RESEARCHHIGHLIGHTS 2018
A publication of the WPI Advanced Institute for Materials ResearchTABLE OF CONTENTSMESSAGE FROM
THE DIRECTOR
1

11 Block copolymers: Mussels inspire
magneto-optical film

12 Superconductors: Finding superconductivity

Establishing a truly global presence

in unexpected places

13 Aromatic hydrocarbons: Polyacenes offer

RESEARCH HIGHLIGHTS
2
3
4
5
6
7
8
9

Graphene: Opening up for the hydrogen economy
Metallic glasses: Non-uniformity uncovered
Oxide materials: Fabricating 2D conductors
Nanoporous materials: A universal synthesis
Lithium-ion batteries: Grinding out a better battery
Encapsulation: Wrapping up in a hurry
Magnetic materials: Atoms near boundary
determine magnetism
Soft-matter physics: 3D printing a liquid
into a liquid

10 Charge density waves: Metal films mimic
substrate’s waves

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

electronic surprises

14 Block copolymers: How to make virus-like nanoparticles
15 Colloidal nanocrystals: Mesostructured matter in a jam
16 Metal oxide nanoparticles: Scrutinizing cerium oxidefrom all angles

17 Superconductivity: A potential hide-out
for Majorana fermions

IN THE SPOTLIGHT
18 Deepening existing connections
with Europe and Asia

20 Transcending research boundaries
22 New beginnings in materials science and spintronics

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

The AIMR is host to about 100 leading
researchers, around 40 percent of whomcome from abroad, including 27 principal
and junior principal investigators. In
addition to the research hub at Tohoku
University, the AIMR collaborates withresearch centers in China, Germany,
Poland, the UK and the US. Close ties
with other leading overseas institutes aremaintained, going along with the efforts
of foreign principal and junior principal
investigators, as well as adjunct professors
and associate professors.

MESSAGE FROM THE DIRECTOR

Establishing a truly
global presence
The Advanced Institute for Materials Research (AIMR)At the beginning of this year, more than 370 researchers

was founded in 2007 with support from the World Premierfrom eight countries participated in the Kick-off SymposiumInternational Research Center Initiative (WPI), a govern-

for World-Leading Research Centers–Materials Science andment program for creating world-class research centers in

Spintronics, which has jointly held with the new spintronics

Japan. Since then, the AIMR has embraced the four WPI

center in February 2018. The 25 distinguished invited speakers

goals: advancing top-level research, establishing international

included Dan Shechtman, a chemist at the Israel Institute ofresearch environments, reforming research organizations,Technology and Nobel laureate, David Awschalom, a physicist

and exploring new fields through interdisciplinary research. It

at the University of Chicago, and Alfio Quarteroni, a math-has become a materials science center that attracts prominentematician at the Polytechnic University of Milan and École

researchers from around the world. From 2017, the AIMR

Polytechnique Fédérale de Lausanne. To further accelerate thehas been promoting the global circulation of the world’s best

establishment of international networks based on the AIMR’s

brains, while continuing to pursue world-class research as apioneering research, the Tohoku–Purdue Workshop and themember of the newly established WPI Academy.

Tohoku-SG-Spin Workshop were held in conjunction withAn international hub for materials science, the AIMR

this symposium, followed by the 2018 AIMR Workshop. In

promotes collaboration between mathematics and materi-addition, Tohoku–Tsinghua Joint Workshops were held inals science. By using the universal language of mathematics

July 2018, and there were active discussions in the sessions

to describe materials, which are extremely broad in scope,on novel electronic materials and spintronics and on new

the institute is seeking to uncover commonalities between

structural and functional materials.

different materials and generate novel outcomes through

The AIMR is constantly engaged in exchanges with re-

new research themes. This initiative to get mathematicians

searchers and institutes outside of Japan. It participated in theand materials scientists collaborating on an instituteEuropean Materials Research Society held in France in Junelevel is rare and marks the AIMR as an advanced hub for2018 and ran a booth together with the other three materials-

materials science.

science-based WPI centers. Many researchers visited the

In June 2017, Tohoku University was selected as abooth, which significantly promoted international exchange

