RESEARCH HIGHLIGHTS 2016
A publication of the WPI Advanced Institute for Materials Research

SPECIAL FEATURE:
MATHS AND MATERIALS SCIENCE COLLABORATIONTABLE OF CONTENTSMESSAGE FROM THE DIRECTOR
1

Past
decadelaysmaterials science

foundation

for

new

18
19

Graphene: Tying ribbons of graphene
Gold catalysis: Examining catalysis on an 		
atomic scale

20 Graphene: A dose of calcium yields 			

SPECIAL SECTIONa superconductor

MATHS AND MATERIALS SCIENCE COLLABORATION

21

2
4

22 Silicon monoxide: Atomic structure revealed at last
23 Lithium-ion batteries: Nanocarbon electrodes are

Spotlight: Experimenting with maths and materials
Spotlight: A mathematician, an experimentalist andtheir interpreter

Photonics: Multitasking molecule simplifies organic
LED design

true lifesavers

6

Persistent homology: Uncovering order in a seaof randomness

7
8
9

Block copolymers: Predicting polymer shapes
Carbon nanostructures: In the loop

24 Metallic glasses: Spotting secret relaxations
25 Spintronics: A clean look at magnetic 			semiconductors

26 Three-dimensional graphene: Sponge-like 		
nanomaterials soak up electrons

Metallic glasses: Mathematics nails 			diameter distribution

10

27

Quantum materials: Massless particles jump out
from a sea of electrons

1112

28 Nanoporous gold: Sensitive biosensor for 		

Metallic glasses: All in orderElectrocatalysis: Splitting water without breaking
the bank
muscle chemicals

Batteries: A crash course in nanofabrication

RESEARCH HIGHLIGHTS
13
14

Metallic glasses: ‘Revolutionary’ advance in MEMS

15

Lithium–oxygen batteries: Super-sized storage with
nanoporous graphene

16Band structure engineering: Massless electrons put
on weight

17

Titanium dioxide: Atoms mapped at border 		between crystals

Three-way catalysts: Cool way to make 		
catalytic converters

29 Single-cell analysis: Double-barrelled probe for 		
exploring single cells

IN THE SPOTLIGHT
30 Mathematics and materials in harmony
33 A decade of remarkable achievement
35 Raising awareness in Europe
37 A new center of excellence in nanotechnology 		in China

WPI Advanced Institute forMaterials Researchamong its four groups — Materials

whom come from abroad, including

Physics, Non-equilibrium Materials, Soft

31 principal investigators. In addition toMaterials, Device/System — and thethe research hub at Tohok­­u University,

The Advanced Institute for Materials

Mathematical Science Group.

the AIMR collaborates with research

Research (AIMR) at Tohoku University
in Sendai, Japan, is one of nine World
Premier International Research Center
Initiative (WPI) programs establishedwith the support of the Japanese Ministryof Education, Culture, Sports, Scienceand Technology (MEXT). Since its
inauguration in 2007, the AIMR has beenbringing together world-class researchers
from Japan and abroad to carry out
cutting-edge research in materials sciencethrough interdisciplinary collaboration

Led by distinguished mathematician

centers in China, France, Germany,and director Motoko Kotani, the institute

Poland, the United Kingdom and thepromotes interdisciplinary research acrossUnited States. Close ties with otherthe different groups while fostering young

leading overseas institutes are maintained

researchers through the Global Intellectual

through its Adjunct Professor andIncubation and Integration Laboratory

Associate Professor programs.

(GI Lab), where international joint
3

research is carried out in close cooperation
with high-profile researchers invited fromcountries throughout the world.
The AIMR is host to about 140
leading researchers, around half ofMESSAGE FROM THE DIRECTOR

Past decade lays
foundation for new
materials science2017 marks the tenth anniversary of the

22 invited speakers, including Alexander

Advanced Institute for Materials Research

Mikhailov, a theoretical scientist at the Fritz(AIMR). The institute was established in

Haber Institute of the Max Plank Society, and2007 with the support of the World Premier

Akira Fujishima, a chemist and president ofInternational Research Center Initiative (WPI)

Tokyo University of Science. The symposium wasprogram of the Japanese Ministry of Education,

attended by more than 230 researchers in every

Culture, Sports, Science and Technology

field of materials science, from 14 countries. In(MEXT), which seeks to create world-class

May, the AIMR also joined other WPI centers

research centers in Japan. Over the past decade,in attending the 2016 Spring Meeting of thethe AIMR has consistently pursued top-level

European Materials Research Society (E-MRS),

research in specific areas of materials science andconvened in Lille, France.

striven to create new materials science.

In a new development that seeks to connect

As a global center for materials science,basic research with society, the AIST-Tohoku

a defining feature of the AIMR has been the

University Mathematics for Advanced Materials

close collaboration between mathematics andOpen Innovation Laboratory (MathAM-OIL)

materials science. By describing the very broad

was established in July to promote data-

scope of materials science in the universal terms

driven materials science. AIMR researchersof mathematics, researchers at the AIMR arefrom Tohoku University are already active in thetrying to uncover commonalities between various

laboratory, advancing research in mathematics,

materials and so create new research topics andcomputational science, theoretical physics,

results. This bold attempt to team up mathemati-

theoretical chemistry and materials science tocians and materials scientists is unique in theaccelerate materials development and the applica-

world and epitomizes AIMR’s position at thetion of research to industry.

cutting edge of materials science research.

Having established a firm foundation in its

In publishing this edition of AIMResearch on

first decade of activity, the AIMR is entering a

the occasion of the institute’s tenth anniversary,

new phase in which it seeks to generate novel

we have included a special feature that focusesmaterials science. We would like to take thison fusion research in mathematics and materials

opportunity to express our thanks to all ourscience. In it, we introduce research results that

supporters. We at the AIMR will continue tocharacterize the last decade of AIMR’s outputs.

advance high-quality research, act as a hub for

While immersed in such front-line research,

international brain circulation, and contribute

AIMR has also spent the past year actively

to the development of global materials scienceengaged in exchanges with internationaland society.

researchers and research institutions and acrossdifferent fields of materials science. The AIMR

Motoko KotaniInternational Symposium 2016 (AMIS2016)

Director

convened in February 2016 and featured

AIMR

RESEARCH HIGHLIGHTS

SPECIAL SECTION

Published online on 30 January 2017

INTERVIEW WITH A MATHEMATICIAN

Experimenting with maths
and materials

Yasumasa Nishiura gives a mathematician’s perspective on the five-year
collaboration between mathematics and materials science at the AIMRW

hat happens when you bringmathematicians and materials
scientists under one roof ?
The Advanced Institute for Materials
Research (AIMR) at Tohoku University
is five years into a bold experimentthat uses mathematics to glean insights
into materials. AIMResearch talks to
Yasumasa Nishiura — an applied mathematician and unit leader of the AIMR’s
Mathematical Science Group — about
the unexpected results from the AIMR’s
radically new way of thinking.

AIMResearch: What unique perspective do es mathematics bring tomaterials science?
Nishiura: The language of mathematics
brings new concepts and viewpoints tothe understanding of materials science.
Without it, some material properties
cannot be described explicitly.
Mathematics is also a very powerful way to overcome rigid and obsolete
conceptual frameworks. A typicalexample is chaos theory, a field of study
in mathematics that tries to predict theunpredictable. Chaotic systems behave in
unexpected ways and yet are entirely controlled by their initial conditions. Abouthalf a century ago, nobody knew about
this concept of chaos, so they just threw
data away because it was too ‘noisy’ anddidn’t contain any definable structures.
But today, researchers recognize that evenvery noisy-looking data sometimes haveinternal structures that contain extractable
information. To do that, they need mathematical concepts like chaos. Otherwise,
they’re just wandering in the dark.
AIMResearch: What are some interesting results that have come out of2

combining materials science and mathematics at the AIMR?
Nishiura: We have applied concepts in thewell-established mathematical field of topology, which studies the twists and turnsof shapes, to materials science. Topology
offers a new framework for understanding
amorphous structures that lie between theperfectly ordered arrangements of crystals
and random structures like liquids. Morespecifically, we have used an analyticaltechnique for uncovering geometries
hidden in large data sets, called persistenthomology, to analyse structures that
nobody has succeeded in characterizing,
and to pin down the definition of theterm amorphous.
Related to topology is an emerging
field in materials science known as

An applied mathematician by background, Yasumasa
Nishiura is excited about the collaboration between
materials scientists and mathematicians at the AIMR
and believes that it is a two-way process that can leadto advances in both disciplines.

spintronics. Conventional electronics
uses electrons to carry energy and information. In contrast, spintronics relies onelectron spin. Many aspects of spintronics can be explained by a mathematicalframework used to study very advanced
geometries known as K-theory. Take, forexample, promising materials in the fieldof spintronics known as topological insulators, which are insulators on their inside
but conductors on their surface. K-theory
can clarify why this phenomenon is so
robust in topological insulators.
Another area I am deeply involved in
is self-organization processes. A standard
way of fabricating nanomaterials is fromthe top down — gradually chippingaway at a solid block using techniquessuch as nanolithography. The alternative approach starts from the bottom
up — constructing something fromnothing. Self-organization is one suchtechnique, in which basic building blocks
are left to spontaneously form larger
building blocks. It lets nature do its work.
In materials science, self-organization
is a fertile but undeveloped area. My
work specifically involves confining
polymers that are extremely averse toeach other in very tiny spheres. The
polymers seek to decrease the free energy
and, in the process, form interesting patterns. We have developed a qualitative
mathematical model that can be used
to control the size and morphologies ofthe patterns that pop up, which has wide
applications including in the medical
sciences. For example, structured particles could be used to test immunity byemploying reactions between antibodies
and antigens.
Finally, we have applied a mathematical discipline known as discrete differential geometry to explore the design of

AIMResearch 2016

SPECIAL SECTION: IN THE SPOTLIGHT

carbon structures. Discrete differential
geometry structures contain a distinct
number of elements, such as atoms. We
have used its concepts to make many
interesting structures from carbon atoms,
such as large carbon cages with 20-sided
polyhedrons. We have even placed molecules inside these cages.
AIMResearch: Can mathematicians also
learn from materials scientists?
Nishiura: Yes, collaboration is notjust one way; it goes both ways. We
mathematicians often get very freshand intriguing feedback from experimentalists. This is quite new for
us and has led to the generation of newmathematics, or at least the discovery of
new problems.
At the AIMR, such two-way feedback
is greatly accelerated. For example,
we have explored together the dynamical
evolution of material structures, which
demands generalizing the concept of
persistent homology in space and time.
We sit very close to each other andwork together in one building. As far as
I am aware, the AIMR is the only institute in the world where this happens inmaterials science.
AIMResearch: What are some challenges
you face?
Nishiura: Overcoming cultural differences is not easy. Mathematicians
and materials scientists have different
answers to questions about what theimportant and interesting aspects of aproblem are and what they value most.
They also have very different styles ofworking. Experimental laboratories
are more hierarchical in structure andrequire a lot of space and money since
they need expensive facilities and large
teams of technicians. But mathematicians
are more private. We like to discuss, but
we also need periods of solitude. At the
AIMR, we have been given the time towarm up to each other.
AIMResearch: What policies has the
AIMR introduced to facilitate thiscollaboration?
Nishiura: Five years ago, we set ourselves
three main targets: non-equilibrium
structures, topological structures andhierarchical structures. A healthy mix of

AIMResearch 2016

Nishiura is researching the maths of self-organization processes and how it can be applied to synthesize newmaterials through bottom-up approaches.

materials scientists and mathematicians
work together to achieve these goals.
We also established the Interface
Unit, a group of researchers who act
as free electrons, with the freedom tochoose which projects they want to get
involved in. They are young and ambitious — younger people tend to be more
flexible and curious.
Another characteristic of the groupis its heterogeneity. The researchers havebackgrounds in applied mathematics,
physics, statistics, information science, computer science and modeling,
as well as physical and theoreticalchemistry. This is important because
you don’t know a priori what tools or
methodologies will be important in materials science. Heterogeneity catalyzes
serendipitous discoveries.
AIMResearch: What areas do you expect
the AIMR to further develop in the
coming years?
Nishiura: Experiments today generatehuge amounts of data, which has fueled
an entire field of science devoted to extracting knowledge from large data sets.
Traditionally, this has involved processing

information using statistics, computerscience and information technology. In
materials science, this approach is characterized by the popular phrase materials
informatics. Mathematics can help to
explain how these information processing
systems work.
AIMResearch: Could the AIMR model
be applied to other fields besides materials science?
Nishiura: Yes. That is the most important message that the scientificcommunity should take from the AIMR.
In just five years, we have become extremely successful. Our success springs
from the nature of mathematics. Sincemathematical methods treat only the
relations between objects and are independent of material properties, they havegreat potential to be applied to otherdisciplines besides materials science.
The AIMR is a sort of trial for what
happens when you inject mathematics
into materials science. We have formedsome interesting collaborations andobtained some interesting results. So
why not try injecting mathematics into
other disciplines?
■3

SPECIAL SECTION: IN THE SPOTLIGHT

Published online on 26 September 2016

ROUNDTABLE INTERVIEW

A mathematician, an experimentalist
and their interpreter
By pooling their unique perspectives, three AIMR researchers with very
different backgrounds have used a powerful new mathematical technique todiscover structures lurking in amorphous solids

R

emarkable things happen when
researchers get together to explore
new territories at the marginsof their disciplines. This is an approachthat the AIMR at Tohoku University has
been actively pursuing in recent years
at the border between mathematics andmaterials science.
In 2010, a seminar held at the AIMR
spawned discussions between a mathematician, an experimentalist and aphysicist. Six years later, this initial
discussion has blossomed into groundbreaking findings in an emerging areaof mathematics known as persistenthomology, with the three researchers able
to characterize the underlying atomicorder of a class of materials having mostly
random structures. Until now, this order
had remained elusive to scientists using
conventional methods.
An adventurous mathematician
For a mathematician, Yasuaki Hiraoka
certainly has an unconventional resume:
he started off studying electrical engineering at Osaka University and now works
at a center for materials science — theAIMR. He is passionate about exploring
the interface between mathematics andapplied sciences. Hiraoka first learned
that there could be more to a career inmathematics than abstract thought fromhis master’s supervisor, Yuji Kodama,
who is now a professor at The Ohio State
University. “He’s my inspiration in that hedoes serious mathematics — he’s a puremathematician — but he’s also famousin the field of optical communications,”
Hiraoka says. “I wanted to become
like him.”
Hiraoka is not just interested in applying mathematics to real systems; he also4

For example, before coming to the AIMR,
Hiraoka used persistent homology to explore the structures of bioproteins, and, inparticular, used it to link the structure of aprotein to how compressible it is.
Today, Hiraoka heads a group at the
AIMR that is leading the charge in applying persistent homology to materials science. “We are the only group in the world
seriously applying persistent homology tomaterials,” he says.
Hiraoka had just finished writing abook on the subject when the AIMR
invited him to speak at a seminar. It
was there that he first met his futurecollaborators, Akihiko Hirata and
Takenobu Nakamura.
Inspired by a former supervisor, Yasuaki Hiraoka is amathematician interested in applying mathematics
to materials science and, in the process, generating
new mathematics.

works in the opposite direction — using
applications to generate new mathematics. “I’m eager to develop my own mathematics,” he says.
These interests explain why Hiraoka is soenthralled by the emerging field of persistent homology — a powerful mathematicalframework that can uncover patterns buried in large sets of data. First developed at
the beginning of the twenty-first century,
persistent homology has taken off in recent
years, finding applications in fields as diverse as neuroscience, linguistics, particle
theory and artificial intelligence. Hiraoka
considers it a tremendously exciting time
to be working in the field.
The power and versatility of persistenthomology lie in its ability to mathematically express the multiscale organization
so often observed in natural phenomena.

