RESEARCH HIGHLIGHTS 2017
A publication of the WPI Advanced Institute for Materials ResearchTABLE OF CONTENTSMESSAGE FROM THE DIRECTOR
1Advancing collaboration and globalization

RESEARCH HIGHLIGHTSIN THE SPOTLIGHT

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Topological insulators: In control of current
Electrocatalysis: Graphene catalyst splits water
Molecular self-assembly: Entropy versus chemistry
Superconductivity: Fixing electron instability witha dab of molecular glue

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Two-dimensional materials: Atomic sheet not 		so thin after all

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9Magnetization dynamics: Unveiling a hidden effect

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Chemistry: Metals on cloud nine

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Organic optoelectronics: A versatile electrodeMaths makes a material difference in less thanten years

20 Planting the seeds for brand new materials 		
and technology

22 Creating a world-leading materials science center
that transcends borders

Ionic hydrocarbons: Putting an unexpected spinon things
Block copolymers: Mimicking viruses
Topological insulators: Peel-and-stick ultrathin films
Lithium–oxygen batteries: Reactions observed 		
under the microscope
Nanoporous gold: Engineering surfaces to makebetter catalysts

WPI Advanced Institute forMaterials Research
The Advanced Institute for Materials
Research (AIMR) at Tohoku University
in Sendai, Japan, was launched in 2007 as
one of the centers established by the World
Premier International Research Center
Initiative (WPI) with the support of theJapanese Ministry of Education, Culture,
Sports, Science and Technology (MEXT).
Since then, the AIMR has been bringing
together world-class researchers fromJapan and abroad to carry out cuttingedge research in materials science throughinterdisciplinary collaboration among its
four materials-related groups — Materials
Physics, Non-equilibrium Materials, Soft
Materials, Device/System — and theMathematical Science Group.

In 2017, the AIMR became a memberof the WPI Academy, which consists of
WPI centers that have achieved worldpremier status. The institute will continue
to maintain its world-class research
environment and further promote global
brain circulation.
Led by distinguished mathematician
and director Motoko Kotani, the institutepromotes interdisciplinary researchacross the different groups. It also fosters
young researchers through the Global
Intellectual Incubation and Integration
Laboratory (GI3 Lab). This uniqueprogram, which is currently supportedby the WPI Academy, promotesinternational joint research conductedin close cooperation with high-profile
researchers invited from countries
around the world.

The AIMR is host to about 100 leading
researchers, around half of whom comefrom abroad, including 28 principal
and junior principal investigators. In
addition to the research hub at Tohoku
University, the AIMR collaborates withresearch centers in China, Germany,
Poland, the UK and the US. Close ties
with other leading overseas institutes aremaintained, going along with the efforts
of foreign principal and junior principal
investigators, as well as adjunct professors
and associate professors.

MESSAGE FROM THE DIRECTOR

Advancing collaborationand globalization
Established in 2007 as part of the Japanese govern-

Innovation Laboratory (MathAM−OIL) has madement’s World Premier International Research Centersteady progress in fusing fundamental research by

Initiative (WPI), the AIMR was tasked with becoming

the AIMR with AIST’s research, which focuses ona world-class research center. Since then, it has beencollaborating with industry. MathAM−OIL has been

striving to fulfill the four missions of the WPI: advanc-working to rapidly develop next-generation materi-ing top-level research, creating international research

als and create new research fields. Researchers at

environments, reforming research organizations

MathAM−OIL and Tohoku University (predominately

and exploring new fields through interdisciplinary

AIMR researchers) take part in daily events at bothresearch. To this end, it has attracted top researchers

institutions, including MathAM−OIL’s seminars andfrom all over the world. In April 2017, the AIMR

laboratory meetings and AIMR’s Friday Tea Time,embarked on a new stage of expanding its international

deepening cooperation between the two institutions.

collaboration while maintaining top-level research as amember of the newly established WPI Academy.

Another milestone has been the selection of
Tohoku University by the Japanese government as

The AIMR stands alone in its goal of promoting

one of three Designated National Universities in June

collaboration between mathematics and materials

2017. These universities are expected to contribute toscience. By using the universal language of math-global development through education and researchematics to describe materials, AIMR researchers areat a world premier level and represent Japanese

discovering commonalities between diverse materials

universities on the world stage. Tohoku University

and creating new research topics and outcomes. Thishas developed strategies for human resource educa-

rare approach of institute-level collaborations between

tion, research capabilities, governance reform andmathematicians and materials scientists demonstrates

collaboration with society, and will further advancethat the AIMR is a truly progressive institution.

internationalization. As a part of the effort to improve

To promote this exciting vision, the AIMR

research capabilities, research centers are planned

exchanges with overseas researchers and institutions

in four fields in which the university is renowned:

with the aim of building an international network

materials science, spintronics, next-generation

based on its pioneering research. In February

medical care and disaster science. The AIMR will play2017, the AIMR International Symposium 2017a central role in establishing the materials science(AMIS2017) drew over 270 researchers fromresearch center, and it will continue working toward

11 countries. The 23 invited speakers included Albert

the creation of new materials science.

Fert, a physicist at the University of Paris-Sud andI would like to thank all of you who have support-

recipient of the 2007 Nobel Prize in physics, Hideo

ed us. We at the AIMR are happy to be at the heart

Hosono, a materials scientist of the Tokyo Institute ofof building an international research environment at

Technology and 2016 Japan Prize winner, and math-

Tohoku University in its new capacity as a Designatedematician John Ball, the Sedleian Professor of Natural

National University. We will continue to advance

Philosophy at the University of Oxford and a former

forefront research and maintain our standing as a hub

president of the International Mathematical Union.

of global brain circulation, as well as contribute to the

To forge closer links with society, the newdevelopment of materials science and society.

joint research center AIST−Tohoku University
Mat hemat ics for Advance d Mater ia ls−O p en

Motoko Kotani, Director of AIMRRESEARCH HIGHLIGHTSRESEARCH HIGHLIGHTS
The AIMR advances research in materials physics, nonequilibrium materials, soft materials and devices/systems, andactively promotes collaboration among these divisions toward
the development of ground-breaking technologies that crossthe boundaries of conventional fields of study — bridging thedisciplines of materials science, physics, chemistry and precision,mechanical, electronics and information engineering. The
Mathematical Science Group further complements the AIMR’s
research activities.

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AIMResearch 2017

RESEARCH HIGHLIGHTS

Topological insulators:

In control of current

ce

ur

So

Reproduced from Ref. 1 and licensed under CC BY 4.0 (creativecommons.
org/licenses/by/4.0/legalcode ) © 2016 N. H. Tu et al.

A device capable of controlling the currents that flow on the surfaces of topologicalinsulators has been demonstrated for the first time

ain

Dr

SiO2 (300nm)

Si (Back gate)

AIMR researchers have fabricated a topological p–n junction in a three-dimensional topological insulator and used it to control surface currents.

A junction that can be used to control
currents flowing on the surfaces of aclass of exciting new materials has beendeveloped by AIMR researchers1. It
promises to be useful for realizing compact, ultralow-power memory devices.
Exotic materials known as threedimensional topological insulators
are generating a lot of buzz amongscientists because they could realize therevolutionary, power-saving technology of spintronics. Unlike electronics,
which relies on the charge of electrons,
spintronics mainly exploits a quantum
property of electrons known as spin.
While the interior of a topologicalinsulator is an electrical insulator, currents can freely flow on its surface withvery low loss. But before these materials
can be used for spintronics, researchers
need to find ways to control the flow ofcurrent on their surfaces.
Elements known as p−n junctions
are often used to control current inconventional electronic devices. They
are so-called because they consist of

AIMResearch 2017

two sections: one containing a dearth ofelectrons (the positive ‘p’ side) and theother containing an excess of electrons(the negative ‘n’ side). Currents can flowfrom the p to the n side, but not in the
opposite direction.
However, conventional p−n junctions
cannot be used to control current flowon the surfaces of topological insulators.
Thus, the researchers needed to find aconvenient way to switch currents on
and off in these promising materials.
Katsumi Tanigaki, Yoichi Tanabe andtheir colleagues of the AIMR at Tohoku
University fabricated their topologicalp–n junction on the surface of an ultrathin film of the topological insulator
Bi1.5Sb0.5Te1.7Se1.3. They created the p sideof the junction by adding a layer of anelectron-accepting organic molecule totune the chemical potential of the topological insulator.
But that by itself was not enough toform the junction. “Because the threedimensional topological insulator has
top and bottom surfaces, the chemical

potentials of both surfaces have to becarefully controlled,” explains Tanabe,leader of the project in Tanigaki’s group.
The researchers achieved this by combining the organic molecule layer with afield-effect transistor technique.
When they did this, they observed adramatic change in electrical transport
on varying the gate voltage. Thus, thecurrent flow could be controlled bysimply varying the voltage applied tothe junction.
The scientists are now working on
optimizing their junction. “A very
high gate voltage is needed to switch
the topological p–n junction on andoff,” says Tanabe. “We are trying to
reduce the switching voltage by using
different combinations of materials andorganic molecules.”
1. Tu, N. H., Tanabe, Y., Satake, Y., Huynh, K. K. &Tanigaki, K. In-plane topological p-n junctionin the three-dimensional topological insulator
Bi2−xSbxTe3−ySey. Nature Communications 7,13763 (2016).