Designated National University by the Japanese government,

and international collaboration. The AIMR also organized

and it is expected to implement education and researcha joint workshop with Science and Technology of Advanced

activities of the highest levels in the world and contribute

Materials, an open-access materials science journal. Throughsignificantly to global development as a representative

such international events, the institute seeks to strengthen its

university of Japan. To enhance its research capabilities, theglobal network and promote internationalization.

university is developing research centers in its four strongest

I would like to extend my sincere gratitude to everyone

fields: materials science, spintronics, next-generation medical

who has supported us. With the recognition of Tohoku

care and disaster science. The AIMR is playing a central

University as a Designated National University, the AIMR

role in establishing the materials science center. In addition

aims to play a core role in developing its international

to launching five projects in the areas of energy materials,

research environment and to continue making advances inelectronic materials, biomaterials, high-strength materials

high-quality research. As a hub for the international circula-and structural control materials in collaboration with othertion of the world’s best brains, the AIMR aims to benefit

departments, the AIMR is developing a system to promotesociety by advancing materials science.

fusion research among young researchers by overcoming
boundaries between departments and between fields.

Motoko Kotani, Director of AIMRRESEARCH HIGHLIGHTS

Graphene:

Opening up for the hydrogen
economyHigh-resolution spectroscopy by a teamat the AIMR and Tohoku University has
revealed how exposing graphene sheets —layers of carbon just one atom thick — tohydrogen gas under controlled conditions
can transform them into fuel-storage
devices as well as produce magnetically
active energy states1.
Chemists have long known that inserting atoms and ions into layered crystals,
a process known as intercalation, canenhance ordinary materials. For example,
many rechargeable batteries rely on intercalation of lithium within graphite toachieve stable power generation. Because
the effects of introduced atoms are expected to be heightened for single-layer
graphene, researchers are actively working
to create devices based on intercalation.
A natural target for graphene intercalation is hydrogen. That is because theory
predicts it can create band gaps in highconductivity graphene and produce thesemiconductor-like properties needed fortransistors and sensors. However, inserting lightweight hydrogen between carbon
sheets requires careful adjustment, notes
Katsuaki Sugawara from the AIMR.
“Because hydrogen’s radius and bondlengths are so much smaller than those ofgraphene, it’s hard to make it stay between
the graphene layers,” he says. “We worked
to fix that by tuning the conditions ofhydrogen exposure.”
Sugawara and his team explored thisproblem using an analytical techniqueknown as angle-resolved photoemission
spectroscopy, which probes the electronicenergy bands that hold solids together andshape their conductivity. By growing single
graphene layers on silicon carbide wafers

2© 2018 Katsuaki Sugawara

Observations of electron behavior when hydrogen atoms cram their way undergraphene sheets could speed the development of fuel cells

New electronic states that form
when hydrogen atoms (redspheres) adsorb and squeeze
underneath graphene layers(sheets of blue spheres) on asilicon carbide substrate (orange
and blue spheres) could help
develop band-gap-controlled
high-speed transistors.

and pumping in hydrogen gas for specifictimes, they aimed to monitor changes toband gaps induced by the hydrogen atoms.
After optimizing temperatures for intercalation, the researchers observed thatin pristine samples a new buffer layer ofmeshed carbon atoms appeared between
the outer graphene sheet and the siliconcarbide wafer. But longer exposures tohydrogen reduced the intensity of thebuffer-layer energy bands and madebands associated with aromatic bondingin graphene more prominent — clear evidence that hydrogen atoms had entered
between the layers and were disrupting
existing chemical links (see image).
Further analysis of the band structure
revealed that hydrogen exposure not
only increased the available band gap

for ballistic devices, but also createdelectronic states within the gap region.
These states could tune the efficiency ofultrathin hydrogen fuel-storage devices orform a foundation for spintronic transistors, notes Sugawara.
“Theory predicts that the new gap states
can introduce magnetic properties tohydrogen-adsorbed graphene,” he states.
“We want to elucidate which hydrogen
additions are ferromagnetic and whichlead to insulators.”

