall centres.

Manganite-carbon nanotube-manganite devices. Ferromagnetic metallic manganite electrodes connected by a carbon nanotube also display magnetoresistance. This demonstrates micron-scale spin coherence in the nanotube, and spin injection between an inorganic half-metallic crystal and the organic molecule.

Carbon nanotubes are cylinders from graphene with fascinating physical
properties. Many of them depend critically on the arrangement of carbon
atoms on the cylinder surface, as defined by the chiral index (n,m). In
this talk, I will first show how to determine (n,m) by resonant Raman
scattering. Simultaneous measurement of optical transition energies and
vibrational frequencies directly reveals the chiral index, without using any empirical parameters. The assignment allows to analyze and understand the properties of carbon nanotubes, such as electron-phonon coupling, as a function of their chiral index. The measured transition energies deviate from any calculations performed within a single-particle picture. As I will discuss in the second part of my talk, this is caused by strong Coulomb interaction between excited electron and hole. The excitonic nature of the optical excitations in carbon nanotubes is demonstrated by two-photon absorption spectroscopy, indicating binding energies on the order of 400 meV.

Control over spins in the solid state forms the basis for spintronics and quantum information technologies. Here, I provide an overview of the study of coherent spin dynamics in two very different systems, an insulating quantum magnet and a nonmagnetic semiconductor, including a discussion of temporally-resolved magnetic and
optical measurements. I will discuss the dynamic properties of the low temperature spin liquid phase observed in a dilute magnetic compound Li(Ho,Y)F [1,2]. Here we show that the excitation spectrum consists of collections of discrete, fluctuating spin clusters with well-defined normal mode frequencies that can be addressed via the technique of spectral ?hole burning?. Once set into resonance, these clusters, composed of hundreds of spins, remain coherent for up to tens of seconds. Spin dynamics in semiconductor microcavities is another new and promising research field as it offers unique means of controlling light-matter interactions. I will discuss the photonic manipulation of electron spins in optically-pumped GaAs microcavities [3]and its implications for the underlying physics of quantum information processing in the solid state.
1. S. Ghosh, R. Parthasarathy, T.F. Rosenbaum and G. Aeppli, Science 296, 2002,2195-2198
2. S. Ghosh, T.F. Rosenbaum, G. Aeppli and S.N. Coppersmith, Nature 425, 2003, 48-51
3. S. Ghosh, W.H. Wang, F.M. Mendoza, R. C. Myers, X. Li, N. Samarth, A.C. Gossard, and D.D. Awschalom, submitted, Nature Materials (2005).

The surface of a ferroelectric material is a critical determinant of its properties, as the dimensions of the material approach the nanoscale.? The relationship between oxide surface properties and bulk polarization is elucidated, both for two-electrode ferroelectric capacitors, and for one-electrode supported ferroelectric films and nanowires.

Plastic flow in crystalline materials is size dependent over length scales of the order of tens of microns and smaller. This size dependence arises in a variety of contexts; e.g. the grain size dependence of the flow strength, the indentation size effect and the size dependence of the thermo-mechanical response of thin films. One well-appreciated origin of size effects is associated with imposed plastic strain gradients and geometrically necessary dislocations. In addition, strain gradients and boundary layers leading to size-dependent response can occur in circumstances where, at least in principle, a more or less homogeneous response is possible but where the physics of dislocation motion prevents it. Discrete dislocation plasticity analyses of various plastic flow processes will be used to illustrate a range of size effects. Particular attention will be given to the scaling, both with size and with material properties that is predicted by the calculations.

Mesoscopic S/N/S Josephson junctions exhibit several intriguing phenomena when driven out of equilibrium. This talk will focus on three experiments in 3-terminal S/N/S devices, in which quasiparticle current is injected into the middle of the junction from a normal (N) reservoir. 1) If one of the superconducting contacts is left floating, the I-V curve measured between the other S contact and the N contact exhibits a change of slope at a critical current, demonstrating coexistence of quasiparticle current and supercurrent in the sample. 2) Pushing the system further from equilibrium reverses the sign of the current-phase relationship in the SNS Josephson junction, creating a controllable "pi" junction. 3) Injection of both quasiparticle current and supercurrent generates a spatial gradient in the effective electron temperature along the junction, whose direction is controllable by the supercurrent. We visualize this effect using tunneling spectroscopy to measure the local electron energy distribution function.

