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JAPAN NANONET BULLETIN
-- 15th Issue -- April 1, 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:
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
Associate Professor, Graduate School of Information Science and Technology,
Hokkaido University
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
Beyond the diffraction limit
-- Photonics explores the nano world --
(Issued in Japanese: May 6, 2003)
Satoshi KAWATA, Professor, Applied Physics, Graduate School of
Engineering, Osaka University and Chief Scientist, Nanophotonics
Laboratory, The Institute of Physical and Chemical Research (RIKEN)
The world's smallest bull, which will appear in next year's Guinness
Book of World Records, is 8 mm in length and 5mm in height. The legs,
horns, and the tail are so small as to be beyond the diffraction limit
and can not be imaged by visible light. The bull's body is made from
photopolymerizable resin, a polymer that solidifies by absorption of
light. Prof. Kawata has developed a nanophotonics method to manipulate
nanoscale structures using an ultrafast femtosecond laser of several
hundred nm wavelength.
When photons are strongly confined both temporally and spatially, two
photons can simultaneously excite an electron in a target. The
femtosecond laser has made this strong confinement possible. A 1kW
peak power femtosecond laser compresses energy into a 100fs pulse so
that strong confinement is achieved with an exposure of only 1mW near
infrared light for 10ns. When this compressed pulse meets the resin
target, the multiphoton process is confined to the region of high
photon density and solidification occurs only at the focal point.
Nanodevices can be developed from this new method, completely
different from the conventional method of "cutting". The micro-bull is
proof indeed.
Femtosecond lasers have also proved to be very powerful as a tool for
biology. Since a cell is transparent, a femtosecond laser beam can
propagate through the interior of a cell without damaging the surface
and manipulate only the subcellular organelles at the focal point.
Photonics is becoming indispensable in the field of biology, as well
as the more conventional semiconductor applications.
Another field of photonics research that Prof. Kawata is active in is
the optical near-field. He has observed DNA and carbon nanotubes by
near-field microscopy based on Raman scattering where the light
spectra is shifted by molecular vibrations in the sample. The ability
to simultaneously observe and analyse the sample is one primary aim of
photonics. Prof. Kawata aims to develop optical microscopy that can
observe the vibrations of single molecules. "I am still in the world
of 10nm; I intend to go into the world smaller than 1nm to really see
what is there. I intend to observe DNA in its natural state, without
cutting or using chemical preparations. I have the ideas for how to
get there and I think I will be able to reach it within a few years."
Prof. Kawata has been the Director of the Handai Frontier Research
Center (FRC) at Osaka University since October 2001. The FRC has
established the e-learning nano-engineering program within FRe-
University for people who are now working in related fields. "Those
with science or engineering degrees have never taken nanotechnology
class at university before, and even people with non-science or
engineering degrees can now learn nanotechnology. Take DNA as an
example; it cannot be categorized precisely as biology, chemistry or
physics. Nanotechnology explores not just a single field but a
combination of cutting-edge science." Along with pursuing great
advances in science, he also realizes the necessity of bringing
nanotechnology to the wider society.
(Interviewer: Kuniko Ishiguro, Cosmopia Inc.)
For more information,
http://www.nanonet.go.jp/english/mailmag/2004/015a.html
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YOUNG RESEARCHERS' INTRODUCTION
Control and applications of novel spin properties found in
semiconducting nano structures
(Issued in Japanese: May 6, 2003)
Takaaki KOGA, Researcher, Precursory Research for Embryonic
Science and Technology (PRESTO), Japan Science and Technology Agency
(JST) and Associate Professor, Graduate School of Information Science
and Technology, Hokkaido University
Electrons have spin degree of freedom in addition to charge degree of
freedom. It is the charge degree of freedom that various conventional
electronic devices to date have been based on. The ultimate purpose
in the new research area of semiconductor spintronics is the
development of electronic devices that actively utilize the spin
degree of freedom of electrons in order to realize functionalities
that have never been realized in conventional electronic devices.
What I specially focus on in my PRESTO research is the gate-control of
the spin properties in semiconductor heterostructures. Electron spins,
which are exemplified by small magnets, have conventionally been
controlled by externally applied magnetic fields. Although it had
also been proposed that electron spins could be controlled by an
electric field (via so-called Rashba spin-orbit interaction) instead
of a magnetic field, the main accomplishment in my PRESTO research
includes the quantitative clarification of the gate-controlled Rashba
spin-orbit coupling using the weak antilocalization analysis as
itemized below:
(1) We performed a quantitative analysis on the weak antilocalization
phenomena that are observed in a magneto-resistance at low
temperatures in the InAlAs/InGaAs/InAlAs quantum well system. We then
discovered an existence of zero-field spin-splitting in this system,
which should be caused by the asymmetry in the potential shape of the
quantum wells. The magnitudes of the spin splitting energies turned
out to be consistent with those predicted in theory.
(2) We showed, theoretically, that a spin filter device can be
realized using a triple barrier resonant tunneling structure. This
spin device is composed of InGaAs and InAlAs for the well and barrier
layers, respectively. These are both nonmagnetic materials, hence
proposing a spin filter device without the use of any magnetic
materials.
(3) We examined a spin interference effect in a square loop array that
is nanolithographically fabricated on an InAlAs/InGaAs/InAlAs quantum
well heterostructure.
Regarding the above item (3), recent experimental results showed that
the magnitude of the self-interference of the electron wave function
varies as a function of the gate voltage. This result indicates that
the electron wave function interferes with itself constructively or
destructively depending on the value of the applied gate voltage,
which supports the fact that spin precession angle is controlled by
the magnitude of the spin-orbit interaction.
For future projects, I would like to make every effort, on the basis
of the academic results accumulated to date, in experimental
realization of the proposed spin filter device that utilizes resonant
tunneling structure, as well as exploration of new research areas such
as the examination of the relation between spin-orbit effect and phase
relaxation time in a two-dimensional electron gas system.
For more information,
http://www.nanonet.go.jp/english/mailmag/2004/015b.html
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WHAT'S IN THE NEXT ISSUE?
Nanonet Interview:
Masayoshi ESASHI, Professor, New Industry Creation Hatchery Center,
Tohoku University
Young Researchers' Introduction:
Akira YAMADA, Associate Professor, Research Center for Quantum
Effect Electronics, Tokyo Institute of Technology
The next issue of JAPAN NANONET BULLETIN will be delivered on April 15,
2004.
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Nanotechnology Researchers Network Center of Japan distributes
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JAPAN NANONET BULLETIN contains articles, "Nanonet Interview", in
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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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