1. Sugawara, K., Suzuki, K., Sato, M., Sato, T. &Takahashi, T. Enhancement of band gap andevolution of in-gap states in hydrogen-adsorbed
monolayer graphene on SiC(0001). Carbon 124,
584–587 (2017).

AIMResearch 2018

RESEARCH HIGHLIGHTS

Metallic glasses:

Non-uniformity uncovered

Using state-of-the-art analytical instruments, AIMR researchers have probed
the nanoscale structure of a group ofmaterials known as metallic glasses
and discovered the origin of their nonuniformity on a nanometer scale for the
first time1.
Metals generally have highly ordered
crystalline structures. But under certain conditions, some form disordered,glass-like structures. Known as metallic
glasses, these materials have intrigued
materials scientists since they were firstreported in 1960.
One aspect that has puzzled researchers is that, while metallic glasses havea random structure on a macroscale,nanoscale measurements have shownthat their responses to stimuli vary at
different sites on a sample. This indicatesthat metallic glasses are non-uniform
on a nanoscale, but attempts to discover the reason for this non-uniformity
had failed.
Now, by using scanning transmission
electron microscopy and angstrom-beamelectron diffraction, Akihiko Hirata of
the AIMR at Tohoku University andhis co-workers have found that metallic
glass consists of two distinct regions on
a nanoscale: dense regions, which havethe order of a distorted 20-sided polygon(icosahedron), and less-dense regions,which are more disordered but still possess some crystal order (see image).
“It is extremely difficult to determine
the structural differences between
nanoscale regions using conventional
X-ray, neutron or electron-scattering
methods,” says Hirata. “By utilizing the
angstrom-beam electron diffraction
developed by our group, we have beenable to detect the local structure order of

AIMResearch 2018© 2018 Akihiko Hirata

The source of the nanoscale non-uniformity in metallic glasses has been shown
to be due to the existence of two distinct regions

This scanning transmission electron micrograph shows the two distinct regions in metallic glass: high-density
regions (red areas) and low-density regions (blue areas). The crystal structures of the two regions have beensuperimposed.

spatial heterogeneity of metallic glass forthe first time.”
Discovering the nanostructure ofmetallic glasses is a key factor in determining their properties. “The grain size anddislocation density basically determine
the strength and hardness of crystalline
materials,” says Hirata. “Metallic glasses,
however, lack such key structural indicators due to their disordered amorphous
structure. We believe that the spatial
non-uniformity may play an importantrole in determining the mechanical anddynamic properties of metallic glasses.”
The finding has significant implications for understanding metallic glasses.
“Many intriguing phenomena of glassy
materials stem from their complexity,”says Hirata. “In a simplistic model, glassy

materials are treated as being completely
disordered. But our work has shown thatat the nanoscale there are two distinct
kinds of disorder in metallic glass. There
must be an underlying mechanism forthe formation of this disordered system.”In the future, the team intends to
explore the effect of this non-uniformity
on the mechanical properties of glass.
They will also search to see whether thesame non-uniformity exists in othermetallic glasses.

1. Zhu, F., Hirata, A., Liu, P., Song, S., Tian, Y., Han,
J., Fujita, T. & Chen, M. Correlation between
local structure order and spatial heterogeneity
in a metallic glass. Physical Review Letters 119,215501 (2017).

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RESEARCH HIGHLIGHTS

Oxide materials:

Fabricating 2D conductors

By using transmission electron micro­
scopy and first-principles calculations, ateam of AIMR researchers has elucidated
the origin of electron transport in a classof crystals that could be engineered torealize materials that conduct electricity in just two dimensions1. Such twodimensional conductivity is promising fordeveloping advanced electronic devices.
Solid oxides have been extensively
studied by physicists and materials scientists alike because of the fascinating anduseful properties that specific compounds
can exhibit, including superconductivity,
magnetism and ferroelectricity.
In particular, some oxide materials
and structures exhibit electrical conductivity that is confined to two dimensions.
One example is the family of compounds
known as strontium niobates, whichhave the chemical formula SrnNbnO3n+2 .
Depending on the value of n, the members of this family can be conductors or
insulators or exhibit quasi-one-dimensional conductivity (in other words, twodimensional conductivity that is nearly
confined along a line).
“Materials with two-dimensional
conductivity have potential applications
for novel electronic devices, such as
metal–oxide–semiconductor field-effecttransistors and transistors with highelectron mobilities,” says Chunlin Chen,a researcher at the AIMR at Tohoku
University.
To discover the cause of the unusualelectrical behavior of SrnNbnO3n+2 , ateam led by Yuichi Ikuhara of the AIMR
and Johannes Georg Bednorz of IBM
Research − Zürich investigated the precise atomic and electronic configurationsof various members of the family.