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Electrocatalysis:

Graphene catalyst splits water

A carbon-based material has been transformed into a catalyst that uses electricity
to split water, producing clean-burninghydrogen gas1.
“Electrolysis of water is becoming
more important as a way to store energy
from renewable sources such as wind,sunlight and water,” says Yoshikazu Ito of
the AIMR at Tohoku University. “Since
conventional platinum electrodes areprohibitively expensive, we are exploring
the use of metal-free electrodes.”The new catalytic electrode is basedon graphene — atom-thin sheets ofcarbon atoms that are strong, flexible
and electrically conductive. Theoreticalpredictions suggest that adding atoms ofsulfur, phosphorus and nitrogen shouldmake graphene-based electrodes as
effective as platinum ones. But, in practice, the performance of these ‘doped’graphene electrodes has not met these
expectations.
Now, a team led by AIMR’s Ito andMingwei Chen has improved these graphene electrodes by carefully controllingthe amounts and positions of different
dopant atoms in the material.
Using nickel nanoparticles as porous
templates, the researchers added different
mixtures of gases that contained carbon,hydrogen, sulfur, nitrogen or phosphorus. When heated to 750 degrees Celsius,
this coated the nickel’s nanopores witha layer of graphene three to six atoms
thick and included various amountsof dopant atoms. Dissolving the nickel
template with acid left graphene withpores ranging in size between 50 and
2,000 nanometers. These pores provide
a larger surface area for the hydrogenions in water to access catalytically active
chemical sites within the material.

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x85,000© 2017 Yoshikazu Ito

A sprinkling of nitrogen, sulfur and phosphorus boosts the ability of nanoporousgraphene to generate hydrogen gas

0.2µm

The tiny pores in this graphene particle contain traces of nitrogen, sulfur and phosphorus that help to liberatehydrogen gas from water.

Employing templates with smaller
pores produced graphene that was morecurved, creating defects in its structurethat could be occupied by dopant atoms.
Graphene with pores between 50 and
100 nanometers across had the highest
loading of all three dopant atoms, inpositions that were more chemicallyreactive (see image).
The team measured the hydrogengenerating performance of various
nanoporous graphene samples, variously
containing one, two or all three typesof dopants, and compared them with
undoped nanoporous graphene. They
found that the tri-doped nanoporousgraphene offered the greatest improvement in catalytic activity, although it did
not match that of a platinum electrode.

The researchers suggest that thepresence of three different types of
dopant atoms alters the distributionof electrical charge on graphene’s
surface, offering a balance of negativeand positive regions that first adsorb
hydrogen atoms (H) and then desorb
hydrogen molecules (H2) during thereaction. Using pore size to control
this doping should allow them to finetune the material and further boost its
catalytic properties.
1. Ito, Y., Shen, Y., Hojo, D., Itagaki, Y., Fujita, T.,
Chen, L., Aida, T., Tang, Z., Adschiri, T. & Chen,
M. Correlation between chemical dopants
and topological defects in catalytically active
nanoporous graphene. Advanced Materials 28,
10644–10651 (2016).

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Molecular self-assembly:

Entropy versus chemistry

There is more to entropy than the concept of disorder, a team from the AIMRat Tohoku University and the iCeMS
at Kyoto University has shown. Theymodeled entropy’s role in molecular
self-assembly reactions and found that,
under certain conditions, using entropy
rather than chemistry to control areaction can enhance the formation ofordered nanostructures1. This discovery
is significant for the manufacture ofnanoscale electronics.
Most methods for manufacturing
electronic components employ top-down
approaches that involve ‘chiseling away’at large structures. In contrast, bottom-up
methods involve connecting small parts
to form larger structures. As electronic
components become ever smaller, there
is an increasing push to use bottom-up
processes to fabricate them. A particularly promising bottom-up method is molecular self-assembly in which groups ofmolecules spontaneously cluster together
to form complex structures.
“Using molecular self-assembly, it’scurrently possible to create tiny electricalwires with diameters of just a few carbon
atoms,” says Daniel Packwood, leader ofthe research team. “By improving ourability to control the molecular selfassembly process, we can imagine moving from making tiny electrical wires
to making tiny electrical circuits, andeventually to tiny electrical devices.”
To better understand the factors
controlling the self-assembled structuresthat form, Packwood and colleagues
examined the self-assembly of a seriesof anthracene-based organic molecules
on a copper surface. Two factors are atplay: chemical control — a measure of
the strength of the chemical interaction

AIMResearch 2017© 2017 Daniel Packwood

The factors controlling the bottom-up synthesis of nanomaterials have been madeclearer by a new mathematical model

Increasing the entropic control of a self-assembly reaction can enhance the formation of ordered wire-likestructures.

between molecules; and entropic control, which varies according to the temperature the reaction is run at. The teamconsidered the conditions under which
wire-like structures formed, as opposed
to disordered islands of molecules clustered on the metal’s surface.
“We first deduced an accurate mathematical formula for entropic control,”
Packwood explains. “By studying how
this formula worked, we could unambiguously deduce the effects of entropic
control.” By running a simulation of theself-assembling reaction, any effects not
explained by the formula for the entropic control could thus be identified as
effects of chemical control.
Surprisingly, the team showed that
adjusting the reaction temperature toincrease entropic control of a reaction

made it more likely that large disordered islands of molecules would break
up into their molecular components
again — freeing them to form ordered
wire-like structures and increasing the
proportion of ordered structures that
ultimately form.
“Our results show that a careful analysisof entropy, beyond the broad concept ofdisorder, is necessary to properly understand how entropy affects molecular selfassembly,” Packwood says. “We intend
to apply these rules to a real laboratory
setting and demonstrate their value inproducing new materials,” he adds.
1. Packwood, D. M., Han, P. & Hitosugi, T. Chemicaland entropic control on the molecular
self-assembly process. Nature Communications
8, 14463 (2017).

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RESEARCH HIGHLIGHTS

Superconductivity:

Fixing electron instability
with a dab of molecular glue
Electrons in superconductors made of carbon nanospheres remain paired even whensubjected to high magnetic fields

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e-

-k
e

-

H

k
© 2017 Kosmas Prassides

Most superconductors are made frommetal atoms and usually achieve
resistance-free electron transport at
frigid temperatures. AIMR researchers and colleagues at the University ofTokyo and Kyoto University have now
shown that switching to unorthodox‘buckyball’ molecules can keep electrons superconducting under morepractical conditions1.
Below a certain temperature, known
as the critical temperature, electrons insuperconductors experience strong attractions that cause them to pair up andtransport charge without losing energy.
However, this coupling can be disrupted
by other forces, including external
magnetic fields. This makes it tricky toincorporate superconducting elements
into devices that operate at high fields or
carry large electric currents, hence limiting their applications.
“The critical magnetic field reflects thepairing interactions in a superconductor — it shows how strong the glue is thatkeeps the electrons together,” explains
Kosmas Prassides from the AIMR. “Oneof the holy grails of this field is to find asuperconductor that is not affected bymagnets at useful fields, regardless ofwhich direction the field points in.”Prassides and his co-workers recently
discovered that hollow carbon spheres
known as buckyballs (C60) may provide
the answer. When synthesized into
cubic crystals alongside cesium ions,
C60 is an insulator. But by applying
pressure to the crystal — either by using
external anvil presses or by substituting atoms in its internal lattice — thematerial becomes superconducting.
Balancing contributions to this statefrom C60 molecular distortions and theAn unconventional superconductor made from buckyballs (large ‘soccer balls’) and metal ions (small red andgreen spheres) can withstand stronger magnetic fields than any known three-dimensional solid.

conductive crystal lattice produced thehighest working temperature ever seen
for a molecular superconductor.
Although theory predicts materials
with high critical temperatures should
resist magnetic fields, the team was taken
aback at the magnitude of buckyballresilience — trials with a full complement of modern magnetic instruments
could not decouple its electrons. Now,
thanks to the powerful National High
Magnetic Field Laboratory at Los
Alamos in the US, the researchers havemeasured its direction-independent,
critical magnetic field value: a recordsetting 90 teslas, or nearly two million
times the Earth’s magnetic field.
“Our glue was remarkable — it
far exceeded our expectations,” says
Prassides. “The strength comes from theelectronic structure of the C60 moleculeand how it cooperates with the electron
correlations.”
Prassides notes that this mechanism
enables fine-tuning of superconducting
behavior using synthetic chemistry — amore promising way to increase theoperating temperature than the conventional method based on substituting
metal atoms. “A challenge for chemists
is to design molecular materials to be
the fundamental building units of asuperconductor,” he says.
1. Kasahara, Y., Takeuchi, Y., Zadik, R. H.,
Takabayashi, Y., Colman, R. H., McDonald, R. D.,
Rosseinsky, M. J., Prassides, K. & Iwasa, Y. Upper
critical field reaches 90 tesla near the Mott
transition in fulleride superconductors. Nature
Communications 8, 14467 (2017).

