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From
•>>June 2002 Dr. Justin D. Holmes,
Professors
Brian Korgel and Keith P. Johnston answer a few questions
about this month's Emerging Research Front in field of Materials
Science: Field:
Materials Science
Title:
"Control of thickness and orientation of solution-grown silicon nanowires"
Authors: Holmes,
JD;Johnston,
KP;Doty, RC;Korgel, BA
Journal: SCIENCE, 287: (5457) 1471-1473, FEB 25 2000
Addresses:
*Univ Texas, Dept Chem Engn, Austin, TX 78712 USA.
*Univ Texas, Dept Chem Engn, Austin, TX 78712 USA.
*Univ Texas, Texas Mat Inst, Austin, TX 78712 USA.
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Dr.
Justin D. Holmes:
 Why
do you think your paper is highly cited?
I believe the paper is highly cited for a number of reasons
including:
- Our process of forming Si nanowires has great potential
for producing nanoscale circuitry. In particular bulk
quantities of semiconductor nanowires can be readily
produced using simple processing equipment.
- In the paper we show for the first time that the
orientation of the Si nanowires produced can be readily
controlled with reaction pressure. Certainly the lattice
orientation would be expected to affect electron transport
within the silicon nanowires and could be exploited in the
design and manufacture of numerous nanodevices.
Does
it describe a new discovery or new methodology that's useful to
others?
The paper describes a new supercritical fluid
solution-phase method for nanoengineeering bulk quantities of
semiconductor nanowires with controllable lattice
orientations. The paper therefore impacts on every scientist
working in the field of nanotechnology.
Could
you summarize the significance of your paper in layman's terms?
Many technologies, including electronics, will be enhanced
by the ability to control the structure of materials on a
nanometer-length scale. In particular, silicon nanowires are
expected to lead to a generation of nanocomputers thousands of
time smaller and faster than current silicon based processors.
Realization of these new devices is now possible through the
ground breaking 'fast approach' developed by the researchers
at UT and UCC for producing in large quantity
semiconductor nanowires.
How
did you become involved in this research?
I was originally working at UT on CdS nanoparticles
with Prof Johnston. When Prof. Korgel arrived at UT we
started working together on the synthesis of silicon
nanocrystals in supercritical fluids—this project was
extremely successful. The nanowire work was a natural
extension of the Si nanocrystal work.
Dr. Justin D. Holmes, College Lecturer
University College Cork
Cork, Ireland
Professor
Brian Korgel:
Why
do you think your paper is highly cited?
The paper is highly cited because it was the first demonstration
of silicon nanowires below 10 nm in diameter with a relatively
narrow distribution of diameters using a chemical synthetic
approach. We also demonstrated that our methods could provide
control over the crystallographic orientation in the wire.
Does
it describe a new discovery or new methodology that's useful to
others?
The paper describes a useful new methodology, but also
demonstrated the potential of chemical methods to synthesize
nanowires with controlled diameters.
Could
you summarize the significance of the paper in layman's terms?
The chemical methods developed for silicon lead to materials with
new and potentially useful properties. The chemical methods provide
a cost-effective, time-efficient means of producing these materials
that cannot be made any other way.
How
did you become involved in this research?
Our research group became involved in the research of nanowires
through our initial work with silicon nanocrystals. We had developed
a new way to use high temperature supercritical fluids to produce
silicon nanocrystals through the use of capping ligands and
organosilane precursors. I told the post-doc working on this
project, Justin Holmes (who is now a lecturer at University College
Cork in Ireland) to try using sterically stabilized gold
nanocrystals to seed wire growth in this chemical environment. We
found that it worked beautifully and have since developed the
process for Ge and are extending this process to other materials. It
turns out that we can isolate individual nanowires and are in the
process of developing single nanowire transistors using these
materials. The nanowires themselves are optically active and we have
also been creating nanowire liquid crystals.
Brian Korgel
Assistant Professor and Chevron Centennial Teaching Fellow
Department of Chemical Engineering
University of Texas at Austin
Austin, TX 78712-1062
Professor Keith P. Johnston:
Our group had studied reactions in high temperature
supercritical fluids for 20 years up to 500 C and 5000 psia. Kirk
Ziegler, a Ph.D. student, was studying spectroscopy of inorganic
reactions in supercritical water in a project funded by the Army
Research Office and later by DOE for destruction of wastes. We were
familiar with the work of Tad Adschiri from Tohoko University to
form metal nanoparticles by hydrolysis reactions in supercritical
water. A postdoc in our lab, Justin Holmes, was studying the
synthesis of semiconductors in carbon dioxide utilizing surfactants
to stabilize CdS particles. Several students in the group had
studied steric stabilization in supercritical fluids both
experimentally and theoretically for a decade. Brian Korgel, a
professor in our department, proposed that we form silicon
nanoparticles in supercritical fluids stabilized with capping
ligands by arrested growth precipitation. Holmes and Ziegler
utilized the reactors from the supercritical water project to
synthesize the nanoparticles. Korgel then proposed that we utilize
stabilized gold nanoparticles to seed the growth of silicon
nanowires.
Keith P. Johnston
Kenneth A. Kobe Professorship in Chemical Engineering
THE UNIVERSITY OF TEXAS AT AUSTIN
Dept. of Chemical Engineering, Austin, TX 78712-1062
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