4

© 2018 Chunlin Chen and Yuichi Ikuhara

Understanding the electronic properties of a family of oxides could lead to thefabrication of two-dimensional conductors by sandwiching insulators between thinmetal layers

This scanning transmission electron micrograph shows zigzag-like slabs sandwiched between chain-like slabs
where quasi-one dimensional conductivity can take place (indicated by the blue electrons and white arrows).

Scanning
transmission
electronmicroscopy revealed that each of thesecompounds consists of alternating stacks
of zigzag-like and chain-like atomic slabs.
The insulating or conductive behavior of
the slabs depends on the valence of theniobium ions, which the team probed
using a technique known as electronenergy-loss spectroscopy. They discovered that zigzag-like slabs are insulating,whereas chain-like slabs are conducting.
Density functional theory calculations
provided more insight into the origin of
the insulating and conductive behaviors.
Each slab has a backbone formed by
NbO6 octahedra. The electrons associated with the atoms in these octahedra
can move along the crystals, thus contributing to the conductivity. However,
the team found that the octahedra in zigzag slabs are severely distorted, inducing

a localization of the associated electrons
and hence insulating behavior.
Aside from providing fundamental
insights into the electrical propertiesof these materials, the results show that
two-dimensional conductivity can beobtained by inserting insulating layers
inside conductors. The AIMR team willattempt this experimentally. “We will try
to confirm the concept of segmenting athree-dimensional conductor into a stackof quasi-two-dimensional conducting
thin layers by inserting insulating layers
in other materials,” says Chen.

1. Chen, C., Yin, D., Inoue, K., Lichtenberg, F., Ma, X.,
Ikuhara, Y. & Bednorz, J. G. Atomic-scale origin of
the quasi-one-dimensional metallic conductivity instrontium niobates with perovskite-related layered
structures. ACS Nano 11, 12519−12525 (2017).

AIMResearch 2018

RESEARCH HIGHLIGHTS

Nanoporous materials:

A universal synthesis
A generic, green route offers an easy way to make an extensive range of useful holeymaterials with tunable pore sizes

AIMResearch 2018

Vapor-phase dealloying method
New, easy, environmentally friendly
Nanoporous
cobaltZinc

RecoverydeviceProtectivegas© 2018 Mingwei Chen

The first universal route to materials
containing extensive networks of tiny
voids has been developed by AIMR
researchers1. It is a highly controlled,environmentally friendly approach to
make so-called nanoporous materials,
which are finding a growing number ofapplications thanks to their lightness,high internal surface areas, high electrical and thermal conductivities, and fastmass transport.
“Nanoporous materials are being usedas large-surface functional materials forapplications such as supercapacitors,
electrodes for lithium ion and lithium–
air batteries, and plasmonic materials formolecular detection,” explains Mingwei
Chen, a lead researcher at the AIMR at
Tohoku University and Johns Hopkins
University, USA.
Typically, nanoporous materials are
made using a process known as dealloying, which involves selectively removing
one or more components from an alloyand leaving empty holes behind. But
traditional electrochemical dealloying
methods work on only a limited numberof alloys and produce significant chemical waste.
In contrast, the novel vapor-phasedealloying approach developed by
Chen’s team can in principle be used tomake nanoporous versions of all stable
solid elements in the periodic table.
Furthermore, it produces no chemical
waste and even captures the components removed from the alloys. “These
recovered materials are highly pure andcan be reused to make alloys or surface
coatings,” says Chen.
His team built a bespoke dealloying
system containing a high-temperature
furnace, a vacuum system and a

Heat

Mingwei Chen and his team have developed a vapor-phase dealloying system that can be used to tune the size ofthe pores in a material.

