Highlights of Collaborated ResearchHighlights of Collaborated ResearchCollaborative works with outside researches are carried out in consideration of the joint research
program. Accepted applications are performed in following each division and facility of IMR.
1) Research Laboratories
Joint research conducted individually byoutside researchers and IMR staff members at
each research laboratory in the following view
points: Originality, Fundamentality, Initiation
and Promptness. Four categories "Research inPriority Area", "General Research", "Exploratory
Research for Young Researchers" and"Workshop"
areprepared.
Outstandingachievements are posted in HP and in thepresent issue.

2) International Research Center for Nuclear
Materials Science
This facility is open to university scientists allover Japan to support experiments using Japan
Materials Testing Reactor, JMTR, the fast
experimental reactor, JOYO, and the test
reactor, JRR-3, operated by JAEA (Japan
Atomic Energy Agency). The overseas reactor,
BR2, located at the Belgian Nuclear ResearchCenter, is also used for irradiation experiments.
This facility acts as a hub for international
collaborations;specimens
irradiatedinoverseas reactors are accepted here for postirradiation examinations by participating
university researchers. Research subjects
covered here include fundamental studies andR&D on fusion structural materials, high heatflux materials, and a variety of functional

67

IMR KINKEN Research Highlights 2011

materials, as well as engineering-oriented
studies for the safety of light water reactors andbasic researches supporting them. Materials
studies utilizing radio-isotopes are also being
conducted
3) Advanced Research Center of Metallic
Glasses (ARCMG)
ARCMG was established in April 2006,
succeeding the Laboratory for Advanced
Materials (LAM), investigating metallic glasses
and other materials. This facility is open to
domestic and international collaborations forresearch on all aspects of materials science,
consisting of two major divisions: (i) scientificresearch on fundamental properties ofmaterials, and (ii) development of engineering
materials for practical usage. Micromotors,pressure sensors, fuel cell separators, soft
magnetic material and many other devises
using metallic glasses are proposed for practicalapplications.

4) High Field Laboratory for Superconducting
Materials
Thislaboratory
restartedin2001,
succeeding “High Field Laboratory for
Superconducting
Materials”
which
was
established in 1981. The main equipment is ahybrid magnet which generates steady highmagnetic fields up to 31T. In addition, many
cryogen-free superconducting magnets whichhave been developed by our laboratory are
installed. Especially, we succeeded indeveloping the world’s first cryogen-free hybrid
magnet, which generates 27.5 T. The laboratory
also provides instruments for measuring various
physical properties. These facilities are open toscientists and engineers on superconductors

IMR KINKEN Research Highlights 2011

and other materials research.

Osaka Center for Industrial Materials
research
The Osaka Center was established at
Osaka as a special unit in IMR in April 2006
based on the agreement between Tohoku
University and Osaka Prefecture Government.
The mission is as following; solve the encountering
technical problems in the enterprise, transfer
academic findings to industries and provide
education programs for the development ofmetallic materials. Research in the Osaka
Center is focused on the understanding of thefundamentals of nano-structured metallic
materials and the rapid realization of theirapplication to industry, in particular, the small
and medium enterprises in Osaka area.

supercomputing system network, 3) general
support for the usage of the supercomputing
system, 4) support of materials design by
supercomputing simulation with vectorizationand parallelization, 5) construction of factual
database for materials, and 6) general support
for the usage of Asian Consortium on
Computational Materials Science - Virtual
Organization.

5)7) International Collaboration Center (ICCIMR)
ICC-IMR was founded after the International
Frontier Center for Advanced Materials in April
2008. It has evolved into the international
research collaboration center of Institute forMaterials Research. As such, ICC-IMR’s programs
have been expanded to include collaborative
research projects by international teams. It
works as a gateway of diverse collaboration
between international researchers and IMR
members. Currently, ICC-IMR coordinates sevendifferent programs: 1) International Integrated
Project Research, 2) Visiting Professorships, 3)
Short Single Research Visits, 4)Fellowship, 5)International Workshops and 6) Coordination ofInternational Collaboration and 7) Material
Transfer Program to foreign research institution
for the international exchange. We welcome
applicants from around the globe to participate
in these international programs.

6) Center for Computational Materials Science
This center was developed from theLaboratory of Materials Information Science
which was established in February 1989. Its
main tasks are 1) administration andmaintenance of the supercomputing system in
thisInstitute,2)
maintenanceofa
IMR KINKEN Research Highlights 201168

highlights collaborated reseach

New Insight into Magnetic Interactions in Organic Radical Crystals

Magnetic properties of 2,3,6-trifluorophenyl nitronyl nitroxide have been examined in static andpulsed magnetic fields. The complementary analysis of the static susceptibility and high-fieldmagnetization revealed the formation of two kinds of spin dimers each of which has a ground stateof triplet (S = 1) and singlet (S = 0). Special molecular arrangements responsible for the magnetic
interactions are extracted and the experimental evidence on the importance of the molecular
overlap between the phenyl groups has been first observed.

One of the characteristic features inorganic radicals is the softness andpentafluorophenyl nitronyl nitroxide has beenreported to show the lattice distortion below 5
K, which suggests the presence of strong
coupling between the phonon and magnetic
exchange coupling. We have developed aseries compound of fluorinated phenyl nitronyl
nitroxides in order to reveal the magnetostructural correlations. The crystals of
2,3,6-trifluorophenyl nitronyl nitroxide show
peculiar magnetic properties and new insight
into the magnetic interactions were observed.
The temperature dependence of the
product of the susceptibility and temperature(χpT) takes a constant at two-thirds the roomtemperature-value within 2 - 4 K. Magnetization(M) at 0.5 K is constant at half the value of fullsaturation within 2 - 5 T. The stationary values
are seemingly curious but the complementary
analysis of χpT and M has revealed the formationof two kinds of spin dimers with S = 1 and S = 0
in the ground state. This model well describes
the χpT behavior and M in the low field region(Fig.1)
The full magnetization curve measured at
0.4 K is compared with the calculation in Fig.2.
The gradual increase of magnetization above
10 T means the existence of the interdimer
interactions.
The antiferromagnetic and ferromagnetic
intermolecular interactions are assigned to themolecular arrangement shown in Fig.3(a) and

Fig. 2: Magnetization curve at 0.4 K in pulsed
magnetic fields. Inset; dM/dB curve.

(a)

(b)

Fig. 3: Molecular arrangements responsible for (a)antiferromagnetic
and(b)
ferromagnetic
interactions, respectively.

(b), respectively. This is the first evidence for theimportant role played by the relative
arrangement of the phenyl groups among
phenyl nitronyl nitroxide derivatives in themagnetic interactions.
References[1] T.Kanzawa, S.Nishihara, H.Nojiri and Y.Hosokoshi. Bull.
Chem.Soc.Jpn., 83, 1447(2010).

Fig. 1: Temperature dependence of χpT. Inset:
Magnetization curves below 5 T compared with
Brillouin functions.

69

IMR KINKEN Research Highlights 2011

Keywords: magnetic properties
Y.Hosokoshi1 and H.Noiri21)Graduate School of Science, Department ofphysical science. Osaka Prefecture University,2) IMR, Tohoku University,
E-mail: yhoso@p.s.osakafu-u.ac.jp
URL:ht tp://w w w.p. s.osakafu - u.ac.jp/~yhoso/
index.html

highlights collaborated reseachAppearance of Unique Strengthening Behavior of Dental
Silver Alloy by Simple Heat Treatment

D

ental silver alloy, Ag-20Pd-14.5Cu-12Au (mass%) exhibits unique hardening behavior after solution
treatment. In this study, the effect of microstructure on the unique hardening behavior of this alloy
was investigated. Results obtained from this study indicate that precipitated β’ phase leads to thisunique hardening behavior.
Ag-Pd-Au-Cu alloys are widely used indental applications because they are cheaper
than gold alloys, have good corrosion
resistance, and exhibit good biocompatibility.
Recently, it was reported that the mechanicalstrength of Ag-20Pd-12Au-14.5Cu (mass%) alloys
subjected to solution treatment (ST) at
temperatures over 1073 K followed by waterquenching (WQ) without aging treatment wassignificantly enhanced. The origin of the uniquehardening mechanism is not yet clear; only the
relationship between the unique hardening
behavior and the L10 -type ordered β’ phase
precipitated in Ag-Pd-Au-Cu alloys has beenreported [1]. However, studies of the formation
processes or mechanisms of the L10 -typeordered β’ phase in as-solutionized Ag-Pd-AuCu alloys have been few in number. The
purpose of this study is to investigate the effectof microstructure on the unique hardening
behavior of Ag-Pd-Au-Cu alloy. In order toinvestigate, we compared with received
materials (As-material) subjected to ST and thematerials subjected to liquid rapid solidification(LRS) process and ST.
The microstructure of As-material isconsisted of α1, α2 and β phases. The
microstructure of As-material changes to a, β,and β’ phases through solution treatment (ST).
The microstructure of LRS material is consistedof α, α1, and a2 phases without β phase. The
microstructure of LRS material through ST
becomes single a phase. a1, a2 and β phase
are Cu-rich material, Ag-rich material and
PdCu intermetallic compound, respectively.
Fig.1 shows bright field image obtained by
TEM, diffraction pattern and key diagram of
As-material subjected to ST for 3.6 ks. The
coherent participation of β’ phases with longand short axes of around 100 nm and 10 nm,
respectively, also occurs during ST although theamount of β’ phase decreases with increasing
the ST time. The hardness and tensile strengthof LRS material and LRS material subjected to
ST are relatively smaller than those of Asmaterial and As-material subjected to the ST.
The Vickers hardness of As-materials with ST
decreases with increasing the ST time longer
than 3.6 ks. On the other hand, in the case of
LRS materials, the Vickers hardness is notdependent on the ST time. In the case of Asmaterials with ST, the amount of precipitationof metastable β’ phase is influenced by ST timeand it leads to precipitation strengthening[2].

