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The densities of surface ligands and solvent
molecules are being followed during the self-assembly of CdSe nanocrystals
into arrays by using multiple-reflection attenuated total internal
reflection (ATIR) spectroscopy. This is performed in a Fourier transform
infrared (FTIR) spectrometer in which the arrays formed on a ZnSe prism.
During the self-assembly of CdSe nanocrystals passivated by pyridine that
are dissolved in pyridine, the 1436.1 cm-1 peak of neat
pyridine is followed along with that at 1445.2 cm-1 due to
pyridine bound to the CdSe surface. The solvent evaporates in about 30
minutes during the self-assembly of ~200-monolayer thick arrays in an
argon ambient. The pyridine bound to the surface slowly leaves the
surface, but about 35% remains after drying for several days. Since
pyridine only weakly binds to the surface, it had been commonly thought
that no pyridine would remain after extensive drying. While this is not
true, there are still significant changes to the surface during drying.
This result is important for the MRSEC studies of the self-assembly of
arrays and the properties of these arrays. This monitoring method is also
being used to follow the surface of exchange of TOPO and pyridine ligands,
and related processes. For more details contact Irving_Herman. A publication describing this work can be downloaded by PDF. |