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RESEARCH HIGHLIGHTS

Two-dimensional materials:

Atomic sheet not so thin after all

AIMR researchers have succeeded inmeasuring the three-dimensional structure of single layers of molybdenum
disulfide (MoS2)1.
Two-dimensional materials are socalled because they are single sheets ofunit cells. While graphene is the twodimensional material that has been
grabbing the most headlines, its lack ofa band gap limits its use in electronic
applications. A class of materials known
as transition-metal dichalcogenides(TMDs) shares some of the advantagesof graphene but also has band gaps.
Now, Ziqian Wang, a graduate
student of Mingwei Chen, of the AIMRat Tohoku University, and co-workers
have shown for the first time that it ispossible to glean three-dimensional
information from a monolayer of the
TMD molybdenum disulfide by using
dynamic electron scattering. This
technique allowed them to distinguishbetween two phases of the material:
the semiconducting 1H phase and themetallic 1T phase. These two phases
have different symmetries and can betransformed from one to another by‘gliding’ a layer of sulfur atoms in MoS2.
Characterizing the three-dimensional structure of a two-dimensional
material may seem like a contradictionin terms. But not all two-dimensional
materials are perfectly flat — there is an
intrinsic structure in the three-atomiclayer material so that some of theiratoms lie above and beneath the planeof the sheet.
This intrinsic structure is important.
“The three-dimensional structure may
influence MoS2’s material properties
as well as the properties of heterojunctions or stacking layers formed

AIMResearch 2017© 2017 Ziqian Wang

Electron diffraction reveals the three-dimensional structure of a promisingmonolayer material for the first time

Different electron diffraction patters are obtained from the semiconducting 1H phase (left) and the metallic
1T phase (right) of molybdenum disulfide (large blue spheres: molybdenum atoms; small yellow spheres: sulfur
atoms). One phase can be converted into the other by ‘gliding’ a layer of sulfur atoms (indicated by black arrows).

by combining MoS2 monolayers withother two-dimensional materials,”
explains Wang. In the case of MoS2,
the three-dimensional structure of thetwo-dimensional TMD material is critical for gaining a better understandingof the underlying mechanisms of themetal−semiconductor transition as
well as for designing TMD electronic
devices containing 1T−1H interfaces as
metal−semiconductor conducts.
Images obtained by high-resolution
electron microscopy techniques suppress this steric structure because they
are basically two-dimensional projections of three-dimensional structures.
In contrast, the dynamic scattering that
occurs when an electron beam interacts
with a monolayer sample encodes
three-dimensional information in the
resulting diffraction pattern. Thus, bycomparing the intensities of diffraction

spots within the pattern, researchers
can recover information about thethree-dimensional structure.
“Extracting three-dimensional information by analyzing electron diffraction
patterns may compensate the weak pointsof transmission electron microscopy andscanning transmission electron microscopy imaging, especially for studying
two-dimensional materials,” says Wang.
“This technique should also be
applicable to other monolayer TMDs withthe same phases and structures,” notes
Wang. “And similar analyses of diffraction patterns should be useful for determining the three-dimensional structuresof other two-dimensional materials.”
1. Wang, Z., Ning, S., Fujita, T., Hirata, A. & Chen, M.
Unveiling three-dimensional stacking sequencesof 1T phase MoS2 monolayers by electron
diffraction. ACS Nano 10, 10308–10316 (2016).

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RESEARCH HIGHLIGHTS

Magnetization dynamics:

Unveiling a hidden effect

A neglected aspect of the physics of magnetic thin films plays a crucial role in theirmagnetic properties, AIMR researchers
have discovered1. This finding has important implications for practical technologies employing spin-based nanodevices.
Many emerging technologies rely on
how the magnetism of a material varies
with time. Magnetization dynamics, as
it is known, is especially important for
spintronic devices, which exploit theangular momentum of an electron — its
spin — rather than its charge, which isthe basis of conventional electronics.
The spectroscopic technique known
as ferromagnetic resonance (FMR) is astandard tool that material scientists employ to explore magnetization dynamics.
It is used to probe the magnetization offerromagnetic materials — those which,like iron, have a permanent magnetization because the spins of their electrons
are aligned.
Now, Fumihiro Matsukura of the
AIMR at Tohoku University and his coworkers have found that a missing pieceof physics is needed to correctly interpret
FMR spectra of ferromagnetic systems
made from different materials.
They explored how the widths of thelines in FMR spectra of thin films of
CoFeB–MgO — a promising building
block for high-performance nanoscale
spintronic devices — varied with temperature and film thickness. To theirsurprise, the team found that the FMR
linewidths became narrower with increasing temperature. After eliminatingother possible causes, they concluded
that this was due to motional narrowing — an effect that originates fromthermal fluctuations at the interface between two different materials. Motional8© kyoshino/E+/Getty

An overlooked mechanism is found to be critical in material systems used forspintronic applications

AIMR researchers have found a missing piece of physics that is needed to correctly interpret ferromagnetic
resonance spectra of systems made from different ferromagnetic materials.

narrowing had been overlooked inprevious studies as it was masked by thebulk properties of ferromagnetic materials. It has come to light now becauseof advances in technology associatedwith ferromagnetic systems made fromdifferent materials.
“This finding came as a surprise to us,”says Matsukura. “About two years ago,
research groups at Tohoku University
and Nanyang Technological University in
Singapore independently observed thatthe widths of some lines in FMR spectra
varied strangely with temperature. We
started collaborating with these groups,
but we initially couldn’t explain the experimental results. It was through discussions with a theoretical group at the Japan
Atomic Energy Agency that we came tounderstand what was happening.”“Since systems containing interfaces
between two different materials havebeen used to develop many spintronic
applications, it’s vital to examine motional narrowing in other material systems
besides CoFeB–MgO,” notes Matsukura.
“Our result is expected to bring a newconcept to spintronic devices, namely
the control of interfacial anisotropy byexternal means,” he adds.
1. Okada, A., He, S., Gu, B., Kanai, S., Soumyanarayanan, A., Lim, S. T., Tran, M., Mori, M., Maekawa,S., Matsukura, F. et al. Magnetization dynamics
and its scattering mechanism in thin CoFeB
films with interfacial anisotropy. Proceedingsof the National Academy of Sciences USA 114,
3815–3820 (2017).

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Ionic hydrocarbons:

Putting an unexpected spinon things
Inserting alkali metals into hydrocarbons containing multiple aromatic rings
has long been touted as a promising way
to make high-temperature superconductors, but issues with their characterization have prevented this from being
confirmed. AIMR researchers and theirinternational collaborators have now
developed two complementary routes
for synthesizing these materials, allowing them to be fully scrutinized for the
first time — with surprising results1,2.
“Previously, it was claimed that because an alkali metal and a polyaromatichydrocarbon had been heated together
at high temperatures, the resulting
black solid was an ionic salt. Since noone was able to isolate phase-pure materials, it wasn’t possible to determine
the stoichiometry, structure, etc., andno property was ever authenticated,”
explains team leader Kosmas Prassides
from the AIMR at Tohoku University.
“The previous high-temperature routes
produced complex mixtures due to thedecomposition of polyaromatic hydrocarbons molecules,” he adds.
The two soft-chemistry methods
designed by his team avoid destroying
the polyaromatic hydrocarbons. The first
involves a low-temperature reduction
in a solution to produce two cesium
salts of phenanthrene: Cs(C14H10) andCs2(C14H10). The second is a solid-stateroute using a redox-controlled reducing
agent to make two potassium–C22H14
structures: K2picene and K2pentacene.
The team obtained crystal structures
for all four polyaromatic hydrocarbons.
“No experimentally determined crystal
structures had previously been reported
for any member of this class of materials,” notes Prassides.

AIMResearch 2017© 2017 Kosmas Prassides

Two gentle synthetic routes offer access to pure ionic salts of polyaromatichydrocarbons for the first time

The structure of the ionic hydrocarbon that hosts a quantum spin liquid. Each molecular ion has one spin(shown as a gray arrow), and the spins perpetually fluctuate, even down to low temperatures. The figure
shows one of an infinite number of entangled spin arrangements.

When the team assessed the propertiesof the polyaromatic hydrocarbons, they
were surprised to discover that none ofthem were superconductors.
Even more unexpectedly, one of thematerials, Cs(C14H10), turned out to bea candidate quantum spin liquid (seeimage) — a state of matter proposedover four decades ago but that had notbeen experimentally realized until now.
“The spins in a quantum spin liquid
never order — they continue to fluctuate
rapidly even at a temperature of absolutezero,” says Prassides. “Each individual
spin points simultaneously along an
infinite number of directions and ishighly entangled with other spins. As
such, quantum spin liquids are predicted
to host many exotic phenomena of
fundamental and technological interest.”Potential applications include data storage for quantum computers.
“Cs(C14H10) adopts a complex
magnetically frustrated topology andprovides a rare example of a candidate

quantum spin liquid, the first one
arising from carbon π-electrons,”
Prassides says.
Since there is a vast number ofpolyaromatic hydrocarbons, these routes
will allow access to a compositionally,
structurally and electronically diverse
class of materials, notes Prassides. “We
are currently synthesizing more of themand exploring their conduction andmagnetic properties at temperatures
close to absolute zero.”
1. Takabayashi, Y., Menelaou, M., Tamura, H.,
Takemori, N., Koretsune, T., Štefančič, A., Klupp,
G., Buurma, A. J. C., Nomura, Y., Arita, R. et al.
π-electron S=½ quantum-spin-liquid state inan ionic polyaromatic hydrocarbon. Nature
Chemistry 9, 635–643 (2017).
2. Romero, F. D., Pitcher, M. J., Hiley, C. I., Whitehead,
G. F. S., Kar, S., Ganin, A. Y., Antypov, D., Collins,
C., Dyer, M. S., Klupp, G. et al. Redox-controlled
potassium intercalation into two polyaromatichydrocarbon solids. Nature Chemistry 9,
644–652 (2017).

