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Introduction
The
evolution and revolution of all modern technologies depend on the
improvement of existing materials and the development of new materials:
information processing and storage require materials that can transfer
data at greater speeds and store data in smaller dimensions; transport
requires materials that can withstand higher mechanical and thermal
loads; environmental protection requires materials that can remove
pollutants from air, water, and soil; energy requires materials that can
convert solar radiation and fossil fuel efficiently into electricity;
human health requires materials that can diagnose and treat different
diseases. The research in our group thus focuses on the development of
new materials and devices that can enable the evolution and revolution
of our modern technologies. In particular, we are currently exploring
the design and synthesis of two types of materials: organic-inorganic
hybrid nanostructured materials and nanoscale materials. We will study
their fundamental physical and chemical properties, with an emphasis on
their electronic and optical properties, and fabricate novel electronic
and photonic devices on different length scales (nanoscopic,
microscopic, and macroscopic scales), depending on the specific type of
devices.
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Innovative organic-inorganic hybrid materials
All
living organisms in nature, whether very basic or
highly complex, possess a multiplicity of materials, architectures,
systems, and functions. Two remarkable features of naturally occurring
materials are their finely carved appearances such as observed in
coccoliths (right top picture) and diatoms (right middle picture), and
intimate associations between organic and inorganic components such as
observed in mollusc shells and bone or teeth tissues in vertebrates. ¡@ The
formation of complex biological structures is mediated by a variety of
biological macromolecules, such as proteins, nucleic acids, and
polysaccharides, which are localized either within (nucleus, cytoplasm)
or outside (extra-cellular)
cells. This biologically mediated organization and assembly of organic
and inorganic materials occur hierarchically, on scales ranging from
nanometers, micrometers, to millimeters, which allows biological
organisms to develop  different functions at different levels. In
principle, this biological
macromolecule-induced assembling approach can be used to design and
construct advanced materials with integrated electronic, optical,
magnetic, and chemical functions controlled by their structures, sizes,
shapes, orientations, and chemical compositions. ¡@ The
assembling approach derived from living organisms has indeed been
successfully applied to the
design and synthesis of mesoporous materials although
in this case, simple amphiphilic molecules instead of complex biological
macromolecules have been used. A variety of amphiphilic molecules,
including small cationic, anionic, neutral molecules and large block
copolymers, have been explored in the formation of mesoporous materials
that exhibit varying mesostructures (right bottom picture) via
electrostatic, dydrogen bonding, and van der Waals between organic and
inorganic
components. ¡@ We
are going to use the organic molecule-directed assembling approach to
design and synthesize innovative organic-organic hybrid materials with
intimately contacted nanoscale organic and inorganic domains organized
in a three-dimensional lattice. We will design and use specific organic
and inorganic components both of which carry electronic or optical
functions. The unique structural properties, including nanoscale organic
and inorganic domains that have tunable sizes, three-dimensional
periodic organizations, and an enormous interface area between organic
and inorganic domains, could bring improved and even higher-performing
new electronic and optical materials.
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Novel
nanoscale materials
Metal
nanocrystals exhibit fascinating size- and shape-dependent optical
properties, which results from the surface plasmon resonance, where
electrons oscillate in response to the alternating electric field of
incident light. Only gold, silver, copper, and the alkali metals possess
the surface plasmon resonance in the visible spectral region. Spherical
metal nanocrystals exhibit only one plasmon band, while ellipsoidal and
rod-like metal
nanocrystals exhibit two distinct plasmon bands, which are related to
transverse and longitudinal electron oscillations (right picture). The
longitudinal oscillation is very sensitive to the aspect ratio of metal
nanocrystals, so that slight deviation from spherical geometry can lead
to dramatic color changes.
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We
will focus on gold nanocrystals because of their well-developed chemical
synthesis and surface functionalization. Their longitudinal plasmon
resonance wavelength can be tuned via the control of their aspect ratio
from the visible to the infrared spectral regions. Gold nanocrystals
exhibiting such a wide spectral range of optical response are excellent
components that can be used in the synthesis of organic-inorganic hybrid
nanoparticles, the construction of organic-inorganic hybrid materials,
and the fabrication of a variety of sensing devices. The hybrid
nanoparticles and materials containing gold nanocrystals will exhibit
remarkable optical and optoelectronic properties.
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