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JAPAN NANONET BULLETIN
-- 73rd Issue -- June 22, 2006
Nanotechnology Researchers Network Center of Japan
Ministry of Education, Culture, Sports, Science and Technology (MEXT)
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IN THIS ISSUE
Nanonet Interview:
"Unraveling optical properties of nanoparticles
-- Nonlinear optical response from ultrafine particles --"
Arao NAKAMURA, Professor, Department of Materials, Physics and Energy
Engineering, Graduate School of Engineering, Nagoya University
Young Researchers' Introduction:
"Creation of new functional pi-electron organic materials based on
main group chemistry"
Shigehiro YAMAGUCHI, Professor, Department of Chemistry, Graduate
School of Science, Nagoya University and Researcher, Solution Oriented
Research for Science and Technology (SORST), Japan Science and
Technology Agency (JST)
Nano Info:
"The 3rd Japan-US Young Researchers Exchange Program on
Nanotechnology (March 5-18, 2006)"
-- NANO CALENDAR --
For information on nanotechnology related symposiums and conferences
held in the world,
http://www.nanonet.go.jp/english/calendar/
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NANONET INTERVIEW
Unraveling optical properties of nanoparticles
-- Nonlinear optical response from ultrafine particles --
(Issued in Japanese: July 21, 2004)
Arao NAKAMURA, Professor, Department of Materials, Physics and Energy
Engineering, Graduate School of Engineering, Nagoya University
Ultrafine metal particles, such as gold and silver, dispersed in glass,
color glass beautifully. Conduction electrons in the metals do not
generally interact with electromagnetic waves, such as light. However,
when surface plasmons are generated on metal surfaces, conduction
electrons interact with light, and therefore, beautiful colors appear
on stained glass. Prof. Nakamura says, "Only ultrafine metal particles
cause this phenomenon. The finer the particles, the more influence the
surface plasmons have on the interaction between ultrafine metal
particles and light." He has been studying ultrafine particles and
trying to determine their optical properties.
When a transparent insulator, such as glass, with dispersed ultrafine
metal particles is irradiated with light, local electric fields around
the ultrafine particles which have different dielectric constants than
that of the glass are generated. Prof. Nakamura says that when there
are ultrafine metal particles with a negative dielectric constant,
which has a large absolute value, the electric fields around the
particles are high. Therefore, surface plasmons localized on the
surfaces of the ultrafine particles strongly resonate with the incident
light. He has confirmed that, as the ultrafine particle size becomes
larger, resonance effects, caused by the local electric field and the
nonlinear susceptibility of the glass, are larger. Ultrafine particles
larger than 20 nm in diameter have large optical nonlinearity.
The particle size also strongly influences the speed of the optical
response. When fine metal particles are irradiated with light, the
electrons go into a state called hot electrons, in which the electron
temperature is high. Normally, the hot electrons and lattices gradually
go into a thermal equilibrium state, due to electron-lattice
interactions, and then, the thermal energy transfers to the glass
around the particles. Prof. Nakamura says, "However, nanoparticles in
the glass vibrate in a so-called 'breathing mode'. The frequency of the
vibration becomes higher as the particle radius becomes smaller. When
the frequency is approximately equal to the rate of energy transfer
from the electrons to the lattice vibration, the electron energy
directly transfers to the glass, and not to the metal lattice.
Therefore, the rate of energy relaxation increases." As the energy
relaxation rate increases, the response time becomes shorter. In other
words, ultrafine particles with a diameter of several nanometers must
have shorter response times.
For a higher nonlinear susceptibility, large particles are required,
and for a shorter response time, fine particles are required. The trade
-off relationship between the nonlinear susceptibility and response
time for the particle size is resolved by a quantum size effect. In
ultrafine semiconductor particles, dispersed in glass, a quantum size
effect appears when a particle's diameter is 1 to 10 nm, and the
nonlinear susceptibility of the materials increases. It also appears in
ultrafine metal particles with a diameter of 2 nm, but it was unclear
whether nonlinearity would increase or not. In early 2005, Prof.
Nakamura confirmed that an increase in nonlinearity occurred due to
quantum size effects in glasses with ultrafine metal particles. The
measured nonlinear susceptibility of synthesized gold particles with a
diameter of 1.0 nm, which were dispersed in solution, was 7.2x10^(-15)
esu cm. This is comparable to the value for particles with a diameter
of 15 nm. The nonlinear susceptibility, resulting from quantum size
effects and a response time shorter than one picosecond due to a
breathing mode, was obtained with these ultrafine particles.
Prof. Nakamura's other main research field is bandgap engineering using
semimetal/semiconductor hetero-structures. He fabricated quantum disks
of semimetal ErP on an InP substrate by organometallic vapor phase
epitaxy, in collaboration with Prof. Yoshikazu Takeda at Nagoya
University. He discovered that the bandgap in the disks becomes larger
due to the quantum size effect when the disk thickness is less than 3.5
nm and that an increase in the bandgap converts the disk from a
semimetal to a semiconductor. It was difficult to fabricate ErP films
because the crystal structure and lattice constant of InP were
different from those of ErP. However, he was able to fabricate ErP
films by replacing the InP substrate with a GaInP substrate and
bringing the lattice constants of the substrate closer to that of ErP.