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RESEARCH HIGHLIGHTS

Chemistry:

Metals on cloud nine

A quartet of chemical compounds, eachcontaining metal atoms surrounded bya remarkable nine hydrogen atoms, hasbeen created by researchers at the AIMR1.
These compounds are potentially usefulfor hydrogen-storage applications or as
battery components, and one of them
may also exhibit superconductivity.
Such nine-fold coordination of hydrogen is extremely rare. Until now, only
two metals, rhenium and technetium,
were known to form such complexes,
with other metals coordinating fewerhydrogen atoms.
Shigeyuki Takagi, a member of Shinichi Orimo’s laboratory in the AIMR at
Tohoku University, and colleagues used
thermodynamic and electron distribution calculations to predict that the metals molybdenum, tungsten, niobium andtantalum should be able to coordinate
nine hydrogen atoms.
The team then made the complexes
by mixing the powdered metals withlithium hydride and forming the ingredients into pellets. They squeezed
the pellets under a very high pressure
with hydrogen gas and heated them toaround 700 degrees Celsius for up to
2 days. After isolating the products, theresearchers characterized them using
techniques such as neutron diffraction
and Raman spectroscopy.
This analysis revealed that each metal
atom was surrounded by nine hydrogenatoms, forming a shape known as a tricapped trigonal prism, which matched
the team’s predictions (see image). These
metal hydride clusters formed a regular
crystalline lattice, with lithium andhydrogen atoms filling the gaps between
them. This arrangement gives the compounds a very high hydrogen density,10

© 2017 Shigeyuki Takagi

An impressive nine hydrogen atoms can crowd around metal centers, forming
compounds that are promising for storing hydrogen gas or fabricating
battery components

Metal atoms (green spheres: molybdenum, tungsten, niobium or tantalum) can draw nine hydrogen atoms(blue spheres) around themselves, forming crystalline compounds that contain potentially mobile lithium
ions (red spheres).

which makes them promising for storinghydrogen. “One of our next targets is toexperimentally demonstrate the superiorhydrogen-storage properties of our materials,” says Takagi.
The materials are all electrical insulators, but the team calculates that undereven higher pressures the molybdenum
complex could become metallic, allowing it to conduct a current. Moreover,the electrons mobilized under these
conditions may even enable the material to superconduct at relatively hightemperatures, says Takagi.
Calculations also indicated that themetal hydride complex in the molybdenum compound should be able to rotate,suggesting that lithium ions between thecomplexes might be able to move aroundinside the crystal and conduct electricity.

“We recently conducted first-principles
molecular dynamics calculations to examine lithium-ion conduction in the material and found a very high conductivity
that exceeds those of currently known
lithium-ion conductors,” says Takagi.
The team now hopes to experimentallyconfirm that this lithium-ion conduction
occurs. “Subsequently, we will try toassemble all-solid-state lithium-ion
batteries using our hydrides as solid-stateelectrolytes,” says Takagi. “We will also
continue to further explore hydrogenrich materials.”
1. Takagi, S., Iijima, Y., Sato, T., Saitoh, H., Ikeda,
K., Otomo, T., Miwa, K., Ikeshoji, T. & Orimo, S.
Formation of novel transition metal hydridecomplexes with ninefold hydrogen coordination.
Scientific Reports 7, 44253 (2017).

AIMResearch 2017

RESEARCH HIGHLIGHTS

Block copolymers:

Mimicking viruses

An AIMR researcher and two co-workers have successfully produced nanoparticles with virus-like properties by using
a diblock copolymer — a polymer whose
chains consist of alternating sections,or blocks, of two polymers1. Not only
are these particles similar in size to viruses, they also have surface structures
resembling those of viruses. This makes
them promising for various applications,
including vaccines, drug delivery andtesting for infectious diseases.
A virus is essentially a piece of genetic material wrapped in a protein coat,
which has a regular array of proteins
protruding from it. Chemists have longdesired the ability to make virus-likeparticles from synthetic polymers, as
they would be useful as vaccines andfor delivering genes or drugs. But it has
proved challenging to control the stringing together of monomers — the building blocks of polymers — in the same
way that nature does. It is also difficult
to form structures consisting of different
phases in nanoparticles.
Now, Yutaro Hirai of Tohoku
University, together with Hiroshi Yabu of
AIMR at Tohoku University and Takeshi
Wakiya of Sekisui Chemical Co. Ltd,
have realized this by making sphericalpolymer particles that have regularly
arranged bumps on their surfaces (upper
left of image) — just like viruses do.
The team achieved this by using a
diblock polymer whose chains consistof alternating sections made up ofpolystyrene and poly(butyl acrylate)monomers. They were able to vary theshapes of the particles’ surface structures by adding a third component to
the mixture: pure polystyrene of different molecular lengths.

AIMResearch 2017

Adapted from Ref. 1 with permission from The Royal Society of Chemistry

Scientists are closer to synthesizing artificial molecular machines in the lab with the
production of virus-like polymer particles

By forming phase-separated structures in particles, researchers have produced virus-like particles witha regular array of bumps on their surfaces (upper left). When these particles are treated with acid, theydisintegrate into small particles (bottom right).

“These results are a significant step
toward realizing synthetic molecularmachines, which are expected to havea wide variety of applications,” comments Hirai. “For example, antigens or
antibodies can be fixed to the bumps bycontrolling their density. Such particles
should enable efficient and highly sensitive immunological assays.”“Also, enzymes or catalysts can be
attached to the bumps and then transported to specific sites in the body,”
continues Hirai. “Unlike conventionalsmooth nanoparticles, the density andposition of the antibody or catalyst canbe controlled and there is no danger ofsuch molecules aggregating together.”
Furthermore, when treated with acid,the virus-like particles disintegrated

into daughter particles that were only
a few tens of nanometers in diameter(lower right of image). This property
also mimics viruses since they disassemble in response to environmental
conditions in order to enter cells,
which they subsequently infect with
their DNA.
The team plans to phase-selectively
modify the virus-like particles withcatalysts or enzymes to achieve a higher
chemical performance than conventional spherical particles.
1. Hirai, Y., Wakiya, T. & Yabu, H. Virus-like particles
composed of sphere-forming polystyrene-blockpoly(t-butyl acrylate) (PS-b-PtBA) and control ofsurface morphology by homopolymer blending.
Polymer Chemistry 8, 1754–1759 (2017).

11

RESEARCH HIGHLIGHTS

Topological insulators:

Peel-and-stick ultrathin films

A clever way of making thin films of
exotic materials known as topologicalinsulators has been developed by AIMR
researchers1. It promises to overcome
obstacles to the use of these emerging
materials in electronic devices, including
high-mobility transistors and thermoelectric devices for converting waste heat
into useful electricity.
Topological insulators are generating much excitement among scientists
because of their intriguing electricaland magnetic properties. In particular,
they conduct electricity on their surfaces
but are insulating in their interiors. This
makes them suitable for use in the burgeoning area of spintronics, which isbased on manipulating the spins ofelectrons rather than their charges. But
to realize applications, a way is needed to
produce large areas of high-quality threedimensional topological insulators thatare highly insulating in their interiors on
a variety of substrates, including silicon.
Now, Katsumi Tanigaki and colleaguesof the AIMR at Tohoku University haverealized such a method for fabricating
one of the most important topological insulators, Bi2−xSbxTe3−ySey (BSTS),on a wide range of surfaces. They firstgrew an ultrathin film of high-quality,
single-crystal BSTS on a mica substrateusing physical vapor deposition. The
researchers then immersed the system inwater, peeled the film from the mica andtransferred it to other substrates.
The transferred thin films exhibited
excellent properties, including good electron and hole mobilities and spin chirality texture, indicating that they had notbeen damaged during transfer between
substrates. Importantly, the researchers
could produce large areas of BSTS films

12© 2017 Katsumi Tanigaki

A new fabrication technique produces large areas of ultrathin films of a topologicalinsulator on a variety of substrates

A photograph showing a large-area ultrathin film of the topological insulator Bi2−xSbxTe3−ySey (BSTS).

of about 1 square centimeter in size (seeimage). Furthermore, the fabrication
method does not require a catalyst — acommon source of impurities in othercrystal-growth techniques.
“The most serious problem withthree-dimensional topological materials has been that defects in their crystal
structures have meant that their interiors
are not perfectly insulating,” explains
Tanigaki. “To achieve a pure topologicalsurface, it is thus vital to minimize holes
and electrons coming from the interior.
Our thin-film crystal-growth techniquerealizes such an ideal situation.”
The ability to transfer films to different
substrates is very useful. “Today’s electronic devices are fabricated almost exclusively by silicon-based technology. Our
technique is a promising way to produce

three-dimensional topological thin films
on silicon substrates,” says Tanigaki.
“Such thin films can also be transferred totransparent plastics for applications suchas flexible wearable electronics.”
The researchers are exploring using
the technique to produce thin films ofother three-dimensional topological insulators. They are also looking at developing thermoelectric materials based on
topological surface states, which could
be used in devices that convert waste
heat into electricity.
1. Tu, N. H., Tanabe, Y., Satake, Y., Huynh, K. K., Le,
P. H., Matsushita, S. Y. & Tanigaki, K. Large-area
and transferred high-quality three-dimensional
topological insulator Bi2−xSbxTe3−ySey ultrathin
film by catalyst-free physical vapor deposition.
Nano Letters 17, 2354–2360 (2017).

