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The forefront of science today exists
at the boundaries of many of the traditional fields of chemistry.
This is particularly true in the area of dimensionally
confined solid state materials. The technology of "small
matter" holds enormous potential in sensor technologies, and
optical, electronic, and magnetic applications. However, for
a successful development of nanotechnology, many key challenges
in nanoscience must be tackled and a number of fundamental problems
must be scientifically explored and solved.
The research effort can be divided into three primary areas:
a) Developing systematic routes for the preparation, assembly,
and characterization of nano-scale materials; b) Surface, defects,
and structural analysis of nanomaterials by correlated optical,
magnetic, mass spectroscopic, and thermodynamic spectroscopies;
and c) Analysis of coupled structural, magnetic or electronic
phase transitions in single crystal materials.
The synthetic design team focuses on the development of synthetic
methodologies for preparation of new materials, ternary materials,
and industrially relevant synthetic methodologies. We have demonstrated
a novel crystal seeding methodology
for the preparation of high-yield, low-temperature grown nano-crystalline
semiconductors (2-10 nm, 5% rms batch, >5 g quantities) using
molecular cluster precursors that cleanly separate the nucleation
event from the growth step. We have extrapolated these strategies
to allow doping and production of ternary lattices of nanomaterials
with both phosphor and magnetic centers in both II-VI and III-V
materials.
The close interplay among charge, spin, and lattice degrees
of freedom in solid state materials is widely believed to play
an important role in the properties of materials. For nanoscale
materials the surface is also fundamental to the behavior of
materials. In our research effort we have correlated the vibrational,
structural, and theoretical properties to explore the relationship
between structure and transport properties on varying length
and time scales for a range of classical solid state materials,
CMR, epasolites, and nanoscale
materials. Analysis of vibrational,
pressure dependence, and photoluminescence
data suggest three specific confinement regimes in nanoscale
systems. The regimes correspond to the involvement of surface
state perturbations to core electronic levels in these materials.
Magnetic and optical studies on dilute magnetic semiconductors
suggest enhancement of magnetic superexchange between dopant
ions in confined system that arises from changes in the nature
of coupling in size-restricted materials.
Our efforts on engineering next generation nano-material assemblies
through bio-scaffolding, organic
assembly, or acid base chemistry has allowed development of
unique systems. Bio-scaffolding targets the application of DNA,
proteins, or a combination of site-specific binding proteins
and DNA duplex structures for the assembly of nano-scale materials.
While the assembly of nanocomponents by DNA is not new, the
use of enzymes to control structure, and probe bio-activity
of these constructs is new. In conjunction with this effort,
we have explored the use of rigid rod oligomers based on polyacetylene
to connect individual nanomaterials and have analyzed the energy
transport properties of these systems. Recent studies have shown
potential for these materials as memory devices, in fact, we
have been able to generate optical write-read/ thermal erase
memory images by taking advantage of changes in the nature of
energy transfer following thermal
fluctuations in the polymer assemblies. We have shown fine-control
over the production of polycrystalline
mesoscopic lattice composed of a 6:1 ratio of 5 nm Au and
CdSe assembled using acid-base equilibria. These materials possess
unique opto-electronic properties due to rapid carrier injection
following photoexcitation of the sub-components.
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