Fig. 1 TEM observation of As-material subjected to ST:(a) bright field image, (b) diffraction pattern and(c) key diagram. Beam direction is parallel to [100].

Fig.2 Tensile properties of As-materials and LRS
materials subjected to ST.

References[1] Y. Tanaka, Boundary 19 (2003) 14–17.
[2] T. Akahori, M. Niinomi, M. Nakai, H. Tsutsumi, T. Kanno,
YH. Kim, H. Fukui, J. Japan Inst. Metals, 74 (2010) 6, 337344.

Keywords: Biomedical, microstructure, strength
H. Fukui1, M. Niinomi2, M. Nakai21) School of Dentistry, Aichi-Gakuin University, 2)
IMR, Tohoku University
E-mail: fukui@dpc.aichi-gakuin.ac.jp

IMR KINKEN Research Highlights 201170

highlights collaborated reseachHigh-purity Multicrystalline Silicon Production in a
Unidirectional Solidification Furnace for Solar Cells

For accurate prediction of carbon and oxygen impurities in a single crystal produced by the

Czochralski method, global simulation of coupled oxygen and carbon transport in the whole furnace
was implemented. Both gas-phase transportation and liquid-phase transportation of oxygen andcarbon were considered. With five chemical reactions considered, SiO and CO concentrations in
gas and C and O atom concentrations in silicon melt were solved simultaneously.

References[1] H. Matsuo, R.B. Ganesh, S. Nakano, L.J. Liu, Y. Kangawa,K. Arafune, Y. Ohshita, M. Yamaguchi, K. Kakimoto, J.
Cryst. Growth 310 (2008) 2204.
[2] D.E. Bornside, R.A. Brown, J. Electrochem. Soc. 142(1995) 2790.
[3] L.J. Liu, S. Nakano, K. Kakimoto, J. Cryst. Growth 303(2007) 165.

71

IMR KINKEN Research Highlights 2011

(3)
SiO

CO

heatercrucible

CO
(4)

SiO
(2)

C

O

(5)

O

C

(5)
O

silicon melt
Si

(1)

SiO2
crystalFig. 1 Basic processes of carbon and oxygen
incorporation into a crystal.

3

oxygen concentration (atoms/cm )Multicrystalline silicon has now become
the main material in the photovoltaic market
because of its low production cost and becauseof the relative high conversion efficiency ofsolar cells made from this material. The
unidirectional solidification method is a costeffective technique for large-scale productionof multicrystalline silicon material. Similar to the
Czochralski
method,theunidirectional
solidification is connected with transport of
impurities [1]. Carbon and oxygen are two of
the major impurities in multicrystalline silicon. If
the carbon concentration exceeds 1x1016
atom/cm3, it will markedly influence theprecipitation of oxygen during thermal
annealing of crystals and during device
processing of the wafers cut from these crystals[2].
The basic configurations of unidirectional
solidification furnaces used in the study havebeen shown in the papers [3]. The graphite
components in a furnace include heat shields,
heaters and the crucible pedestal. They are
the main sources of carbon elements in agrown crystal. The basic processes of carbon
and oxygen incorporation into a crystal fromthe graphite components are shown in Fig. 1
Since most of carbon impurity in crystal iscaused by the CO back-diffusion, we proposed
to use a crucible cover to reduce the CO backdiffusion in the unidirectional solidification
furnace [3]. The global simulation of coupledoxygen and carbon transports within the
furnace was used to validate the feasibility of
the improved design [3].
Numerical results shown in Fig.2 indicatesthat the oxygen concentration in the crystal
can be reduced by at least 30% due to theincrease of gas flow velocity near the melt
surface if the crucible cover is placed. The
detail can be referred to the paper [3].

+177.5x10

Furnace without coverFurnace with carbon cover+17

6.0x10

Furnace with tungsten cover4.5x10+17

3.0x10+17+17

1.5x10

0

10

20

30

40

50

height of crystal (mm)60

Fig. 2 Comparison of oxygen concentrations in the
crystal for the old furnace and improved furnaces
with different cover materials.

Keywords: simulation, solar cells
K. Kakimoto B. Gao, S. Nakano,
Research Institute for Applied Mechanics, Kyushu
University, 6-1 Kasuga-koen, Kasuga, Fukuoka
816-8580, Japan
Tel) 81-92-583-7744
E-mail: kakimoto@riam.kyushu-u.ac.jp
URL: http://www.riam.kyushu-u.ac.jp/taiharou/index.html

highlights collaborated reseach

Low energy magnetic excitations in the iron-based
superconductor Fe(Se1-xTex)yMagnetic fluctuations of Fe Se

1+x
0.45 Te 0.55 (x = 0, δ) are investigated by using neutron scattering
technique. Non-superconducting Fe1+δSe0.45Te0.55 shows a pronounced magnetic fluctuation arounda reciprocal lattice 2D vector Q2D = (0.5,0). On the other hand, superconductor FeSe0.45Te0.55 showsa magnetic fluctuation at Q2D = (0.5,0) and (0.5,±0.5). This result suggests that the AF fluctuations
characterized by Q2D = (0.5,±0.5) may play an important role in superconductivity.

The discovery of Fe-based superconductor
has led to intensive studies on related
superconductors including iron group. Their
non-doped counterparts commonly exhibit an
antiferromagnetic (AF) ordering, so that a
precise understanding of the magnetic
properties of the related compounds would
provide a useful guideline for understanding
the superconductivity. Therefore, the dynamicalmagnetic properties of the anti-ferromagnet(AF) Fe1+δSe0.45Te0.55 (TN ≈ 11 K) and superconductor(SC) FeSe0.45Te0.55 (Tc ≈ 15 K) have been investigatedby inelastic neutron scattering techniques.
The measurements reported here show
conclusively that a significant evolution occurs
in the magnetic excitation spectra between AF
and SC sample. Fig. 1 and 2 shows constantenergy scans with the Gaussian fitting lines for
AF and SC, respectively. For AF sample, thepronounced enhancement of the magnetic
fluctuations at low energy (E = 4 meV) andsignificant decrease of intensity with increasing
E were observed. The behavior confirms that
this system is close to the AF ordered phase. On
the other hand, for SC sample, a discernible
scattering intensity peaks centered at k = 0(Q2D = (0.5,0)) and k = ±0.5 (Q2D = (0.5,±0.5))
appear at 2 meV < E < 6 meV, and at 2 meV < E< 10 meV, respectively.
Qualitative difference between two
samples is also observed from the peak
position. Red lines of bottom of Figures show
the peak centers of the magnetic excitation
spectra for both samples at several
temperatures. For AF sample, the magnetic
excitations are located at Q2D = (0.5,0) at low
energies (E < 4 meV). As E increases, the peak
centers branch into substantially up to (0.5,±0.5)
at E ≈10 meV. For SC sample, the inelastic
scattering intensities at Q2D =(0.5,0) decrease
with increasing E, as is the case of AF sample.
On the other hand, scattering intensities at Q2D= (0.5,±0.5) appears obviously, even above 6
meV. This suggests that the AF correlation with
Q2D = (0.5, ±0.5) may play an important role inthe mechanism of superconductivity in Febased superconductors[1].

Fig. 1 Energy dependence of the inelastic scattering
intensity for Fe1+δ Se 0.45 Te 0.55 with E = 4, 8, 10, 11 and
15 meV at 10 K. Solid lines represent the results offittings the data with a Gaussian line.

Fig. 2: Inelastic scattering intensity for FeSe 0.45 Te 0.55
with E = 2, 4, 6, 8 and 10 meV at 10 K.