AIMResearch 2017

RESEARCH HIGHLIGHTS

Lithium–oxygen batteries:

Reactions observed underthe microscope
A specially designed liquid cell for an electron microscope enables lithium–oxygen
batteries to be probed as never before

AIMResearch 2017

Electron beam

Liquid electrolyte

electrolyte

Li2O2electrode© 2017 Jiuhui Han

By using a state-of-the-art electron
microscope, AIMR researchers have explored the inner workings of a lithium–oxygen battery1. The insights gained
from these observations will facilitate
the development of high-performance,next-generation batteries.
All batteries consist of an ionically conductive material (electrolyte) sandwiched
between two electrodes. Lithium–oxygen
batteries can potentially store more energy per battery weight than any other kindof battery, making them suitable as nextgeneration batteries for powering electricvehicles and storing electricity generated
by renewable sources. But many hurdles
need to be overcome before they can beused in practical applications.
Most of these problems stem from lithium–oxygen batteries’ high overpotential— the difference between the theoreticalpotential predicted by thermodynamics
and that observed in actual experiments.
One way around this deficit is to use a‘redox mediator’, which transfers charge
between the electrode and the lithiumoxide that forms during discharging.
However, a better understanding of theprocesses occurring inside batteries isneeded to optimize this approach.
Now, Chuchu Yang, Jiuhui Han and
Mingwei Chen of the AIMR at Tohoku
University, along with co-workers,
have used a state-of-the-art scanningtransmission electron microscope toobserve the dynamics of the reactions ina lithium–oxygen battery with a redox
mediator and a liquid electrolyte as theyoccurred. The observation conditions
were designed to imitate those underwhich actual batteries operate.
“In situ transmission electron
microscopy has been used for years toUsing a specially designed liquid cell (left) for a scanning transmission electron microscope, AIMR researchers
have observed reactions at the interface between the electrode and electrolyte of a lithium–oxygen
microbattery (right).

study the electrochemical reactions ofbattery electrode materials,” notes Han.
“However, previous microbatteries usually had solid-state electrolytes and wereoperated under vacuum and discharged
and charged at far-from-equilibrium
states. Consequently, they functioned
very differently from actual batteries.”
To better emulate the conditions ofconventional lithium–oxygen batteries,
the team used a liquid cell that holds theliquid electrolyte and can be operated
under ambient pressure (see image). In
addition, they charged and discharged
the microbattery in a similar mannerto conventional battery testing. “Theexperimental setup mimics well theconditions of actual batteries and hence
the phenomena observed in our study
should translate well to real-worldbatteries,” says Han.
“Our findings have important
implications for the fundamental

understandingoflithium–oxygen
electrochemistry,” says Han. “And they
will promote the development of highperformance lithium–oxygen batteries
as next-generation electrochemicalenergy-storage devices through inspiring design principles for electrodes andredox mediators.”
The team intends to use the findings of this study to develop advanced
cathodes and redox mediators for highperformance lithium–oxygen batteries.
They will also use their liquid-cell transmission electron microscopy techniqueto study other interesting chemical orelectrochemical reactions in situ.
1. Yang, C., Han, J., Liu, P., Hou, C., Huang, G., Fujita, T.,
Hirata, A. & Chen, M. Direct observations of theformation and redox-mediator-assisted decomposition of Li2O2 in a liquid-cell Li–O2 microbattery
by scanning transmission electron microscopy.
Advanced Materials 29, 1702752 (2017).

13

RESEARCH HIGHLIGHTS

Organic optoelectronics:

A versatile electrode

Electrodes capable of injecting bothelectrons and their positively charged
counterparts — holes — into flexible
semiconductors made from organic materials have been devised by a team ofresearchers at the AIMR and Tohoku
University1. These electrodes are promising for realizing high-performanceorganic-based optoelectronic devices, aswell as organic logic circuits and lasers.
Organic semiconductors offer many
advantages over conventional siliconbased ones. For a start, they are flexible,
which means they can be used in wearable
electronic devices and smart clothing.
They are also printable and lightweight,
can be made at low temperatures, andcan generate light at high efficiencies.
But unlike their inorganic counterparts,
it is hard to inject electrons into organic
semiconductors because metals suitablefor electron-injection electrodes, such as
calcium, are unstable in air.
Now, Thangavel Kanagasekaran of
the AIMR at Tohoku University and hiscolleagues have overcome this problem
by coming up with an electrode thathas a unique structure: a disordered organic semiconductor layer sandwiched
between a metal thin film and a singlecrystal organic semiconductor layer.
The structure has a novel carrier
injection mechanism that results in avery low carrier injection barrier, so that
there is very little resistance between theelectrode and the organic semiconductor, regardless of the material that theelectrode is made from. The electrodeis also effective for efficiently injecting
both electrons and holes; previously,electrodes made from different materials
had to be used to inject holes and electrons into organic semiconductors.

14

© 2017 Thangavel Kanagasekaran

An electrode with a special structure can be used to inject both electrons and holes
into organic semiconductors

A photograph showing the experimental setup employed in the study. Electrodes made from the samematerial inject electrons and holes into an organic semiconductor.

The team demonstrated the possibilities of their electrodes by using
them in field-effect transistors based ona single-crystal organic semiconductor. Using this setup, they achieved thehighest electron and hole mobilities for
two terminals so far. The electrodes alsoenabled bright light emission from theorganic semiconductor with a very highcurrent density.
“With this structure, the effective barrier height for carrier injection is almost
independent of the metal, allowing us to
use any metal that is stable in air for electron injection,” explains Kanagasekaran.
“The great thing about this method is its

versatility: it can be applied to any metalor organic semiconductor and can beused to inject both electrons and holes,”he adds.
Kanagasekaran notes that while thesingle-crystal organic semiconductor
the team used is stable in air, it cannot
conduct electrons in air. He and theteam are now working on extending thetechnology by developing devices thatare able to be operated in air.
1. Kanagasekaran, T., Shimotani, H., Shimizu, R.,
Hitosugi, T. & Tanigaki, K. A new electrode design
for ambipolar injection in organic semiconductors. Nature Communications 8, 999 (2017).

AIMResearch 2017

RESEARCH HIGHLIGHTS

Nanoporous gold:

Engineering surfaces to makebetter catalysts
Nanoporous gold catalysts can be made even more effective by tailoring the surfacesof their pores

AIMResearch 2017

Initial nanoporous gold

5mV/s

50mV/s

{111}
{100}

© 2017 Zhili Wang

An easy way to enhance the effectivenessof nanoporous gold catalysts that involves
sculpting their surfaces by applying acycling voltage to the catalyst has been
demonstrated by AIMR researchers1.
Gold is renowned for its low chemical reactivity, which is why you need
not fret that your gold ring will tarnish
or corrode. But if gold is made smallenough — on the order of nanometers— it begins to take part in chemical
reactions and can be used as a catalyst
to speed up reactions.
Gold nanoparticle catalysts havebeen widely investigated, but a morestable form of gold has recently been
attracting attention — gold riddled withnanoscale wormholes, known as nanoporous gold. It is made by forming an
alloy of gold and silver and then using
a strong acid to strip away the silver,leaving the gold with pores that are tensof nanometers in diameter.
A team led by Mingwei Chen of the
AIMR at Tohoku University has found a
way to enhance the catalytic propertiesof nanoporous gold by tuning the surface
structure of its pores. During fabrication, they applied a cycling voltage tonanoporous gold and were able to obtain
different kinds of surfaces by varying thescan rate. For example, when the teamvaried the voltage up and down at a rateof 5 millivolts per second, they obtained{111} surfaces, the closest-packed planesof gold, but when they cycled it at ten
times that rate, they obtained {100} surfaces (see image).
The team demonstrated their catalyst
by using it to catalyze the ethanol oxidation reaction, an important reaction
for realizing fuel cells based on theenvironmentally friendly fuel ethanol.

By controlling the scan rate of potential cycling, AIMR researchers can produce different kinds of surfaces.

Nanoporous gold containing an abundance of {111} surfaces had a higher
activity than conventional nanoporous
gold. Indeed, it had the highest activity for the reaction of any gold catalyst
reported to date.
“This not only opens up a new avenue
to improve the catalytic activity of threedimensional nanoporous catalysts bysurface engineering, but also provides a
direction to develop three-dimensional
nanoporous catalysts with controllable
surface structures for chemical and electrochemical reactions related to energy
and the environment,” says Zhili Wang, a
postdoctoral fellow of the team.
Unlike previous techniques, themethod does not use a surfactant,which is important because surfactants
can be hard to flush out fromthe pores and residual surfactant
can lower the catalytic activity ofnanoporous catalysts.
The team will use the method to produce other nanoporous catalysts. “Weintend to prepare three-dimensional
nanoporous platinum and silver with
controllable surface structures forcarbon dioxide reduction and nitrogen
fixation,” says Wang.
1. Wang, Z., Ning, S., Liu, P., Ding, Y., Hirata, A.,
Fujita, T. & Chen, M. Tuning surface structureof 3D nanoporous gold by surfactant-freeelectrochemical potential cycling. Advanced
Materials 29, 1703601 (2017).

