|
One
challenge in preparing new nanomaterials is fabricating three-dimensional
designer materials assembled from two different types of nanoparticles.
Professor Stephen O'Brien, in collaboration with Dr. Chris Murray
of the IBM T. J. Watson Research Center, MRSEC/IBM bridging postdoctoral
scientist Dr. Franz Redl, and co-workers at the University of
New Orleans have done precisely that by tailoring the experimental
conditions so that nanoparticles with dissimilar, yet complementary
properties would assemble themselves into repeating 3-D patterns.
One type is composed of lead selenide, a semiconductor that has
applications in infrared detectors and thermal imaging and can
be tuned to be more sensitive to specific infrared wavelengths.
The other material, magnetic iron oxide, is best known for its
use in the coatings for certain magnetic recording media. This
combination of these nanoparticles may have novel magneto-optical
properties as well as properties key to the realization of quantum
computing. For example, it might be possible to modulate the material's
optical properties by applying an external magnetic field. To
produce an ordered structure, such as that shown in the accompanying
transmission electron micrograph (TEM), the particles had to be
very uniform, all within 5 percent of the target size. The iron
oxide particles were 11 nanometers in diameter, and contained
approximately 60,000 atoms, and the lead selenide particles 6
nanometers were in diameter, and contained approximately 3,000
atoms. Forming these so-called "crystal structures,"
as opposed to random mixtures of nanoparticles, is essential for
the composite material to exhibit consistent, predictable behavior.
Such new materials with otherwise unattainable properties, are
sometimes referred to as "metamaterials." Posted
September 29, 2003. |
 |
