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JAPAN NANONET BULLETIN
-- 87th Issue -- January 11, 2007
Nanotechnology Researchers Network Center of Japan
Ministry of Education, Culture, Sports, Science and Technology (MEXT)
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JAPAN NANO 2007: Call for Registration
-Nanotechnology, Progress for Five Years and Expectation to The Future-
The Nanotechnology Researchers Network Center of Japan (nanonet), MEXT
organizes the 5th International Symposium on Nanotechnology (JAPAN
NANO 2007) on February 20 - 21, 2007, at Tokyo Big Sight (Ariake,
Tokyo).
The constitution of JAPAN NANO 2007 is : Plenary lectures, symposia on
nano-IT devices, nano-physics, nano-materials, nano-biology, nano-
process, metrology and nano-implications and the oral presentation &
poster session.
Lectures will be given by the world-leading researchers on the state-
of-the-art nano science and technology. Posters will be introduced by
the best young researchers who will lead the next generation of this
area. JAPAN NANO 2007 provides you the current topics and future
perspective of nano science and nanotechnology.
For more information,
http://www.nanonet.go.jp/english/event/japannano2007/index.html
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IN THIS ISSUE
Nanonet Interview:
"Molecular magnets and shell nanomagnets -- Combining "controllability"
of organic materials and "magnetism" of inorganic materials --"
Kunio AWAGA, Professor, Department of Chemistry, Graduate School of
Science, Nagoya University
Introduction to Laboratory:
"Advanced NEMS (Nano ElectroMechanical System) - Micromachined tools
for investigating the nanoworld"
Beomjoon, Kim, Associate Professor, Department of Precision
Engineering, Graduate School of Engineering, and Center for
International Research on MicroMechatronics (CIRMM), Institute of
Industrial Science, The University of Tokyo
-- 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
Molecular magnets and shell nanomagnets --Combining "controllability"
of organic materials and "magnetism" of inorganic materials --
(Issued in Japanese: June 8, 2005)
Kunio AWAGA, Professor, Department of Chemistry, Graduate School of
Science, Nagoya University
In a paramagnetic material, the magnetic moments of atoms caused by
unpaired electron spins are randomly oriented. When magnetic moments of
atoms spontaneously align parallel to each other, the material becomes
ferromagnetic. Organic molecules with even numbers of electrons become
diamagnetic because the electron spins' magnetic moments are cancelled
out. In organic molecules, although there are molecules with an
isolated unpaired electron, such as a radical, it was extremely
difficult to align magnetic moments parallel within or between
molecules. However, in 1967, Prof. Koichi Ito (Professor Emeritus,
Osaka City University) published his experimental results, which
indicated that when a small number of unpaired electron spins align
parallel to one another, an organic ferromagnet can be obtained. In
1991, Prof. Minoru Kinoshita (Professor Emeritus, The University of
Tokyo) discovered the world's first organic molecular ferromagnet,
p-nitrophenyl nitronyl nitroxide (p-NPNN), in which electron spins
between adjacent molecules in the molecular crystal align parallel to
each other. Prof. Awaga, who was involved in the discovery with Prof.
Kinoshita, says, "Adjacent unpaired electron spins tend to align
antiparallel to each other. In other words, molecules are more stable
when they are chemically bound. Obtaining a molecular ferromagnet was
not about how to chemically bind the molecules but how to align
parallel the spins of adjacent radicals." He also says, "In order to
avoid chemical bonding, spin polarization of the radicals must be
increased, and the polarized spins must align with those of the
adjacent molecules in antiphase." p-NPNN has a NO group with a polarized
unpaired electron spin and a substituent group with very little
polarization. p-NPNN is crystallized by intermolecular electrostatic
interaction between the NO group and the substituent. This contact
between the NO ligand and the substituent group causes propagation of
the antiphase spin polarization between the adjacent molecules.
The Curie temperature, below which p-NPNN shows ferromagnetism, is
0.65 K. Research on cyclic thiazyl radicals (SN radicals) to attain
higher Curie temperatures has led to an increase in temperature of one
order of magnitude. While researching the properties of SN radicals,
Prof. Awaga discovered a unique property of TTTA (1,3,5-trithia-2,4,6-
triazapentalenyl) derivatives. TTTA shows paramagnetism at high
temperatures because the molecules arrange themselves in a regular
array; however, it is diamagnetic at temperatures below 180 K due to
dimerization of the molecules. This phase transition occurs with
a thermal hysteresis loop over a wide temperature range including room
temperature. Prof. Awaga says, "The magnetic bistability, in which
paramagnetism and diamagnetism coexist, was discovered in TTTA. If we
could control the transition between these two stable states, memory
devices and sensors may be fabricated by using organic molecular
crystals." Since the crystal colors differ between high-temperature
phases and low-temperature phases, photo-induced phase transitions are
possible.