15

IN THE SPOTLIGHT

IN THE SPOTLIGHT
The AIMR has grown rapidly since its inauguration in 2007.
It now boasts about 100 leading researchers from all over theworld, including 28 internationally renowned principal investigators who are charged with pioneering new and innovative
breakthroughs in materials science. The institute is also active indeveloping young, promising researchers with a focus on strong
cross-disciplinary collaboration and creativity. AIMResearch
spotlights these talented researchers of the present and future,detailing their daily research activities and scientific ambitions.

16

AIMResearch 2017

IN THE SPOTLIGHT

INTERNATIONAL SYMPOSIUM

Published online on 27 March 2017

Maths makes a material differencein less than ten years
AMIS2017 celebrated a decade of transformative research in materials science

The AIMR International Symposium (AMIS) 2017 celebrated 10 years of transformative research in materials science with 271 participants representing 11 countries.

S

ome big ideas take generations togain a foothold, especially when
they challenge the establishedorder. But it took only a few years for the
Advanced Institute for Materials Research(AIMR) to bring mathematics into the foldof materials science.
Held on the AIMR’s tenth anniversary, the AIMR International Symposium(AMIS) 2017 celebrated this remarkableachievement. Congratulations echoedthroughout the five-day event, includingfrom Nobel laureate Albert Fert, Japanesematerials science star Hideo Hosono andworld-renowned applied mathematician Sir
John Ball. “Mathematics has transformed
the scientific scene,” said AIMR Director
Motoko Kotani, who has led the effort.

AIMResearch 2017

Dream team
When Tohoku University decided in 2007
to assemble a ‘dream team’ of materials
scientists from diverse backgrounds, it
had a century of success in traditional
approaches to materials research behind
it. The AIMR was established to find new
ways of controlling atoms and moleculesby bringing together physicists, chemists
and engineers in one place.
Five years later, Kotani, as the new
AIMR director, reframed the institution’s
goals in the language of maths. She little
expected that maths would revitalize thefield of materials science so rapidly. She
laid out a conservative timeframe forresults to emerge. “I envisioned it as along-term investment.” But within two

years, experimentalists and theorists at
the AIMR had solved a problem that had
dogged materials scientists for 50 years— the atomic structure of amorphousmaterials such as glasses. They found that
atoms in metallic glasses form 20-sided
geometric shapes known as icosahedrons.
This prevents crystal structures fromforming because, unlike other polyhedra
such as cubes and tetrahedrons, icosahedrons cannot be packed together in a
regular array such that there are no gaps.
The idea that scientists can findcommon ground in maths is not entirely
new, but the AIMR resurrected it in amodern context. “The mathematiciansthat we all revere — Newton, Cauchy,
Riemann — didn’t distinguish between

17IN THE SPOTLIGHT
graduate from the WPI program. “TheAIMR has achieved world-premier status,”
said Toshio Kuroki, program director of
the WPI at AMIS2017. This qualifies theinstitute for an elite alumni association
called the WPI Academy, established toensure the continuation of the cross-disciplinary, cross-cultural and cross-borderbrand of the WPI.

Nobel laureate Albert Fert studies electronic properties protected by the geometry of a material — its topology— to bring us the next generation of spintronic devices.

pure and applied mathematics. They saw
it all as one spectrum,” said Ball, Sedleian
professor of natural philosophy at the
University of Oxford and former president of the International Mathematical
Union, who was invited to speak at
AMIS2017. As long ago as 1623, Galileo
Galilei described the Universe as a “grandbook”, written in the language of maths,“without which one wanders in vain
through a dark labyrinth.”“Somehow at the beginning of the20th century, things got very polarized,”
said Ball, but “people now are less likely
to divide things between pure and applied.” The reunification has energized
the field.
Global presence
The AIMR, said Tohoku University
President Susumu Satomi in his welcome address, has forged “an extensive
international network in the researchcommunity,” which serves as a contemporary model for global problem-solving.
“A world-leading organization has been
established within ten years.”Almost half the researchers at the
AIMR come from abroad, working
in an English-speaking environment
with a strong support system. The institute has formed close partnerships with
15 international institutions, including
four research satellites in China, theUnited States and the United Kingdom,

18

where joint laboratories have been
established. Almost 2,000 scientists from
more than 15 countries have attended
the annual AMIS gatherings in Sendai
over the past 8 years. Some 271 participants representing 11 countries wereat AMIS2017, including 23 speakers and
98 poster presenters.
Another milestone for the AIMR sees
it join the first group of institutions to

Super-smart society
The AIMR is expected to play an
integral role in Japan’s plans to realizea super-smart society, dubbed Society
5.0 — “the fifth generation of society after
the hunter-gathering, agricultural, industrial and information societies,” explained
Kazuo Kyuma, an executive memberof the Council for Science, Technology
and Innovation.
“In Society 5.0, cyberspace andphysical space are integrated to achieve
economic growth and social development simultaneously.” Japan’s materials
industry made up more than a fifth of its
total exports — amounting to 76 trillion
Japanese yen in 2015 alone. The AIMR
is expected to find innovative ways ofcontributing to the industry’s competitiveness through the development ofcyber–physical systems.
Initiating this transition from basic
to applied research, the AIMR is collaborating with the National Instituteof Ad v an c e d In du s t r i a l S c i e n c e
and Technology (AIST) to promote

Materials scientist Hideo Hosono has created transparent, electrically conducting materials that power the latest
flat-screen displays.

AIMResearch 2017

IN THE SPOTLIGHT
data-driven science. It also plans to takethe lead in the revolution from electronics to spintronics. “Spin-centered science
is developing very rapidly, and Tohoku
University, especially the AIMR, has
become a world leader in this area,”said Kotani in her opening speech at
AMIS2017. The AIMR also plans tomathematically deepen investigations
into the hidden order of amorphousmaterials, she said, to better understandthe relation between structure, function
and property.
Japan is particularly strong in nanotechnology and materials science research,and the pursuit occupies an important position in national science and technology
policy, according to Masami Watanabe,
director of the Basic Research Promotion
Division, Research Promotion Bureau,
Ministry of Education, Culture, Sports
and Technology, speaking on behalf ofthe director general of the bureau. “It’s remarkable that, within ten years, the AIMR
has become a new core center for materials
science research in Japan.”Nanobatteries and flat panels
The scientific session at AMIS2017
opened with a talk by Fert, a physicist at
the University of Paris-Sud who sharedthe 2007 Nobel Prize in Physics for his
discovery of the physical effect of giant
magnetoresistance, which gives miniature
hard disks the ability to read data. Hispresentation focused on extremely robustelectronic properties protected by a material’s geometric shape — a mathematicalconcept known as topology.
Picture a belt. If one were toaccidentally buckle the belt with a twist
looped into it, the only way to untwist it
would be by unhooking the clasp. “Youcannot twist the belt to restore the initialconfiguration,” explained Fert. This intractable twist, defined by the belt’s geometry,is an example of a topologically protected
property. Fert studies a similarly protected
locking of electron spin with momentum
in topological materials, a property thattoday’s computer memory devices use toconvert spin into charge. Most research
has focused on three-dimensional topological materials, but Fert has developed
two-dimensional materials that produce
an order of magnitude more charge current for the same amount of injected spin,
which could be harnessed in spin-based
nanobatteries.
From one exotic material to another,
Hosono, a professor at the Tokyo Institute

AIMResearch 2017

Mathematician John Ball has collaborated with experimentalists to describe the sudden changes that occur in the
microstructure of everyday metal objects.

of Technology and a longtime collaborator with Peter Sushko, who spent someyears at AIMR as an associate professor,
described the “heroic” role of electride
materials in developing next-generation
flat-panel displays.
Electrides are charged compounds
in which electrons act as anions. In
2003, Hosono turned a popular cement
compound, 12CaO • 7Al 2 O 3 , into thefirst room-temperature-stable electride.
Hosono has since discovered many unusual, but potentially useful, properties
of electride materials. In 2011, his groupconverted ordered crystalline electrides
into disordered glassy states, which weretransparent, electrically conducting andsuitable for industrial applications. Theseelectrides have been incorporated into
Microsoft’s Surface Pro 4 laptops andLG’s 4K televisions.
Shape-shifters
John Ball described another type oftransformational change in the crystal
structure of alloys known as martensites.
At a certain temperature, the crystal
lattice of these materials suddenly, witha sound of a ‘click’, changes shape, forexample from aligned cubes to stretchedtetragons. This molecular shift affects
the material’s overall properties, in thesame way that heating liquid water turns
it into gaseous mist. And the change
is reversible.