References[1] S. Iikubo, M. Fujita, S. Niitaka, H. Takagi, H. Ohtani, and M.
Hasebe, Physica C 470, S401 (2010)

Keywords: neutron scattering, superconducting,magnetic properties
S.Iikubo1, M.Fujita2, G.D.Gu3, and J.M.Tranquada3
1) Kyushu Institute of Technology 2) IMR, Tohoku
University 3) Brookhaven National Laboratory,
E-mail:iikubo@life.kyutech.ac.jp

IMR KINKEN Research Highlights 201172

highlights collaborated reseachComputational Approach to Properties of Thermoelectricand Other Materials

T

hermoelectric properties of clathrate compounds have been investigated by first-principles
electronic structure calculations in order to explore the possibilities of high performance
thermoelectric materials. Multi-scale simulations based on the molecular-dynamics/continuum
hybrid method have been performed for polymer melt in order to demonstrate the usefulness of thepresent hybrid method.
We have studied thermoelectric propertiesof type-VIII Ba8Ga16 Sn30 (BGS) clathrates. BGS is
an intrinsic semiconductor when the atomic
composition is 8:16:30, being one of promisingthermoelectric materials. Sn and Ga atoms
compose the host cage structure and Ba atoms
are encapsulated in the cages. The carrier
type and the carrier concentration in BGS canbe controlled by changing the atomic
compositions of Sn and Ga. Ga atoms are
distributed at random in the host framework.
In the previous work [1], we calculated theelectronic structures and thermoelectric
properties of BGS with the Ga configuration
determined by experimental results. In thepresent study we have calculated theelectronic structures of BGS with different Ga
configurations to discuss the effect of Ga
distribution on thermoelectric properties.
We
haveperformed
first-principles
electronic structure calculations of type-VIII
BGS using the super-cell approximation, andthen calculated the thermoelectric power(TEP) using the calculated electronic structures.
The temperature dependences of TEP fordifferent Ga configurations are shown in Fig. 1.
We have developed a computational
method coupling atomic model and macroscale continuum [2], and applied the method
to polymer melt consisting of long chain
polymers. The polymer molecule is coarsegrained into a meso-scopic model by the socalled spring-beads model. This spring-beads
model is coupled with an elastic continuum
using our hybrid method.
Fig. 2 shows the usefulness of multi-scale
simulations based on our hybrid method. The
simulation time required to achieve theequilibrium state is reduced drasticallycompared with conventional equilibration
methods. The polymers can move with a wide
range of energy due to large scale fluctuations
generated by the elastic continuum, and avariety of chain structures are generated in thepolymer melt. This situation results in the fast
convergence to the equilibrium state of long
chain polymers.

73

IMR KINKEN Research Highlights 2011

Fig. 1: Calculated thermoelectric power of BGS withn-type carriers.

Fig. 2: Time evolution of the end-end distance ofpolymers and chain structures of a polymer.

References[1] Y. Kono, N. Ohyama, T. Taguchi, K. Suekuni, T. Takabatake,
S. Yamamoto, and K. Akai: J. Appl. Phys., 107, 123720/1-6(2010).
[2] Y. Senda and G. Kim, Prog. Theor. Phys. Suppl. Vol. 178,
141 (2009).

Keywords: ab initio calculation, thermoelectric,
simulation
K. Akai1, Y. Senda2,and S. Shimamura2
1) Media and Information Technology Center,
Yamaguchi University
2) Faculty of Engineering, Yamaguchi University
E-mail: akai@yamaguchi-u.ac.jp
senda@yamaguchi-u.ac.jp
simamura@yamaguchi-u.ac.jp

highlights collaborated reseach

Plasma Purification of Ag Nanoparticles to Control
Localized Surface Plasmon Resonance

Remarkable changes, blueshift and narrowing, in localized surface plasmon resonance of silver

NPs without significant morphological modifications have been demonstrated with plasma
treatments. Our findings provide information on the reason why most of the experimental extinction
spectra of the NPs on substrates are considerably different from those generated by simulation basedon Mie’s theory.
0.3

Ar plasma

Optical Density

Exposure time (s)
0
20
40
80
160
300

0.2

Ag NPs with contamination

0.1

200

300

400

500

600

700

800

Contamination free Ag NPs

Wavelength (nm)Fig. 1: Optical extinction spectra of Ag NPs deposited
onto SiO2 before and after plasma treatments(left), together with a schematic drawing of Ar
plasma purification (right).

460

1.0

Peak position in
optical absorption
Raman intensity

450

0.8
0.6

440
430

0.4

420

0.2

410

0

50

100

150

200

250

300

Normalized Raman intensity

470

Peak position (nm)The control of the surface plasmon
resonance property, which is well characterized
by the plasmon resonance wavelength λp andline width Δωp, is required for silver nanoparticles(NPs) supported on substrates to realize
applications of chemical and biologicalsensors. In the survey of the λp of supported
silver NPs, it is found that the reported λp values
are between 380 and 500 nm, larger than thatpredicted by the Mie’s theory (370 nm); theexperimental data vary from lab to lab. Further,most of the optical extinction spectra reported
are found to be much broader than thecalculated one. The shape and density (ordegree of dispersion) of silver NPs on substrates
are, of course, factors to govern their opticalproperties, but the variation of the reported λp
as well as the discrepancy between
experimental and theoretical extinction
spectra cannot be explained completely bythese two factors. To control the surface
plasmon properties, all the occurring effects
should be clarified.
We have demonstrated that plasma
purification of silver NPa brings about blueshift
and narrowing in their localized surface
plasmon resonance, as has been shown in Fig.
1 [1]. To confirm the origin of the changes in thesurface plasmon property, Raman scattering,
scanning electron microscopy, Rutherford
backscattering spectrometry were conducted.
Extremely high sensitivity for adsorbed
molecules on silver NPs can be expected due
to surface enhanced Raman scattering (SERS).
The SERS analysis revealed that hydrocarbons
adsorbed on silver surfaces were removed
effectively by plasma exposure. As can be seenin Fig. 2, the decrease in Raman intensity forhydro-carbons is correlated well with theblueshift.
Our findings indicate that one of the mostimportant factor for remarkable differences inplasmon resonance wavelengths and line
widths reported for the silver NPs supported on
substrates between most of the experimental
data and calculations based on Mie’s theory is
due to the impurity adsorption on silver surfaces.
Plasma purification would enable us to control
the optical properties of other metallic NPs.

0

Plasma exposure time (s)Fig. 2: Peak positions of surface plasmon resonanceband in the extinction spectra (filled circles) andnormalized Raman intensities (open squares) as afunction of plasma exposure time. A line is drawn
to guide the eyes.

References[1] K. Kawaguchi, M. Saito, K. Takahiro, S. Yamamoto, M.
Yoshikawa, Plasmonics, 6, 535 (2011).

Keywords: nanoparticle, optical absorption
K. Takahiro1 and S. Nagata2
1) G raduate School of Science and Technology,
Department of Chemistry and Materials
Technology, Kyoto Institute of Technology, 2)
IMR, Tohoku University.
E-mail: takahiro@kit.ac.jp

IMR KINKEN Research Highlights 201174

highlights collaborated reseachDevelopment of Rapid Surface-Nitriding System Using a
Microwave-Induced Nitrogen Plasma at Atmospheric Pressure

Rapid surface-nitriding system for surface modification of steels has been developed by using anapparatus equipped with a microwave-induced nitrogen-plasma generator. The new system canproduce the nitrided layer having a thickness of several micrometer within one minute, which is 10 -2times of the conventional surface-nitriding techniques.