An experimentalist and an interpreter
Akihiko Hirata is the experimentalist of
the trio. His interest lies in using analytic
techniques such as electron diffraction
and transmission electron microscopy
to probe the atomic structures of socalled amorphous materials such as bulk
metallic glasses and other glasses. Unlike
crystalline materials, these glasses do nothave periodic arrangements of atoms or
molecules, which makes experimental
analysis of them far from straightforward.
Their disordered structures produce
blurry diffraction patterns and complex
micrographs, which are extremely challenging to glean meaningful structural
information from. To make sense of thedata, Hirata needed to consult with amathematician familiar with persistenthomology — Hiraoka’s visit offered theperfect opportunity.
It was not the first time that Hirata
had collaborated with a mathematician.
Together with mathematician Kaname
Matsue (then an assistant professor at the

AIMResearch 2016

SPECIAL SECTION: IN THE SPOTLIGHT

Akihiko Hirata (left) is an experimentalist who uses
powerful analytical techniques to explore amorphousmaterials. He is very appreciative of the help from
Takenobu Nakamura (right), a physicist who helps
interpret mathematical terminology and concepts
into physical ones and vice versa.

AIMR), Hirata had previously exploredthe structure of metallic glasses using
an angstrom-beam electron diffraction
technique he helped develop, which uses
an electron beam only several atoms
thick to obtain diffraction patterns. They
produced the first experimental evidence
for order with the same symmetry as
a 20-sided polygon (icosahedron) inmetallic glasses. “It was a great, fresh experience for me,” says Hirata of the study
published in Science in 20131. “I was
inspired by mathematicians.”
Interpreting between the two worlds
comes naturally to Takenobu Nakamura,a physicist who understands the terminologies used by mathematiciansand experimentalists. He has honed
his interpretive skills through studying
subjects heavy in mathematics, such as
statistical physics and non-equilibrium,
nonlinear physics.
At the AIMR, Nakamura works as a
researcher in the Interface Unit, which
serves as a bridge between materials
scientists and mathematicians. Even
with that background, it still takes him
some time to become proficient enoughto tackle a new project. “The first thing I
do is learn both terminologies by making
a translation table for the two fields,” hesays. “Then we can start the conversation.”
Persistence pays off
Seeing the potential of using persistenthomology to characterize the structureof amorphous solids, the trio began establishing common ground. Nakamura’s
experience proved invaluable in thisendeavor. “Before seriously starting thiswork, we took several months just to set
up a common terminology and frame ofreference,” says Hiraoka. “We wanted tofind our ‘sweet spot’.”
Working together, the three researchers eventually discovered that they could
use a special diagram based on persistent

AIMResearch 2016

The trio discussing the application of persistent homology to amorphous materials.

homology — known as a persistence
diagram — to visualize the structure ofamorphous solids. Curves in a persistence
diagram indicate the presence of local
structures. The researchers demonstrated
this for pure glass and found that it contains different ring-like configurations ofatoms (see related highlight on page 6).
“The first time we found this curve, we
knew it was what we had been searchingfor,” says Hiraoka. Such structures had
never been seen before in glass. The results were published in Proceedings of the
National Academy of Sciences USA in June
20162. “I don’t think any two of us working
together could have obtained this result,”
says Hiraoka. “It took all three of us.”More importantly, the approachdemonstrated the power of persistenthomology to unveil structures hiding in
the randomness of amorphous solids. The
researchers intend to apply this approachto other amorphous materials and to generate new mathematics. “We first focusedon silica, but the developed methods areapplicable to a wide range of other glass
structures,” says Nakamura.

Recent successes flowing from thisoutlook include the synthesis and exploration of belt-shaped ‘nanohoops’ by
Hiroyuki Isobe’s team3. Various othercollaborative studies have led to discoveries in the stoichiometric control ofdeposited thin films using a stochastic
model, formulation of the bulk-edgecorrespondence of topological insulators based on K-theory, mathematicalmodeling of periodic structures observed
along grain boundaries, as well as theprediction of phase separation morphologies of block copolymers using
Cahn−Hilliard equations.
Hiraoka is appreciative of the environment at the AIMR. “Director Kotani allowed me to establish a laboratory, whichis really unusual in the mathematics community,” he says. “Mathematics is usually
done by individuals working alone. But
in some cases, it’s also good to organize
a team to enhance the research field moreaggressively. Persistent homology has
now become such a field.”
■1. Hirata, A., Kang, L. J., Fujita, T., Klumov, B.,
Matsue, K., Kotani, M., Yavari, A. R. & Chen, M. W.

A collaborative environment
The finding was also due to the special
environment cultivated at the AIMR. The
institute has created many opportunities
for mathematicians and materials scientists to interact and work with each otherthrough target projects, fusion research,workshops and seminars, including theTarget Project–Interface Unit Joint Forum.
The culture of exploring the interface between mathematics and materials science
is deeply ingrained in the institute’s DNA.

Geometric frustration of icosahedron in metallic
glasses. Science 341, 376–379 (2013).
2. Hiraoka, Y., Nakamura, T., Hirata, A., Escolar, E. G.,
Matsue, K. & Nishiura, Y. Hierarchical structuresof amorphous solids characterized by persistenthomology. Proceedings of the National Academyof Sciences USA 113, 7035–7040 (2016).
3. Sun, Z., Suenaga, T., Sarkar, P., Sato, S., Kotani, M.
& Isobe, H. Stereoisomerism, crystal structures,and dynamics of belt-shaped cyclonaphthylenes.
Proceedings of the National Academy of Sciences
USA 113, 8109–8114 (2016).

5

SPECIAL SECTION: RESEARCH HIGHLIGHTS

Published online on 29 August 2016

Persistent homology:

Uncoveringorder in a seaof randomnessBy harnessing the power ofan emerging mathematicaltechnique known as persistenthomology, AIMR researchers
have extracted important geometric
information about the atomic configuration of the mostly random structureof glasses1.
Glasses range from window glass
made from silica to metallic glasses. In
contrast to the periodic atomic order ofcrystals, the atoms in glasses are largely
randomly distributed. But glasses do
not have entirely random structures,and their local atomic order can strongly influence their properties. However,characterizing this atomic order inglasses has proved very challenging because the order is largely masked by theoverall randomness of glass structure.
Yasuaki Hiraoka of the AIMR at
Tohoku University and his co-workers
turned to applied mathematics for help.
In particular, they explored a recently
developed mathematical techniquecalled persistent homology. This powerful analytical method can characterizegeometric structures that lie hidden inlarge sets of data, and it is being appliedin a wide range of fields.
“We used persistent homology toinvestigate one such geometric structure,

6

Structural features in silica glass appear against a random background. The
persistence diagram reveals ring-like structures of atoms (red spheres) in silica glass.

namely the hierarchical relationshipof rings in the atomic configuration ofglasses,” explains Hiraoka.
Employing a model of the atomic
positions of a glass as the input, theresearchers used software basedon persistent homology to generate a graphical representation of
the structure, which is known as apersistence diagram.

along with the presence of a few ringlike structures, which are characterized
by curves in the persistence diagram(see image).
This ability of persistent homology to
uncover hierarchical structures that are
hidden to conventional techniques is a
powerful demonstration of the potentialof this method for studying the structure
and properties of glasses and other

Our next target for amorphous structural analysis is totry to mathematically characterize the glass transition.
The persistence diagram reveals thepresence of local multiscale structuresin a material. Depending on geometricalparameters such as the size of the atoms
and the distances between them, different ring-like configurations of atoms
exist. For a perfectly random structure,
no local ring structure is favored and thedata background looks uniform. For acrystalline structure, geometric features
are preferred and clear structures appear
in the analysis. In the case of the silica
glass studied, the results are intermediate
between these two extremes: a uniform
random-like background is observed

amorphous materials.
For the future, the team has set its
sights even higher. “Our next target foramorphous structural analysis is to try
to mathematically characterize the glasstransition — one of the most important
problems in current condensed-matterphysics,” says Hiraoka.
1. Hiraoka, Y., Nakamura, T., Hirata, A., Escolar,
E. G., Matsue, K. & Nishiura, Y. Hierarchicalstructures of amorphous solids characterized
by persistent homology. Proceedings of the
National Academy of Sciences USA 113,
7035–7040 (2016).

AIMResearch 2016

Reproduced, with permission, from Ref. 1 © 2016 Y. Hiraoka et al.

A new analytical technique proves
to be a powerful method forstudying multiscale order in glasses

SPECIAL SECTION: RESEARCH HIGHLIGHTS

Left: Scanning electron microscope imagesof experimentally synthesized diblock
copolymer structures. Right: Diblock
copolymer structures of polystyrene (blue)
and polyisoprene (green) generated by anumerical model.

100 nm

100 nmPublished online on 26 September 2016

Block copolymers:

Predicting polymer shapes
100 nmReproduced from Ref. 1 with permission of The Royal Society of Chemistry.

A model that accurately predicts the structures of block copolymers is
promising for developing designer polymer nanoparticles

B

y applying a new mathematical
approach, AIMR researchers have gained insights
into the nanostructures that
mixtures of two plastics form undervarious conditions1.
Most commercial plastics, or polymers,
consist of long chains of one type ofmolecule. But just as different metals canbe combined to produce alloys that havesuperior properties to their constituent
metals, so polymer properties can betuned by mixing different polymers.
Polymers made up of two types ofpolymer molecules are known as diblock
polymers. The two chains can arrange
themselves into a wide range of different
configurations as a result of the attractive
and repulsive forces acting between them.
Even more shapes can be generated byconfining diblock polymers to different
volumes, such as a sphere or cylinder. Thisability to modify the shapes, and hence
the properties, of diblock polymers is
generating much interest because it holds
promise for making tiny chemical reactors and nanoparticles for drug delivery,
among other possible applications.
“Understanding the phase behaviors of
diblock copolymers in confined spaces is
one of the major problems in soft-matterphysics,” says Hiroshi Yabu of the AIMR

AIMResearch 2016

at Tohoku University. “Unique structureswith separated microphases emerge inthree-dimensionally confined spaces.
While such ‘frustrated phases’ have been
investigated experimentally and theoretically, little is known about the energetics
of such systems.”
Now, Yabu and co-workers, by building on a previous mathematical analysis2,
have used a set of coupled equations tonumerically explore the morphologies
and phases of diblock copolymers confined within spheres. They synthesized
nanoparticles containing mixtures of thepolymers polystyrene and polyisoprene(the polymer of natural rubber).
Depending on the conditions used, theresearchers obtained a variety of configurations, including some that resembled
tennis balls, onion layers or hamburgers.
When they compared transmission electron micrographs of diblock copolymers
with predictions based on their numerical model, they found that the results
were strikingly similar (see image).
“This model, which shows the relationship between the free energies and morphologies of diblock copolymers confinedin small particles, has great predictive
power and consistency with experimental
results,” says Yabu. “It provides not only
explanations of phenomena, but also

Understanding thephase behaviors of
diblock copolymers in
confined spaces is oneof the major problems
in soft-matter physics.
reliable guidelines for designing new experiments. In particular, it could be used
to suggest how to make new complex
morphologies experimentally and be useful for finding new functional materials
for applications such as drug delivery.
The researchers intend to use theirmodel to explore other mixtures ofpolymers as well as the effect of factors
such as the copolymerization ratio andmolecular weight.
1. Avalos, E., Higuchi, T., Teramoto, T., Yabu, H. &Nishiura, Y. Frustrated phases under threedimensional confinement simulated by a set of
coupled Cahn–Hilliard equations. Soft Matter 12,5905–5914 (2016).
2. Teramoto, T. & Nishiura, Y. Morphologicalcharacterization of the diblock copolymer
problem with topological computation. Japan
Journal of Industrial and Applied Mathematics 27,
175–190 (2010).

7

SPECIAL SECTION: RESEARCH HIGHLIGHTS

Rigid

Flexible

Published online on 31 October 2016

Carbon nanostructures:

The larger the nanohoop, the more flexible and less nanotube-like it becomes.

In the loop

S

tronger than steel, lighter thanaluminum,more
conductive than copper — carbon
nanotubes boast some exceptional properties.
One key to these properties is thenanotube’s unique shape: a hollow cylinder of tightly bonded carbon atoms,
across which a sea of electrons freely
flows. To gain a deeper understanding of
how the curved shape contributes to theproperties of carbon nanotubes, AIMR
researchers have synthesized a series ofbelt-shaped carbon ‘nanohoops’, whichmimic the nanotube structure, but areshorter and simpler1. In creating thesecarbon structures, the team discoveredthat the nanohoops have a rich chemistry of their own.
Hiroyuki Isobe and his colleagues fromthe AIMR at Tohoku University madethe series of nanohoops by combining
flat carbon structures called arylenes.
The arylenes join together to form a loop
in a process akin to threading flat beads
together to form a necklace. Using anapproach called random synthesis, theteam produced nanohoops ranging insize from six to eleven arylene units.
The researchers showed that the true
structural diversity was considerably
greater than just six nanohoops of different

8

We are now trying to reveal the secrets hidden in thepersistent cylindrical shape, and hope that many new
surprises will enrich the chemistry and its allied areas.
sizes. Each arylene ‘bead’ can attach to
the growing nanohoop in two possible
orientations, forming different structures
known as stereoisomers. Teaming up witha mathematician, the researchers calculated the total number of possible stereoisomers that a nanohoop of any given size
could have. These calculations predictthat the largest, 11-arylene nanohoop canform 126 different stereoisomers.
More significantly for carbon nanotube research, the team used variabletemperature nuclear magnetic resonance(NMR) to show that the larger the nanohoop, the more flexible its structure becomes (see image). To be a good model
for a carbon nanotube’s stiff cylindricalshape, rigid nanohoops are required. Of
Isobe’s nanohoops, only the smallest,six-arylene nanohoops showed sharp
peaks in the room-temperature NMR
spectrum, which indicate the necessary
rigid cylindrical structure.
“Our study is the first to show thisthreshold between rigid, cylindricalmolecules and fluctuating molecules,”Isobe says. The team found that of themany structural variants of nanohoops
that have been designed to mimic
nanotubes, very few of them successfully
mimic the persistent cylindrical shape ofcarbon nanotubes.
The work lays the foundations forfurther studying the unique structuralchemistry of nanohoops. “This study
shows that we are at a very fundamental, early stage of understanding thechemistry of these materials,” Isobe
adds. “We are now trying to reveal thesecrets hidden in the persistent cylindrical shape, and hope that many new
surprises will enrich the chemistry andits allied areas.”
1. Sun, Z., Suenaga, T., Sarkar, P., Sato, S.,
Kotani, M. & Hiroyuki, I. Stereoisomerism,
crystal structures, and dynamics of beltshaped cyclonaphthylenes. Proceedings of
the National Academy of Sciences USA 113,
8109–8114 (2016).

AIMResearch 2016

© 2016 Hiroyuki Isobe

Nanoscale hoops of carbon atoms are poised to reveal the advantages of curved structures

SPECIAL SECTION: RESEARCH HIGHLIGHTS

Published online on 28 November 2016

Metallic glasses:

Mathematics nails
diameter distribution

The structures produced by gas atomization of
palladium-based metallic glass depend on a parameter
known as the Ohnesorge number: microdroplets (left)form at low values of the Ohnesorge number, whereas
nanowires (right) are produced at higher values.

