======================================================================
JAPAN NANONET BULLETIN
-- 59th Issue -- December 8, 2005
Nanotechnology Researchers Network Center of Japan
Ministry of Education, Culture, Sports, Science and Technology (MEXT)
======================================================================
IN THIS ISSUE
Nanonet Interview:
"Use of undesirable fine particles as new materials
-- Synthesis and measurement of nanoparticles --"
Kikuo OKUYAMA, Professor, Chemistry and Chemical Engineering,
Graduate School of Engineering, Hiroshima University
Young Researchers' Introduction:
"Exploration of electron transport phenomena in atomic-scale wires
fabricated through surface reconstruction"
Takashi UCHIHASHI, Senior Researcher, Electro-nanocharacterization
Group, Nanomaterial Laboratory, National Institute for Materials
Science (NIMS)
-- NANO CALENDAR --
For information on nanotechnology related symposiums and conferences
held in the world,
http://www.nanonet.go.jp/english/calendar/
----------------------------------------------------------------------
NANONET INTERVIEW
Use of undesirable fine particles as new materials
-- Synthesis and measurement of nanoparticles --
(Issued in Japanese: May 12, 2004)
Kikuo OKUYAMA, Professor, Chemistry and Chemical Engineering,
Graduate School of Engineering, Hiroshima University
Prof. Okuyama says, "Fine particles floating in a gas, that are called
aerosol particles, are thought to be unclean, undesired substances
because they could cause asthma and allergic reactions." He had been
conducting basic research on the behavior of aerosol particles.
However, after he returned to Japan from the US in 1980, he decided to
study fine particles as new materials. As materials become smaller,
from the sub-micron scale to the nanometer scale, their electric and
optical properties change extensively. He targeted his research on the
development of new materials, making use of new functions, when fine
particles are scaled down to the nanometer scale. Various types of
nanoparticles developed by Prof. Okuyama are now used in a wide range
of fields. A composite material made of nanoparticles of TiO2 and SiO2
is used in cosmetics because TiO2 and SiO2 nanoparticles are able to
block ultraviolet light, while visible light can pass through the
particles. For electronic materials, a composite of polymers and
nanoparticles that have high heat-resistance property could be
applicable for LSI packaging, photoluminescence materials for use in
display materials, etc.
Generally, there are three methods for synthesizing such particles;
a solid phase method, a vapor-phase method and a liquid-phase method.
However, among these methods, the solid phase method has limits, in
terms of producing nanometer scale particles. The liquid phase method
and the vapor phase method are suitable methods for the synthesis of
nanoparticles. In the conventional spray pyrolysis (CSP), a liquid
-phase method, droplets are sprayed to a heated furnace and fine
particles are produced through evaporation of the solvent and chemical
reactions. They are finally sintered to make their shapes and
structures almost uniform. However, it is difficult to produce uniform
-sized nanometer scale particles using the CSP method. Therefore, he
developed the salt-assisted spray pyrolysis (SASP) to overcome
limitations associated with the CSP method. In the SASP method, salts
such as NaNO3, KNO3, LiNO3 and KCl are added to the spray solution
since salt promotes nucleation and prevents nanoparticles from
agglomerating. As a result, uniform-sized nanoparticles are produced.
The diameters of nanoparticles produced by the SASP method range from
several nm to several ten nm. These sizes are about one-30th to one-
80th those of fine particles produced by CSP. For using nanoparticles
in commercial applications, it is indispensable to develop a new
manufacturing method for rapidly and inexpensively producing highly
functional nanoparticles. Besides the SASP method, Prof. Okuyama is
also working on the development of a low-pressure spray pyrolysis
since this would permit the production of nanoparticles 100 times
faster than CSP as well as the SASP method.
Prof. Okuyama is also studying the preparation of porous structures
using nanoparticles, and has devised a method for producing porous
structured SiO2 fine particles and porous SiO2 films with ordered
holes using polystyrene latex (PSL) particles as a template and silica
nanoparticles. When a colloidal solution of SiO2 nanoparticles and PSL
particles is sprayed and dried at low temperatures, silica particles
precipitate around self-organized PSL particles and fill spaces
between particles. When these particles are heated, the PSL particles
burn and disappear and only SiO2 fine particles with ordered holes
remain. These particles may be used in many applications, including
carriers for the controlled releases of drugs. To prepare porous SiO2
films, a substrate is soaked in the colloidal solution and lifted at a
constant speed. The films may be used to form photonic crystals, low
dielectric constant films, catalyst films and others.