“If you look at a knife or a fork undera microscope, you will see similar patterns of microstructure,” explained Ball.
Understanding how these changes occur
can help scientists make materials thatdo things they want them to do, “Themacroscopic materials of all sorts ofeveryday metal objects are determinedby their microstructures.” Working withan experimentalist, Ball has used maths
to understand and predict how and when
the shape-shifting occurs. Given that themartensitic transformations are induced
by very slight temperature variations, they
could be used to harness mechanical motion from small temperature fluctuations
such as those in the oceans, said Ball.
“Vast quantities of such energy could be
extracted.”
A focused session and panel discussion
on future prospects for the maths–materials science collaboration was held on thethird day of the symposium, followed by
two days focused on work at the AIMR
joint research centers. “Tohoku University
has a long and distinguished record inmaterials science, which makes it an
obvious match,” said A. Lindsay Greer, an
AIMR principal investigator who heads
the School of the Physical Sciences at the
University of Cambridge. From a narrowfocus on non-equilibrium materials, collaboration between the two institutions
has expanded into chemistry and maths,
with plans to delve into disaster science. ■19IN THE SPOTLIGHT

NEW CENTER

Published online on 31 July 2017

Planting the seeds for brand newmaterials and technology
Researchers at a new initiative, MathAM-OIL, are collaborating with both the AIMR and AIST to seed
the development of clever materials for cutting-edge technologies

W

hen two or more metals are
mixed together, they often
form alloys with properties
superior to the individual metals. In asimilar way, a new initiative known as
Mathematics for Advanced MaterialsO p en Innovation L ab orator y, or
MathAM-OIL, combines the strengthsof two research centers and promises
to produce results that exceed theirisolated efforts.
The new MathAM-OIL center is abold collaboration between Advanced
Institute for Materials Research (AIMR)at Tohoku University and the National
Institute of Advanced Industrial Scienceand Technology (AIST). It is the third ofabout ten Open Innovation Laboratories(OIL) that are being established by theJapanese government. These laboratories
are tasked with bridging the gap between
academia and industry through collaboration with the AIST, a body set up by theJapanese government to integrate scientificand engineering knowledge.
MathAM-OIL was established inJune 2016. Already, Chief Researcher
Akihiko Hirata has been part of a study
published in Nature in April 2017 on producing ultrastrong and yet ductile steel inwhich the expensive cobalt and titanium
alloying elements are replaced with lightweight and inexpensive aluminum. This
could have important implications forthe automotive and energy industries,
among others.
“We intend to make seeds for new technologies, which will fast track the industrial development of materials,” says Takeshi
Nakanishi, director of MathAM-OIL.
“Since the researchers at MathAM-OIL aremathematicians and theoretical physicists,
we won’t actually physically produce any
new materials. Rather, we will generate
new concepts, functions and analysis
methods for material structures.”Postdoctoral researchers at MathAM-OIL find it a stimulating environment because of the diversity of expertisethat exists there.

20

Takeshi Nakanishi, director of MathAM-OIL, is
excited about the potential to generate new seeds formaterial technologies through collaborations with
AIMR and AIST researchers.

B oth the AIMR and the AIST
bring their own unique perspectives to
MathAM-OIL — the AIMR specializes
in using mathematics to inform research
into materials science, while the AIST
uses computer-based design to produce
materials that have exciting new functions. By collaborating with researchers
from both institutions, mathematicians at
MathAM-OIL will help to accelerate thedevelopment of next-generation advanced
materials as well as create new fields of research that will aid industry. In particular,
they will theoretically predict structuresneeded for realizing new material functions and then design novel materials
based on these structures.
Using pure and applied math to lookat materials
There are currently 12 postdoctoral
researchers at MathAM-OIL who are
working across a wide range of fields.
Shin Hayashi is a pure mathematician
with an interest in topology, the study ofthe properties of space that are preserved
under continuous deformations. He isparticularly fascinated by topological

AIMResearch 2017

IN THE SPOTLIGHT

materials — work into which earned
three physicists a Nobel prize in 2016.
For example, topological insulators,
which are a hot topic in materials science,
conduct electricity on their surfaces but
are insulators in their bulk. They have thepotential to be used in new-generationelectronic devices as well as in future
quantum computers.
Hayashi really appreciates thediverse backgrounds of researchers at
MathAM-OIL. “There are many researchers outside mathematics,” says Hayashi.
“Through interacting with them, I canunderstand mathematical problems thatare important not just from a mathematical perspective but also from a broader
scientific viewpoint.”
His research is related to condensedmatter physics, which overlaps withchemistry, materials science and nanotechnology. “One big goal is to predict
new types of materials,” he says. Becauseof this, he hopes to form collaborations“with not just theoreticians but
also experimentalists.”
Yueyuan Gao, an applied mathematician, also finds the diversity at
MathAM-OIL stimulating. Gao is using
simulations based on ‘stochastic phasefield’ models, to study structures that arechanging. “At MathAM-OIL, we have pureand applied mathematicians, theoreticalphysicists and experimentalists,” Gaosays. “Through seminars and discussions,
we can share our different points of view,which exposes us to new ways of thinking
and sparks new ideas.”
Computer-aided materials science
Computers necessarily play a key part in
the research at MathAM-OIL. “Computer
simulations are very important forstudying advanced materials,” Nakanishi
explains. “MathAM-OIL will propose
new simulation methods and also ways
to automate the analysis of measured or
calculated data using computers.”
Since materials are very complex
systems, experiments on them can generate an overwhelming amount of data.
Researcher Satoru Tokuda specializes in
information theory, a branch of appliedmathematics that can help experimentalists make sense of the data they gather.
One project he is working on is using
machine-learning techniques to analyze
data generated by angle-resolved photoemission spectroscopy — a techniquematerial scientists use to measure electron

AIMResearch 2017

Uyen Tu Lieu giving a presentation. She is using computer simulations to explore the formation processes ofsoft materials.

energy bands in solid materials, which
determine properties such as resistance toan electrical current.
Tokuda also values the wide rangeof backgrounds at MathAM-OIL.
“Mathematics is helpful for understanding the mechanisms of machinelearning, while physics often provides
the analogies and motivations that help
drive information science,” he says. “Anenvironment such as that at MathAM-OIL
in which I can discuss common problems
with mathematicians and physicists isreally valuable.”
Another researcher who is using
computers to explore materials is Uyen
Tu Lieu. She is using computer simulations to examine the formation of soft
materials — useful for personal care andcleaning products among other things.
In particular, she is working on the selfassembly of anisotropic colloidal particles
and their self-assembly behavior. Lieu isalso interested in the flow of matter in aliquid, soft solid or specialized solid statein mixtures in which microscopically dispersed insoluble particles are suspended inanother substance.
Like her colleagues, Lieu enjoys working
at MathAM-OIL: “MathAM-OIL is a greatlab. The working environment is intellectually stimulating. The people at MathAMOIL have different backgrounds anddisciplines, including mathematics, physics
and engineering. They thus have different

interpretations, points of view and ideas on
the same problem.”Having an impact on industry
An important goal of MathAM-OIL is
to act as bridge between academia andindustry. “We intend to achieve thisthrough the AIST,” explains Nakanishi,
who notes the AIST’s strong ties withcommercial companies. “Universities andthe AIST have very different cultures,
but collaborative laboratories such as
MathAM-OIL can play a vital role inbridging the divide.”
Many of MathAM-OIL’s proposed
projects involve materials useful to industry such as metallic glass, which can bestrong and very malleable. Metallic glass
has been hailed as a potential wondermaterial for decades, but requires further
research. It is currently used to make golfclub heads. Others at MathAM-OIL want
to study ion transport in the materials
used in batteries. Some want to study
active or smart materials that change theircolor, stiffness, transparency and shape in
response to a signal or stimulus.
Just over a year since it was established, MathAM-OIL is already showing
signs of being a very promising amalgam
with the potential to generate synergies
between the academic research being
conducted at the AIMR and the moreindustrially focused work being done at
the AIST. ■21

IN THE SPOTLIGHT

TOP-LEVEL INTERVIEW

Published online on 27 November 2017

Creating a world-leadingmaterials science center thattranscends borders
Tohoku University has been selected by the Japanese government to be one of three Designated National
Universities. The directors of the three materials research institutes at Tohoku University talk about strategies
they will employ to advance the university’s research in materials science and establish one of the world leading
centers in the field.