Using molecules in electronics has an enormous appeal. Reaction chemistry offers vast diversity of molecular substructures and chemical transformations. However, wiring the molecules in a macroscopic circuit remains a challenging problem. In this talk, I present three approaches that we use to build small molecular structures. The first group of experiments is targeted toward wiring of a single or just a few molecules. We found that the conductance mechanisms observed in such ultrasmall devices differ dramatically from the predicted transport through the molecules. The electronic states mediating the transport are low energy defect states rather than the electronic states of the molecules. To detect the conductance associated with the molecular states, we have developed high-yield process based on prefabricated nano-templates to screen the properties of larger molecular junctions with characteristic size of ~50-300 nm. The approach readily permits to experiment with the topography, the chemical bonding at metal-molecule interface and to significantly reduce the defect density. For the first time, we directly compare the properties of conjugated versus saturated molecules with the length ~ 1.5 nm. In the last case, we build molecular junctions by imprinting ~100 nm Au pads on top of self-assembled monolayers. The pads are contacted by conducting AFM. Surprisingly, the results of all experiments show that the conductance of molecules is 4-5 orders of magnitude smaller than is commonly believed.

After a brief overview of the Advanced Photon Source, the nation?s most brilliant x-ray source for research, we will discuss the atomic origin of magnetic hardness in our best permanent magnet ? Nd2Fe14B. Rare-earth (RE) ions dramatically enhance magnetic stability through the interaction of their anisotropic (4f) electron clouds with the electric field of surrounding charges. Here we show that the simultaneous presence of RE ions in dissimilar atomic environments undermines the intrinsic stability of the highest performance permanent magnets. Experiments were done by using helicity-dependent resonant diffraction technique in combination with a digital lock-in detection scheme that synchronizes the measured x-ray diffracted intensity with the helicity modulation of the incoming x-ray beam. Our results, supported by theory, show that unequal neodymium sites in the unit cell of a neodymium-iron-boron single crystal prefer local magnetic moment orientations orthogonal to one another, reducing magnetic stability. These findings highlight the need for manipulating the local atomic structure around rare-earth ions for complete optimization of future magnets.

*Work at Argonne was supported by the U.S. Department of Energy Office of Science, under Contract No. W-31-109-ENG-38.

We use intermolecular interactions and selective chemistry to direct
molecules into desired positions to create nanostructures, to connect
functional molecules to the outside world, and to serve as test
structures for measurements of single or bundled molecules. Interactions
within and between molecules can be measured, understood and exploited at
unprecedented scales. We look at how these interactions influence the
chemistry, dynamics, structure, and other properties. Such interactions
can be used to advantage to form precise molecular assemblies,
nanostructures, and patterns. These nanostructures can be taken all the
way down to atomic-scale precision or can be used at larger scales. We
select molecules to choose the intermolecular interaction strength and
the structures formed within the film. We selectively test hypothesized
mechanisms for electronic switching by varying molecular design, chemical
environment, and measurement conditions to enable or to disable functions
and control of these molecules with predictive and testable means.
Critical to understanding these variations has been developing the means
to make tens to hundreds of thousands of independent single-molecule
measurements in order to develop sufficiently significant statistical
distributions, comparable to those found in ensemble-averaging
measurements, while retaining the heterogeneity of the measurements.