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

Mathematical analysis reveals that the threshold between the formation of awire and a droplet made from metallic glasses hinges on a single parameterBy mathematically analyzing
the nanostructures of metallic glasses, AIMR researchers
have gleaned new insights into
how these useful materials form. Thisknowledge will help to optimize the
manufacturing process.
Metallic glasses are attracting a lotof interest because their disorderedstructures give them different properties
from conventional metals, which havehighly ordered structures. In particular,
nanowires made from metallic glasses
are promising for use in magnetic sensors, fiber-reinforced composites andheterogeneous catalysts.
Koji Nakayama of the AIMR at
Tohoku University and co-workers
previously demonstrated that metallic
glass nanowires can be produced by gas
atomization — a common process forthe commercial production of metal
and alloy powders. In this method, amolten metal is ‘atomized’ into small
droplets by high-speed jets of a chemically unreactive gas. But the complexityof the atomization process makes it difficult to control the sizes and shapes ofmetallic glass nanowires.
Now, by teaming up with mathematicians at the AIMR, Nakayama’s grouphas statistically analyzed the formation

AIMResearch 2016of microdroplets and nanowires madefrom a palladium-based metallic glass1.
They found that the forms of the droplets and wires are related to a parameter known as the Ohnesorge number,which relates the viscous forces ofatomization, which will eventually lead
to better control of the process.
The researchers selected palladiumbased metallic glass for the study because of its strong glass-forming ability
and high resistance to reacting with ox-

Collaboration with mathematicians was vital because
they helped us to develop the statistical models.
a fluid to its surface tension forces.
In particular, microdroplets form at
low values of the Ohnesorge number,whereas nanowires are produced at
higher values (see image).
The researchers also found that the distribution of nanowire diameters follows awell-known statistical pattern in nature,
called the log-normal distribution. “Thelog-normal distribution is defined as the
distribution of a random variable whose
logarithm is normally distributed,”
explains Nakayama. “It has been widely
applied for fitting data such as the sizesof organisms, the numbers of species inbiology and incomes in economics.”
These findings will assist researchers todevelop a clearer picture of how nanowires of metallic glasses form during gasygen, but Nakayama notes that the same
analysis can be carried out on othermetallic glasses.
Nakayama values mathematicians’
input to the analysis. “The study was donewith the support of the AIMR Fusion
Research Program, which promotes crossdisciplinary research between materials
science and mathematics to gain new
insights into industrial products,” says
Nakayama. “Collaboration with mathematicians was vital because they helped
us to develop the statistical models.”
1. Yaginuma, S., Nakajima, C., Kaneko, N.,
Yokoyama, Y. & Nakayama, K. S. Log-normal
diameter distribution of Pd-based metallic
glass droplet and wire. Scientific Reports 5,10711 (2015).

9

SPECIAL SECTION: RESEARCH HIGHLIGHTS

Fermi arc
Published online on 26 December 2016

Quantum materials:

Tadpole-shaped surface states on metal
crystals confirm the presence of exotic
quasiparticles ideal for three-dimensional
computing devices

An elusive quantum state thatcan polarize charge carriers
for spintronic applications
and move them, undisturbed,
at ultrahigh speeds has been directly
observed by a team at the AIMR1.
First predicted in 1929 but only
observed in 2015, Weyl fermions area special class of quantum particle
that have the same spin properties aselectrons but are massless, like photons.
This combination enables electronic
charges to be transported at muchhigher speeds than possible in today’s
computing devices. It also allows thequasiparticles to effortlessly move past
defects in a crystal structure instead ofbeing scattered by them.
Researchers, however, were unable to spot Weyl fermions until the
recent discovery of ‘semimetals’ madefrom binary transition metals. Thesematerials split electrons into pairs of
Weyl fermions at points in the crystal
lattice where empty conduction bands
cross over into electron-containing
valence bands. At these crossover
points, Weyl semimetals exhibit properties analogous to a three-dimensional
form of graphene but with valuablespin-polarized bands absent in atomic
carbon sheets.

10

Fermi arc

Weyl
pointsIdentifying graphene-like Weyl points inside metal crystals by their distinct
surface Fermi-arc patterns could help usher in ultrahigh-speed electronics (thethick black arrows indicate the spin direction).

Calculations suggest that several
types of Weyl semimetals can exist. Now,
Seigo Souma from the AIMR at Tohoku
University and colleagues in Japan andGermany have made it easier to identify
materials with these technologically exciting properties. Souma explains that
Weyl fermions always appear with adefinite handedness, or chirality. This
property is manifested by surface statesthat have unusual shapes such as those
resembling a tadpole or a dog bone.
But spotting these ‘Fermi-arc’ states ischallenging and time consuming sincemetals contain many surface states.

These particles aresuperior to graphenein several ways and canhandle large currents
because they’re
so robust.

To detect Fermi-arc states purely
by experiment, the AIMR teaminvestigated a niobium–phosphorous material reported to have an
ultrahigh charge mobility and large
magnetic forces. The team realizedthat cleaving this metal along specificlattice orientations could produce thincrystal sheets with niobium exposedon one side and phosphorous on theother. By measuring the electronic
states of each side with photoemission spectroscopy and contrasting thedifferences, they mapped the Weyl
crossover points and the branch-like
Fermi-arc states connecting them(see image).
“No matter how much the surface
potential deforms Fermi-arc states,
the Weyl points never move,” explains
Souma. “These particles are superior
to graphene in several ways and canhandle large currents because they’re
so robust.”
1. Souma, S., Wang, Z., Kotaka, H., Sato, T.,
Nakayama, K., Tanaka, Y., Kimizuka, H., Taka-“It’s necessary to use band calculations
to assign Fermi-arc states from the manyobserved surface bands,” says Souma.
“Without performing these computations,
you normally can’t see which is which.”hashi, T., Yamauchi, K., Oguchi, T. et al.
Direct observation of nonequivalent Fermi-arc
states of opposite surfaces in the noncentrosymmetric Weyl semimetal NbP.
Physical Review B 93, 161112(R) (2016).

AIMResearch 2016

© 2016 Seigo Souma

Masslessparticles jumpout from a seaof electrons

SPECIAL SECTION: RESEARCH HIGHLIGHTS

Published online on 26 August 2013

Metallic glasses:

All in order

The assumed icosahedral local atomic structure of metallic glasses (left, blue), theface-centered cubic (fcc) structure of the corresponding metal crystal (right, red) andthe actual distorted icosahedral arrangement of metallic glasses (center, yellow). The
top and bottom rows show the same structures from a different angle.

© 2013 Akihiko Hirata

The local atomic order of metallic glasses has been solved by electron-beamimaging at the atomic scaleM

ost of the glasses that we
encounter everyday aretransparent and appear to
be rather ordinary. A closer
look, however, reveals an intriguing
composition: glasses are basically frozen liquids, meaning that their atoms
are randomly arranged. Researchers
from the AIMR at Tohoku University
and international collaborators havenow shown that, surprisingly, theatoms of some glasses containing metallic components also display a local
order that is based on icosahedral
geometric structures1. “We provide
the first direct experimental evidenceof the existence of icosahedral orderin metallic glasses,” explains Mingwei
Chen, who led the research team tothis discovery, which confirms previous theoretical predictions.
Atoms in metals behave like perfectspheres, forming perfect crystals withatomic arrangements in the form offace-centered cubic (fcc) or bodycentered cubic (bcc) structures, forexample. Some metallic compounds
can also form glasses when cooled fastenough after melting. Scientists were
unsure as to why some metals form
glasses instead of crystallizing and assumed that upon fast cooling, atoms in

AIMResearch 2016

We have just reached the starting point to understandthe true relationship between structure and propertiesof disordered materials.
the metal are prevented from forming acrystal when they arrange into icosahedra. Such arrangements are similar inappearance to fcc crystal structures but
importantly cannot form large-scale,periodic structures (see image).
To study the structure of metallic
glasses, Chen, Akihiko Hirata and colleagues used an angstrom-beam electron diffraction technique in which atiny beam of electrons is guided onto asample of glass that is only a few atoms
wide. As the electrons pass through theglass, they are reflected by the atoms
and subsequently hit a screen thatrecords the pattern of their reflection.
With the help of computer analysis, thepositions of the atoms in the sample
can be determined from these patterns.
While the researchers were able
to confirm the icosahedral atomic
structure of metallic glasses, they also
found that the icosahedra were not perfectly formed, as previously assumed.
Interestingly, this slight distortion

occurs in a way that makes the icosahedra appear even closer in structure to
the fcc arrangement.
Beyond the discovery of local orderin metallic glasses, the Angstrombeam electron diffraction techniqueitself is a powerful way of studying
compounds on the atomic scale, comments Chen. “We have just reached
the starting point to understand thetrue relationship between structure
and properties of disordered materials.
We now have a reliable experimental
method to directly investigate local
atomic structure, and in the present
case to show the correlation between
atomic-scale structure and glass formation, and perhaps even the structural origin of the glass transition.”
1. Hirata, A., Kang, L. J., Fujita, T., Klumov, B.,
Matsue, K., Kotani, M., Yavari, A. R. & Chen,
M. W. Geometric frustration of icosahedron in metallic glasses. Science 341,
376–379 (2013).

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SPECIAL SECTION: RESEARCH HIGHLIGHTS

Published online on 26 August 2013

Batteries:

A crashcourse innanofabricationDeveloping high-capacity lithium
ion batteries is an importantresearch problem in materials
science, and the realization ofhigh-quality thin films of lithium metaloxides is a step toward this goal. Pulsed
laser deposition (PLD) is a promising method of creating such films. In
this technique, atoms from a lithiumcontaining source are vaporized using
high-powered bursts of light, and theresulting ‘plume’ of plasma-phase atoms
subsequently lands on a designated surface as a nanometer-thin coating.
However, when depositing films ofelectroactive materials such as lithium,the composition of the final thin film
often differs from that anticipated. This
‘non-stoichiometric’ behavior makes it
hard to predict the final result of particular fabrication strategies. Although thecauses of the non-stoichiometry may be
attributed to the volatile and chemicallyreactive nature of lithium atoms, quantitative explanations of this phenomenon
have been lacking. Daniel Packwood,
Susumu Shiraki and Taro Hitosugi fromthe AIMR at Tohoku University1 havemade a discovery that should significantly
improve the quality of PLD lithiumbased thin films thanks to a model that
describes collisions between high-energy

12

A representation of the combined mathematical and materials study
into the deposition of electroactive thin films. The simulated trajectoryof a lithium atom at an oxygen pressure of 10-6 torr (black line) is
superimposed over a plot of a lithium plasma plume after expanding for
5 microseconds at an oxygen pressure of 10-2 torr (background).

The team expects that their analysis can guide thefabrication of higher-quality interfaces that would leadto lithium ion batteries with higher charge–discharge
rates by reducing the effects of electrical resistance.
atoms during the deposition process.
During experimental trials, theresearchers noticed that adding background pressures of oxygen gas to the
PLD chamber could change the proportion of lithium in the thin film structures.
Intrigued by this result, they investigatedthis behavior — and the role of oxygen —with a theoretical model of the scattering
process as a series of two-dimensional,
head-on collisions between classicalparticles (see image).
After synthesizing several prototypicallithium–manganese oxide thin films at
different oxygen pressures, Packwood,
Shiraki and Hitosugi compared the films’
chemical composition to the predictionsof their new model. The results were
striking: the theory correctly mirrored
the experimental results and revealed
that the presence of oxygen gas caused
lithium ions to scatter in erratic trajectories, often violently. Heavier manganese
atoms pushed through oxygen practicallyunimpeded. According to the team, thesefindings indicate that lighter atoms will
always show deficiencies when background gas pressures rise above a certain
threshold — thus, source materials must
be chosen carefully to achieve desired
lithium compositions.
Packwood notes that the model works
well because it captures the physics behindthe critical energy exchange occurring
during atomic scattering. This ensures reasonable thermal equilibrium in the modeland predictions of spatial distribution thathave proven experimentally valid. The
team expects that their analysis can guidethe fabrication of higher-quality interfacesthat would lead to lithium ion batteries
with higher charge–discharge rates byreducing the effects of electrical resistance.
1. Packwood, D. M., Shiraki, S. & Hitosugi, T. Effects
of atomic collisions on the stoichiometry of thinfilms prepared by pulsed laser deposition. PhysicalReview Letters 111, 036101 (2013).

AIMResearch 2016

Modified from Ref. 1 © 2013 American Physical Society

A collaborative study reveals thatatomic collisions play critical roles
during laser-driven assembly ofelectroactive thin films

RESEARCH HIGHLIGHTS

Metallic glasses:‘Revolutionary’ advance in MEMS
Replacing silicon with a metallic glass enables a low-powered
microelectromechanical system with a high rotational performance to be realized
Now, by exploiting the high robustnessof metallic glasses, AIMR researchers
have constructed a MEMS device thatboasts an ultrahigh rotational performance as well as a very low power
consumption, making it attractive for next-generation
sensors and actuators1.
Metallic glasses are alloys
that are characterized by anon-crystalline
structure
and a low elastic modulus.
Yu-Ching Lin first encountered them when she
joined the AIMR at Tohoku
University, and she was immediately struck by their potential for MEMS. “Metallic
glasses are amorphous andare very strong on micro andnanoscales,” she explains. “I
thought they would be very
promising for MEMS, which
need tough micro and nanostructures to prevent breakage during actuation.”
Lin realized that, because
they have lower elastic
moduli than silicon, metallic glasses could be used torealize a higher degree ofmovement in MEMS. Thisis exciting for sensing andactuating applications, sincelargerdeflections
mean
higher performance.
To test this idea, Lin andher collaborators constructeda microscanner that contained a zirconium-based
metallic glass (see image).
The metallic-glass-based microscanner in action. Its metallicThe scanner had a large rotaglass components enable a much higher rotation angle to betion angle of 146 degrees at aachieved than that of a conventional silicon-based device.

© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

The fragility of silicon after it has been
subjected to microprocessing limits
the use of silicon-based microelectromechanical systems, or ‘MEMS’, in devices with large rotational movements.

AIMResearch 2016

low power consumption in the microwatt range. Lin notes that it would be
exceedingly difficult to realize such alarge deflection angle and low power
consumption simultaneously in asilicon-based MEMS.
To explore the potential of thescanner, the team deployed it as partof an optical coherence tomography
imaging system, which they used toobtain images of a human finger. The
metallic-glass MEMS scanner obtained
images at a lateral resolution about
ten times better than silicon-based
scanners reported in the literature,says Lin. “Many MEMS researchers
are developing microscanners for
optical coherence tomography imaging based on silicon, with very slow
scanning speeds.”
Its high performance and enviably
low power consumption make MEMS
fabricated from metallic glasses promising for emerging wearable technology, for which fast-draining batteries
are a concern. Looking further ahead,“if we can combine our device with aself-generation device, maybe in the
future we won’t even need a battery,”says Lin.
Lin notes that both metallic glasses
and MEMS are strong research fields
at Tohoku University, and that working
at the AIMR has enabled her and hercollaborators to bridge the two fields
and create this novel metallic-glass
MEMS device.
1. Lin, Y.-C., Tsai, Y.-C., Ono, T., Liu, P., Esashi, M.,
Gessner, T. & Chen, M. Metallic glass as amechanical material for microscanners.
Advanced Functional Materials 25,
5677–5682 (2015).

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RESEARCH HIGHLIGHTS

Three-way catalysts:

Cool way to make catalytic
converters
A new, mild-temperature method for
producing cerium oxide nanorods has
been developed by AIMR researchers.
The nanorods show an excellent oxygenstorage capacity at temperatures below
200 degrees Celsius, making thempromising for use as catalysts to control
harmful emissions from vehicles1.
Catalytic converters in cars use
so-called three-way catalysts to convert
noxious pollutants such as carbon
monoxide and nitrous oxides into
more benign compounds. Cerium
oxide is an attractive material for suchcatalysts due to its high oxygen storage capacity — a critical parameter for
three-way catalysts.
However, most methods for fabricating nanostructures require hightemperatures, which induce crystal
growth and thereby have the detrimental effect of reducing the surface area of
the nanostructures — another crucial
parameter for catalysts. This has madeit challenging to produce cerium oxide
nanostructures that possess high oxygenstorage capacities at temperatures below
about 400 degrees Celsius.
Now, a team of five researchers fromthe AIMR at Tohoku University led by
Naoki Asao and Koji Nakayama has
devised a mild-temperature method for
producing nanorods of cerium oxidethat exhibit an excellent oxygen-storage
capacity at moderate temperatures.
The nanorods are about 5 to 7 nanometers in diameter as measured byhigh-resolution transmission electron
microscopy (see image). The cool
reaction conditions made it possible toproduce such fine structures.
The team adopted a method that they
had previously developed to produce

14© 2016 Naoki Asao and Koji Nakayama

Nanorods with high oxygen storing capacities at moderate temperatures have beensynthesized using a simple reaction

5 nm
A high-resolution transmission electron microscopy image showing fine cerium oxide nanorods fabricated by amild-temperature method.

nanowires of sodium titanate. It basically involves corrosion of ribbons of
cerium–aluminum alloys in an alkaline
medium; in this reaction, aluminumis leached, whereas cerium is oxidized.
Importantly, this reaction occurs under
mild conditions.
“This technique is really different fromprevious methods. Its key aspect is themild fabrication conditions, which makeit possible to fabricate fine structures,”says Asao. “Based on our work with titanate nanowires, we had a feeling that thecorrosion-based method would resultin some unexpected properties. But thefindings far exceeded our expectations.”
Asao is very excited about the potential of this new method. “We believethat this research will have a significant

impact on the automobile industry,” hesays. In addition, the researchers anticipate that the nanorods could be usedin other applications, including fuels
cells, ultraviolet blockers, solar cells
and sensors.
By optimizing the reaction conditionsand varying the composition of thecerium–aluminum mother alloys, thescientists will seek to further enhancethe oxygen storage capacity and otherproperties of the nanorods to makethem suitable for practical applications.
1. Ishikawa, Y., Takeda, M., Tsukimoto, S.,
Nakayama, K. S. & Asao, N. Cerium oxide
nanorods with unprecedented low-temperature
oxygen storage capacity. Advanced Materials
28, 1467−1471 (2016).

