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278 Appendix D. Site Reports—Japan
RESEARCH AND DEVEOPMENT HIGHLIGHTS
Dr. M. Kobayashi described his work on particle assemblage. At present
this work is focused on micron-scale particles (~ 5 µm particles) and toward
the preparation of “smart” materials. Particles are assembled by electrostatic
force by several methods involving, for example, the atom probe or
electrostatic patterning by electron beams with particles attracted to the
patterned regions. Examples of materials include SiO 2 particle assemblages
for gas (e.g., CO) sensors and Ni-base magnetostrictive particles for actuators.
Dr. I. Nakatani has a program involved with research on quantum
magnetic properties. Studies involve magnetic substances with sizes of
around (a) 100 nm, (b) 10 nm, and (c) 1 nm in dimension.
a) A novel reactive-ion etching method was developed and applied to
producing ferromagnetic Fe-Ni thin wire arrays with 250 nm width and
spacing.
b) Magnetic relaxation phenomena of iron nitride or cobalt ferrofluids were
studied. These are colloidal 10 nm diameter ferromagnetic particles.
The relationship between the viscosities of the magnetic fluids and
volume fractions of solid particles was determined. It was stated that
these ferrofluids possess the highest performance achieved in the world.
c) Giant magnetoresistance (GMR) was observed for 2 nm Fe particles
embedded in SiO 2 or MgF 2 . The GMR effect is due to spin-polarized
electrons tunneling between the Fe particles.
Dr. N. Koguchi described his group’s work on direct formation of
GaAs/AlGaAs quantum dots by droplet epitaxy. The process consists of
forming Ga droplets on the inert S-terminated AlGaAs substrate and reacting
the droplets with As to produce GaAs microcrystals. First, a molecular
beam of Ga is put on the substrate, followed by an As molecular beam.
About 10 nm GaAs particles are formed. The photoluminescence of these
structures is being studied.
Dr. M. Murayama and Dr. W.T. Reynolds (on sabbatical from VPI)
described their studies of the microstructure of a variety of structural
materials with nanoscale features. Included in their studies are fine atomic
clusters in Al-base alloys in which clusters not resolvable with high
resolution electron microscopy were revealed by special tomographic threedimensional
atom probes. NRIM has two of the three existing in the world.
All materials they study with the atom probe are nanostructured, including
• magnetic materials — Co–12Cr–2Ta thin films
Fe-Zr-B amorphous/nc structures
• structural materials — steels (e.g., piano wire)
high strength Al-base alloys
(from A. Inoue’s group at Tohoku University)