In an electron gas at very low density a regime can be obtained where the magnetic exchange energy J between neighboring electrons is exponentially suppressed relative to the Fermi energy, E_F. At finite temperature T, the energy hierarchy J << T << E_F can be reached, and we refer to this as the spin incoherent Luttinger liquid state. We theoretically explore the signatures of spin incoherence in momentum resolved tunneling and in transport, and compare the results with recent experiments. In momentum resolved tunneling the spin modes of a Luttinger liquid are thermally washed out leaving only the charge modes in the spectral function with a shift from +/- k_F to +/- 2k_F in momentum space. These modes are also broadened in momentum space by an amount of order k_F and the energy dependence of the tunneling density of states qualitatively changes from that of the spin coherent Luttinger liquid regime. The effects of an external magnetic field in the spin incoherent regime are also discussed. Transport in the infinite system can be mapped onto spinless electrons and various crossovers in temperature and for finite systems connected to Fermi liquid leads are also discussed.

In this talk I will discuss growth of semiconductor nanowires based on epitaxial nucleation of nanowires from lithographically defined anoparticles, allowing arrays of position-and dimension-controlled nanowires to be formed. Of special interest for the use of nanowires in studies of low-dimensional physics and for applications in electronics and photonics is the opportunity to form designed and abrupt heterostructures in nanowires. I will give examples of our studies of electrical and optical properties of nanowire structures as well as devices implemented in this technology, for instance in single-electronics, resonant tunneling and in storage applications. I will conclude with examples of new opportunities offered by nanowires, e.g. for formation of nanowire networks and for interfacing with neural systems.

This talk will focus on the electronic properties of carbon nanotube networks, and their application potential as passive and active electronic components in the area of electronics, photovoltaics, optoelectronics and sensors. Percolation issues, together with the frequency, and temperature dependent conductivity will be discussed. I will also review of the transistor characteristics of devices that incorporate a network conducting channels. Room temperature fabrication routes that allow integration into an all-plastic architecture will be discussed, and a comparison will be made with characteristics of other conducting/transparent films and devices. Finally, some applications in the area of opto-electronics and in-vitro biosensing will be touched upon.

Dimensionality is one of the most defining materials parameters such that the same chemical compound can exhibit dramatically different properties, depending on whether it is arranged in a 0, 1, 2 or 3 dimensional structure. While quasi-0D, quasi-1D and, of course, 3D atomic crystals have been well known and their properties investigated, dimensionality 2 is conspicuously absent among experimentally known crystals. In this talk, I will describe free-standing atomic crystals that are strictly 2D and can be viewed as individual planes pulled out of bulk crystals or, alternatively, as unrolled single-wall nanotubes. After discussing the preparation and characterization of such crystals, this talk will concentrate on electronic properties of graphene that is the most ?clean? of the 2D crystals obtained so far. Our experiments show that charge carriers in graphene exhibit a spectrum that mimics relativistic particles (Dirac fermions). This spectral feature results in new transport phenomena such as the existence of Mott?s minimum conductivity e?/h and half-integer quantum Hall effect.

The ultra-high vacuum (UHV) scanning tunneling microscope (STM) allows individual molecules to be imaged, addressed, and manipulated on semiconducting surfaces with atomic resolution at room temperature. This seminar will consider three different molecules on the Si(100) surface: styrene, cyclopentene, and 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO). In all cases, STM current-voltage characteristics on individual molecules mounted on degenerately n-type Si(100) show multiple NDR events at negative sample bias. On the other hand, at positive sample bias, the current-voltage characteristics do not show NDR, although a discontinuity in the differential conductance is observed. When the Si(100) substrate is changed to degenerate p-type doping, the charge transport behavior is qualitatively similar but at the opposite bias polarity. These empirical observations can be quantitatively explained using a capacitive equivalent circuit model and the energy band diagram for a semiconductor-molecule-metal junction. In addition, using multi-step feedback controlled lithography, heteromolecular nanostructures consisting of both styrene and TEMPO molecules have been fabricated on hydrogen passivated Si(100). Atomic-scale characterization of these structures will be discussed in the context of silicon-based molecular electronics.