75

IMR KINKEN Research Highlights 2011

It is expected that the present surfacenitriding system is applicable to the surface
treatment of various base metals such asaluminum and titanium. The application to thesematerials is in progress now.
Iron plate
PlasmaPower supply

Microwave
generator

Nitrogen gas

Wave
guide

Gas for plasma

OkamotocavityPlasma torch

Nebulizer gas
Nitrogen gas

Fig. 1 Schematic diagram of the setup of the rapid
surface-nitriding system using a microwaveinduced nitrogen plasma.
60

Concentration (at%)

Nitriding treatment has been extensively
used for surface modifications of steels. Nitrogenradicals such as excited nitrogen molecules andnitrogen molecule ions act as reactants in theplasma nitriding process. The conventional
plasma-nitriding
techniques,
which
are
conducted under evacuated atmospheres,
require several hours for obtaining nitrided layers
having several-micrometer thickness. According
to our studies, the population of the nitrogenradicals affects the surface-nitriding reaction [1],suggesting that the slow nitriding reaction of theconventional techniques can be ascribed to thelow population of the nitrogen radicals. Therefore,
to achieve the rapid nitriding treatment, wedeveloped a new plasma-nitriding apparatus,
which can produce high-population nitrogenradicals by the plasma in atmospheric pressure.
Fig. 1 shows the setup of the newly developed
apparatus. The apparatus comprises a
microwave generator, a waveguide, an Okamoto
cavity [2] and torch. The microwave power istransmitted to the Okamoto cavity through the
waveguide. N2 gas was introduced into the torch
at atmospheric pressure, and a flame-like N2
plasma was formed above the torch. In this study,
an iron plate was used for a specimen, which
was located near the apex of the plasma. The
microwave power was fixed at 700 W to heat the
sample at a moderate temperature between
700 and 800 K.
Fig. 2 shows a depth profile of elements forthe nitrided iron surface [3]. The nitridingtreatment time was 40 s. Whereas conventional
plasma-nitriding techniques would require
several hours for nitriding treatments, this result
demonstrates that the newly developed system
is able to produce a nitrided layer having athickness of several micrometer within one
minute. The nitrided layer is composed of twolayers containing different nitrogen concentrationof about 20% and 10%. According to the X-ray
diffraction pattern of the specimen, the
20%-nitrogen and 10%-nitrogen layers consist of
Fe4N and γ-Fe, respectively. It should be notedthat the nitrogen concentration of γ-Fe layer
almost reaches the solubility limit of nitrogen in
γ-Fe, suggesting that the nitrogen reactant is
supplied at a high rate into the specimen surface
by the radical-rich plasma. This phenomenon
also exhibits a peculiar feature of the nitrided
layer formed with the new system.

▼
▼

40

20
O

0

20

25
30
35
2θ for Mo Kα / deg

40

γ -Fe

N

0

▼

▼

Fe4N

Fe4N
γ -Fe
α -Fe

α -Fe

2
4
6
8
Sputtering depth / μm

10Fig. 2 Depth distribution of elements of the iron plate
nitrided by the newly developed apparatus. The
inset shows the X-ray diffraction pattern of thenitrided specimen.

References[1] S. Sato, K. Omori, S. Araki, Y. Takahashi, K. Wagatsuma,
Surf. Interface Anal., 41, 496 (2009).
[2] Y. Okamoto, Anal. Sci., 7, 283 (1991).
[3] Y. Arai, S.Sato, N. Yamashita, A. Kojyo, Y. Okamoto, K.
Wagatsuma, CAMP-ISIJ, 23, 478 (2010).

Keywords: nitride, surface reaction
Y. Okamoto* (Toyo University)
S. Sato and K. Wagatsuma (Tohoku University)* Faculty of Science and Engineering, Toyo
University
E-mail: okamoto@toyo.jp

highlights collaborated reseach

Microscopic Evidence for the 8.5 K Phase Transition in
Americium Dioxide Proved by NMR

More than 30 years ago, a phase transition was suggested to occur in americium dioxide at 8.5 K

based on magnetic susceptibility data, while no evidence had been obtained from microscopic
measurements. Owing to the limited number of experiments, the mechanism of this phase transition
has remained a mystery. Recently 17O NMR provides the first microscopic evidence for a phasetransition as a bulk property in this system.
with careful attention paid to effects of sample
aging. To determine the order parameter of
AmO2, the NMR in a fresh sample is now in
preparation.
paramagnetic
state

AmO2

T =200 K

Signal Intensity ( a.u.)

A phase transition in americium dioxide(AmO2) was first reported in 1975 from magnetic
susceptibility data, which showed a broad
maximum around T0 =8.5 K [1]. This behavior has
been attributed to an ordinary magnetic
dipolar ordering similar to that of UO2. However,this interpretation was not consistent with twoother experimental results reported aroundthat time: 243Am Mössbauer spectroscopy andneutron diffraction measurements indicatedthe absence of ordered dipolar moments at
the Am sites below T0. Up to now, except for thesusceptibility data, there has been no
experimental result to support the occurrenceof a bulk phase transition in AmO2.
In this study, we have prepared a powder
sample of 243AmO2 containing 90 at. % 17O andhave performed 17O NMR [2]. The phasetransition has been detected as a sudden lossof NMR signal intensity below T0. With further
decrease of temperature, the NMR signal
reappears and a spectrum with extreme
broadening has been observed. The observed
spectrum covers a range of ~14 kOe in appliedfield, as shown in Fig.1. These data provide thefirst microscopic evidence for a phase transition
as a bulk property in this system. Interestingly,
the spectrum has been found to split into two
peaks even in the paramagnetic state, aneffect which has not been reported for actinide
dioxides studied up to now. We suggest thatthe splitting is induced by self-radiation
damage from the alpha decay of 243Am.
In localized f-electron systems, the electronstate is represented in terms of multipole
degrees of freedom. For AmO2, the Am4+
crystalline electric field (CEF) ground state wasbelieved to be the Γ7 doublet, which carries
only dipole degrees of freedom. Recently,
however, Hotta has pointed out that the groundstate could be a Γ 8 quartet for the same CEF
potential [3]. For such a case, multipolarordering is expected, since the Γ 8 quartet
carries quadrupolar and octupolar degrees of
freedom.
The present NMR also tells us that to avoid
complexities arising from sample aging, datafrom a very fresh sample are essential for the
study of AmO2. In this context, we suggest thatthe past results for Mössbauer spectroscopy
and neutron diffraction need to reexamined

-600

-400

T =1.5 K

-8000

-200

0

200

400

magneticordered state

-4000
0
4000
Internal Field (Oe)Fig. 1 Temperature dependence ofspectrum in AmO2.

8000
17O

NMR

References[1] D.G.Karraker, J. Chem. Phys. 63, 3174 (1975).
[2] Y.Tokunaga, T.Nishi, S.Kambe, M.Nakada, A.Itoh, Y.
Homma, H.Sakai, and H.Chudo, J. Phys. Soc. Jpn. 79,
053705 (2010).
[3] T.Hotta, Phys. Rev. B 80, 024408 (2009).

Keywords: actinide, magnetic properties, nuclear
magnetic resonance (nmr)
Yo Tokunaga1 and Yoshiya Homma2
1) ASRC, Japan Atomic Energy Agency, 2) IMR,
Tohoku University
E-mail: tokunaga.yo@jaea.go.jp
URL:http://asrc.jaea.go.jp/soshiki/gr/kambe-gr/
EnglishSites/

IMR KINKEN Research Highlights 201176

highlights collaborated reseach

New Kind of Volcano on the Earth —Geochronological Studies
of Neutron-Irradiated Lavas Erupted on the Sea Floor—Tectonic plate boundaries are marked by volcanoes, earthquakes, and related geologic activity;
however, a new kind of volcano, named “petit-spot”, has recently been found in regions located far
from plate boundaries. Newly discovered lavas produced by petit-spot volcanoes have been dated
using the Ar–Ar technique.

77

IMR KINKEN Research Highlights 2011

characteristics of the asthenosphere remain
largely unknown, despite its importance interms of plate tectonics. Further studies of petitspot lavas will provide important informationon the asthenosphere and the nature oftectonic plates [6-8].
Site A: petit-spots that formed at Site B andwere transported into the subduction zoneJapan
TrenchSite B: petit-spot eruptions(at 0.05〜1, 1.8, 4.2, 6.0, 8.5 myBP)〜800 m uplift

Paciﬁc Plate（formed at 135 myBP）
W
of ater d
800 ep0m th

Rigid tectonic plates move around thesurface of the Earth on top of the asthenosphere(ductile part of the mantle), which marks theupper limit of convection in the mantle. Hirano
et al. [1] reported the discovery of young
volcanoes located far from tectonic plateboundaries (e.g., mid-oceanic ridges andvolcanic arcs), which are the usual sites of
volcanoes, earthquakes, and related geologic
activity. The newly found volcanoes, named“petit-spot”, occur in a region of the PacificPlate that is susceptible to fracturing prior toplate subduction at the Japan Trench off NE
Japan. The magmas originate from theasthenosphere immediately under the plate.
Radiometric Ar–Ar dating is commonlyused to determine the ages of deep-sea lavas.
Samples for dating were irradiated by neutrons
in a reactor (JMTR or JRR3) to produce 39Ar from
39K. Then, radiogenic 40Ar, daughter nuclide ofradioactive 40 K and parent (39Ar instead of 40 K)
were simultaneously analyzed using a multistep heating technique and mass-spectrometer[2]. This method is employed to distinguishradiogenic 40Ar from inherited one from the
mantle, which inhibits the dating of lava
especially erupted in deep sea.
Ar–Ar dating of four petit-spot volcanoes
indicates that the magmas were erupted from
1.8 to 8.5 million years ago [1-3]. Much younger
date (an age between 0.05 and 1 million yearsago) was obtained afterward for another petitspot [1]. These ages are surprisingly young,because nearby seamounts and the PacificPlate were formed at around 100 million years
ago.
Other geophysical and geochemical
evidence indicates that lavas from petit-spot
volcanoes derive from partially melted rockfrom the asthenosphere, where melt forms andaccumulates due to concave flexing of theplate as it approaches the subduction zone [4];the magma is squeezed through cracks in theoverlying tectonic plate (Fig. 1). This model
would indicate that such volcanoes are
ubiquitous on the ocean floor, where incipient
melts are squeezed upward through fracturesby tectonic forces associated with plate flexure[3]. Several research cruises have found petitspot volcanoes in other areas of the Pacific(e.g. off the Chile Trench [5]).
The physical state and geochemical

10 cm／yr.
Outer-rise(plate ﬂexure)

Subduction

Water depthof 6000 m〜50 kmPlate fractures

Magma immediately
below the plate (asthenosphere) Plate thicknessof 70‒100 km

Fig. 1: Schematic model of the petit-spot volcanoes
generation [1]. myBP = million years before present.
White arrows show the motion of the Pacific Plate,which moves at 10 cm per year. Petit-spots erupt
along the fractures that develop in response to thissurface stress due to plate flexure (black arrows).

