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last updated - Apr. 19, 2012Research Statement
As a materials scientist with an interest in
applied mathematics, semiconductor physics, biomaterials, and
nanotechnology, my research is very interdisciplinary. My research
has its theoretical basis in materials science and applied
physics, looking into both fundamental questions such as the
growth and formation of nanostructures and also applied questions
such as the characterization and use of nanowires and new
microscopy techniques. My research focuses on the creation,
characterization, and uses of nanomaterials. The most significant
of my contributions to scholarship have been:
1.
Creating novel ZnS one-dimensional
nanostructures and characterizing them and their growth
mechanisms. This included a review article on the topic and 6
journal articles.
2.
Developing whisker growth theory as
it applies to one-dimensional nanostructures being grown by vapor
deposition techniques, allowing also for the explanation of
secondary growth on the nanostructures (such as nanosaws,
nanocombs, etc.).
3.
Developing novel metrology
techniques for semiconductor and nanoscale characterizations
including method for using hybrid metrology, reference measurement
calibration, and using fractal dimension for characterizing
roughness.
4.
Developing awareness of and
framework for thinking about nanotechnology and military
applications, including several talks and papers outlining how
nanotechnology represents a different approach to thinking about
the role of technology in society.
5.
Publication of “What is
Nanotechnology and Why does it matter”, in collaboration with
philosophers Patrick Lin and Fritz Allhoff,
a tome which explains
nanotechnology as it is practiced today, with a focus on the
materials challenges, and then explain the role that
nanotechnology will play in shaping many different areas of
society. My primary work has been in developing
techniques for creating and using nanomaterials and nanoscale
structures in devices. As a graduate student, I worked in Dr.
Zhong Lin Wang’s group at Georgia Tech, developing processes and
scholarship leading to the inclusion of piezoelectric nanowires in
nanogenerators.
Current and Future Research My research for the last few years has been
in industry (for Cree and IBM) and has focused on developing the
growth, characterization, and implementation of nanomaterials into
LEDs and semiconductor devices.
This has involved developing new techniques for creating
nanoscale materials, such as InGaN quantum dots and quantum wells,
and also new techniques for characterizing materials and surfaces
using new microscopy and data analysis methods. The main
techniques that I have used for creating nanoscale materials are
vapor deposition techniques such as MOCVD, PVD, and ALD. I have
developed new microscopy techniques with electron microscopy,
scanning probe microscopy, and optical microscopy techniques,
particularly as they relate to semiconductor devices.
As a researcher for IBM, I
have also regularly been involved in discussions involving
developments in nanotechnology. These include developments with
DNA origami, atomic scale magnetic memory, and silicon photonics. This work is important because of the growing
role of nanotechnology and nanoscale engineered materials in
devices ranging from semiconductors to microelectromechanical
systems (MEMS). For example, DNA origami, in which controlled
folding of single stranded DNA is used to scaffold nanomaterials
such as Si nanowires, offers a promising post-lithography route
for smaller semiconductor devices.
Recent reports have pressed the importance of new
materials in fields ranging from energy to drug delivery. For
example, the use of one-dimensional ZnO nanowires, aligned along
the <01-10> axis so that their piezoelectronic properties are
accentuated, are being developed as “nanogenerators” able to
transform the energy ambient motion into electrical energy.
Controlling the synthesis of the one-dimensional nanostructures is
important to their further use of wurtzite nanostructures and
applying them. It is also important to their use in
multi-component systems (i.e. systems of structures containing
more than one type of material – CdSe/ZnS or ZnS/SiO2 nanowires)
and in hierarchical structures (i.e. structures with more than one
growth type and phase connected in one larger structure). The
research that I will pursue would continue and expand on the body
of work that has been researched on wurtzite nanostructure. It
would expand to include other wurtzite structures such as GaN and
work to control the synthesis of nanowires with respect to their
length, synthesis site, and other dimensional factors. Not only
will this help with understanding the mechanisms behind the
synthesis of these materials, but it will contribute to the easy
use of wurtzite nanostructures in electronic applications and
systems. Using wurtzite nanostructures allows for a leap forward
in nanoscale devices and functionality, because of the unique
properties of the structure. Another important aspect of work with
wurtzite nanostructures is functionalizing the surface of the
individual nanowires. Complex architectures, sensing applications,
and other uses of ZnS and GaN nanowires all rely on the successful
functionalization of the surface. Sensing applications, both
chemical and biological, will benefit from the functionalization
of the surfaces. Though some sensing of chemical species can occur
without the benefit of functionalization, chemical species
adsorbed onto the surface of the nanostructure will enhance the
sensitivity and the specificity of the sensor. Surface functionalization will also be useful
in developing complex architectures of nanostructures. For
example, well-placed single strands of DNA on the surface of
nanostructures could allow for the self-assembly of multiple
nanowires into very complex architectures. Developing selective
functionalization, with respect to both the species
functionalizing and the material/crystallographic face being
functionalized, will be a boon to the use of nanostructures in
devices. The difficulty with functionalization is
two-fold. First, an appropriate species must be found to adhere to
the surface of the nanostructure through a method that does not
degrade the properties of the material. It is preferable that the
species can adhere to specific surfaces. Second, an appropriate
functionalizing species for each material must be found that has
specificity for other species and successfully adsorbs to the
nanomaterial. Most wurtzite materials are also very useful
in luminescent applications. GaN has been used extensively in LED
applications and ZnS is the top material for electroluminescent
display applications. The development of the luminescent
applications of these materials in nanoscale structures will be an
important development and provide many unique applications. For
example, a nanoscale UV source could be used in biomedical
applications, targeted in vivo.
In order to utilize the luminescent and
phosphorous properties of these materials, it is important to
develop doping of the materials. One method for doing this is ion
implantation. Another
method is introducing doping species during the synthesis of the
nanostructures, as is done in the current growth of Nitride LEDs.
Further, luminescent structures require somewhat complex layered
structures. For example, a ZnS-based ELD uses the phosphorous ZnS
surrounded by an insulator on either side. Recently, ultra-long
ZnS nanowires have been synthesized.
With the use of gold and ITO electrodes and proper doping,
these could be used in electroluminescent displays. For the next step in my research, I am
planning on integrating my nanomaterials synthesis and
characterization research and knowledge with device development,
in particular MEMS/NEMS and sensors, with an eye towards energy
optimization and creation. With nanomaterials, I am particularly
interested in the synthesis of semiconductor one-dimensional
nanostructures, such as Si nanowires or II-VI semiconductors, due
to their wide range of potential uses. I am also interested in
integrating these synthesized nanomaterials with macromolecules,
such as DNA, and using techniques for organizing the nanomaterials
in device orientations, such as DNA origami. This will involve
integrating II-VI nanowires and nanoribbons into MEMS devices. I
am particularly interested in pursuing the integration of
piezoelectronic nanowires (such as ZnO nanogenerators) into MEMS
devices that utilize moving liquids to transfer power – in
particular, MEMS devices using photoelectrowetting on
semiconductors. |