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Lithium–oxygen batteries:

Super-sized storage with
nanoporous graphene
By converting flat graphene sheets into
three-dimensional (3D) architectures,
AIMR researchers have developed alightweight, metal-free electrode forlithium–oxygen (Li–O2) batteries that
may have a transformative effect on
all-electric vehicles1.
The excess weight and moderate capacities of today’s lithium-ion batteries
have prompted a search for alternativetechnologies. Rechargeable lithium–oxygen batteries are a promising substitutebecause of their ultrahigh theoreticalenergy densities and ability to generate
power by ‘breathing’ in oxygen from theatmosphere, negating the need for typical battery components.
These experimental batteries generally use a form of charcoal known as
activated carbon as cathodes, and mix
them with transition-metal catalysts.
Activated carbon, however, becomes
unstable under typical lithium–oxygen
operating conditions — after several
charge–discharge cycles, the carbon begins to decompose battery electrolytes,
causing premature device failure.
Another approach is to use
two-dimensional graphene lattices aslithium–oxygen cathodes because of
their high surface area, good chemical and mechanical stability, and highelectrical conductivity. But integrating
graphene into electrochemical cells is
problematic: graphene connects poorly
with metal electrodes and catalysts and isgeometrically difficult to pack into cellswith sufficient density.
Mingwei Chen and Jiuhui Han of the
AIMR and co-workers have recently
developed a way to coax graphene outof its planar geometry by growing it on
the nanoporous surfaces of disposable

AIMResearch 2016

© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Unconventional electrodes made from three-dimensional graphene structures
enable batteries to hold 100 times more charge than conventional lithium-ion cells

A nanoporous electrode made from graphene complexes can dramatically boost charge storage in ‘breathable’lithium–oxygen batteries.

nickel templates. This produces 3D
materials with abundant pore space fortrapping molecules, and the same highspeed electron mobility as their flat
counterparts. In their latest work, theresearchers teamed up with colleague
Tadafumi Adschiri to investigate 3Dgraphene as a potential electrode forlithium–oxygen batteries.
One advantage of nanoporous graphene is that bending the flat lattice
into 3D shapes introduces defects that
can host dopants — small guest atoms
that alter the surface chemistry of thelarger carbon framework. The teamstudied nitrogen- and sulfur-doped 3D
graphene because these atoms can promote lithium–oxygen reactions without
metal catalysts.
The researchers fabricated centimeterscale, flexible graphene electrodes
and placed them into ‘coin-cell’ typelithium–oxygen batteries (see image)that snap together without the needfor complex assembly or binding
agents. Electrochemical tests revealed
the benefits of these electrodes — thenitrogen-doped nanoporous graphene
had a discharge capacity two orders ofmagnitudes greater than that of commercial lithium batteries and could be
reliably recharged for hundreds of cycles.
“These excellent performances surpass
state-of-the-art metal-free, graphenebased lithium–oxygen batteries,” says
Han. “With such large capacities, they
could transform portable electronics
and power electric vehicles for extended
ranges of more than 500 kilometers.”
1. Han, J., Guo, X., Ito, Y., Liu, P., Hojo, D.,
Aida, T., Hirata, A., Fujita, T., Adschiri, T.,
Zhou, H. & Chen, M. Effect of chemical dopingon cathodic performance of bicontinuous nanoporous graphene for Li-O2 batteries. Advanced
Energy Materials 6, 1501870 (2016).

15

RESEARCH HIGHLIGHTSBand structure engineering:

Massless electrons put on weight
Massless electrons can be made massive by exploiting the spins in a layer of ironatoms on tungsten

16

Massless

Massive

Adapted with permission from Ref. 1. Copyrighted by the American Physical Society.

AIMR researchers have struck upon aconvenient way to convert ultrafast electrons known as ‘massless Dirac fermions’into ones that possess mass1. This has
promise for realizing new devices suchas magnetic-field sensors and magnetic
memory devices.
Electrons moving through ultrathin
layers on top of blocks of novel materials
such as topological insulators have generated a lot of interest among materials
scientists recently. Such electrons behaveas essentially massless particles andmove at speeds approaching that of light.
Researchers strongly desire a way to manipulate Dirac fermions so that they canbe easily changed between their massive
and massless states.
Seigo Souma and co-workers at the
AIMR, Tohoku University, have founda simple and effective way to convert
massless Dirac fermions into massive
ones: evaporate an atomically thin layerof iron atoms onto a small block of tungsten metal.
Unlike normal massive conduction
electrons in metals, massless electrons
lack a gap in their band structure. The
ferromagnetism of the iron atoms opens
a gap in the electrons’ band structure,making the electrons massive. “This is
the first spectroscopic observation ofa gap opened by a magnetic effect fora system in which ferromagnetism has
been confirmed,” says Souma.
The researchers found that theelectrons could be switched between
massless and massive states by varying
the direction of the spins of the ironatoms — the electrons are massless when
the spins lie in the plane of the layer,
but become massive when the spins areperpendicular to the layer (see image).

Electrons in an iron film (top yellow layer) on a tungsten substrate (bottom brown layer) are massless (no gap
in the band structure) when the spins (indicated by purple arrows) of the iron atoms are in plane and massive(gap in the band structure) when the spins are perpendicular to the film.

The direction of the electron spins canbe controlled by tuning the thickness of
the iron film or adsorbing oxygen onto
the film.
Their method has two advantages
over alternative schemes. First, the ironlayer exhibits strong ferromagnetismthat should persist well above room temperature (roughly 300 kelvin). This is incontrast to systems doped with magnetic
ions where ferromagnetism disappears
above about 30 kelvin.
The second advantage is that the gap
size is considerably larger than previous
systems, being over twice that achievedin topological insulators doped withmagnetic ions. Since this gap size isapproaching the thermal energy atroom temperature, it holds the promiseof realizing devices that operate atroom temperature.
The team is excited about applying theconcept to other systems, particularly topological insulators. “Our idea is rather
simple and should be applicable to othersystems,” notes Souma. “If we can find an
appropriate overlay film that can be epitaxially grown on a topological insulator,
various exotic phenomena will become
experimentally accessible.”
1. Honma, K., Sato, T., Souma, S., Sugawara, K.,
Tanaka, Y. & Takahashi, T. Switching of Diracfermion mass at the interface of ultrathin
ferromagnet and Rashba metal. Physical Review
Letters 115, 266401 (2015).

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RESEARCH HIGHLIGHTS

Titanium dioxide:

Atoms mapped at border
between crystals
By pinpointing the precise positions ofatoms in titanium dioxide, AIMR researchers have studied how temperatureand pressure affect the materials’ structure and properties1.
As their name implies, polycrystalline
materials are made up of many small
crystals. The interfaces between two ofthese small crystals are known as grainboundaries, the structure of whichstrongly affects material properties suchas strength and electrical conductivity.
Temperature or pressure changes cancause defects in a crystal’s atomic lattice
to migrate to a grain boundary, which reshapes the structure of the boundary andhence modifies the material’s properties.
This process is extremely difficult to
study because researchers need to see
exactly where atoms sit relative to a grainboundary. While scanning transmission
electron microscopy (STEM) can offersome insights, its usefulness is limited
if the material contains low-mass atoms
such as oxygen, which scatter electrons
only weakly and hence are difficult toimage by conventional STEM.
Now, Yuichi Ikuhara of the AIMR at
Tohoku University and co-workers haveapplied two advanced STEM techniques— aberration-corrected high-angle annular dark-field (HAADF) STEM andannular bright-field (ABF) STEM — tostudy titanium dioxide, which is used ina wide range of applications, including
catalysis, solar cells and gas sensors. The
position of oxygen atoms in titanium
dioxide’s grain boundaries can significantly affect the material’s conductivity
and catalytic activity.
To simulate a grain boundary, the researchers bonded two crystals of titanium
dioxide together (see image) and used

AIMResearch 2016

© 2016 Yuichi Ikuhara

Manipulating the structure of grain boundaries could fine-tune the properties ofpolycrystalline materials

A scanning transmission electron micrograph showing a simulated grain boundary produced by combining two
crystals of titanium dioxide.

HAADF and ABF STEM to reveal a neatline of oxygen atoms along the boundary.
When they heated these samples to
800 degrees Celsius under low pressure,the team found that some oxygen atoms
were missing from the grain boundary.
This should increase electrical conductivity along the boundary, says Ikuhara.
But heating the sample under avacuum caused oxygen atoms to adopt a
zigzag pattern along the grain boundary.
“It is very surprising that these conditions could dramatically modify theatomic structure of grain boundaries intitanium dioxide,” says Ikuhara. Whenthe researchers performed theoretical
calculations to simulate these changes,
they obtained good agreement with theexperimental observations.

The results suggest that the propertiesof polycrystalline materials could be
fine-tuned through heat or low-pressure treatments, optimizing them foruse in electronic devices, for example.
“We could control the grain boundary
atomic structures to convert an insulating grain boundary into a conductive
one,” suggests Ikuhara.
The team next plans to study howtemperature and pressure affect thegrain boundaries of other materials.
1. Sun, R., Wang, Z., Saito, M., Shibata, N.
& Ikuhara, Y. Atomistic mechanisms
of nonstoichiometry-induced twinboundary structural transformation intitanium dioxide. Nature Communications 6,7120 (2015).

17

RESEARCH HIGHLIGHTS

Graphene:

Tying ribbons of graphene

A method that produces tiny units of graphene and joins them together to form
highly connected stripes has been foundby AIMR researchers. This ‘bottom-up’
fabrication technique could unleash graphene’s potential for use in high-speed,
low-power electronic devices.
Since its discovery in 2004, graphenehas generated much excitement due to
its remarkable electronic and mechanicalproperties. But for it to become useful
in applications, scientists need a way to
combine graphene nanostructures suchthat they form macroscale components
while still preserving graphene’s excellent properties.
Extremely narrow (thinner than
50 nanometers) stripes of graphene,
known as graphene nanoribbons, promise to achieve this, but current processing
methods produce either well-connectednanoribbons that contain defects orentangled bundles of nanoribbons thatare defect free.
Now, Patrick Han of the AIMR at
Tohoku University and his co-workers
have found a way to produce wellconnected strings of nanoribbons
without defects1. Their method produces
good-quality graphene nanoribbons andconnects their ends so that they formchemically and electronically connectedstructures (see image).
The researchers found that, on applying heat, a copper substrate guides
precursor molecules to form and connect graphene ribbons. The lengths andgrowth directions of the nanoribbons
could be controlled by varying the substrate properties and the temperature.
“There are two outstanding questions
regarding how graphene can be appliedin electronics,” comments Han. “One18

© 2016 Patrick Han

Extremely thin ribbons of graphene grown on copper could open applications forthe ‘miracle material’

A topographic scanning tunneling microscopy image showing graphene nanoribbons (green) grown on acopper substrate (blue).

is how to fabricate atomically precise
graphene structures with high aspectratios at desired locations, while theother is how to make electronic connections between these structures to accessgraphene’s properties.”
The method provides answers to bothquestions. “If precursor molecules areallowed enough time and space to align,graphene nanoribbons with very highaspect ratios can be produced without
defects. Moreover, graphene nanoribbon
interconnections yield smooth electronic
connections, showing that bottom-up
strategies can access graphene’s amazing properties.”
Han notes that while other two-dimensional materials have recently beenstealing the spotlight from graphene, it
still has a unique advantage — organic

chemistry can be used to fabricate defectfree structures from designer precursors.
“In this regard, our method is a significant advance — the use of bottom-up
graphene fabrication strategies may lead
not only to the production of future
graphene nanodevices, but also to theintegration of non-graphitic materials.”
Since copper substrates limit growth
to six directions, growing graphene
nanoribbons inevitably collide, limiting
their length. The team intends to overcome this restriction by finding strategies to limit growth to a single direction.
1. Han, P., Akagi, K., Federici Canova, F., Shimizu, R.,
Oguchi, H., Shiraki, S., Weiss, P. S., Asao, N. &Hitosugi, T. Self-assembly strategy for fabricating connected graphene nanoribbons. ACS
Nano 9, 12035–12044 (2015).

AIMResearch 2016

RESEARCH HIGHLIGHTSGold catalysis:

Examining catalysis on an
atomic scale
By mapping the three-dimensionalarrangement of gold atoms in gold
structures containing nanoscale pores,
researchers at AIMR have shown that
surface defects play an important rolein their catalytic ability1.
Gold nanostructures are widely used
to accelerate oxidation reactions. For
example, they can catalyze the oxidationof toxic carbon monoxide to benign
carbon dioxide. But just how they speed
up these reactions has been vigorously
debated for many years.
One complicating factor is that gold
nanoparticles are often supported onoxide surfaces, which makes it difficult to determine the degree to which
substrate effects contribute to catalysis.
Ideal systems for studying gold’s intrinsic catalysis are gold structures riddledwith tiny pores — nanoporous gold —because, unlike nanoparticles, they do
not need to be attached to a substrate.
Now, Mingwei Chen and Pan Liu of
the AIMR at Tohoku University andco-workers have combined a state-ofthe-art electron microscopy techniquewith tomography to visualize in three
dimensions the atomic arrangementsof narrow bridges in nanoporous gold(see image). They then compared thesethree-dimensional maps with measurements of catalysis.
In addition to showing the positionsof atoms, the images also reveal theirdegree of coordination to surrounding
atoms. Atoms far from a surface arecompletely surrounded by atoms andhence have high coordination numbers,
whereas those near or on a surface
have lower ones. The researchers foundqualitative agreement between the electron microscopy characterization and

AIMResearch 2016

© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

A comparison of atomic maps of nanoporous gold and catalysis reveals that surface
defects are important catalysis sites

The atomic positions of a narrow bridge in nanoporous gold. The colors indicate the coordination numbers(red: five or six; blue: seven; pink: eight; yellow: nine to eleven). The inset shows the same structure from adifferent perspective.

catalytic measurements at active atomic
sites and low-coordinated surface
atoms. This implies that defects on thesurface play a major role in the catalysis
of nanoporous gold.
“The curved surface of nanoporous
gold is composed of flat terraces, atomic
steps and kinks, which correspondto different coordination numbers,”
explains Liu. “Generally, under-coordinated sites with low coordination
numbers of five and six are thought
to be highly active sites in oxidation
reactions, whereas those with coordination numbers greater than nine areconsidered to be relatively inactive. Our
study has confirmed this and provides
compelling evidence that catalysis may
originate from the under-coordinatedsurface atoms alone.”