condensation trap for capturing vaporized alloy components (see image). Using
the cobalt–zinc alloy Co5Zn 21 as a model
system, they explored the effects of varying the dealloying time, temperatureand pressure on the size and locationof the resulting pores. By tweaking
these parameters, the researchers could
tailor the size of cobalt’s pores fromtens of nanometers to micrometers. For
example, lower pressures in conjunction
with slightly lower temperatures resulted
in an even network of copious, very small
pores. The evaporated zinc was fully recovered from the trap.
Chen has demonstrated this technique on eight zinc-containing alloys.
“These materials span from inorganic tometallic elements, lightweight to noble
metals, low-melting-point elements to
refractory metals,” he says. The team is

continuing to demonstrate the different
nanoporous materials that can be madein this way.
“This is a scalable method for fabricating nanoporous materials,” Chen adds.
His team can currently make tens ofcentimeters of material at a time, but
it should be possible to scale it up forindustry applications. But Chen firstwants to better understand the process.
“We have started the basic research tounderstand the kinetics of nanopore
formation and evolution during vaporphase dealloying.”

1. Lu, Z., Li, C., Han, J., Zhang, F., Liu, P., Wang, H.,
Wang, Z., Cheng, C., Chen, L., Hirata, A. et al.
Three-dimensional bicontinuous nanoporous
materials by vapor phase dealloying. Nature
Communications 9, 276 (2018).

5

RESEARCH HIGHLIGHTS

Lithium-ion batteries:

Grinding out a better battery

Simply grinding a lithium-based material can dramatically improve its conductivity, a study by AIMR and Tohoku
University researchers has found1. This
discovery could help to develop all-solidstate batteries that are safer and more
efficient than conventional batteries.
Lithium-ion batteries are used to
power everything from mobile devices toelectric cars. Most commercial batteries
use a liquid electrolyte to ferry charged
lithium ions between the battery’s electrodes during charging and discharging.
But liquid electrolytes can leak and may
be flammable, raising safety concerns.
Researchers are considering alternative solid electrolytes, including a family of materials known as closo-boranes.
These materials have cage-like anions
that contain boron, hydrogen and sometimes carbon. The spaces between theseanions can act as conduction channels
for lithium ions. But the anions also
have strong bonds between boron andhydrogen atoms, making it difficult tomodify the materials’ structure to finetune their properties.
Sangryun Kim from the Institute ofMaterial Research, Hiroyuki Oguchi
from the AIMR at Tohoku University,and colleagues have now shownthat introducing atom deficiency
through ball milling — a method of
mechanical grinding — can alter the
structure of closo-boranes and enhancetheir conductivity.
They milled lithium dodecahydrocloso-dodecaborate (Li 2B12H12) for 5
hours and then heated it to remove any
trace of water. Analytical tests revealed
that the material had lost lithium andhydrogen atoms and that some of6

Reprinted with permission from
Ref. 1. Copyright (2018) American
Chemical Society.

By introducing atom deficiency, ball milling boosts the conductivity of alithium borane material by 1,000 times, significantly enhancing its performance
as a solid electrolyte

Dodecahydro-closododecaborate (Li2B12H12)contains cage-like anions ofboron (green spheres) andhydrogen (blue spheres),along with lithium ions(red spheres). Ball milling
removed hydrogen andlithium, improving thelithium-ion conductivity
significantly.

the remaining lithium ions had beenrearranged in its crystal structure.
Computer simulations of the material
confirmed that relatively little energy wasneeded to free small amounts of lithium
and hydrogen in this way.
These structural changes meantthat the remaining lithium ions were
better able to hop between vacant sites
in the crystal structure, improving thelithium-ion conductivity. Indeed, further experiments showed that the ionic
conductivity of the milled material was
almost 1,000 times higher than that ofunmilled material.
The researchers then used the milledmaterial as an electrolyte in a battery,
sandwiching it between a negativeelectrode made of lithium metal and apositive electrode made of titanium sulfide. The device maintained a good energy capacity over 20 charge−discharge

cycles, whereas batteries that usedunmilled material had a smaller energy
capacity and a poorer capacity retention
after cycling.
The researchers hope that milling
could be used to tweak the compositionof other materials based on cage-likeanions. “We will investigate systematicroutes to forming atom deficiencies aswell as the precise relationship between
atom deficiencies and lithium-ion
conductivity,” says Kim. “Based onthese fundamental insights, we will
try to develop high ion-conducting
hydride materials.”