On 30 June 2017, the Ministryof Education, Culture, Sports,
Science and Technology (MEXT)
announced that Tohoku University
would become a Designated National
University, along with the University ofTokyo and Kyoto University. Under thisnew framework, the selected universities
have been charged with honing theirinternational competitive edge by pursuingworld-class education and research.
Prior to the application, Tohoku
University had assessed its strengths andweaknesses and discussed its universitywide vision for the coming decades. The
university will now focus on strengthening
its research over the long term basedon concepts established by the whole
institution. In particular, it will pool its
outstanding resources to create worldclass research centers in four fields that theuniversity is already strong in — materials
science, spintronics, next-generation
medical care and disaster science.
Tohoku University’s strength inmaterials science is due to the depth of its
expertise and its many researchers working
in the area. Drawing on these advantages,
the university will form a world-leading
research center in materials science. The
Advanced Institute for Materials Research(AIMR) will play a leading role in this newcenter, in collaboration with the Institutefor Materials Research (IMR) and theInstitute of Multidisciplinary Research
for Advanced Materials (IMRAM), theGraduate School of Engineering and the
Graduate School of Science.
Leading the way for Japanese
universities
Researchers are spurred on when they22

receive global recognition for theirresearch. “In my view, it is important toensure that we release as many research
results as possible that can be regarded
as world leading,” says Koki Takanashi,
IMR’s director. Tohoku University
operates on the principle of practiceoriented research and education.
Researchers at the university believethat academic interest is not the only
driving motivation; rather, they seek
to make significant findings that will
ultimately change society. The university
will strive to further develop its strengths
and accelerate the process of turning
world top-level research into disruptive
innovations. “Not only is this a traditionof ours, but it is also a point where
Tohoku University can play a leadingrole,” adds Takanashi.
To create centers that attract excellent
researchers from all around the world, it
is vital for Japanese universities to pursue
internationalization. In general, Japanese
universities have fewer overseas students
and researchers than universities in othercountries, and the number of young
Japanese students and researchers spending
extended periods overseas is decreasing.
“I believe we have to become aninternationally open university towhich students and researchers comefrom around the world,” says Atsushi
Muramatsu, IMRAM’s director. “At
the same time, we need to encourage
Japanese students and researchers to
become more active overseas.”“One key way for Japanese universities
to join the global brain circulation
is to develop an understanding ofmultiple cultures and realize that there
is another world out there,” says Motoko

Kotani, AIMR’s director. Researchers
constantly explore new territories thatlie at the margins of disciplines and are
inspired by the interactions between
different worlds.
New initiative for world-leading
research in materials science
Tohoku University is recognized as being
strong in materials science. Each instituteand department within the university
has different strengths and specialties.
AIMResearch talked to the three institutedirectors about those of their institutes.
Takanashi: To date, the IMR hasemphasized fundamental research,
but an important aspect of our work
involves going beyond it. We strive
to commercialize our findings basedon the principle of practice-oriented
research and education. The IMR has

IMRAM’s director, Atsushi Muramatsu, wants both toattract researchers from around the world to cometo Tohoku University and to encourage Japanesescientists to be active overseas.

AIMResearch 2017

IN THE SPOTLIGHT

Motoko Kotani (left), Koki Takanashi (center) and Atsushi Muramatsu (right) discuss plans for Tohoku University in light of its recent selection as a Designated National University.

100 years of experience in doing this.
A good example of how fundamental
research has bolstered industr y is
Sendust — a magnetic alloy invented
at our institute over 80 years ago andstill widely used in magnetic heads andother components. Another example
is the high-performance sinteredneodymium–iron–boron permanent
magnets developed by Masato Sagawa
when he joined a company after
conducting research for his PhD at our
institute. Neodymium magnets havebecome indispensable today. Both ofthese are magnetic materials, and theseachievements can be considered partof Kotaro Honda’s legacy, the founding

AIMResearch 2017

director of the IMR, who developed
the strongest magnets in the world
at that time. Of course, the IMR has
also developed many valuable nonmagnetic materials, and we continue
to strive to apply fundamental research
to practical applications by setting up
venture companies.
Muramatsu: Traditionally, t he
IMRAM has tackled research targeting
resources and materials — not only
metals, but also oxides, sulfides, ceramics,
as well as organic and biomaterials.
Hence, we cover a rather broad range ofmaterials science fields. But that doesn’tmean that we work haphazardly in a wide
range of fields. Broadly speaking, ourresearch falls into three main themes.
The first is using inorganic materials
with new functions, including recycling
scarce resources. The second is scientificmeasurements for analyzing all kinds ofmaterials. Under this theme, progress isbeing made on the Synchrotron Lightin Tohoku, Japan (SLiT-J) project, aplan to develop a synchrotron facility
in the Tohoku region of Japan. Thirdly,
we are exploring and developing hybridmaterials made from organic andinorganic sources, which will enable thedevelopment of materials possessing
multiple functions. This is an area of
research not widely investigated by otherresearch centers. I want our institute to23

IN THE SPOTLIGHT

Koki Takanashi, director of IMR, notes that theinstitute has a long history of applying the resultsof fundamental research.

utilize its strengths to help consolidate
materials science at Tohoku University,
while compensating areas in which otherdepartments are lacking.
Kotani: Since the AIMR was launchedunder the World Premier International
Research Center Initiative (WPI) in
2007, our mission as a WPI center has
been to advance the frontiers of scienceby attracting talented researchers fromaround the world. The AIMR is also
seeking to promote cross-disciplinary
research to create new scientific fields.
In particular, we have been exploring
the interface between mathematics
and materials science — AIMR is thefirst center in the world to do this at an
institutional level. Tohoku University’s
bid to become a Designated National
University was bolstered by AIMR’sachievements under the WPI program.
As part of its strategy to generate worldleading research, Tohoku University
established a Research Innovation
System that has three foundational layers,
consisting of groups of departments(including s cho ols and g raduate
schools), interdisciplinary researchalliances (including research institutes,
international joint graduate programs andother institutions), and an Organization
for Advanced Studies. The AIMR, whichis in the Organization for Advanced
Studies, has a vital mission to pursue
world-leading research. The AIMR
also plays a major role in creating newscience by conducting cross-disciplinary
research and using mathematics andinformation technology.

24

T he s e t h re e mate r i a ls - s c i e nc e
based institutes will forge ahead withthis project playing their respectiveroles. “It is my hope that we can link
the AIMR’s innovation to areas ofpractice-oriented research that theinstitutes and departments of Tohoku
University, such as the IMR and the
IMRAM, have traditionally addressed,
so that we can sustainably grow stronger
across the whole university,” Takanashi
says. He stresses that the key to successlies in the cooperation between threefundamental layers in the university’s
innovation system.
Muramatsu thinks it is important toactively exchange human resources andto improve the system within the newmaterials research center. “I believe it isnecessary to promote personnel exchangethat transcends the borders of institutes
or departments, as exemplified by theEnsemble Project for Young Researchers,
which we are currently implementing,”
he says.
Toward an era of global cooperation
As stated in the purpose of the DesignatedNational University program, it is vitalfor Japanese universities to enhance theirinternational competitiveness. Yet Kotani
says, “Despite the term ‘international
competitiveness,’ I feel it does not mean
competition; rather, it refers to an eraof international partnership, in which
researchers are like players performing
together in a musical ensemble.”
Und e r t he W PI pro g r am , t he
AIMR has constructed a framework
for international joint research. It has
also established joint-appointment
post-doctoral researchers in the jointlaboratories set up in its satellites andsought out the best partners withwhom they could achieve joint researchwith other countries. This results ina win–win situation and best-withbest relationships, and creates anenvironment where researchers can‘perform’ together.
“Active participation in international
joint research would allow us to discover
the advantages on both sides. I hope
we can increase opportunities to makeforeign researchers think ‘Japan has
many benefits; I want to go there’,”says Takanashi.
More ove r, t he u n ive rs it y w i l llaunch an international joint graduate
program in materials science to promoteinternational collaboration in education.
The new initiative will consider
strategies for assisting students to create
international networks. These students
will go on to become the next generationof leaders.
“We should consolidate friendly
relationships with China, South Korea
and Southeast Asia,” Muramatsu says.
Japan’s research investment is gradually
declining, but in terms of fundamental
science, it remains as strong as ever.
Meanwhile, China and South Korea
have accelerated research investment
and developed human resources at anenormous speed, so Japanese universities
may b e able to form ver y go o dcollaborations if they can combine thefundamental science with their strengths.
“I think we should take the opportunity
presented by our appointment as a
Designated National University tofurther solidify such collaboration,”
Muramatsu adds.
Tohoku University has over 100
years of history in materials science.
Building on this proud tradition, theuniversity intends to establish a newparadigm of materials science throughthe innovation system of brain circulation
being promoted inside and outside theuniversity. Tohoku University’s status as a
Designated National University has given
it the chance to analyze and understanditself. Thus, the designation provides theperfect impetus to create a world-leading
research center in materials science that
attracts skilled researchers from aroundthe world. ■Director of AIMR, Motoko Kotani, likens theinternational cooperation between researchers as
being like musicians playing together in an ensemble.

AIMResearch 2017

AIMResearch
AIMResearch is an online and print publication that highlights the scientific achievements and activities of
the AIMR. First published in June 2009, AIMResearch selects the most important papers from the wealthof research produced by AIMR scientists throughout the year, distilling the essence of the achievements
into timely, concise and accessible research highlights that are easy to digest, but retain all of the impact andimportance of the original research article. Published monthly on the AIMResearch website in both English
and Japanese, AIMResearch research highlights bring the very best of AIMR research to a global audience ofspecialists and nonspecialists alike. AIMResearch also publishes a range of feature articles introducing otheractivities of the AIMR’s research groups. Visitors to the website can register for monthly email alerts in either
English or Japanese to keep abreast of the latest developments and discoveries made at the AIMR.
wpi-aimr.tohoku.ac.jp/en/aimresearch/

wpi-aimr.tohoku.ac.jp/en/aimresearch/
AIMResearch is published by the Advanced Institute for Materials Research (AIMR)at Tohoku University in collaboration with the Partnership and Custom Media unitof Nature Research, a division of Nature Japan KK.
© 2018 AIMR, Tohoku University. This publication may be reproduced in its
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Editorial
AIMR, Tohoku University
2-1-1 Katahira, Aoba-ku, Sendai,
Miyagi 980-8577, Japan
Editor-in-Chief

Motoko Kotani

Managing Editor

Takashi Takahashi

Editorial AssistantEtsuko Hagita

ISSN 1884-491X

Advanced Institute for Materials Research
Tohoku University