References[1] N.Hirano, E.Takahashi, J.Yamamoto, N.Abe, S.P.Ingle, I.
Kaneoka, J.Kimura, T.Hirata, T.Ishii, Y.Ogawa, S.Machida
and K.Suyehiro. Science, 313, 1426 (2006).
[2] N.Ebisawa, H.Sumino, R.Okazaki, Y.Takigami, N.Hirano,
K.Nagao and I.Kaneoka. J. Mass Spectr. Soc. Japan, 52,
219 (2004).
[3] N.Hirano, A.A.P.Koppers, A.Takahashi, T.Fujiwara andM.Nakanishi. Basin Res., 20, 543 (2008).
[4] G.Valentine and N.Hirano. Geology, 38, 55–58 (2010)[5] N.Hirano. EOS Trans. AGU., 91, V13F-07 (2010)[6] N.Hirano. Geochem. J., 45, 157 (2011).
[7] S.Machida, N.Hirano and J.Kimura. Geochim. Cosmochim.
Acta, 73, 3028 (2009).
[8] J.Yamamoto, N.Hirano, N.Abe and T.Hanyu. Chem.
Geol., 268, 313 (2009).

Keywords: geologic, mass spectroscopy, neutron
irradiation
Naoto Hirano(Center for NE-Asian Studies, Tohoku University)
E-mail: nhirano@m.tohoku.ac.jp
URL: http://www.f2.dion.ne.jp/~nhirano/highlights collaborated reseach

Co-Doping of Mn and V to LaNbO4 for FerromagneticFerroelastic Novel MaterialFor realization of ferromagnetic-ferroelastic novel material, Mn and V were co-doped to LaNbO4.
Ferromagnetic transition occurred at ≈ 200 K for the LaNb 0.6V0.1Mn 0.3O4 sample having monoclinic
crystal structure. Glassy behavior reflects exchange interaction between Mn4+(d3)NbO7 clusters via
VO˙. Formation of magnetic nanoclusters by acceptor doping is advantageous for development ofstress-switchable information storage material.
challenge of material development toward
stress-switchable nanoscale memory.

m-LaNb0.6V0.1Mn0.3O4

2

M (µB/Mn)

LaNbO4 has two polymorphs: the scheelite
structure with tetragonal symmetry (t-LaNbO4;
I41/a) and the fergusonite structure withmonoclinic symmetry (m-LaNbO4; I2/c). Below
770 K, t-LaNbO4 transforms into more stable
m-LaNbO4. Ferroelasticity of m-LaNbO4 isadvantageoustodevelopnon-volatileinformation storage material controllable withnanoscale stress by piezoresponse force
microprobe.
For extension of functionality of m-LaNbO4
to ferromagnetism (FM) in nanoscale, we
substituted Nb5+ by Mn4+ and V5+ [1]. Bothincreasing the dopant content and introductionof oxygen vacancy (VO) are important forrealizing FM in nanoscale. The solution energy
with doping depends on ionic radii (rion).
Although rion of V5+ (0.036 nm) is smaller thanthat of Nb5+ (0.048 nm), V5+ substitutes for Nb5+
and forms t-LaNb0.7V0.3O4 crystal (Fig. 1 upper
left). Since rion of Mn4+ (0.039 nm) is similar to thatof V5+, substitution of Mn4+ for V5+ is expected toshow the lowest solution energy, and generate
VO to maintain electrical neutrality.
Powders of La2O3, Nb2O5, V2O3, and MnO2
weighed with the molar ratio of [La] : [Nb] : [V]: [Mn] = 1 : 0.6 : 0.1 : 0.3 were mixed in grinding,and then heated at 1573 K in flowing oxygengas for 4 h. The sample with nominal compositionof LaNb 0.6V0.1Mn 0.3O4 demonstrated X-ray
diffraction pattern (Fig.1 upper right) of
isomorphous with m-LaNbO4. As seen in Fig. 1
middle panels, the sample exhibited FM
behaviorintemperatureandfielddependences of magnetization (M-T & M-H).
The (1/M)-T curve indicated the Curie
temperature of ≈ 200 K. A small coercive fieldof the sigmoidal M-H curve suggests that the
FM behavior is originated from magnetic
nanoclusters. Frequency dependence of thein-phase ac-magnetization (M') showed glassy
behavior (Fig.1 lower left) based on exchangeinteraction between the nanoclusters.
The tetrahedron, where Mn4+ substituted
for V5+, loses oxygen, and reconstruction
occurs to form MnNbO7 linking cluster sharing
a corner-oxygen (Fig. 1 lower right). Thus,
exchange interaction between Mn4+(d3)NbO7
clusters via singly ionized VO˙ results in effective
M of ≈ 2μ B/Mn for the nominal composition.
Our research on LaNb 0.6V0.1Mn 0.3O4 is a

2

FC
ZFC

1

H = 0.5 T

0

100

T (K)

1

200K

t-LaNb0.6V0.4O4

0

75K

0
200

300

0

0.5

H (T)

1.0

Fig.1 Schematic representation of t-LaNb 0.7 V0.3O4
crystal structure (upper left), X-ray diffraction
pattern of the LaNb 0.6V0.1Mn 0.3O4 sample (upper
right), M-T (middle left) of the sample with that of
LaNb 0.6V0.4O4 as a reference (ZFC), M-H (middle
right) and M'-T at various frequency (lower left) of
the sample, and schematic representation of
MnNbO7 cluster formation with VO (lower right).

References[1] K.Okada, S.Kawakami, S.Kohiki, H.Shimooka, H.Deguchi,
M.Mito, T.Shishido and M.Mitome: Ext. Abst. 71st Autumn
Meeting, 2010; Jpn. Soc. Appl. Phys. 16a-NH-4.

Keywords: ferromagnetic, nanocluster, defects
S.Kohiki1 and K.Yubuta2
1) Department of Materials Science, Kyushu
Institute of Technology, 2) IMR, Tohoku University
E-mail: kohiki@che.kyutech.ac.jp
URL: http://w w w.che.k yutech.ac.jp/chem13/
chem13.htm

IMR KINKEN Research Highlights 201178

highlights collaborated reseachDevelopment of Diamond Photonic Crystals Composed of
Metallic and Oxide Glasses Lattices for Terahertz Waves Controlphotonic crystals with periodic arrangements of magnetic permeability and dielectric constantwere fabricated to diffract and control electromagnetic wave propagations in terahertz frequency
ranges. Metallic glass particles of Fe72B14.4 Si9.6Nb4 composite were dispersed into micro oxide glasslattices of B2O3•Bi2O3. The photonic crystals with diamond structures were created by using micro
pattering stereolithography and powder sintering process.
Photonic crystals with periodic vibrations inmagnetic permeability or dielectric constantexhibit forbidden gaps in electromagnetic
waves transmission spectra by Bragg diffraction.
Introduced air cavities of structural defects canresonate and localize the electromagnetic
waves with specific wavelengths and form
localized modes of transmission peaks in thephotonic band gaps. By applying original micro
pattering stereolithography and powder
sintering process [1,2], the photonic crystals witha diamond structure composed of minute oxide
glass lattices of B2O3•Bi2O3 including metallic
glass particles of Fe72B14.4Si9.6Nb4 were fabricatedsuccessfully as shown in Fig. 1. The iron based
metallic glass is soft magnetic amorphous alloys
with the high glass forming ability and highmagnetic permeability. Geometric patterns of
the dielectric or magnetic micro lattices weremodified and optimized to control theelectromagnetic waves belonging to terahertz
frequency ranges effectively by using computer
aided design, manufacture and evaluation. The
terahertz waves can be synchronized withcollective vibration modes of various organic
matters and biological microbes. The formed
photonic crystals are expected to be applied
for environmental sensors to detect harmful
substances and bacteria seedbeds forobservation of the living behaviors thoroughterahertz wave time domain spectroscopy. To
create the micro lattices, the metallic and oxide
glasses particles of 5 µm in average diameter at
17 and 23 vol. % were dispersed into photosensitive acrylic resins, respectively. The resin
paste was spread on a substrate with 10 µm inlayer thickness by using a mechanical knifeedge, and cross sectional images of an ultra
violet ray were exposed by a digital micro mirror
device with 2 µm in part accuracy. After thelayer stacking, the obtained precursors were
heated at 490 °C for 0.5 hs in vacuum for the
dewaxing and sintering. This heating temperature
is above the melting point of the oxide glass andunder the crystallization point of the metallic
glass. Fig. 2 shows a microstructure of the oxide
glass lattice including the metallic glass particles.
In the X-ray analysis, diffraction profiles indicating
amorphous structures were observed.