Liu notes that the method could
also be applied to other catalytic systems. “This study also demonstrates
that quantitative measurements on an
atomic scale can provide vital knowledge about the catalytic mechanismsof nanomaterials.”
In the future, the team intends to improve the catalytic performance of gold
catalysts by fabricating and measuring
the catalytic properties of nanoporous
gold particles with larger surface areas
and more under-coordinated atoms.
1. Liu, P., Guan, P., Hirata, A., Zhang, L., Chen, L.,
Wen, Y., Ding, Y., Fujita, T., Erlebacher, J. &Chen, M. Visualizing under-coordinatedsurface atoms on 3D nanoporous gold
catalysts. Advanced Materials 28,
1753–1759 (2016).

19

RESEARCH HIGHLIGHTS

Graphene:

A dose of calcium yields asuperconductor
Sandwiching calcium atoms between two layers of graphene produces a device thatmoves electrons with zero resistance20

Ca atom

Graphene© 2016 Takashi Takahashi

The first direct evidence of graphene
acting as a superconductor has beenreported by AIMR researchers1. This
demonstration, which occurs at temperatures close to absolute zero, sets thestage for molecular-scale devices thatcan move electrons effortlessly and do
not generate waste heat.
Ever since layers of graphene — oneatom-thick sheets of carbon atoms —were first isolated, researchers have beenfascinated with the way electrons behave
as near-massless particles when they
move between its carbon atoms. This
remarkable electron mobility has raised
the exciting possibility of producing
superconducting graphene, but unfortunately graphene has too few electrons torealize zero-resistance flow.
Now, Takashi Takahashi and colleagues from the AIMR at Tohoku
University and the University of Tokyo
have developed a method that boosts
the electron density of graphene to therequisite levels for superconductivity.
They grew two layers of graphene on
top of silicon carbide and then sandwiched calcium atoms between the twographene sheets to improve the material’s conductivity.
“Fabricating genuine bilayer graphene
is challenging because other products,
such as single- and tri-layer graphene,
can form, and they complicate data
analysis,” says Takahashi. To overcome
this problem, the researchers performed
their experiments in extremely clean,ultrahigh-vacuum environments andmonitored graphene growth as it occurred. They found that optimizing the
precise timing of temperature changes
was critical for controlling the numberof graphene layers.

SiC substrate‘Bilayer’ graphene, controllably grown from a silicon carbide (SiC) substrate, becomes superconductive wheninfused with calcium (Ca) atoms.

Finding the best way to insert calcium
into the bilayer graphene was just as vexing. Simple deposition techniques were
unsuccessful, probably because calcium
atoms are too large to squeeze into thesandwich. “Instead, we developed a
special ‘atom-replacement’ method,”notes Takahashi. In this technique,smaller lithium atoms are deposited intobilayer graphene, thereby expanding theinterlayer distance. Calcium atoms arethen placed on top of the graphene, andthey swap places with the sandwichedlithium atoms on heating (see image).
The researchers used a custommade four-point probe to measure thecalcium–graphene material inside theultrahigh-vacuum chamber. When they
gradually lowered the temperature to
4 kelvin, they saw the much-desired

zero-resistance state. In contrast, purebilayer graphene and the lithiumdoped material showed no signs ofsuperconductivity.
“We were all excited when we saw
these experimental results,” says
Takahashi. “They indicate that superconductivity is driven by chargetransfer from the calcium atoms to thegraphene sheets.”
The team is currently exploring using
different graphene layer structuresand metal atoms to raise the onset ofsuperconductivity to more practicaltemperatures.
1. Ichinokura, S., Sugawara, K., Takayama, A.,
Takahashi, T. & Hasegawa, S. Superconducting
calcium-intercalated bilayer graphene. ACS
Nano 10, 2761–2765 (2016).

AIMResearch 2016

RESEARCH HIGHLIGHTS

Photonics:

Multitasking molecule simplifies
organic LED design
A ring-shaped molecule can play multiple roles in an organic light-emitting
diode (OLED)1. This finding by AIMR
researchers could simplify the manufacture of these devices without reducing
their performance.
OLEDs contain a layer of carbonbased molecules that emit light when
an electric current passes through them.
They have many advantages, including
being thin, light and potentially flexible,
as well as consuming relatively little
energy. They are thus being increasingly
used in electronic devices like mobile
phones and displays.
Many OLEDs contain multiple layersof different materials, each of which performs a specific function. For example,
one layer carries negative electrons,
while another transports positive holes— the gaps left by missing electrons.
When electrons and holes meet, theybind to produce a high-energy ‘exciton’state. Some OLEDs use a phosphorescent material that converts excitons into
light; this requires yet another layer toprevent electrons or holes escaping fromthe phosphorescent emitter.
Hiroyuki Isobe of the AIMR at
Tohoku University and co-workers
have studied a family of moleculesthat can perform most of these tasks
in a single layer, potentially allowing
for much easier fabrication of OLEDs.
These molecules, known as cyclo-metaphenylenes (CMPs), are based on a large
ring consisting of five or six benzene
molecules.
The team tested these ring-shaped
molecules in combination with a common phosphorescent emitter. Severalof them were “completely useless”,
says Isobe. But one of them, a ring

AIMResearch 20162015 © The Authors. From Ref. 1. This work is licensed under CC BY-NC 3.0 (creativecommons.org/licenses/by-nc/3.0/legalcode)

Ring-shaped organic molecules simplify the design of organic light-emitting
diodes, without sacrificing efficiency

This white-light organic light-emitting diode contains a single layer of multitasking ring-shaped molecules.

of five substituted benzenes called
5Me-[5]CMP, far exceeded expectations.
It could transport electrons and holes,
provide a place for them to form excitonsand pass excitons on to the phosphorescent emitter. Crucially, it also slowed
holes down so they could not escape,ensuring their complete conversion tolight. Consequently, this OLED had an
external quantum efficiency of up to
about 23 per cent — almost as good as
the best single-layer OLED and comparable with those of multilayer OLEDs.
One reason for this high efficiency is thatthe 5Me-[5]CMP is a flexible moleculethat can get very close to the iridiumbased emitter to pass on excitons.
The team then blended 5Me-[5]CMP

with red, blue and green emitters to makea white-light OLED, which had an efficiency of about 10 per cent (see image).
“This is still a very premature demonstration, because the device architecture was
not optimized,” notes Isobe.
The team is improving the chemical
synthesis of the CMPs to create moleculesthat reach even higher device efficiencies.
Isobe adds: “AIMR is an ideal place forsuch interdisciplinary investigations.”
1. Xue, J. Y., Izumi, T., Yoshii, A., Ikemoto, K.,
Koretsune, T., Akashi, R., Arita, R., Taka, H., Kita, H.,
Sato, S. et al. Aromatic hydrocarbon macrocycles
for highly efficient organic light-emitting devices
with single-layer architectures. Chemical Science7, 896−904 (2016).

21

RESEARCH HIGHLIGHTS

Silicon monoxide:

Atomic structure revealed at last

AIMR researchers have used state-of-theart experimental techniques and calculations to definitively determine the atomic
structure of amorphous silicon monoxide(SiO) for the first time1.
Lithium-ion batteries power everything from mobile devices to electricvehicles, yet the race to improve theircapacity continues. Silicon-based anodes
are promising in this pursuit, because
silicon can hold more lithium than common carbon-based materials. However,the structure of crystalline silicon deteriorates over charging cycles, reducing
cell performance. In contrast, amorphous(non-crystalline) silicon monoxide does
not suffer from such deterioration.
But despite having been extensively researched for nearly a century, the atomic
structure of amorphous silicon monoxide
had not been fully determined, making it difficult to exploit the material’s
full potential.
“Amorphous silicon monoxide is apromising electrode material for lithiumion batteries,” says Akihiko Hirata of
the AIMR at Tohoku University. “But tounderstand its charge–discharge mechanism at the atomic level, it is vital to know
the details of its atomic structure.”
Hirata, Mingwei Chen and co-workers,
along with collaborators at the National
Institute for Materials Science (NIMS)
and Nissan, have succeeded in determining the atomic structure of siliconmonoxide by using an array of impressive
experimental techniques and calculations.
They used angstrom-beam electron
diffraction, a technique that Hirata andChen had previously developed, to obtaindiffraction data from nanoscale regionsof the material. In combination with synchrotron X-ray scattering and computer

22

Atomic structure of amorphous silicon monoxide. The green spheres represent silicon atoms that form part ofa silicon cluster, while the red and blue spheres respectively indicate silicon and oxygen atoms that make up asilicon dioxide matrix.

simulation results, their investigation
revealed that on an atomic scale, siliconmonoxide consists of a mixture of clustersof silicon and silicon dioxide with ‘suboxide’ regions in between (see image).
There had been much debate about
the atomic structure of amorphoussilicon monoxide. Previous studies had
suggested that it consisted of an equilibrium mixture of amorphous siliconand silicon dioxide, but this model
could not explain X-ray diffraction
patterns. Conventional experimental
techniques lack the spatial resolution
to discover the atomic-scale structure,
but angstrom-beam electron diffraction overcomes this restriction using
an electron beam smaller than 1 nanometer in diameter.
The team is excited about the potential of their method for determining

local atomic structures in amorphousmaterials. “Heterogeneous amorphousmaterials such as silicon monoxide
are important for next-generationenergy devices,” says Hirata. “Ourmethod will enable more-reliable
models to be obtained. It promises tobe a powerful tool for understanding
their atomic structures as well as forproviding valuable information about
their functions.”
The team intends to use their technique to analyze other amorphousoxides for batteries and chalcogenides
for phase-change memory devices.
1. Hirata, A., Kohara, S., Asada, T., Arao, M., Yogi, C.,
Imai, H., Tan, Y., Fujita, T. & Chen, M. Atomic-scale
disproportionation in amorphous siliconmonoxide. Nature Communications 7,11591 (2016).

AIMResearch 2016

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

A powerful new diffraction technique exposes the atomic structure of amorphoussilicon monoxide, a promising electrode material for lithium-ion batteries

RESEARCH HIGHLIGHTS

Lithium-ion batteries:

Nanocarbon electrodes aretrue lifesavers
A material that packs high levels oflithium ions into well-ordered nanochannels can open the door to all-solidstate batteries, reports a joint team fromthe AIMR1.
Rechargeable batteries, such as thoseused to power mobile phones, employ
graphite as negative electrodes to store
and release lithium ions. To meet consumer demand for longer-lived batteries, researchers are exploring different,
nanostructured electrodes. In addition,
the emergence of solid-state electrolytes,
which are safer than conventional liquid
electrolytes, is further driving the search
for novel electrodes.
Now, Hiroyuki Isobe, Sota Sato andShin-ichi Orimo from the AIMR at
Tohoku University and colleagues havedeveloped a nanostructured substancethat can reversibly store and supply morelithium ions than conventional graphite
electrodes. The team’s compound,known as [6]cyclo-2,7-napthylene(CNAP), is a flat, aromatic molecule. It isbased on ultrathin graphene molecules
but with a critical difference — it has an
empty, central opening that spans almosta nanometer.
The Isobe group originally designed
CNAP as a material for organic lightemitting diodes. They demonstrated
bipolar charge transport with thiscompound but did not find any uniqueeffects arising from its hole-like defect.
Instead, through collaboration with
the Orimo group, the team exploredwhether CNAP’s pore could be used forlithium-ion electrodes.
The researchers fabricated a solid-statebattery by milling and then pressing a
mixture of CNAP and the crystalline
electrolyte lithium borohydride (LiBH4)

AIMResearch 2016

A porous, graphene-like compound that forms ordered nanochannels in the crystal state can hold high amountsof lithium ions (yellow spheres) to realize longer-lasting batteries.

together into a pellet. Supplying thecomposite with a lithium foil completed
the cell and enabled the battery’s capabilities to be examined. The team saw
a dramatic increase in lithium storage— nearly double the levels in graphite
electrodes — that remained high evenafter multiple charge–discharge cycles.
Synchrotron X-ray analysis revealed
that the doughnut-shaped CNAP stacked
side-by-side to produce extended networks of one-dimensional, nanoscalepores (see image); nearly 10 per cent of
the electrode contained empty space tohold excess charge. Quantum mechanical models showed that this process isenergetically favorable, with each CNAP
able to capture up to 18 lithium ions.
Discovering that CNAP was compatible with solid-state electrolytes was apleasing surprise for Sato and Isobe.
“Naphthalene and LiBH4 are ubiquitous
reagents that appear in any basic textbook for organic chemists,” they note.
“But according to received wisdom,
they are not expected to react together.
This ‘no-reaction relation’ of our composite electrode was key to its quick,reversible operation.”
The team is currently exploring thedesign of functional pores by synthesizing new additions to their library ofhydrocarbon-based cyclic molecules.
1. Sato, S., Unemoto, A., Ikeda, T., Orimo, S. &Isobe, H. Carbon-rich active materials withmacrocyclic nanochannels for high-capacity
negative electrodes in all-solid-state lithium
rechargeable batteries. Small 12,3381–3387 (2016).

23

Figure courtesy of Takuji Ikeda, National Institute of Advanced Industrial Science and Technology (AIST)

Doughnut-shaped materials are key to the design of safer rechargeable batteries
with impressive storage capacities

RESEARCH HIGHLIGHTS

Metallic glasses:

Spotting secret relaxations

Despite being stronger than steel, metallic
glass alloys suffer from a heating-induced
brittleness that limits their use in practical applications. A team from the AIMR
has now used dynamic microscopy techniques to shed light on nanoscale structures that play key roles in determining
the properties of metallic glasses1.
Metallic glasses are made by supercooling molten metal atoms, such as
zirconium, aluminum and copper, sothat they form tightly packed solids withrandom molecular structures insteadof regular crystals. When the atoms aretaken out of their high-energy state,
they mechanically relax through two
processes: α- and β-relaxations. Primary
α-relaxations disappear as the mixture iscooled below its glass transition temperature, whereas secondary β-relaxations
keep occurring well after the alloy has
been cast — these atom movements canlead to ‘aging effects’ as well as permanent plastic deformation.
Despite their importance, β-relaxations
are only partially understood. Theoreticalmodels indicate that spatial nonuniformity in the glass is responsible foraging effects, but corroborating experimental evidence had been missing. “It’sa dynamic process, so the key obstacle isdesigning a characterization experimentthat can catch such a time-dependent
phenomenon,” says Fan Zhu from the
AIMR at Tohoku University.
Zhu, Mingwei Chen and their colleagues developed a technique to tune
the degree of β-relaxations in a metallic
glass by heating at temperatures below
the glass transition point for varying
lengths of time. They then characterized
the samples using amplitude-modulation
atomic force microscopy (AM-AFM)

24

5 nm
A scanning transmission electron microscopy image of a metallic glass shows that the structure contains
cluster regions (dark areas in the micrograph) where atoms can still move after cooling to room temperature.

and scanning transmission electron microscopy (STEM) to see any disruptionof nanoscale structures.
While most AFM experiments use
a tiny vibrating cantilever to trace theheight of surface atoms, AM-AFM
measures variations in the amplitude
and phase of the oscillating tip. These
dynamic tip movements, explains Zhu,
are very useful for measuring how metallic glasses behave both as elastic solids
that snap back into shape after being
twisted and as viscoplastic materials
whose atoms can permanently flow into
new locations.
By comparing the structural characteristics of relaxed metallic glasses withthose of a hypercooled metallic glass,
the team found that atomic movements
were confined to small, isolated regions

during β-relaxation. These regions wereclear enough to resolve in STEM images
as contrasting dark and bright regions,just a few nanometers in diameter(see image).
Zhu notes that this establishment of adefinite link between β-relaxations andnanoscale inhomogeneous zones can
aid researchers to exploit the uniqueproperties of amorphous materials.
“With this structural scheme, we canfill in the knowledge gaps between
the properties and models of glasses,”
he adds.
1. Zhu, F., Nguyen, H. K., Song, S. X., Daisman, P. B.
A., Hirata, A., Wang, H., Nakajima, K. & Chen, M.
W. Intrinsic correlation between β-relaxationand spatial heterogeneity in a metallic glass.
Nature Communications 7, 11516 (2016).