Prof. Okuyama also stresses the importance of measurements. He says,
"In evaluating the manufacturing processes of nanoparticles, we do not
know how or under what conditions nanoparticles nucleate and grow
unless we are able to measure accurately the sizes of suspended
nanoparticles being formed." Prof. Okuyama has developed
a differential mobility analyzer using electrostatic force to measure
particle size distributions. The accurate sizes of nanoparticles and
ions with a diameter of 1 nm to several hundred nm can be measured
using his equipment. "Developing a method for measuring the sizes of
nanoparticles is an important aspect of nanotechnology. It is very
important to develop equipment yourself that will satisfy your own
needs, which off-the-shelf machinery cannot meet." This is his motto
and that of the members of his research team as well.
Prof. Okuyama encourages young researchers to attend quality
universities abroad as early as possible to conduct research jointly
with young professors who are not much older than they are. He says
that if the researchers conduct joint studies with young professors,
they will be able to contact them for many years thereafter. Prof.
Okuyama attended the California Institute of Technology as a visiting
researcher every summer from 1985 to 1991 and is still in contact with
Caltech professors John Seinfeld and Richard Flagan, who are well
known for their work on atmospheric aerosols. In addition, students
whom Prof. Okuyama instructed at Caltech are now professors at various
universities. He also advises young researchers to send their papers
to authoritative journals, even if those journals do not completely
match their own fields. He says that if their papers appear in those
journals, they can become very confident in their abilities as
researchers and will be motivated through unexpected questions from
reviewers of their papers. He believes researchers need to be active
in order to receive such feedback.
(Interviewer: Yu Tatsukawa, Cosmopia Inc.)
For more information,
http://www.nanonet.go.jp/english/mailmag/2005/059a.html
----------------------------------------------------------------------
YOUNG RESEARCHERS' INTRODUCTION
Exploration of electron transport phenomena in atomic-scale wires
fabricated through surface reconstruction
(Issued in Japanese: June 23, 2004)
Takashi UCHIHASHI, Senior Researcher, Electro-nanocharacterization
Group, Nanomaterial Laboratory, National Institute for Materials
Science (NIMS)
Various kinds of surface reconstructions can be grown on the surface
of clean semiconductor substrates by depositing a monolayer atoms
followed by the appropriate processing. Generally, surface
reconstructions are fundamentally distinct from their bulk
counterparts due to strong interactions with the substrate and low-
dimensionality of the systems.
Among the different surface structures, we are focused on one-
dimensional (1D) reconstructions, i.e. atomic-scale surface nanowires.
Our objectives are to elucidate experimentally their electron
transport properties and to develop them for use in nanoelectronics in
the future.
One example of 1D surface reconstructions is indium atomic wire arrays
on silicon, which are two-atom wide chain assemblies. We have, for the
first time, determined their electron transport properties, and
remarkably, over a large area, the reconstruction has high
conductivity that corresponds to a sheet resistance of about 30 k ohm.
Furthermore, current through the atomic wires is strongly suppressed
by defects near surface steps and/or a minute amount of point defects
introduced into the wires themselves.
The conductivity of the atomic wires decreases drastically at around
130 K, accompanying a metal-insulator transition. The phenomenon,
which is interesting from the viewpoint of fundamental physics, is
ascribed to the so-called Peierls instability intrinsic to a 1D
electron system.
In order to measure the electron conduction through individual atomic-
scale wires, we are now developing a technique to connect the wires to
microelectrodes without contaminating the sample surface. So far, we
have attached microelectrodes to a single erbium disilicide nanowire
grown on silicon. In the future, we will incorporate organic molecules
into the constructs and utilize the magnetic properties of the wires.
For more information,
http://www.nanonet.go.jp/english/mailmag/2005/059b.html
--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--
Nanotechnology Researchers Network Center of Japan distributes
this e-mail newsletter, "JAPAN NANONET BULLETIN", every other Thursday
with the aim of promoting information exchange and cooperation among
researchers in nanotechnology and related fields.
The next issue of JAPAN NANONET BULLETIN will be delivered on
December 22, 2005.
JAPAN NANONET BULLETIN contains articles, "Nanonet Interview", in
which we interview a leading researcher about current issues and/or
research strategies for the future and "Young Researchers'
Introduction", in which a young researcher in the nanotechnology field
introduces his/her own recent research.
We appreciate your support very much and promise to continue to gather
and disseminate information for your benefit.
Read details on our privacy policy at:
http://www.nanonet.go.jp/english/mailmag/policy.html
Subscribe at:
http://www.nanonet.go.jp/english/mailmag/index.html
Change or cancel your subscription at:
http://www.nanonet.go.jp/english/mailmag/upd_del.html
Inquiry about the newsletter:
----------------------------------------------------------------------
Nanotechnology Researchers Network Center of Japan
Ministry of Education, Culture, Sports, Science and Technology (MEXT)
Our website: http://www.nanonet.go.jp/english/
Inquiry:
Copyright(c) 2003-2005, Nanotechnology Researchers Network Center of
Japan,
All rights reserved.