79

IMR KINKEN Research Highlights 2011

Fig.1 A diamond photonic crystal composed ofmagnetic and dielectric lattices formed by micro
pattering stereolithography and powder sintering
process.

Fig.2 A microstructure in oxide glass lattice of
B2O3•Bi2O3 including metallic glass particles of
Fe72B14.4 Si9.6Nb4 observed by using a scanningelectron microscopy.

References[1] S.Kirihara, N.Komori and N.Ohta, Advanes in Scienceand Technology, 63, 141 (2010).
[2] S.Kirihara, T.Niki and M.Kaneko, Ceramic Transactions,
126, 113 (2010).

Keywords:photonic crystals, metallic Glass
S.Kirihara1 and H. Kato2
1) JWRI, Osaka Univ., 2) IMR, Tohoku Univ.
E-mail: kirihara@jwri.osaka-u.ac.jp
URL: http://www.jwri.osaka-u.ac.jp/~mri1

highlights collaborated reseachHydrogen Production from Methanol Steam Reforming
over Catalysts Prepared from Cu-Zr Amorphous Alloys

Amorphous metallic alloys, Cu-Zr, have been studied as catalyst precursors for methanol steam
reforming to produce hydrogen. The addition of a very small amount of noble metals enhanced theactivity without an increase in carbon monoxide formation. Recently, the activity was increased bya factor of 100 by improving the conditions of pretreatment.
above 100 ppm and it is required to improve
this point.
100
Improved
Previous-ln(1-xA)

10
1
0.1
0.01

1.4

1.6

1.8
2
1000/T [1/K]

2.2

2.4

Fig. 1: Increase in the catalytic activity by improving
pretreatment method.
8060xA [%]

Methanol steam reforming is one ofpromising method to produce hydrogen forsmall-size fuel-cell units. It is reported thatcatalysts prepared from Cu-Zr amorphousalloys had the activity for this reaction when asmall amount of noble metals such as platinum
and rhodium were contained [1]. Carbon
monoxide is a poison for the electrodes of fuelcells and is formed over Pt catalysts. However,by controlling the noble metal content, theformation of carbon monoxide was successfully
suppressed.
The amorphous alloy ribbons wereprepared at the IMR, Tohoku University, bysingle-roll rapid solidification. The alloy was cut,calcined in the air and reduced by hydrogenin the previous study. After these treatments,
the reaction was performed and was followedby regeneration involving calcination andreduction. The activity reached a maximum
after several repetitions of the regeneration
and reaction.
We have studied the pretreatment method
and condition [2]. The experiments provided
that the activity was drastically increased bysuitable pretreatment. In the improved method,
after the hydrogen reduction, the alloy was
ground and used for the reaction test.
Fig.1 shows the comparison between theconversions by the previous pretreatment andby the improved method. The methanol
conversion, x A, was converted a function using
a logarithmic function; –ln(1-x A) to indicate theactivity linearly. The horizontal axis is the reverseof temperature. The apparent activationenergy was estimated from the slope of theline in this figure to be 73.2 kJ/mol.
The activity of the catalysts prepared by
the improved pretreatment shows an increaseof 2 orders of magnitude. The temperature toobtain the same activity was decreased byabout 100 K for the improved catalyst.
The optimum Pt content to obtain the highactivity had both the lower and upper limits.
When the alloy, Cu50Zr50 was used, the optimum
Pt content was between 0.1 and 0.2 at% asshown in Fig.2.
When the previous method was applied,
the activity gradually decreased with process
time. The activity was stable after an initial
decrease for the improved method. However,the selectivity for carbon monoxide was still

40
20
0

0

0.2

0.4

0.6

0.8

1

Pt content [at%]Fig. 2: Effect of platinum content on the catalytic
activity.

References[1] T.Takahashi, M.Kawabata, T.Kai, H.Kimura and A. Inoue,
J. Japan Inst. Metals., 71, 615 (2007).
[2] A.Hirata, T.Kai, T.Nakazato, H.Kimura and T.Goto, Proc.
of 23rd Int. Symp. on Chem. Eng., PF-03, Fukuoka, Japan(2010).

Keywords: alloy, amorphous, catalytic
T.Kai1 and H.Kimura2
1) Department of Chemical Engineering, Graduate
School of Science and Engineering, University ofKagoshima, 2) IMR, Tohoku University
E-mail:t.kai@cen.kagoshima-u.ac.jp

IMR KINKEN Research Highlights 201180

highlights collaborated reseachObservation of Fractional Quantum Hall Effect at ν = 1/3 ina MgZnO/ZnO Heterointerface under High Magnetic Field

T

he Fractional quantum Hall effect (FQHE) is one of the most prominent quantum phenomena andhas been observed in extremely high-mobility electron and hole two-dimensional systems at low
temperature under high magnetic field. Owing to the improved quality of the MgZnO/ZnO
heterointerface, we observed FQHE at ν = 1/3 for the first time in oxide systems.
The MgZnO/ZnO (Mg = 1 %) heterostructure
was grown by molecular beam epitaxy on Znpolar ZnO (0001) substrate. In this structure,high-mobility two-dimensional electron gas(2DEG) is formed at the interface by thepolarization discontinuity between MgZnO andZnO as schematically shown in the inset of Fig.
1 [1]. Unique to our growth system, pure ozone
was employed as an oxygen source, by which
the impurity concentration incorporated to thefilm can be considerably reduced. As a result,the mobility of the 2DEG reached 300,000 cm2V-1 s-1 with the carrier density of 2.0 × 1011 cm -2
at 0.04 K, estimated from low-field Hall effect.
This mobility corresponds to the transport
scattering time of ≈ 50 ps, which is approaching
the supreme value of the extremely clean
2DEG in AlGaAs/GaAs.
For the MgZnO/ZnO sample, we measured
magnetotransport properties in a dilution
refrigerator, where the sample was placed in aperpendicular magnetic field created by acryogen-free hybrid magnet with the maximum
magnetic field of 27.5 T. Fig. 1 shows the result of
the measurement at 0.04 K. Longitudinal
resistance (Rxx) shows clear Shubnikov-de Haas
oscillations starting at a low magnetic field of
0.3 T, which suggests high quality of the sample.
As in the previous report [2], we observed thefractional states at ν = 5/3 and 4/3. Additionally,
a number of fractional states ν = 2/3, 3/5, and
2/5 in the lowest Landau level are observed.
The most remarkable observation is theappearance of the fundamental fractional
state ν = 1/3 at B = 25.5 T [3].
The observation of the ν = 1/3 state in theoxide heterosturucture opened a new door toutilize more degrees of freedom in mesoscopic
systems. In particular, oxide materials havemuch variety of crystal structures because of
their ionic character, which is strongly correlatedwith electronic band structure and spin-orbit
interaction. For example, in wurtzite structure
as in ZnO, linear k dependence in the valenceband is predicted, which is expected to exhibit
a strong relativistic effect. Realizing mesoscopic
systems using such new material systems will
create a new field in condensed matterphysics.

81

IMR KINKEN Research Highlights 2011

Fig. 1: Magnetotransport properties of two-dimensional
electron gas at a MgZnO/ZnO heterointerface at
0.04 K. The inset shows the schematic diagram of
the heterostructure.

References[1] A. Tsukazaki, A. Ohtomo, T. Kita, Y. Ohno, H. Ohno, and
M. Kawasaki, Science 315, 1388 (2007).
[2] A. Tsukazaki, S. Akasaka, K. Nakahara, Y. Ohno, H. Ohno,
D. Maryenko, A. Ohtomo, and M. Kawasaki, Nature
Mater. 9, 889 (2010).
[3] Y. Kozuka, A. Tsukazaki, D. Maryenko, J. Falson, S.
Akasaka, K. Nakahara, S. Nakamura, S. Awaji, K. Ueno,
and M. Kawasaki, Phys. Rev. B 84, 033304 (2011).