SEMINAR IS CANCELLED

We study the effects of spin orbit interactions on the low energy electronic structure of a single plane of graphene. We find that in an experimentally accessible low temperature regime the symmetry allowed spin orbit potential converts graphene from an ideal two dimensional semimetallic state to a quantum spin Hall insulator. This novel electronic state of matter is gapped in the bulk, but supports transport of spin and charge in gapless edge states that propagate at the sample boundaries. The edge states are non chiral, but they are not localized by disorder because their directionality is correlated with spin. The spin and charge conductances in these edge states are calculated and the effects of temperature, chemical potential, Rashba coupling, disorder and symmetry breaking fields are discussed.

After forty years of advances in integrated circuit technology, microelectronics is undergoing a transformation to nanoelectronics. Modern day MOSFETs now have channel lengths of only 50 nm, and billion transistor logic chips have arrived. Moore?s Law continues, but the end of MOSFET scaling is in sight. Many researchers are exploring new materials and devices that might extend CMOS scaling, complement ultimate CMOS, or enable new applications. MOSFETs with strained silicon, SiGe, or III-V channels are one possibility. Another approach is to explore one-dimensional channels made from nanowires or nanotubes. Molecular transistors are yet another possibility. In this talk, I will examine the fundamental limits of transistors and the practical challenges of pushing transistor technology towards those limits.

This talk will begin with a discussion of the fundamental limits of transistors that operate by modulating the flow of charge. I?ll then describe a very general and very simple way to understand nanoscale transistors and mention how it is generalized to the non-equilibrium Green?s function approach to quantum transport at an atomistic scale. Using these approaches, I?ll examine the possibility of 10nm-scale silicon MOSFETs and what new channel materials, such as III-V semiconductors might provide. Next, I?ll discuss one-dimensional transistors made from nanotubes and nanowires and examine how the 1D density of states affects the gate capacitance and scattering in MOSFETs. Finally, I?ll take a brief look at molecular transistors. The talk will conclude with some speculations about where electronic device research is heading.



MARK LUNDSTROM is the Don and Carol Scifres Distinguished Professor of Electrical and Computer Engineering at Purdue University where his teaching and research center on the physics, technology, and simulation of electronic devices. Lundstrom is the founding director of the NSF-funded Network for Computational Nanotechnology, which has a mission of research, education, leadership, and service to the nation?s National Nanotechnology Initiative. He serves on the leadership councils of the NASA-funded Institute for Nanoelectronics and Computing and the MARCO Focus Center for Materials, Structures, and Devices. Lundstrom?s work has been recognized by several awards, most recently, in 2005, from the Semiconductor Industry Association in recognition of his career contributions to the semiconductor industry.

TBD

Despite its importance in controlling key materials properties such as the bioavailability of pharmaceuticals and the color of pigments, the phenomenon of crystal polymorphism remains difficult to control and understand. Recent work in our laboratory involves discovering new crystalline forms of pharmaceutical compounds using polymers as heteronuclei. These results as well as the structure and dynamics of monolayers physisorbed at the solution solid interface, a model system for understanding crystallization phenomena at the molecular level, will be discussed.

Nanostructured magnetic materials offer the opportunity to produce structures with magnetic properties unrealizable in bulk materials. Although size effects have received most of the attention as a means to control material properties, disorder also has an important effect on the magnetic properties of nanostructures. Disordering ordered alloys can change properties such as the coercivity by orders of magnitude. Understanding the effect of disorder ? and being able to control it through fabrication techniques ? offers the potential to create new materials with fundamental interest and potential applications. This talk will start with a short introduction to nanoscale magnetism, and then illustrate the impact of disorder in rare-earth-based nanostructures using the examples of enhanced Curie temperature in inert-gas condensed Gd and the disorder-induced ferromagnet-to-magnetic glass-transition in mechanically milled GdAl2. The talk will conclude with a short description of how our work in magnetic nanostructures has led to our involvement in biomedical applications such as drug delivery and magnetic imaging.

