Young-Gui Yoon's Research Interest
Recent revolutionary technological advances paved a way to fabricate,
assemble, and manipulate nanoscale materials, such as fullerenes, carbon
nanotubes, nanowires, and nanocrystals. Those materials, combined with
modern experimental probing tools such as STM and AFM, have demonstrated
new phenomena characteristic to the nanoscale, for instance, molecular
electronics. Theoretical understanding of those new phenomena is
becoming more important both in predictive power and in quantitative
analysis of measured physical properties.
The focus of my research is to investigate structural, electrical
transport, and thermal transport properties of nanoscale materials using
state-of-art first-principles density functional theory. To build up
solid knowledge base toward cutting-edge technology, strong
collaboration with condensed matter experimentalists is essential,
and interdisplinary research with chemists, and engineers is desirable.
Described below are a few examples that I would like to study with
such combining efforts. In the first part, I will describe NMR chemical
shift study of structural properties of nanoscale materials. I will
then discuss research plans to investigate electrical transport
properties in molecular electronics. Finally, the plan on thermal
transport properties based on molecular dynamics is described.
NMR chemical shifts are very important in structure determination of
complex materials including nanostructures. I have carried out
first-principles studies on the NMR chemical shifts in carbon nitrides,
silica, amino acids, and benzene in water. On the other hand, surface
states NMR have been suggested as a very useful tool in studying
surface structure of the topmost layers of bulk systems.
Careful modeling of surfaces of nanoscale materials and explicit
calculations of NMR chemical shiftes will reveal important surface
structure information.
Theoretical investigation of electrical transport properties in the
context of molecular electronics are particularly interesting because
device application of nanostructures often depends on electrical
conductance. The following two examples illustrate how our theoretical
study contributes to understanding electrical transport properties.
First, our calculated conductance of novel crossed nanotube junctions is
consistent with the unexpectedly large intertube currents seen in
experiment and quantitatively predicts the deformation-driven currents
under varying contact force. Consequently, the prediction leads to
possible nanoscale devices. Second, our study on nanopeapods predicts
that resonant backscattering by the fullerenes could be important in
conductance profiles and possibly be controlled by putting dopant atoms
inside the fullerenes. Interplay between molecular and current degrees
of freedom has been demonstrated to be capable of playing a new role in
nanoscale physics. I plan to continue my research on the electrical
conductance of increasingly important new nanostructures.
Thermal transport properties in extreme conditions, such as at high
temperatures, will be new and important physical phenomena of nanoscale
materials, since such conditions can be easily realized due to high
current densities and small contact areas. To understand and
quantitatively analyze thermal transport in the scale and conditions
described above, molecular dynamics simulations lead to very realiable
thermal properties, whereas accurate experimental probing tools
do not exist. I plan to apply molecular dynamics simulation
to nanostructues as well as to bulk systems.
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