AIMResearch 2016

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

Direct evidence for structural changes that occur during metallic glass relaxation
should facilitate the commercialization of super-tough alloys

RESEARCH HIGHLIGHTS

Spintronics:

A clean look at magnetic
semiconductors
An improved way to prepare ultracleanmagnetic semiconductor surfaces that
includes using a special ‘vacuum suitcase’ to move samples has helped AIMR
researchers crack a two-decade-old
puzzle regarding active charge carriersin these promising spintronic materials1.
Semiconductors made from gallium
arsenide (GaAs) can exhibit intriguing
properties when small amounts of manganese (Mn) atoms are incorporated into
their structure. This is because the manganese dopants add permanent magnetic
fields and positive-charge carriers to thesemiconductor, allowing currents to bepolarized into either up or down quantum spin states.
These characteristics have enabledresearchers to use GaMnAs as a platform
for new devices, such as spin transistors and magnetic memory, which canprocess information using minimalenergy. However, understanding thecarrier-induced magnetic properties ofthis semiconductor is tricky because effects from randomly distributed dopants
are difficult to predict using standard
quantum theory.
To settle this scientific debate,
Seigo Souma of the AIMR at Tohoku
University and his co-workers used
a technique known as angle-resolved
photoemission spectroscopy (ARPES) to
directly probe the electronic band structure of GaMnAs and measure the ‘Fermi
level’ at which dopant carriers are active.
In these ARPES measurements, highintensity ultraviolet light stimulated
crystals to emit electrons, which wereanalyzed to map out the relation betweena charge carrier’s wave-like momentum
and its energy. “This is the only way
to determine the Fermi-level position

AIMResearch 2016

© 2016 Seigo Souma

Probing high-quality crystals with ultraviolet light reveals how spin-polarized
electrons might power future low-energy memory devices

High-powered photon sources have been used to determine how magnetic dopant atoms (green spheres) can
enable control over spin currents in semiconductor devices.

of GaMnAs,” says Souma. “However,there are major problems inherent with
its surface.”
Souma explains that since ARPES
probes the upper few nanometers ofa millimeter-sized scan area, it needs
extremely clean and reliable surfaces.
Unfortunately, merely exposing GaMnAs
to air causes thick oxides to grow, which
obscure the electron signal. The teamovercame this problem by developinga suitcase capable of maintaining avacuum nearly as devoid of atoms asouter space. They then used the suitcase
to transport high-quality samples from agrowth chamber to the ARPES system.
The ARPES results revealed that the
Fermi level of GaMnAs lies deep within
the electron-rich, or valence, band of thesemiconductor — a location that helped

the researchers select an appropriate
theoretical model to describe the carrierinduced ferromagnetism.
Intriguingly, their measurements also
showed that the intensity of emitted
electrons depended on the orientationof an applied magnetic field, an effectknown as magnetic linear dichroism.
“Observing this effect with ARPES indicates strong spin−orbit coupling in our
sample,” says Souma. “This is the main
parameter needed to realize electric
control over spin for computing andmemory devices.”
1. Souma, S., Chen, L., Oszwałdowski, R.,
Sato, T., Matsukura, F., Dietl, T., Ohno, H. &Takahashi, T. Fermi level position, Coulomb
gap, and Dresselhaus splitting in (Ga,Mn)As.
Scientific Reports 6, 27266 (2016).

25

RESEARCH HIGHLIGHTS

Three-dimensional graphene:

Sponge-like nanomaterials soak
up electrons
Using their expertise for growing highly
crystalline, three-dimensional (3D)graphene structures, AIMR researchers have produced a transistor with1,000 times greater capacitance andconductance than transistors made fromflat films of graphene1.
Electrons in graphene films haveextraordinary mobility because they
behave as particles with practicallyzero mass — so-called Dirac fermions.
But graphene’s flat structure limits thenumber of electrons it can hold, making
it challenging to incorporate graphenefilms in devices such as transistors.
One way to boost the capacitance ofgraphene-based devices is to assemble
graphene films into porous nanoarchitectures that have large surface areas.
However, it is tricky to preserve the highelectron mobility of graphene in such 3Dgraphene ‘sponges’ because most fabrication methods introduce many defects,
which retard or scatter charges.
Mingwei Chen from the AIMR at
Tohoku University and colleagues
recently developed a technique that
overcomes this problem using nanoporous nickel templates. These hard
metal surfaces enable the growth of‘bicontinuous’ 3D graphene structuresthat bend and bond smoothly with few
structural gaps.
In their latest work, the AIMR teamshows how to transform their 3D graphene structures into an electric doublelayer transistor (EDLT) (see image).
Unlike most transistors, the gates that
control electron flow in EDLTs are madefrom nanometer-thin, capacitor-likecharge layers that form at interfaces between an ionic liquid and a solid. The remarkably high accumulation of charges

26© 2016 Yoichi Tanabe

Nanoporous graphene becomes an ultra-responsive transistor when filledwith ionic liquids

Photograph of an electric double-layer transistor (EDLT) based on three-dimensional, nanoporous graphene
structures. Its capacitance and conductance are 1,000 times greater than those made from flat graphene films.

in the EDLT enables the electronic statesof graphene to be controlled at very low
operating voltages.
“This is one of the key devices
needed to realize device applications
with nanoporous graphene,” explains
Yoichi Tanabe, a co-author of the study.
“It allows us to control the number ofcarriers in the bicontinuous nanoporous
material through the electric-field effect.”
After drying their 3D graphene structures under supercritical conditions to
avoid damaging them, the researchers
infused them with ionic liquid electrolytes and assembled the components intoan EDLT. Using electrical measurements
under a magnetic field, they developed
a way to evaluate the nanoporous material’s mobility. They discovered thatthe advantageous properties of Diracfermions remained. The device alsooffered exceptional electron switching
behavior and conductance for furthertransistor applications.
“Being able to tune carrier densities
means our nanoporous graphene EDLT
can be a basis to design other electric
devices. For example, high-response
photodetectors could be developedin the future,” says Tanabe. “Also, diminishing the pore size in nanoporousgraphene can introduce energy gaps into
its electronic structure. Our EDLT technique could be one way to access theseelectronic states.”
1. Tanabe, Y., Ito, Y., Sugawara, K., Hojo, D.,
Koshino, M., Fujita, T., Aida, T., Xu, X.,
Huynh, K. K., Shimotani, H. et al. Electric
properties of Dirac fermions captured into 3D
nanoporous graphene networks. Advanced
Materials 28, 10304−10310 (2016).

AIMResearch 2016

RESEARCH HIGHLIGHTS

Electrocatalysis:

Splitting water without
breaking the bank
Exploiting the alloying effect offers a cheaper way to produce clean hydrogen fuelfrom water

AIMResearch 2016

1.0 M KOH

Power supply-+

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

An inexpensive catalyst formed fromtwo common metals could offer a new
way to produce fuel from water, AIMR
researchers have shown1.
‘Water splitting’ is an electrochemical
process in which water molecules arebroken apart to release hydrogen — a
useful fuel. The process is a promising
way to store renewably generated electricity since stored hydrogen can be used togenerate electricity at times when the Sun
is obscured by clouds or there is no wind.
However, most electrochemical catalysts
for efficiently splitting water contain rare
precious metals, such as platinum, making them prohibitively expensive.
Now, by exploiting a phenomenon
known as the alloying effect, Yongwen Tanfrom the AIMR at Tohoku University andhis colleagues have developed an inexpensive alternative. Their electrocatalyst
is a material called a nanoporous phosphide and contains the common metals
iron and cobalt. Tan says it rivals the performances of commercial water-splitting
systems based on platinum.
Alloys are materials in which one element is added to enhance the propertiesof another. For example, adding tin tocopper creates the alloy bronze, which isstronger than copper. But alloying does
not just enhance the strength of materials.
“Alloying has long been known to be aneffective method to create new functionsof catalytic materials,” says Tan.
Tan’s team anticipated that adding
iron to cobalt phosphide would alter thematerial’s electronic properties in such a
way that its water-splitting performance
would be improved. For example, according to their calculations, substituting
cobalt for iron would reduce the energy
of hydrogen adsorption on to the catalyst

H2

O2

H2O

1.0 M KOH

Power supply+ 1-xFex)2P
np-(Conp-(Co1-xFe-x)2P

Electrodes made from nanoporous iron–cobalt phosphide have the potential to split water for a fraction of
the price of electrodes made from precious metals.

surface to the level of platinum at the
optimal composition.
But although the calculations looked
good, producing these alloys was a stumbling block. Traditional ‘wet chemistry’methods of making alloys are unsuitable
as they do not give the necessary control
over the exact ratio of metals. Therefore,
the researchers had to develop a novel
two-step way of making them. Their
process involves using an industrial
technique called melt spinning to rapidly
solidify the precursor alloys, controlling
their composition, followed by electrochemical etching to dissolve metallic
byproducts, leaving an iron−cobalt phosphide with nanoscale pores (see image)whose catalytic activity could be adjusted
by fine-tuning the ratio of iron to cobalt.
The resulting electrocatalyst rivaled theperformance of commercial water-splitting catalysts, but for a 20th of the price,according to Tan’s estimate. The team is
now investigating the possibility of using
their new fabrication technique to makea whole range of nanoporous catalysts,
which could be used for many energyand environment-related applications.
1. Tan, Y., Wang, H., Liu, P., Shen, Y., Cheng, C.,
Hirata, A., Fujita, T., Tang, Z. & Chen, M. Versatile
nanoporous bimetallic phosphides towards
electrochemical water splitting. Energy &Environmental Science 9, 2257−2261 (2016).

27

RESEARCH HIGHLIGHTS

Nanoporous gold:

Sensitive biosensor formuscle chemicals
By employing a gold film that
contains multiple levels ofpores, AIMR researchers haveproduced a sensitive detector
capable of monitoring low levels
0.5µm
of reactive chemicals that are released from muscles in the body.
This detector is promising foradvancing our understanding of
50µm
the metabolism and functionality of skeletal muscle tissue.
Muscles attached to bones
generate small amounts of reactive chemicals known as super500µm
200µm
oxide anions. Normal muscular
activity generates low levels ofsuperoxide anions, but highA gold film that is porous on both a macroscale and a nanoscale has been used to realize a highly sensitive biosensor forlevels can be problematic sincedetecting superoxide anions released by muscles. The pink regions in the fluorescence image on the far right indicate thethe species is quite toxic. “High
nuclei of superoxide-releasing muscle cells.
levels of superoxide anions may
trigger malfunctioning, aging
and damage of muscle tissue,”notes Ali Khademhosseini of thepores (see image). This greatly increased
operation,” notes Khademhosseini.
AIMR at Tohoku University.
the proportion of the film that is exposed“Our sensor, on the other hand, canNow, Khademhosseini and his coto the medium. Since nickel is toxic todetect much lower levels of superoxides
workers have developed a highly sensithe body, the team chemically stripped
and thus can be placed farther from thetive detector that can detect very low
the template away.
site of injury.”levels of superoxide anions1.
The scientists then demonstrated the
The researchers intend to use theireffectiveness of the detector by coatingbiosensor to investigate the rates at
The genius of their detector lies in
it with an enzyme and then using it towhich superoxide anions are released
the fact that it uses a gold film that ismeasure the superoxide levels generwhen skeletal muscle tissue is subjected
porous on both macro- and nanoscales.
ated by muscle cells from mice. The
to electrical stimuli. They also anticipate
Nanoporous gold is riddled with tinybiosensor realized a sensitivity that isthat the multiple-porosity strategy used
pores and consequently has a high
two to three orders of magnitude higher
in the study will be applicable to a broad
surface area. But, as Khademhosseinithan previous devices.
range of biosensing applications.
notes, “Although nanoporous gold has
This high sensitivity makes thea large surface-to-volume ratio, only adetector suitable for non-invasive
small region of the film near the surface
1. Sadeghian, R. B., Han, J., Ostrovidov, S.,
measurements. “Since the physiologiis exposed to the surrounding medium.”
Salehi, S., Bahraminejad, B., Ahadian, S.,
cal concentrations of superoxides are
To overcome this problem, the reChen, M. & Khademhosseini, A. Macroporous
remarkably low, even sensitive electrosearchers imparted the film with a highmesh of nanoporous gold in electrochemicalchemical biosensors must be placed
porosity on a macroscale by fabricating
monitoring of superoxide release from skeletal
close to the region of interest, making
nanoporous gold films on templates ofmuscle cells. Biosensors and Bioelectronics 88,
them impractical for safe, in vivo
nickel foam, which contained macroscale
41–47 (2017).

28

AIMResearch 2016

© 2016 Ali Khademhosseini

A gold film with both large and small holes can detect tiny amounts of chemicals
released by muscle cells

RESEARCH HIGHLIGHTS

Single-cell analysis:

Double-barrelled probe for
exploring single cellsA
double-barrelled
nanopipette is thesecret behind a newtechnique for sampling messenger RNA(mRNA) at different
locations within acell. By filling thetwo barrels with different liquids, AIMR
researchers used thesame nanopipette asa microscope tip for
imaging a sample
of cells and then asa sample-collection
tip for extracting
After imaging the target cell, the team used the resulting map to take one messenger RNA sample from near the nucleus (left) and one
mRNA from sites offrom the cell’s periphery (right; expanded image of the red box in the left image). The red crosses indicate the sampling points.
interest
identified
during imaging1.
The device has the“The microscopy imaging techniquepotential to become a high-throughput
to take mRNA samples at the peripheryis non-invasive, so we can take images
way to measure how gene expresand near the nucleus of single cells,
without any stress to living cells,” says
sion varies within single cells. Thisrevealing differences in gene expresShiku, leader of the project in Matsue’s
information will give scientists a bettersion between these two locations.
group. “We can scan the cell surface
understanding of how cells function in
The scientists also succeeded in fully
at low magnification and then zoom
different tissues.
automating pipette movement for thein to obtain higher-resolution images
The double-barrelled approach, desample-collection process.
to find a location where we want toveloped by Tomokazu Matsue, Hitoshi
So far, the team has detected only
collect cytoplasm.”
Shiku and their colleagues of the AIMR
highly expressed genes using their
The team’s advance was to then colat Tohoku University, combines a pairtwo-step technique. “The next stage islect the cell’s cytoplasm using the sameof techniques for imaging and collectto improve the technique’s sensitivity
electrochemical instrument. By using a
ing samples from single cells.
and increase the types and numbers of
double-barrelled pipette, the researchThe first step is an electrochemicalmRNA molecules we can sample,”ers could fill the second barrel. After
imaging technique that involves sweepShiku says. The team also plans to adapt
lowering the pipette until it punctured
ing a nanopipette filled with an aqueous
the technique to detect proteins andthe cell at the site of interest, the teamsolution across a sample. Applying aorganelles within cells.
switched the applied voltage from posivoltage to the tip causes ions to flow
tive to negative, which drew a minutefrom the nanopipette tip, but ion flow
1. Nashimoto, Y., Takahashi, Y., Zhou, Y., Ito, H.,
volume of cytoplasm into the nanopidecreases as the tip approaches andIda, H., Ino, K., Matsue, T. & Shiku, H. Evaluation
pette for analysis.
passes over a cell. Thus, by detectingof mRNA localization using double barrel
Testing the technique on living
the ion flow, it is possible to construct ascanning ion conductance microscopy.
mouse cells, the researchers were able
topographical map of the sample.
ACS Nano 10, 6915–6922 (2016).

AIMResearch 2016

29

Adapted with permission from Ref. 1. Copyright 2016 American Chemical Society.