Prof. Awaga also conducted research on single-molecule magnets, which
are magnets with the smallest possible size. At cryogenic temperatures,
magnetization curves of some metal cluster complexes are hysteresis
loops similar to those of ferromagnets, because their magnetic
relaxation is slow below their blocking temperatures. Magnetization
reversal also occurs due to a tunnel effect. Mn12 clusters are the most
researched single-molecule magnets. They contain four Mn^4+ ions and
eight Mn^3+ ions and have huge magnetic moments as a molecule, and
uniaxial magnetic anisotropy is induced by Jahn-Teller distortion
caused by Mn^3+. He discovered dipole-biased tunneling of magnetization
and determined the origin of magnetic anisotropy through metal ion
exchange and ligand substitution. He says, "It is quiet thrilling that
physical phenomena, such as single-molecule magnetism and quantum
tunneling of magnetization, could be clarified by molecular
modification, which is a typical chemical method."
Tremendous progress has been made in molecular magnets. However, they
cannot be easily commercialized because their ferromagnetic transition
temperature and their blocking temperature are low. Prof. Awaga says,
"Molecular magnets exhibit changes in their magnetic properties by
external stimulation, such as lights and chemical reactions. It is easy
to control the magnetic properties in organic molecules but difficult
in inorganic molecules. When the size of inorganic molecules becomes
smaller, controlling the magnetic properties becomes easier. I felt
that nanomagnets and molecular magnets are closely related because
nanosized magnets are expected to exhibit quantum effects." He began to
research inorganic shell nanomagnets to develop nanomagnets for
practical applications. He first prepared a hollow sphere of Co3O4 with
a diameter of 500 nm and a wall thickness of 40 nm. When cobalt
hydroxide is uniformly deposited on the surface of polystyrene beads
and burned, hollow structures can be obtained. Although this Co3O4
spherical nanoshell shows antiferromagnetism at room temperature,
spontaneous magnetization appears below the Neel temperature and
exhibits spin glass-like characteristics. This could result from making
Co3O4 a spherical nanoshell, because lattice defects in the wall of the
spherical nanoshell are increased, and thus, spins, which are supposed
to be cancelled out, remain. Prof. Awaga says, "In spherical nanoshells,
remanent magnetization is larger than those of bulk materials by one or
two orders of magnitude. However, remanent magnetization is smaller in
nanomagnets with a diameter of 50 nm. I think nanomagnets with a
diameter of 50 nm are too small to maintain spontaneous magnetization
because magnetic relaxation occurs rapidly." There may be unexplored
mesoscopic properties in the magnets with a diameter of 500 nm.
Prof. Awaga also fabricated nanoshell magnets using cobalt, magnetite
(Fe3O4), hematite (alpha-Fe2O3) and iron. He discovered properties
similar to those of single molecule magnets, such as magnetization
curves, which change remarkably with temperature below 300 K. He
considered that, if the magnets could be properly surface-treated, they
may become soluble magnets or may become catalysts extracted by magnets
because of their large surfaces. He says, "Clockwise magnetization or
counter-clockwise magnetization in the nanoshell wall may be generated
by applying electric current to a nanosphere in one direction.
Controlling magnetization with the current leads to spintronics, into
which I want to expand the research on nanospheres." It has been twenty
years since he started to research on molecular magnets, and his
research has expanded beyond molecular magnets to molecular spintronics.
(Interviewer: Kuniko Ishiguro, Cosmopia Inc.)
For more information including figures,
http://www.nanonet.go.jp/english/mailmag/2007/087a.html
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INTRODUCTION TO LABORATORY
Advanced NEMS (Nano ElectroMechanical System) - Micromachined tools
for investigating the nanoworld
(Issued in Japanese: May 10, 2006)
Beomjoon, Kim, Associate Professor, Department of Precision
Engineering, Graduate School of Engineering, and Center for
International Research on MicroMechatronics (CIRMM), Institute of
ndustrial Science, The University of Tokyo
My lab's research goals are to build nanosystems and fabricate
nanoscale devices by using both bottom-up and top-down approaches.
We are investigating new and novel micro/nano patterning technologies,
like nanostructuring which involves bottom up approaches like self-
assembly from supra-molecular chemistry as well as micro-machining/MEMS
technology, such as micro shadow masks. Self-assembly is a promising
strategy for autonomous organization of nano-components and making
ensembles of nanostructures.
In addition, we are interested in developing novel micro/nano probes
with sizes from micrometer to nanometer through conventional top down
approaches. There are micro-machined near-field optical microscopy
(NSOM) probes for single molecule detection, thermally actuated probe
systems for single cell manipulation, Si-based micro probe cards, micro
electrodes for detection of neuron signals, etc.
Recently, we have been focused on the topic of micro/nano scale of
patterning technology and developing a high-speed, large area
patterning method that is low cost and easy through bottom-up
approaches, e.g. self-assembly, as well as top-down MEMS technology,
e.g. micro shadow masks. We are developing unconventional soft-
lithography and various nano patterning methods using functional self-
assembled monolayers, especially for biological applications.
For more information including figures,
http://www.nanonet.go.jp/english/mailmag/2007/087b.html
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