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JAPAN NANONET BULLETIN
-- 14th Issue -- March 18, 2004
Nanotechnology Researchers Network Center of Japan
Ministry of Education, Culture, Sports, Science and Technology (MEXT)
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IN THIS ISSUE
Nanonet Interview:
Akihisa INOUE, Director/Professor, Institute for Materials Research,
Tohoku University
Young Researchers' Introduction:
Yasunori TODA, Associate Professor, Department of Applied Physics,
Hokkaido University and Researcher, Precursory Research for Embryonic
Science and Technology (PRESTO), Japan Science and Technology Agency
(JST)
What's in the next issue?
-- 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
"Metallic Glass" opens a new field in materials science
--Development of new light-weight, high-strength materials--
(Issued in Japanese: April 15, 2003)
Akihisa INOUE, Director/Professor, Institute for Materials Research,
Tohoku University
Prof. Inoue developed "metallic glass" having excellent mechanical
properties, e.g., high tensile strength and large elastic strains, and
he is currently a leader of worldwide researchers in materials science.
It has been generally known that, when solid lacks a systematic
atomic arrangement, that is, when it is in an amorphous state, its
strength and corrosion resistance are enhanced. People had believed,
to make an amorphous alloy, the rapid cooling of the molten alloys is
required and thus it is quite difficult to obtain amorphous alloys in
bulk. Contrary to this widely conceived belief, Prof. Inoue succeeded,
for the first time in the world, in developing metallic glass which
makes it possible to prepare bulk amorphous alloys without rapid
cooling. The papers published by him and his colleagues about their
discoveries have been highly evaluated by other researchers. Indeed,
the number of their citations is ranked at the highest level, and Prof.
Inoue has been awarded many prizes for his many discoveries including
the Japan Academy Award in 2002.
In 1982, Prof. Inoue became a research fellow at AT&T Bell
Laboratories (currently Lucent Technologies, Bell Laboratories), and
there, met Dr. Chen who had discovered a glass-transition phenomenon
in metals. This led Prof. Inoue to develop an interest in the
structural relaxation phenomena observed among non-equilibrium
materials. From then on, his study on the structural relaxation and
glass transition of non-equilibrium materials advanced steadfastly.
During the course of his study, he came to conceive the belief,
"if it were possible to reveal the principle governing the formation
of a glassy metal which exhibits a glass-transition phenomenon and
supercooled liquid state, it would be possible to produce bulk
amorphous alloys."
When a liquid material is cooled very rapidly, it does not crystallize
even when it is cooled below its freezing point, and maintains its
liquid state, which is called a supercooled state. When Prof. Inoue
began to study metallic supercooled liquids, he decided to reveal the
principle underlying the phenomena, and studied to obtain reliable
thermodynamic data related to the phenomena. In 1987, he found an
alloy having a wide temperature range in which a supercooled state is
maintained. This discovery stimulated his interest in developing bulk
amorphous alloys. In 1988, Prof. Inoue found a Zr-based alloy which
maintains a supercooled state down to a temperature equal to 60% of
the freezing point even when cooled at a rate as slow as 10 K/sec, and
then solidifies as glass. This alloy exhibits markedly different
mechanical properties depending on its microscopic structure: the
crystallized alloy is broken to pieces when hit with a hammer, but the
glassy alloy is quite resistant to the same impact. This glassy alloy
was a "bulk metallic glass" that Prof. Inoue had sought. This new
alloy was found to have excellent mechanical properties. It exhibited
ideal superplasticity. It had a tensile strength three times as high
as that of the crystalline alloys that had the same Young's modulus.
It also had an elastic elongation at least five times as high as that
of conventional crystalline alloys. The elastic energy the glassy
alloy could store just before it reached a yield point was twenty
times or more as high as that of conventional crystalline alloys.
Prof. Inoue reported his discoveries at some meetings in Japan. At
that time, his papers did not attract much attention from the audience.
This was probably because people confounded the metallic glass he had
discovered with an amorphous metal. However, the situation changed
dramatically when the results were made public to scientists around
the world.
In 1993, five years after Prof. Inoue's publication of Zr-based
metallic glasses, a group of researchers in the USA who had secretly
traced his research, published their discovery of a metallic glass
obtained from a beryllium-based alloy system, which in turn suddenly
ignited the interest of researchers in metallic glasses. By that time,
Prof. Inoue had discovered several hundreds of kinds of metallic
glasses, and in 1994 he deduced, from the observations accumulated
during the course of his study, empirical rules determining the glass-
forming ability of an alloy which are now called "Inoue's three
empirical rules." Based on these rules, Prof. Inoue further continued
his search for new metallic glasses, and added new alloys to a list of
metallic glasses he had prepared. Establishment of these empirical
rules is based on his enthusiasm towards finding a fundamental concept
applicable to all materials having a glass-forming ability and thus
profitable to all materials scientists interested in metallic glasses
around the world, rather than being based on a simple desire to devise a
method for finding a new resource of metallic glasses.