He says, "When semimetallic materials are used for quantum well layers
for resonant tunneling diodes, devices that switch rapidly with low
driving voltage can be developed. In addition, since the bandgap
becomes much larger, multiple resonant peaks are obtained. Therefore,
switching based on negative resistance can also be repeated several
times by changing the voltage." Since Er compounds are magnetic, by
determining their magneto-optical properties and magnetic transport
properties, a basic model for a high-order functional optoelectronic
integrated circuit with magneto-optical switches and semimetal-base
transistors is determined.
Prof. Nakamura says to young researchers, "Although it is fine to
research something popular or interesting, you should find its
essential features that will lead to expansion of your research. You
should not try to earn popularity. Publishing your research with
accurate data and an appropriate understanding of the data is essential.
That means that others can verify your research results, and thus, the
results will be available as persisting data."
(Interviewer: Kuniko Ishiguro, Cosmopia Inc.)
For more information including figures,
http://www.nanonet.go.jp/english/mailmag/2006/073a.html
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YOUNG RESEARCHERS' INTRODUCTION
Creation of new functional pi-electron organic materials based on
main group chemistry
(Issued in Japanese: September 15, 2004)
Shigehiro YAMAGUCHI, Professor, Department of Chemistry, Graduate
School of Science, Nagoya University and Researcher, Solution
Oriented Research for Science and Technology (SORST), Japan Science
and Technology Agency (JST)
The creation of new organic pi-electron materials is the central topic
in research fields including organic (opto)electronics, which involves
devices such as organic electroluminescent (EL) devices and thin film
transistors, and molecular-scale electronics. We have based our
synthetic research on main group chemistry. Molecular design
exploiting the characteristic properties of main group elements
provides access to new pi-electron materials with intriguing
photophysical and electronic properties.
In particular, our strategy relies on the incorporation of main group
elements into pi-conjugated ring systems, in which the orbital
interaction between the main group element and pi-conjugated moiety
effectively occurs. Using this approach, we have, so far, synthesized
various pi-electron materials with unique electronic structures. One
example is a silicon-containing pi-electron system, 2,5-bis(bipyridyl)
silole. This molecule is an extremely efficient electron-transporting
material, due to the sigma*-pi* conjugation in the silole ring, and has
already been put into the commercial use in organic EL displays. We
are currently extending this silicon chemistry to other elements and
have synthesized several other types of rigid planar pi-electron
systems, including dibenzoborole-based pi-electron compounds, silicon-
bridged oligo(phenylenevinylene)s, and sulfur- or selenium-containing
heteroacenes, by using newly developed efficient synthetic
methodologies.
The "main group chemistry approach" will lead to new and fascinating pi
-electron materials that cannot be achieved by the ordinary organic
chemistry. We hope to develop platform molecules for the next-
generation electronic and optoelectronic applications.
For more information including figures,
http://www.nanonet.go.jp/english/mailmag/2006/073b.html
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NANO INFO
The 3rd Japan-US Young Researchers Exchange Program on Nanotechnology
(March 5-18, 2006)
The Japan-US Young Researchers Exchange Program on Nanotechnology is
a joint project of the Ministry of Education, Culture, Sports, Science
and Technology (MEXT) of Japan and the National Science Foundation
(NSF) of the United States to promote mutual research exchanges among
young researchers of the two countries in the nanotechnology field and
to help them build personal networks. Thirteen young Japanese
researchers were chosen through open applications to participate in the
third exchange program. Led by Profs Yoshinobu Aoyagi and Kazuhito
Furuya at the Tokyo Institute of Technology, the group visited
nanotechnology-related research facilities in the US for about two
weeks from March 5, 2006, and exchanged information with their US
counterparts at these laboratories and workshops. The facilities which
the group visited were the University of Massachusetts Lowell,
Massachusetts Institute of Technology, Harvard University, Northwestern
University, University, Cornell University, University of California,
Santa Barbara, Stanford University and University of California, Los
Angeles.
The group visited the Evanston campus of Northwestern University on
March 10. They were received by Prof. Manijeh Razeghi, director at the
university's Center for Quantum Device. Her laboratory has an infrared
cascade laser, an infrared detector based on a Type II Super Lattice,
a quantum dot infrared device, a III-Nitride semiconductor ultraviolet
device and other instruments. Some 20 associate professors,
postdoctoral researchers and graduate students work at his laboratory,
and more than half of them are from China, South Korea, Middle East
nations and other foreign countries. The professor told the visitors
that the ratio of Japanese students to the total number of foreign
graduate students at US universities has been declining sharply as
a result of a surging number of students from China and South Korea.
Dr. Kenichiro Tanaka, a special postdoctoral researcher at the
Institute of Physical and Chemical Research (RIKEN), and five other
Japanese researchers presented their research in a workshop at the
university. Dr. Rod Ruoff introduced his research on mechanical
engineering and all other participants from Prof. Razeghi's laboratory
made brief presentations on four research themes at her laboratory.
Prof. Razeghi obtains a substantial amount of research funding from the
Defense Advanced Research Projects Agency (DARPA), NSF and private
companies to run his laboratory.
Cornell University is ...
Continued on the following Website:
http://www.nanonet.go.jp/english/mailmag/2006/073c.html
(Shigeru Okamura, nanonet)
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