A dual-action imaging and sampling technique promises rapid mapping of gene
expression variation within single cells

IN THE SPOTLIGHT

IN THE SPOTLIGHT
INTERNATIONAL SYMPOSIUM

Published online on 28 March 2016

Mathematics and materials
in harmony
AMIS2016 showcased potential real-world applications of fusion research involving mathematics andmaterials scienceS

ince being appointed director of
the AIMR in 2012, Motoko Kotani
has led the charge in promoting
collaboration between mathematics andmaterials science. To keep abreast of
the fields’ newest crossbreeds, researchers from all over the world travel to
Sendai every February for the AIMR
International Symposium (AMIS).
This year’s theme was ‘harmonious collaboration between mathematics andmaterials science’.
“When we started this initiative,the distance between mathematics
and materials science was very wide,”
explained Kotani. “But now materials
scientists have started putting moreemphasis in the direction of using
mathematical modeling, information
technology and data-driven science. To
achieve this, direct interaction between
mathematicians and materials scientists— experimental researchers in particular — is important. We just started thisprocess a bit earlier.”
Speakers at the three-day event on
22–24 February presented research on
everything from tiny molecular machinesthat could one day power factories
invisible to the naked eye, self-cleaning
and antibacterial materials for glazing
surfaces at hospitals and sports stadiums,
to a fast-track route to developing new
structural materials that will reduce

our dependence on rare metals andrare-earth elements.
Upholding the legacy
Tohoku University President Susumu
Satomi welcomed participants to the
opening ceremony. More than 230
researchers representing 14 countries
attended the symposium, including 22
invited speakers and 104 poster presenters. Satomi thanked Director Kotani
and the AIMR for upholding a legacy ofpioneering materials science and establishing extensive international networks.
“The AIMR is expected to play a very
important role toward achieving the goalsof Tohoku University,” he said, referring

The AIMR International Symposium (AMIS) 2016 offered a glimpse of what a world equipped with materials inspired by harmonious collaborations between mathematics andmaterials science would look like.

30

AIMResearch 2016

IN THE SPOTLIGHT

Theoretician Alexander Mikhailov uses simple and efficient models to describe complex cellular phenomena.

to the adoption of system reforms andthe promotion of the university inglobal forums.
The next speaker was Toshio Kuroki,program director of the World PremierInternational Research Center Initiative(WPI), who disclosed plans to continue
the prestigious national project. In 2014,
a WPI program committee assessed thatthe five inaugural WPI centers, including
the AIMR, had achieved ‘world premier
status’. As a result of their success,the government is discussing plans tocontinue the WPI program. The WPI

program will also establish a grants
scheme to support system reforms andinternationalization activities in centersthat have completed their ten-year term.
The highly cited science and interdisciplinary research that exemplify the
WPI brand will be sustained by the WPIcenters and their host institutions — in
the case of the AIMR, this will be throughthe newly established Organization for
Advanced Studies.
AIMR Director Kotani promised to
do her best “to keep the present activityof the AIMR as a world-leading hub of

Chemist Akira Fujishima has discovered fascinating water-splitting and water-loving properties of titanium dioxide.

AIMResearch 2016global brain circulation in materials science.” In 2012, the AIMR initiated threetarget projects to strengthen ties between
mathematics and materials science. In
2013, the AIMR introduced a fourth target project named Core Technology for
Nano Energy Devices to translate the results of these harmonious collaborations
into materials, devices and systems thatwill help solve global energy problems.
AMIS2016 focused on this fourth target
project and its practical applications, anarea in which the AIMR has made significant progress through research into novel
energy generation and storage materials,
lithium-ion batteries, quantum-dot solar
cells, thermoelectric conversion elements,
nano-electronic switching devices andlight-emitting diodes.
Simple science
A series of scientific presentations followed the opening remarks. Alexander
Mikhailov, a theoretician at the Fritz
Haber Institute of the Max Planck
Society, presented his work on the use ofmathematical models to explain, control
and mimic complex phenomena such as
those occurring in living cells. Packed
inside the many cubic micrometers of acell is a factory of nanoscale machines— motors, ion pumps and enzymes.
These tiny biomolecules operate on
millisecond timescales in extremely
turbulent environments.

31

IN THE SPOTLIGHT

Teruo Kishi is director of a major government initiative to develop strong, lightweight and heat-resistant structural
materials involving 27 industry partners, 35 universities and 130 scientists.

The chemical structure of these
proteins is generally known, but their
movement is harder to track. A popular
but problematic technique involves
running detailed molecular dynamics
simulations of every atom in the protein.
“Even using the best supercomputers, we
can only follow the dynamics of a single
protein for up to one microsecond, which
is 10,000 times shorter than a single operation cycle,” said Mikhailov. His groupinstead uses simple and efficient elastic
network models that produce coarser
representations of proteins as a series ofamino acid ‘beads’ connected by elastic‘springs’. These models are so simple thatthey can run on a personal computer.
In 2010, Mikhailov’s team used
these models to identify how the hepatitis C virus helicase splits DNA — “thefirst structurally resolved simulation
for a motor protein.” More recently,
the team has designed a molecularmachine that swings forward using aratchet mechanism similar to that usedby actin and myosin filaments when amuscle contracts.
Presenting another material thatmimics processes found in living organisms was renowned chemist andpresident of Tokyo University of Science,
Akira Fujishima. He recounted his
discovery in 1967 of titanium dioxide’s
ability to use light to split water like inphotosynthetic plants; the results were
published in Nature in 1972. Fujishimalater found that titanium dioxide has astrong affinity for water and oils whenirradiated by ultraviolet light. He has

32

spent the last half century characterizing the photolytic, photocatalytic
and superhydrophilic properties of thisversatile material and developing affordable applications.
“Titanium dioxide is the best material — it’s very cheap and safe and canbe used to coat surfaces as a transparent
film,” he said. The material has been used
to filter out the smell of cigarettes in bullet trains, maintain the stainless exteriorsof train stations and football stadiums,
prevent fogging of rear- and side-view
mirrors, and kill bacteria and viruses
that colonize hospital tiles. Fujishima is
now trying to develop new applications
for this material in water purification,
solar light transmission and mosquito
repellents. Meanwhile, scientific interestin titanium dioxide shows no sign ofabating: close to 11,000 articles havecited Fujishima’s original Nature paper
according to the Web of Science and thenumber of publications on photocatalysis
increases annually.
Next-generation materials
After a break, Teruo Kishi introduced
several large-scale projects on structural
materials funded by the Japan government to support the aviation, automobileand energy industries. Most recently, theCabinet Office has set aside 3.5 billion
yen to develop strong, lightweight andheat-resistant metals, alloys, ceramics,
polymers and resins. These materials will
reduce the energy and carbon footprintof air travel and power generation andmake Japan less reliant on imports ofrare-earth metals and other criticalelements. As director of the Structural
Materials for Innovation program,
Kishi will manage a five-year collaboration between 27 industry partners, 35
universities and 130 scientists. He plans
to integrate computer science and informatics with existing theoretical andexperimental techniques in materials
science to develop tools that can predictthe performance of materials for rapid
development and testing.
From big-picture science to a focus
on synthesis, Kenichiro Itami, synthetic
chemist and director of the WPI Instituteof Transformative Bio-Molecules,
presented his team’s work on carbonbased nanomaterials. Nanocarbons
have been a hot topic for fundamental
research and applied science since thediscovery of spherical fullerene in 1985,
cylindrical carbon nanotubes in 1991
and graphene sheets in 2004, explained
Itami. But these molecules are typically
only available as mixtures of varying sizes,
which means that their bulk properties
represent an average of the individual
molecules’ properties.
Itami’s group uses organic chemistry
to create structurally uniform nanocarbons from flat or ring-shaped moleculartemplates, which could yield entirely
new properties. “The beauty of scienceis purity,” he said. Itami’s team has sincesynthesized the shortest carbon nanotube
with an armchair pattern, and accidentally
synthesized a three-dimensional nanocarbon that has the negative curvature familiar to munchers of Pringles potato chips.
The unique topology of the structure
has even intrigued theoretical scientists.
“Mathematicians are so excited about it,”said Itami.
The opening session concluded withanother chemist, AIMR principle investigator and president of the Universityof Science and Technology of China,
Li-Jun Wan. His team focuses on thesurface of materials, finding ways toassemble organic molecules in highlyordered patterns for potential application
on functional devices, such as sensors.
Specifically, Wan’s group has laid out
large sheets of graphene-like materials
in which the individual molecules areconnected via strong covalent bonds.
“We really need mathematicians tojoin us to predict new structures andproperties,” said Wan. “I can find manycollaborators at the AIMR to exchange
ideas and results.”
■AIMResearch 2016

IN THE SPOTLIGHT

TOP-LEVEL INTERVIEW

Published online on 30 May 2016

A decade of remarkable achievement
This year, the AIMR marks ten years since its foundation. Former director Yoshinori Yamamoto and current director
Motoko Kotani discuss AIMR’s achievements over the past decade and its plans for the next stage of development.
Yamamoto: It’s been ten years since the
AIMR was established. It’s a real milestone.
It generally takes at least a decade to achieve
something innovative.
Kotani: At the AIMR International
Symposium 2016 in February, many participants told us that the AIMR has a sharp
focus. We continually asked ourselves,“What is the AIMR’s identity?” This helped
define our focus. It seems that it takes
at least ten years for something to takedefinite shape.
Establishing AIMR’s identity
Former director of the AIMR, Professor Emeritus Yoshinori Yamamoto (left), and current director, Professor

Yamamoto: Initially, the AIMR’s main
focus was non-equilibrium materials,
including metallic glasses — one of Tohoku
University’s strengths. Research was conducted by drawing on the expertise of physicists and chemists. However, we wanted toadopt a more innovative approach. We
deliberated a lot about what we could do.
While staring at the crystal structuresof some materials, I wondered whether
there might be some connection withgeometry. That was when I read yourpaper. I remember being surprised that amathematician was discussing materials. I
asked you to become director, but you werevery hesitant initially.
Kotani: Yes, I hesitated at first. But after
listening to the researchers and realizingthat the director’s role is to assist in defining
the direction towards mobilizing research, I
thought there might be something I could
do here.
Yamamoto: I recall telling you that we want
to apply mathematics to create a new kindof materials science. I managed to convince
you of our vision, and you became directorof the AIMR in 2012.
Kotani: I specialize in discrete geometricanalysis, a branch of mathematics thatanalyzes how the discrete is linked to thecontinuous. The AIMR is investigating

AIMResearch 2016

Motoko Kotani (right) discuss the AIMR’s influence on the world of materials science and beyond.

how discrete objects such as atoms andmolecules control the continuous andlarge-scale phenomena of materials
properties. It thus gave me a great sense ofsatisfaction to start working at the AIMR.
The World Premier International ResearchCenter Initiative (WPI Program) seeks toestablish research institutions of excellence.
We aimed to become a research center withexceptional originality, unparalleled in theworld. Originality demands accepting thechallenge of addressing something new.
You had set a very ambitious goal — tocreate a new kind of materials science. I
imagine it was extremely difficult to define
your concept clearly. It took five years toclarify the concept and another five years
for it to take shape. The WPI Program gave
us the opportunity to achieve this.
Yamamoto: You adopted three target
projects. I believe these were crucial for
coordinating and aligning materials scienceand mathematics.
Kotani: Yes. As you mentioned, Tohoku
University is strong in non-equilibrium
materials research. So I chose research into
the use of mathematics to control nonequilibrium materials as target project 1.
Since Tohoku University also excels in spin
research, for target project 2, I selected

research into topological materials (which isbased on a branch of mathematics called topology) to investigate spin. Target project 3
was a project using my own specialist area,
discrete geometric analysis, to understandhierarchical structures. These three projects
drove the activities of the second five years.
Some researchers investigate the characteristics of a material out of interest in
the material itself, whereas others search
for a material that satisfies certain targetfunctions. In mathematical terms, the first
approach deals with a forward problem
while the latter one deals with an inverse
problem. The collaboration of materials
science and mathematics at the AIMR
means accelerating and streamlining theconversion of knowledge that has been
accumulated as a forward problem into an
inverse problem. This is the most criticalreason why we need mathematics.
Providing pioneering researchers withan arena for successYamamoto: When MEXT announced the
WPI Program ten years ago, I thought that
it was wonderful. Japan suffers from its
geographical position; our researchers havefewer opportunities for international exchange than their counterparts in Westerncountries. We applied for the WPI Program33

IN THE SPOTLIGHT
because we wanted to become a research
center with a highly visible global profile
and achieve a global exchange of expertise,including researchers from Europe andAmerica. Establishing the AIMR as a
WPI center brought positive outcomes for
Tohoku University and the wider world.
Within Tohoku University, interaction
increased rapidly beyond department andinstitution boundaries. In particular, young
researchers now hold discussions thattranscend disciplinary barriers. Beyond
the university, the concept of materials science founded on mathematics is gradually
propagating. Even MEXT is broadcasting it.
Kotani: A huge achievement of the AIMR
has been establishing a culture in whichyoung researchers step out of their own
laboratories and engage in lively discussions
with researchers in other fields. And they
see that this benefits their own research.
When researchers from around the world
visit the AIMR, they tell us that it differs
totally from their image of a university. Thatmeans we have been motivating them tochange their own research environment into
something like what we have at the AIMR.
We want to make it a spark that ignites arevolution of change in other universities.
Leading on from the AIMR’s experience, Tohoku University inaugurated theOrganization for Advanced Studies last year.
Yamamoto: Interdisciplinary exchange
has made great progress, but it’s impossible
to create a research center with a highly
visible global profile overnight. After ten
years, we have managed to make the AIMR
highly visible.
Kotani: In the context of a research centerwith a highly visible global profile, it was
you who gave me the idea of forming jointlaboratories. You laid the groundwork for
setting up joint labs with the University of

AIMR Director Motoko Kotani sees mathematics as a vital key for unlocking the mysteries of materials science.

Cambridge, the University of California at
Santa Barbara and the Institute of Chemistry,
Chinese Academy of Sciences. These AIMR
Joint Research Centers (AJC) have raised the
AIMR’s visibility internationally. How did
you come up with the concept of joint labs?
Yamamoto: I wanted to create a networkwith the world. I decided to choose attractive research institutions. Since Tohoku
University is a world leader in materials
science, I thought that our core partners
should be universities that are world-leading
centers for materials science and that have ahistory of academic exchange with Tohoku
University. These three AJCs have certainly
increased the visibility of the AIMR.
Kotani: The excellent quality of researchin Japan is acknowledged globally. We haveoriginal ideas. I believe the reason that these
are not necessarily reflected in the numberof citations and world university ranking
is that a lot of collaboration is undertaken
as joint research within Japan. Since there
are many outstanding researchers inJapan, we can obtain good results just byconducting joint research within our own
country. But to achieve further advances,
we need to incorporate new perspectives.
That’s the purpose of international joint

Former AIMR Director Yoshinori Yamamoto came up with the concept of AIMR Joint Research Centers.