Metallic glasses having a thickness ranging from 1 to 100 mm have been
fabricated by employing various casting processes appropriate to the
alloy systems. Indeed, the face plate of a golf club made of a
metallic glass has been put to practical use. Currently, Prof.
Inoue's interest has shifted to nanostructured bulk alloys with high
strength and toughness, and his studies in this field also lead
materials scientists around the world. He carries out research on
strengthening of materials by crystallizing metallic glasses partially.
That is, bulk metallic glasses are partially crystallized by adding a
small amount of elements that do not satisfy the Inoue's empirical
rules into conventional metallic glass systems. The partially
crystallized metallic glasses have nanoscale crystals with a diameter
of 1 nm or more in their glassy matrix. This nanostructural feature
is responsible for the improved tensile strength and toughness of
these new alloys.
Prof. Inoue predicts confidently, "Maybe in ten years the metallic
glasses we have developed will be used as a basic material for
nanotechnology because of their excellent viscosity, fluidity and
workability. This is because there are no metallic materials that are
more readily amenable to fine processing than these metallic glasses."
(Interviewer, Shin Chikushi)
For more information,
http://www.nanonet.go.jp/english/mailmag/2004/014a.html
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YOUNG RESEARCHERS' INTRODUCTION
Quantum mechanical control of quantum dots by using coherently
controlled light
(Issued in Japanese: April 22, 2003)
Yasunori TODA, Associate Professor, Department of Applied Physics,
Hokkaido University and Researcher, Precursory Research for
Embryonic Science and Technology (PRESTO), Japan Science and
Technology Agency (JST)
One of the fascinating characteristics of quantum dots is their atomic
-like discrete density of states with large energy-level spacing, in
which acoustic phonon-mediated scattering should be suppressed
compared with higher-dimensional structures. As a consequence,
excitons in quantum dots are expected to exhibit long coherence time,
which is advantageous for application of quantum information
processing. In such quantum logic devices, it is important to
coherently control quantum units individually.
Our research aims at quantum mechanical control of exciton
wavefunctions by using coherently controlled light. Because laser
light exhibits high coherence, we can easily manipulate its waveform
by a dispersion-free 4-f optical system in conjunction with a spatial
light modulator (SLM), which alters the spectral phase of the pulse.
By optimizing the excitation pulse, we can address the exciton
wavefunctions in individual self-assembled quantum dots (SAQDs).
We here used the sample of SAQDs. In a photoluminescence (PL) spectrum
of the sample, several sharp emission lines originating from different
SAQDs are observed. For the selective excitation, we optimized the
excitation pulse based on the photoluminescence excitation (PLE)
resonances. A contour plot of the PL spectra as a function of the
phase of SLM shows normalized PL intensities at two peaks with fitting
of the data by a sinusoidal function. Both peaks show oscillatory
behavior as a consequence of the quantum interference of the
wavefunctions in each excited states. Furthermore we can address the
exciton wavefunctions even in the collective excitation. This
indicates the feasibilities for selective coherent control of
individual exciton wavefunctions.
For more information,
http://www.nanonet.go.jp/english/mailmag/2004/014b.html
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WHAT'S IN THE NEXT ISSUE?
Nanonet Interview:
Satoshi Kawata, Professor, Applied Physics, Graduate School of
Engineering, Osaka University and Chief Scientist, Nanophotonics
Laboratory, The Institute of Physical and Chemical Research (RIKEN)
Young Researchers' Introduction:
Takaaki KOGA, Researcher, Precursory Research for Embryonic Science
and Technology (PRESTO), Japan Science and Technology Agency (JST) and
Visiting Scientist, Spintronics Research Group, Materials Science
Research Laboratory, NTT Basic Research Laboratories
The next issue of JAPAN NANONET BULLETIN will be delivered on April 1,
2004.
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Nanotechnology Researchers Network Center of Japan
Ministry of Education, Culture, Sports, Science and Technology (MEXT)
Our website: http://www.nanonet.go.jp/english/
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Copyright(c) 2003-2004, Nanotechnology Researchers Network Center of
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