1. Kim, S., Toyama, N., Oguchi, H., Sato, T., Takagi,
S., Ikeshoji, T. & Orimo, S. Fast lithium-ion
conduction in atom-deficient closo-typecomplex hydride solid electrolytes. Chemistry ofMaterials 30, 386−391 (2018).

AIMResearch 2018

RESEARCH HIGHLIGHTS

Encapsulation:

Wrapping up in a hurry
A drop of liquid can be rapidly encapsulated in a polymer by simply being dropped
onto a flexible film floating on water

AIMResearch 2018

0.5mm

From Ref. 1. Reprinted with permission from AAAS.

A fast, versatile and effective method towrap liquids in thin polymer films, developed by an AIMR researcher and his
collaborators, could be used to containhazardous liquids and make containers
for chemical reactants1.
Liquids are often encapsulated
in other liquids; examples include
emulsions used in the food industry
and compounds for containing oil
spills. But for some applications, athin, solid wrapping would provide
greater rigidity.
Now, Thomas Russell of the AIMR at
Tohoku University, Narayanan Menonat the University of Massachusetts
Amherst, along with two other collaborators in the USA, have devised a simple
and elegant method that can encase
liquid droplets in polymer films in a few
tens of milliseconds.
Their straightforward techniqueinvolves simply releasing a drop of liquid from a specific height onto a small,thin polymer sheet floating on thesurface of another liquid. As the drop
sinks into the liquid, the polymer sheet
wraps around it, encasing it completely.
Surface tension ensures the seams thatform in the polymer are nearly perfectwith no gaps or overlaps.
Despite its simplicity, the method ishighly versatile. Unlike conventional
encapsulation strategies that generally produce only spherical droplets,
the technique can produce capsules ofdifferent shapes by varying the shape of
the polymer film (see image). Different
combinations of liquids can be also
used — in the study, the researchers
performed wrapping by dropping
both oil into water and water into oil.
Russell notes that the approach could be

0.5mm

By using films of different shapes (triangle in the main image; circle in the inset), the encapsulation method can
produce different shaped wrappings.

extended to other encapsulating materials: “In this study, we used a polymer towrap liquids, but any thin sheet that is
highly bendable, including thin metal
sheets, for example, could be used.”
The technique has many potential
applications. “Since the sheets can bepreconditioned or made from impermeable materials, they can easily be used tocontain contaminants such as oil from aspill, toxic materials and highly reactive
materials,” says Russell. “Furthermore,
multiple liquids that may react witheach other can be wrapped separately,
packed next to each other and stored.
When it is time to use them, the wrappings can be broken and the contents
allowed to react with each other.”

The team has plans to extend thestudy using more complex systems.
“Since interfacial energy is driving theentire process, we are pursuing studies
using bilayers where the interfacial interactions are different on the two sidesof the composite sheet,” says Russell.
“We are also examining constructs
where the bendability differs in different
directions, for example in composites
containing oriented rod-like fillers, likecarbon nanotubes.”

1. Kumar, D., Paulsen, J. D., Russell, T. P. &Menon, N. Wrapping with a splash: High-speed
encapsulation with ultrathin sheets. Science
359, 775–778 (2018).