34

research. The bridge between Japan andoverseas is where young researchers canplay an important role. The AJCs enable
us to employ young researchers throughjoint arrangements between the AIMR
and overseas centers. For instance, young
researchers belonging to the Cambridge
AJC are jointly employed by the AIMR
and the University of Cambridge. Because
they belong to both institutions, they cancome and go freely between Sendai andCambridge and do their research. This joint
employment, formed by breaking systemic
barriers, originates from your joint lab concept. Professor Alan Lindsay Greer, head of
the Cambridge AJC, recently said to us that
the University of Cambridge would like toprovide research funding so that we can
expand the AJC research activities.
Yamamoto: Attracted by our idea, the historic University of Cambridge is thinking ofextending the joint research center on theirown. That is groundbreaking. Since suchwide-ranging outcomes are being generated, we should really continue using the
research center style adopted by the AIMR.
Because the WPI Program establishes research centers, it also has to maintain them.
Kotani: After the initial sprint of ten years,
the AIMR will now enter a new phasein which we will disseminate the results
we have achieved. I have great hopes thatyoung researchers, who have talked to researchers in different fields and discovered
the benefit of original perspectives, will
leave the AIMR to work in the wider world,
extending their activities to the global arena.
Ten years from now, when it is their turn tolead the scientific world, I think research ofa totally different dimension will emerge.
To provide an arena for researchers whotake up the challenge to pioneer into a new
realm of science, I think is where the AIMR
will continue to offer its greatest value. ■AIMResearch 2016

IN THE SPOTLIGHT

INTERNATIONAL SYMPOSIUM

Published online on 25 July 2016

Raising awareness in Europe
The joint participation of four WPI research centers at the 2016 Spring Meeting of the European Materials ResearchSociety proved to be a rewarding experience for all involvedO

n 2–6 May, researchers from theAdvanced Institute for Materials
Research (AIMR) shared theirinnovative contributions for a sustainable
future at the European Materials ResearchSociety’s (E-MRS) 2016 Spring Meetingin Lille, France. Researchers described advances in efficient solar electricity generation, high-capacity hydrogen storage andclosed-loop energy systems to an attentive
audience of global leaders from industry,
government and academia.
The AIMR attended the E-MRS
Spring Meeting together with a teamof 30 members representing the World
Premier International Research Center
Initiative (WPI) and four of its research
centers — the AIMR, the International
Center for Materials Nanoarchitectonics(MANA), the Institute for Integrated
Cell-Material Sciences (iCeMS) and theInternational Institute for Carbon-Neutral
Energy Research (I2CNER) — including
WPI Program Director Toshio Kuroki and
AIMR Director Motoko Kotani. “In 2014,
we found that joint participation in the
E-MRS Spring Meeting was a very effective
way to boost our presence, so we decided
to attend it together again this year to getfurther exposure in Europe,” said Kotani.
The WPI program was launched in2007 to create globally visible research
centers in Japan that act as hubs for global
brain circulation. One of the most effective
ways to enhance the international presenceof both the WPI program and the individual WPI centers is for centers to jointly
participate in international meetings. The
E-MRS 2016 Spring Meeting was thesecond time the four centers have jointly
participated at the event in Lille and thefourth time they have jointly participated ininternational meetings.
WPI exhibition booth and symposium
The WPI team coordinated their attendance at the E-MRS 2016 Spring
Meeting through three separate venues:
an outreach activity in the exhibition
hall; a one-day WPI symposium; andAIMResearch 2016

Researchers at the reception held at the WPI exhibition booth enjoyed chatting with WPI researchers over Japanesefood and drinks.

presentations by WPI researchers atother symposia.
The WPI exhibition booth was manned
from 3 to 5 May. As in 2014, it contained
furniture decorated with traditional
Japanese designs to pique the interest ofEuropean researchers. Posters about the
WPI program and the four centers weredisplayed on panels, and brochures were
distributed to passers-by. The WPI outreach team was allotted a one-hour timeslot to host an exhibitor workshop in theevening of 3 May, followed by a reception.
Current president of the E-MRS, Luisa
Torsi, vice presidents, Gilles Dennler andGeorge Kiriakidis, and immediate pastpresident, Thomas Lippert, attended theworkshop. Many European researchers,
including executive committee membersof the E-MRS, joined the reception, andenjoyed chatting with members fromthe WPI centers over Japanese food anddrinks. The informal gathering was a great
opportunity to inform attendees about the
WPI One-day Symposium to be held thenext day, and it also served to increase theexposure of WPI in Europe.
On 4 May, Masaru Tsukada, administrative director of the AIMR, and Tomonobu
Nakayama, administrative director of

MANA, organized and chaired the WPI
One-day Symposium, which explored thefunctional assembly of nanomaterials andtheir potential applications in electronics,
energy and biology. The WPI Program
and the individual WPI centers were first
briefly introduced: Kuroki spoke about
the objectives, achievements and future
prospects of the WPI program and AIMR
Director Kotani, iCeMS Director Susumu
Kitagawa, I2CNER Director Petros Sofronisand MANA’s Nakayama introduced theirrespective centers.
New insights into hydrogen materials
The symposium proceeded with a scientificsession of nine talks by WPI researchersand some invited and contributed talks byspeakers from outside the WPI centers. In
the morning session chaired by Tsukada,
two AIMR principal investigators and two
European professors invited by the AIMR
presented their recent research on hydrogen materials and solar cells.
Andreas Züttel, a physical chemist at
the Swiss Federal Institute of Technology
in Lausanne (EPFL) and director of theLaboratory of Materials for Renewable
Energy, described the key challenge
for hydrogen technology today — the35

IN THE SPOTLIGHT
synthesis of hydrocarbons such as octane
using only atmospheric carbon dioxideand hydrogen produced from renewableelectricity. Achieving this recycle process
will help resolve both environmental andenergy demands. “Many hurdles must be
overcome, for example, realizing largescale electrolyzers, hydrogen storage andcarbon dioxide adsorption,” said Züttel. “A
well-controlled reaction between hydrogenand carbon dioxide that produces a specificproduct is needed. But if we can complete
this process, we can realize a whole-energy
conversion cycle that doesn’t produce any
environmentally damaging discharges.”
Züttel is a long-time collaborator with AIMR Principal Investigator
Shin-ichi Orimo, and the two are wellknown for their experimental demonstration of the highest-capacity hydrogenstorage material. At the session, Orimo
introduced recent studies into the synthesisof materials known as hydrides that offer
a compact vessel for storing hydrogen.
He described new high-density hydrides
using a CrH7 pentagonal-bipyramidal
anion, superionic conduction in BnHn-typehydrides with large cage-like units, andnew all-solid-state rechargeable batteries,
including lithium–sulfur batteries that havecomplex hydride electrolytes.
Toward high-efficiency solar cells
Next up was AIMR Principal Investigator
Seiji Samukawa, who described a techniquefor fabricating solar cells containing siliconquantum nanodots to improve the sunlightto-energy conversion efficiency of the cells.
His team used a biotemplate as an etching

Andreas Züttel from the Swiss Federal Instituteof Technology in Lausanne (EPFL) fields aquestion about his plan to realize a whole-energy
conversion cycle.

36

Alain Fave from the National Institute of Applied Sciences in Lyon (INSA-Lyon), giving a talk at the WPI
One-day Symposium.

mask and a low-energy neutral beam to realize quantum dots that are defect free andsmaller than 10 nanometers. Samukawa
found the meeting particularly valuable
as he was able to chat with collaborator
Alain Fave, a photovoltaics researcher at
the Lyon Institute of Nanotechnology,
National Institute of Applied Sciences in
Lyon (INSA-Lyon), and exchange information on recent progress in silicon solar cell
experiments. “Participation at the E-MRS
meeting has been a good opportunity tomeet friends in Europe and consider futurecollaborations,” said Samukawa.
Fave gave a talk on the design, fabrication and characterization of ultrathin-film
crystalline silicon solar cells that trap lightefficiently. A major cost of silicon solar cell
technology is the amount of silicon used
per watt-peak. Reducing the thicknessof the crystalline silicon layer, however,decreases the amount of light it can absorb.
A critical area of research in the field is thedevelopment of technologies that can curbthese optical losses. To achieve this, the
Lyon Institute of Nanotechnology, within
the framework of a European project led
by the nanoelectronics research institute
IMEC, recently fabricated photonic crystals
and pyramidal nanostructures on the surface of the silicon layer by combining laser
holographic lithography, reactive-ion etching, inductively coupled plasma etching andchemical etching. “These are the first steps
toward developing a future generation ofphotonic-crystal-assisted solar cells,” Favesaid. “We hope it will lead to the realizationof high-efficiency solar cells.”
Presentations at other symposia
AIMR researchers also gave oral andposter presentations at other symposia organized at the E-MRS. Alexander Shluger,a professor at the Department of Physics

and Astronomy and the London Centre
for Nanotechnology, University College
London, and a principal investigator at the
AIMR, presented a theoretical study into
the effect of excess electrons in oxides on
the creation of Frenkel defects, in whichan atom is displaced from its lattice position to an ‘interstitial’ site lying between
lattice points. In particular, Shluger’s
calculations indicate that excess electrons
injected from electrodes can be trapped indeep states in amorphous silicon dioxideand hafnium dioxide (HfO2) and form
quasiparticles known as polarons andbipolarons. The formation of bipolaronsfacilitates the formation of Frenkel defects
in these materials. In a poster session,
Moloud Kaviani, an AIMR research
associate in Shluger’s group, presented
related theoretical research with respect tointrinsic electron trapping in amorphous
HfO 2. These results are important forunderstanding dielectric breakdown
mechanisms in electronic devices andconductive filament formation in resistive
random-access memory cells employing
silicon and hafnium dioxide.
Two research associates from the
AIMR group led by Principal Investigator
Ali Khademhosseini — Sahar Salehi and
Majid Ebrahimi — shared their work on
engineering muscle tissue in the biomaterials session. And Akio Higo, an assistantprofessor from Samukawa’s group, presented research into the room-temperature
operation of gallium arsenide quantum
nanodisk light-emitting diodes fabricatedusing a technique called dry nanoscaleetching and regrowth by metal organic
vapor-phase epitaxy. “I really enjoyed thisjoint participation at the E-MRS meetingand had many valuable interactions, which
I’ve not experienced at conventional conferences,” said Higo.
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AIMResearch 2016

IN THE SPOTLIGHT

INTERNATIONAL EXCHANGE

Published online on 28 November 2016

A new center of excellence innanotechnology in China
AIMR researchers visited the Herbert Gleiter Institute of Nanoscience in China to exchange information and ideasHerbert Gleiter was drawn toimperfections. At a time whenmost physicists were fixated on
the perfectly ordered arrays of atoms in
crystals, he got caught up in the defects,
dislocations, grain boundaries and impurities. These deviations from a periodic
arrangement of atoms, he noticed, gave
materials interesting properties. By the
1980s, Gleiter had discovered a broadclass of nanocrystalline — or nanostructured — materials, which contained avariety of irregular arrangements of atoms.
This discovery laid the foundation forexperimental and theoretical studies in an
entirely new branch of nanotechnology.
In October 2012, Gleiter, who ison the international advisory board of
the Advanced Institute for Materials
Research (AIMR) in Japan, as well as asenior scientist and former founding director of the Institute of Nanotechnology
at Karlsruhe Institute of Technology(KIT) in Germany, was invited to become
the director of a new institute at Nanjing
University of Science and Technology(NJUST). The Herbert Gleiter Institute of
Nanoscience (HGI) focuses on research
into nanostructured materials anddevices, with a growing interest in an
unusual type of glassy material known
as nanoglass.
Mutual interests between the two institutes in China and Japan were the impetus for a visit by representatives of the
AIMR in Sendai to HGI in Nanjing on
18 July 2016. The team included AIMR
Director Motoko Kotani, Administrative
Director Masaru Tsukada, Deputy
Administrative Director Susumu Ikeda
and several associate researchers.
Sendai to Nanjing
Gleiter kicked-off the exchange with an
introductory presentation on the HGI.
Five principal investigators lead threeresearch themes at the institute: nanostructured crystalline and non-crystalline

AIMResearch 2016

A team of researchers from the Herbert Gleiter Institute of Nanoscience (HGI) and the Advanced Institute forMaterials Research (AIMR) met in Nanjing to discuss mutual areas of interest.

materials; chemical physics and functional nanobiosystems; and nanostructured
metallic materials. HGI receives strong
support from its host institution, NJUST,
which is constructing a six-story building
for the institute in Nanjing, a metropolis
along the Yangtze River in eastern China.
HGI is also expanding cooperation with
NJUST, KIT, University of Münster,
Shenyang National Laborator y for
Materials Science and City University ofHong Kong.
Vice director of HGI, Jing Tao Wang,
offered further details on the state-ofthe-art facilities at HGI, which include ahigh-resolution scanning and transmission electron microscope, a scanningtunneling microscope, a helium-ion
microscope and an X-ray computed
tomography system with a spatial resolution of 50 nanometers.
Reciprocating these introductions,
Kotani outlined the research activities
at the AIMR, developments at the hostinstitution, Tohoku University, and objectives of the World Premier International

Research Center Initiative (WPI)
program in Japan. She emphasized thecollaboration between mathematicians
and materials scientists at the AIMR anddescribed current trends in data-driven
materials science in the country, with aparticular focus on the AIMR’s role inthese efforts, for example, through theJapanese government’s Cross-ministerial
St r at e g i c In n ov at i on P rom ot i on
Program (SIP).
Nanoglass and 3D graphene
The meeting in Nanjing offered researchers from both institutes a chance to share
their latest scientific finds. Tao Feng,permanent scientist at the HGI, discussed
a material first created by Gleiter anda team of researchers in Germany in1989 — nanoglass.
Crystalline materials such as graniteand quartz have been popular since the
Neolithic age because of their predictability. Researchers can control their physicalproperties by tweaking their atomic structures. But materials with disordered atomic

37

IN THE SPOTLIGHT

structures, known as glasses, are much
more difficult to manipulate. Nanoglassoffers a way to control the chemical andphysical structures of glasses due to its
distinct nanostructures made of patches
containing disordered clusters of atoms.
Because the glassy regions do not quite
match up where they meet, wide interfaces
form between them, which influence theproperties of the material. Feng described
the techniques used to create these materials and some of their interesting thermal,
magnetic and mechanical properties.
Glassy materials are also among the
top areas of interest at the AIMR, and astrong source of collaboration between
mathematicians and materials scientists.
Recently, researchers have borrowed amathematical concept known as topology
to find hidden structures in the atomic
arrangements of glasses.
Yoshikazu Ito, an associate professor at
the AIMR, presented the result of three
years of research into the development ofanother material with surprising abilities— highly crystalline, three-dimensional(3D) nanoporous graphene. The material
behaves like two-dimensional, massless
Dirac fermions, a characteristic previously not believed to be possible in 3D
sheets of graphene. Ito is now trying toenhance the catalytic abilities of the 3D
nanoporous graphene to facilitate thehydrogen evolution reaction in fuel cells.
The material could be a promising alternative to noble metals such as platinum
in realizing a hydrogen-fueled society.
Self-assembly
From novel materials to new ways of

Yoshikazu Ito, an associate professor at the AIMR, has created highly crystalline three-dimensional nanoporousgraphene that could help to realize a hydrogen-fueled society.

building them, permanent scientist at
the HGI Qingmin Ji and associate professor at the AIMR Hiroshi Yabu shared
their research into the spontaneous
process by which structures form on thesurface of materials, which gives them
impressive abilities.
Ji recently joined HGI after working
for several years in Japan at the Universityof Tsukuba, the National Instituteof Advanced Industrial Science andTechnology, and the National Institutefor Materials Science. Ji’s research focuseson the self-assembly of organic molecules
on metal surfaces — useful for designing molecular machines — as well as
the automatic formation of capsules ofmesoporous silica, which could be used

Hiroshi Yabu, an associate professor at the AIMR, has used the power of self-organization to fabricate
polymer nanostructures.

38

to gradually deliver drugs to the bodyover time.
Yabu has used the power of selforganization to fabricate polymer
nanostructures, including those inspiredby the natural world. His talk focusedon diblock copolymers, which are madeof a string of one type of monomer
interacting with a string of another typeof monomer. When the two units cometogether, attractive and repulsive forcesinteract to produce structures containing
different states of matter. Collaboratingwith mathematicians at the AIMR, Yabu
has recently discovered that mathematical formulas known as Cahn–Hilliard
equations can be used to predictthese structures.
Zesheng You, a permanent scientist
at HGI, has taken a different journey
into the nanoscale. He specializes in amechanical property of nanostructured
materials known as fracturing. The way
a material fractures largely depends on its
geometry and size. You is developing new
methods for measuring these properties
in nanomaterials, which has led to some
intriguing observations. For example,
the fracture properties of polycrystalline
materials depend on the size of the individual crystallites.
The exchange meeting in Nanjing
concluded with a consensus to collaborate in mutual areas of interest anda tour of the advanced laboratories andfacilities. The AIMR and HGI hope tomaintain a friendly relationship throughcooperation and healthy rivalry.
■

AIMResearch 2016

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.
research.wpi-aimr.tohoku.ac.jp

research.wpi-aimr.tohoku.ac.jp
AIMResearch is a publication of the Advanced Institute for Materials Research(AIMR), a Tohoku University institute funded by the Ministry of Education,
Culture, Sports, Science and Technology of Japan.
© 2017 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