Keywords: oxide, electrical property
Y. Kozuka1, A. Tsukazaki1,2, D. Maryenko3, J. Falson4,
S. Nakamura4, S. Awaji4, K. Ueno2,5, and M.
Kawasaki1,3,6,7
1)Graduate School of Engineering, QPEC, The
University of Tokyo, 2)JST-PRESTO, 3)CorrelatedElectron Research Group, RIKEN-ASI, 4)IMR,
Tohoku University, 5)Graduate School of Arts andSciences, Department of Basic Science, The
University of Tokyo, 6)WPI-AIMR, Tohoku University,7)JST-CREST
E-mail:kozuka@ap.t.u-tokyo.ac.jp

highlights collaborated reseach

Plastic Working of Metallic Glass Bolts by Cold Thread Rolling

A Zr-based metallic glass (MG) bolt with a single glassy phase was successfully produced by cold

thread rolling. Large plastic strain without destructive crack propagation is induced at the screw
thread near the surface of the cylindrical specimen due to the compressive mean stress distributions
developed throughout the thread rolling process. The process design based on this mechanism cansignificantly contribute to MG applications.

Bolts are commonly employed machineelements used for joining and fastening, andtheir performance and reliability influence theoverall performance of machines. In this study,
we have plastically worked and formed bolts
using metallic glass (MG) that exhibits uniquemechanical properties such as high tensile
strength, low Young’s modulus, and large
elastic limit. The large elastic limit increases thepermissible elongation range of the bolt andhelps avoid bolt loosening, while the low
Young’s modulus effectively resists screwed-inbolt loosening by increasing the frictional forceson both bolt-nut contact area and bearing
surface. We employed a zirconium-based MGforourexperimental
Zr55Al10 Cu30 Ni5
investigations. A pre-form of a hexagon socket
head cap screw (bolt) was fabricated bysqueeze casting. Cold and warm thread rollingwere performed to form a metric screw thread
M3x0.5 (class 6g (ISO)) below the glass transition
temperature using a flat rolling machine asshown in Fig.1. Despite the extremely poor
ductility of MG at room temperature[1], threadrolling was successfully performed[2].
From experimental investigations andstraining analysis by the three-dimensional
finite element method (3D-FEM), we found thatthe mechanisms of the plastic deformation are
as follows:(1) Straining occurred over a limited area
near the surface of the cylindrical specimen
due to the stress distributions during threadrolling.
(2) Large plastic strain without destructive
crack propagation is induced at the screw
thread due to the compressive mean stress
distributions developed throughout the threadrolling process.
(3) Fundamentally, thread rolling is anincremental formation process. The effects ofpreliminarily introduced strain work favorably
by increasing the MG ductility in the deformed
region.
The tensile strength of the thread-rolledbolt was approximately 1600 MPa, which isconsiderably higher than that of conventional
heat-treated high strength steel bolts. We
believe that the process design based on thesemechanisms of plastic working of MG cansignificantly contribute to MG applications.

Fig.1 Processing procedure for Zr-based metallic
glass (MG) bolt

Fig.2 (a) Pre-form for metallic glass (MG) bolt
processed by squeeze casting; (b) thread-rolled
MG bolt at RT (293 K); (c) SEM microphotograph ofscrew thread; (d) magnified image of ridge,
groove, and flank of the screw thread (c)References[1] H. Kato, H. Igarashi and A. Inoue, Mater. Lett. 62, 1592
(2008)[2] S. Yamanaka, K. Amiya, Y. Saotome and A. Inoue, Mater.
Trans., 52, 243(2011)

Keywords: metallic glass, plastic working
Y.Saotome1, K.Amiya1 and S. Yamanaka2
1) Osaka Center for Industrial Materials research
2) Maruemu Works Co. Ltd.
E-mail:saotome@imr.tohoku.ac.jp
URL:http://www.kansaicenter.imr.tohoku.ac.jp

IMR KINKEN Research Highlights 201182

Osaka Center for Industrial Material Research.

C

ollaboration project (Osaka Center) between IMR, Osaka Prefecture Government and enterprises
in Osaka area (especially for Higashi Osaka) sponsored by Ministry of Education, Culture, Sports,
Science and Technology has been completed on March 2011. Through five years activities such as
responding to inquiries from industries and solving them, introducing academic research outputs totransfer to industries, and educate material science regarding application to researchers andtechnicians in industries in order to enhance their core manufacturing technology, Osaka Centerhas established the status in Kansai area to promote academia-industry-government cooperation.

Osaka Center was established in Osaka asa special division in the Institute for Materials
Research, Tohoku University in April 2006 basedon an agreement with Osaka Prefecture
Government. This is the fi rst collaboration
project in Japan between national university
and
local
government
sponsoredbygovernment (Ministry of Education, Culture,
Sports, Science and Technology). It consists oflaboratories dedicated to research anddevelopment of nano-structured metallic
materials with the application viewpoints
based on the materials science, and they areassociated with research organizations in
Kansai area. There are 6 groups in Center;
Preparation, Fabrication, and Processing ofNew
Materials,
AppliedScienceofMicrostructural Controlling, Bio-Materials, andAdministrative Office. The scope of project is tounderstand the fundamentals of metallic
materials and rapid realization of theirapplication to industry, especially, small andmedium enterprises in Osaka area. The second
mission is to solve technical problems in theenterprises
undercollaboration
with
Development Center for New Metallic Material
in Osaka Prefecture University. And the third isto educate material science related to industrial
application to next generation materials
scientists and researchers in universities andenterprises.
Throughout five years' activities, Osaka
Centerproducedseveraldistinguishedachievements. First, six professors in Osaka
Center responded technical inquiries fromindustries by themselves, where the system isdifferent from that of other universities (usually,
coordinators employed by university hear theinquiries and conveyed suitable professors to
respond the inquiries). Figure 1 shows thenumber of inquiries from industries at Creation
Core Higashi Osaka (governmental body,where sixteen local universities and one college
are located to respond inquiries from industries).
A smooth increase of the inquiries with year isevident: 102 in 2007, 263 in 2008, 307 in 2009
and 400 in 2010. The location of the company’shead office is shown in the left figure of Fig. 2,
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IMR KINKEN Research Highlights 2011

and the inquiries are categorized as shown in
the right figure of Fig. 2. This suggests that Osaka
Center has been recognized in whole Kansai
area including Osaka prefecture, and expected
to be a technical advisor in the manufacturingindustry.
Secondly, Osaka Center has opened
technical seminars on special topics twentyfour times to provide scientific knowledge totechnicians and researchers in industries. The

Fig.1 Fraction of inquiries from industries at Creation
Core Higashi Osaka (Sixteen local universities andone college are located): the black part of circle
chart corresponds to Osaka Center.

Fig. 2 Analysis of inquiries from companies to Osaka
Center; the location of company (left) andcategory of inquired content (right).

seminars were organized by the professors inCenter and the topic was selected based on
the industrial needs. Some of the seminars were
held under collaboration with scientificsocieties. Further, the Center professors havelectures on materials design, technical skills
and related fundamentals of materials scienceto the students in Osaka Prefecture University
for the purpose of demonstrating theimportance of material science contributing toindustrial applications. Thirdly, Osaka Center
participates in various technical exhibitions orseminars organized by local governments,
publishers, financiers and incorporated
foundations upon request to introduce theacademic research outputs to industries andtransfer them to applications. Through these
activities, twenty-seven collaboration research

projects between the Osaka Center andcompanies have been established and thirty
innovations were applied for patents. Some of
the collaboration studies have obtainedcompetitive research funds from governments.
As an example, Table I summarizes the output
of production research project sponsored by
Osaka Prefecture in 2007. This project is carriedout by collaboration between Osaka Centerand enterprise in Osaka Prefecture.
Following the Osaka Center project, IMR
has extended the activities of Osaka Center tothe whole Kansai area under collaboration
with Osaka Prefecture Government, which was
adopted by Ministry of Education, Culture,
Sports, Science and Technology. This new
project started in April 2011, and Kansai Center
was launched to replace Osaka Center.

Table 1 Summary of collaborative research project sponsored by Osaka Prefecture(a) Title (b) Academic members

Summary(a) Development of water purification devise
by using TiO2 photocatalysts.
(b) Tohoku University
Prof. Naoya MASAHASHI
Assist. Prof. YoshiteruMIZUKOSHI

Anodic TiO2 photocatalysts
immobilized on the surface of lathstructured Ti effectively bleachedmethylene blue aqueous solution
and exhibits superhydrophilicity. This
device is expected to purify
contaminated water.

