Details
Nanomaterials/nanodevices are
investigated through the trinity of i) prediction/analysis, ii)
synthesis/fabrication, and iii) characterization/application. A new
synthetic approach such as self-synthesis is utilized to synthesize
nanomaterials. Both theory and experiments should be complemented, and
both chemistry and physics approaches should be combined for the effective
study. We create new paradigms for designing and developing innovative
quantum molecular/nanomaterial systems with preconceived properties so
that material itself can be an intelligent device. For practical utility,
nanodevices need to be synthesized with the self-engineering techniques.
Otherwise, the manipulation of each device is not practical, and the
mass-production is not possible. Understanding the intricacies of
self-engineering and transport mechanisms will provide the platform that
the analysis of structure-function relationship, molecular
interactions/dynamics, and nano-recognition in low-dimensional space can
be built on.
New Physics
based on carbon-based devices
Recently, carbon-based devices have
been realized in graphene with low carrier concentration and high
mobility. The unusual quantum Hall effect and Berry¡¯s phase, due to
unusual quantum nature of confined electrons in graphene network, were
observed. This work demonstrated the unusual quantum transport phenomena
in quasi-quantum electrodynamics on two-dimensional fermion system. The
peculiar behaviors are essentially caused by massless Dirac fermions and
the nontrivial topology of the band structure in the graphene. Upon
application of magnetic field, the n=0 Landau level forms at the Dirac
point, reflecting the degenerate levels of an electron and a hole emerging
from the nontrivial topology of a band structure of
graphene.
Molecular
electronics and spintronics for novel devices
The promise of molecules in
electronics comes from the diverse synthetic methodology in creating
complex devices with unusual functionality. Despite this promise,
fabrication of reliable single-molecule device has been technically
challenging, in part, by ill-defined bonding between molecules and metal
electrodes. An improved strategy is needed to create a well-defined
covalent bond between the electrode and the molecule. For the transport
phenomena in nano-scale devices, charge and spin are two important degrees
of freedom contributing the quantum transport. The electron transport
through charge channels has been studied in various experiments. However,
it is very difficult to achieve the spin transport through conventional
spin channels in metal and semiconductors. A graphene and a CNT, both of
which are carbon-based systems, provide intriguing quantum transport
phenomena. Although a CNT itself can be a spintronic device, a molecule
and an impurity can be inserted as a scattering center on a CNT, as a
molecular spin valve. We expect that a sandwiched spin-polarized molecule
between crossed CNTs has the special feature of a magnetic tunnel
junction.
Synthesis and
engineering of longer arrays of ultra-thin carbon nanotubes for
devices
Utilizing the ultra-low friction
between shell layers in a long multi-walled CNT (MWNT) due to the
non-local nature of the ¥ð-¥ð dispersion forces, we have been successful in
nanoscale engineering of MWNT structures by displacing outer shells one by
one with AFM. This striking manipulation permits controlled modification
of the electrical properties. For example, thin single-walled CNTs (SWNTs)
with diameter less than 1 nm are mostly metallic because of the sp3
character against the sp2 character of thick nanotubes.
Shape-controlled
self-assembly of organic molecules as a new strategy for
nanofabrication
Recently, various inorganic
nanomaterials with controlled shapes and properties have been developed.
However, despite the diversity in self-assembling organic molecules, there
is little progress in engineering morphologies of organic nanostructures.
In designing nano-architectures by self-assembling organic molecules, the
interplay between non-covalent interactions is more important than that in
inorganic nanocrystals. Indeed, the strengths of the interactions in
organic solids are comparable to those in solution phase. This results in
a dynamic equilibrium that may enable the shapes of self-assembled
structures to be controlled and optimized into their thermodynamically or
kinetically preferred morphologies. Using this self-synthesis engineering
technique, we can realize self-organizing intelligent nano-materials,
electronic/spintronic nanodevices, nano-optical devices, and
bio-nano-devices. We also investigated the assembly phenomena including
formation of molecular clusters and metal/alloy clusters, and the
synthesis mechanisms and quantum phenomena in functional novel
materials.
Nano-recognition
and dynamics control
It should be noted that intuition
alone is generally impractical in designing nano-devices since the
manipulation of quantum nature can be a subtle process. Thus, we design
novel functional molecular systems through elucidation of molecular
interactions, molecular assemblies, and electron/photon/proton
capture/release/transfer mechanisms/dynamics. Thus,
interatomic/intermolecular interactions are very important in
self-engineering process and in designing molecular devices. Understanding
electron/proton pathways in nano-systems using quantum computation helps
design novel devices/sensors. Through investigations of the governing
forces and dynamics mechanisms in host-guest molecular systems and
nanomaterials, we have designed novel types of superfunctional
molecular/material systems and electronic/mechanical
devices.
Bio-nano
devices
Nanowires and CNTs can be utilized
for bio-sensing, based on the difference in the transport property upon
the binding of biomolecules. Implementation of the dynamics control for
molecular systems would lead to the development of sophisticated molecular
vehicles.
Applications to
green science
Climate change such as global warming
is believed to be a result of an enhanced green house effect mostly due to
an accumulation of greenhouse gases in the atmosphere. The development of
novel low carbon technologies such as capturing and storing CO2 from
industrial point sources for various commercial applications is highly
desirable for sustainable development. Besides, towards a hydrogen economy
is one of the major worldwide projects to solve the global demand for
clean energy.