Despite the importance of crystal growth and aggregation in arenas ranging from pharmaceuticals to specialty chemicals to naturally occurring biominerals, our understanding of these phenomena remains primitive. Advances in atomic force microscopy (AFM) during the last decade, however, now permit in situ visualization (i.e., in fluids) of molecular adsorption on crystal surfaces, crystal surface morphology, determination of rudimentary crystal structure, and real-time analysis of crystal growth processes and dynamics at the nanoscale, all under conditions of practical as well as fundamental interest. AFM also can be used to measure adhesion forces at crystal surfaces at the molecular level. These unique capabilities can be applied to a variety of crystalline materials, including specialty chemicals, proteins, and biominerals. Kidney stones, which afflict roughly 15% of the U.S. population, are biomineralized crystal aggregates, most commonly containing calcium oxalate monohydrate (COM) microcrystals as the primary constituent. Four steps - nucleation, growth, aggregation, and attachment to renal cell surfaces - are believed critical to stone formation, but these processes are poorly understood. Real-time AFM imaging of crystal growth on various faces of calcium oxalate crystals reveals the differences associated with molecular assembly at specific surface sites as well as the influence of macromolecule additives on these processes. The adhesion forces reflect specific interactions between tip-immobilized molecules and various calcium oxalate crystal faces, and these measurements permit identification of the most adhesive functional group-crystal face combinations and the role of urinary proteins on adhesion. The adhesive strength of COM crystal surfaces is substantially larger than those of calcium oxalate dihydrate (COD), whose formation generally is regarded as protective against stone disease. Collectively, these observations corroborate the importance of crystal aggregation and attachment to cells in stone formation, suggesting a path toward a better understanding of kidney stone disease and the eventual design of therapeutic agents. These studies also suggest new approaches for unraveling the complex processes responsible for the formation of other calcium-containing biominerals.

This talk deals with research toward information processing by assemblies molecular components arranged in locally coupled arrays. I will discuss our recent work on 1) self-assembly of 2D nanocomponent arrays by in situ hybridization to DNA scaffolding, 2) the electrical behavior of alkanethiol//oligo(phenylene-ethynylene) bilayer molecular junctions, and 3) information processing by nonlinear phase dynamics in locally connected arrays. This work represents a paradigm shift that could lead to computers with high-level capabilities far beyond those of conventional systems.



BIOGRAPHY

Richard A. Kiehl received the B.S., M.S., and Ph. D. degrees from the School of Electrical Engineering, Purdue University. From 1974 to 1980 he was a member of technical staff at Sandia National Laboratories, where he initiated studies on optical control of microwave semiconductor devices. In 1980 he joined AT&T Bell Laboratories, Murray Hill, as a member of technical staff. He was a leading contributor to the Bell Labs research on heterostructure electronics, particularly heterostructure field-effect transistors. In 1985 he joined IBM as research staff member at the T. J. Watson Research Center and focused his work on III-V and SiGe-based heterostructure CMOS circuitry. In 1993 he became assistant director of the Quantum Electron Device Laboratory at Fujitsu Laboratories Ltd. in Atsugi, Japan, where he lead research on nanoelectronics. He was on the faculty of Stanford University as acting professor of Electrical Engineering from 1996 to 1999, and he is currently the Louis J. Schnell Professor of Electrical & Computer Engineering at the University of Minnesota. He served as associate editor of IEEE Electron Device Letters and was co-editor of the book ?High Speed Heterostructure Devices? of the Academic Press Semiconductor and Semimetals Series. Professor Kiehl is a member of the American Physical Society and the American Chemical Society and a Fellow of the Institute for Electrical and Electronics Engineers.

An overview of our novel attempts in realistic many-body problems from first-principles will be presented, covering the theoretical framework, recent tool development, several case studies, and future developments. Our recent development of multi-energy resolved Wannier functions plays a central role in connecting the chemistry in the conventional density functional theory to local physics essential to strongly correlated systems. The long-standing puzzle of insulating ferromagnetism of half-filled La4Ba2Cu2O10 will be discussed and its underlying microscopic mechanism resolved in great detail, together with its isostructural antiferromagnetic counterpart, Nd4Ba2Cu2O10. Other case studies include chemical tuning of magnetic coupling in edge-sharing quasi-1D spin chains, excitation spectrum of manganites, microscopic origins of orbital ordering of manganites, and system-dependent of low-lying states in high-Tc cuprates.