(a) Development of surface-hardened Nibase dual two-phase intermetallic alloys(b) Osaka Prefecture University
Prof. Takayuki TAKASUGIAssoc. Prof. Yasuyuki KANENO

Optimal plasma-carburizing and –nitriding condition of Ni base dual
two-phase intermetallic alloy was
found.
Also, the alloy compositions suitablefor plasma surface hardening weredeveloped.

(a) Size control of nickel oxide nanoparticles(b) Tohoku University
Prof. Toyohiko KONNO

Ni oxide nanoparticles with anaverage diameter of 90 nm are now
constantly fabricated, and dispersed
in a liquid phase without
agglomeration by taking
an advantage of surfactant
technology.

(a) Development of the diffractive opticalcomponents of metallic glass(b) Tohoku University
Prof. Yasunori SAOTOMEAssoc. Prof. Hisamichi KIMURA

Nano-imprinting technique of themetallic glass was successfully
applied to the fabrication ofdiffraction gratings
with a period of nano-order.

TiO2 coated lath Ti incorporated
in water purification equipment

Plasma-carburized Ni base dual
two-phase intermetallic alloy
used for FSW toolTransmission
ElectronMicroscopy image of Ni
oxide particles

Surface morphology on nanoimprinted metallic glass

Keywords: partnership between industry, academia and government, technology transfer
N.Masahashi (Kansai Center for Industrial Materials Research)
E-mail: masahasi@imr.tohoku.ac.jp
URL:http://www.kansaicenter.imr.tohoku.ac.jp

IMR KINKEN Research Highlights 201184

highlights collaborated reseach

Magic Monatomic Mn Nanowire Self-Assembly on Si(001)w

e show here by ab initio calculations that an atomistic nucleation process of monoatomic Mnnanowire self-assembly on Si(001) to form a new magic 3n+1 atom dense trimerlike linear chains(DTLCs) driven by pedestal site adsorption. Moreover, the length of DTLCs is limited by a competing
process to form three-dimensional D3h -Mn5 clusters in early stages.
There has been considerable interest in
recent years in manganese and manganesesilicide as promising candidates for spintronics
applications. STM studies reveal that room
temperature deposition leads to preferential
formation of monoatomic Mn wires in earlystages, and small clusters appear at higher
coverage and compete with the wire growth.
Understanding the precise nature of Mn
adsorption sites, the bonding to the Si surface
and the growth mechanism of the nanowire
structures is critical to predicting and tailoring
Mn-Si nanostructure properties.
We here first explore possible diffusion
pathways for a single Mn adatom on Si(001).
When a Mn atom adsorbs on the stablepedestal site P, three possible diffusion pathways
P1, P2, and P3 are considered [1]. The relative
energies are plotted in Fig. 1. The energy
barriers are estimated to be 0.49, 0.48, and 1.06
eV for P1, P2, and P3, respectively. These results
clearly show that Mn adatoms can easily
diffuse along or across the dimer rows, but are
kinetically limited for diving into the subsurface
layer or diffuse into the deep layer at room
temperature on Si(100). To understand thecompeting nature in the formation of the DTLC
and 3D clusters, finite dense trimerlike linear
chains starting from an isolated Mn on thepedestal site are examined. In Fig. 2, we plot
the binding energy versus the pathways to form
the dense-monoatomic Mn wires and D3h -Mn5cluster on Si(001). We find that Mn adatoms on
Si(001) prefer forming a finite DTLC with magic
number of 3n+1(4, 7, 10, …), perpendicular tothe surface dimer rows. They always start fromand end on the P site, driven by the favorable
pedestal site adsorption shown above. These(3n+1) magic DTLCs are more stable than the
PM dimer with a large dissociation barrier (1.121.28 eV for n = 1, 2), and their binding energies
become lower monotonically as n increases.
Because of the induced strain along the wire
stretching direction, the Mn on P site is pushed
down into the substrate, and two M site Mn
adatoms over the trough show a buckled
dimerlike configuration with stress relief (seeFig. 2). Meanwhile, D3h -Mn5 cluster exhibits
similar energetic stability, showing thecompeting growth nature between the wireand 3D cluster.

85

IMR KINKEN Research Highlights 2011

Fig.1 Relative total energy versus the reaction
pathways for ad-Mn diffusion on Si(001) surface.
P1: P->H->P is a hopping pathway, across the dimer
rows; P2: P->T->P is a rolling-over pathway, parallelto the dimer rows; P3: P ->I 0 ->P is an insert pathway
along the surface dimer row.

Fig.2 Atomic binding energy versus the pathways toform a monoatomic Mn-wire (○) or cluster (□) on
Si(001).

References[1] J.T. Wang, C.F. Chen, E.G. Wang, and Y. Kawazoe, Phys.
Rev. Lett. 105, 116102 (2010).

Keywords: nanowire, 3d-metal, silicon surface
J.T. Wang1, C.F. Chen2, E.G. Wang1, Y. Kawazoe3
1) Institute of Physics, CAS, 2) Department of
Physics, UNLV, 3) IMR, Tohoku University
E-mail: wjt@aphy.iphy.ac.cn
http://js.caseducation.cn/JS/~wjt

highlights collaborated reseach

Detection of Rare Earth Dopants at the Atomic Level in
YAG-based Optical Ceramics

In complex oxides, metallic and oxygen atoms occupy several crystallographically non-equivalentsites. The electronic states of the impurities are thus expected to have their origin not only in thenature of impurity atoms themselves, but also in the symmetry of the substituted sites. By employing
wave-front reconstruction techniques on high-resolution TEM images taken under Cs-correctedconditions and Z-contrasts in atomically resolved STEM, we can directly clarify the favorable sites for
dopant atoms.
Understanding the optical properties ofmaterials requires a detailed investigation of
their microstructure, especially regarding theexact location of the required dopants (e.g.
rare earth elements such as Ce3+, Nd3+ or Yb3+).
For example, it was recently shown by careful
Transmission
Electron
Microscopy(TEM)
observations that Ce strongly segregates at
grain-boundaries within YAG (Yttrium Aluminium
Garnet Y3Al5O12) [1].
STEM-HAADF imaging (Scanning TEM in
High Angle Annular Dark Field) consists inscanning the electron probe on the sample,
and collecting on an annular detector the
primary electrons scattered at high angle. In
such a process, the scattered signal is roughly
proportional to Z2, where Z is the atomic numberof the probed species. Then, heavy atoms(such as rare-earth elements) give rise to abrighter contrast that lighter species (such as
O, Al and even Y in the YAG structure). Atomic
resolution is achieved if the probe size is smaller
than the interatomic distance within thematerial of interest under some specific viewing
crystallographic directions.
We have performed both High Resolution(HR) and HAADF imaging on pure YAG and Ybdoped YAG polycrystals, using a TITAN FEI
electron microscope, operating at 300 kV. On
the one hand, this instrument is equipped witha Cs aberration corrector on the objective lens,allowing a resolution down to 0.1 nm to beobtained in the HREM mode[2]. On the other
hand, it is also equipped with an annulardetector collecting electrons in a 70-210 mRadangular range. Nanoprobe chemical analysis
was also simultaneously performed using an
EDAX EDX (Energy-Dispersive X-ray) analyser
mounted on the microscope.
Whereas Cs-corrected HREM failed toreveal the distribution of Yb-containing atomic
columns, the STEM-HAADF imaging mode
appeared to be more efficient owing to its
sensitivity to Z. Fig. 1 shows a comparison of a
1.4 at.%Yb-doped and a pure YAG samples
when observed along the [001] azimuth. A highdensity of brighter columns is observed for the
doped material, which can be consistently

Fig. 1 HAADF-STEM images of two regions of similar
thicknesses (as attested by low-loss EELS spectra)
from a 1.4 at. % Yb-doped sample (left) and a pure
YAG sample (right).

analysed in terms of statistics as imaging Ybcontaining atomic columns. Dedicated
HAADF-STEM image simulations confirm thisfinding. This work shows that no segregation,neither clustering of Yb ions occurs inpolycrystalline YAG.
References[1] W. Zhao, C. Mancini, D. Amans, G. Boulon, T. Epicier, Y.
Min, H. Yagi, T. Yanagitani, T. Yanagida, A. Yoshikawa Jpn.
J. Appl. Physics 49 (2010) 022602[2] K Sato, T.J. Konno, Y. Hirotsu, , J. Appl. Phys. 107 (2010)024304.

Keywords: optical ceramics, Yb-doped YAG,
atomic STEM-HAADF
T. Epicier (INSA-Lyon) and T.J. Konno
E-mail: thierry.epicier@insa-lyon.fr, tjkonno@imr.
tohoku.ac.jp
URL: http://clym.insa-lyon.fr, http://konno-lab.imr.
tohoku.ac.jp/

IMR KINKEN Research Highlights 201186