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RESEARCH HIGHLIGHTS

Magnetic materials:

Atoms near boundary
determine magnetism

By employing the latest electron micro­
scopy techniques and calculation methods, AIMR researchers have shed newlight on magnetite, a magnetic material
known since antiquity1. Specifically, they
have shown that the magnetism at crystal boundaries in magnetite depends on
the arrangement of atoms close to theboundary — an important finding thatwill inform the development of advanced
magnetic devices.
Many magnetic materials are mosaics of small crystals whose magnetism
points in different directions. A classic
example is magnetite (Fe3O4), the oldest known magnetic material. Materialscientists have long wondered how thearrangement of atoms at the boundaries between these crystals relates tothe crystals’ magnetism, but it has
been technically challenging to simultaneously and accurately determine
both aspects.
Now, Chunlin Chen of the AIMR at
Tohoku University and his co-workers
have succeeded in doing this in magnetite by using state-of-the-art scanningtransmission electron microscopy withdifferential phase contrast imaging tomeasure the electric and magnetic fields
in the material. They also employed firstprinciples calculations.
The team, led by Yuichi Ikuhara, looked
at a special kind of boundary between
crystals in magnetite in which the atoms
on one side of the boundary are a mirror
image of those on the other side. They
found that the magnetism in the crystals
on either side of this ‘twin boundary’ canbe either parallel (ferromagnetic) or antiparallel (antiferromagnetic; see image),8

Reprinted, with permission, from Ref. 1. Copyright 2018 American Chemical Society.

The relationship between magnetism and atomic structure at crystal
boundaries in magnetite has been clarified for the first time

The magnetism in two adjacent crystals in magnetite as measured by scanning transmission electron microscopy.
The magnetism is antiparallel in this case (as indicated by the green and blue arrows).

depending on the arrangement of atoms
close to the boundary.
This was an unexpected discovery. “Wewere surprised to find that the magnetic
coupling of twin boundaries depends
only on the atomic core structures andresulting electronic structures within a
few atomic layers of the boundary,” says
Chen. “We had previously thought that
atoms far from the interface might also
play an important role.”
The finding is a significant one for thefield. “Establishing the one-to-one correspondence between the atomic structure
and magnetic coupling across individual
boundaries has been long desired in
the field of magnetism and magnetic
materials,” notes Chen.
This insight will be valuable for practical applications, Chen says. “This tells usthat we can tailor the magnetic propertiesof multilayer magnetic films by manipulating their interfacial microstructures,
which will facilitate the development ofhigh-performance devices.”
The team now hopes to establish ageneral rule for the interaction between
the atomic and electronic structures ofmagnetic materials and the magnetic
properties of their grain boundaries bysystematically investigating the magnetic couplings across other types ofgrain boundaries in magnetite.

1. Chen, C., Li, H., Seki, T., Yin, D., SanchezSantolino, G., Inoue, K., Shibata, N. & Ikuhara, Y.
Direct determination of atomic structure andmagnetic coupling of magnetite twin boundaries. ACS Nano 12, 2662–2668 (2018).

AIMResearch 2018

RESEARCH HIGHLIGHTS

Soft-matter physics:

3D printing a liquid into a liquid© 2018 Thomas Russell

A new three-dimensional printing technique allows stable water structures
to be created within oil

A bubble rising through the center of a three-dimensionally printed spiral of water in oil.

In a study that broadens the potentialof three-dimensional (3D) printing,scientists have modified a commercial
3D printer to print a liquid within
another liquid for the first time1. This offers the opportunity to create new kindsof materials that could find a wide range
of applications.
Until now, all printing has used either asolid or a liquid that solidifies on cooling.
For example, printing a photo requires asolid paper-based substrate, while 3D
printers often use liquid polymers that
become solid on cooling.
Now, by three-dimensionally printing water within oil, a team led byThomas Russell of the AIMR at Tohoku
University has printed stable structuresconsisting of a liquid in another liquid.
They added gold nanoparticles to thewater and a surfactant to the oil. The
nanoparticles and surfactant are attracted to each other, but, because of energy
considerations, neither wants to leave themedium it is in. Consequently, they linkup across the interface between the water

AIMResearch 2018and oil, forming a nanoparticle−surfactant layer that straddles this interface.
Despite being only 20 nanometers thick,this layer is stable like a solid, but canreadily deform.
“Conventional 3D printers produce
solid materials like plastics, metals, hydrogels and even biological matter suchas cells and organs,” says first author Joe
Forth at the Lawrence Berkeley National
Laboratory, USA. “All these things areinteresting and useful, but they’re basedon old paradigms. What’s exciting about
our technique is that it allows us to makea completely new type of material.”
The researchers automated the processby modifying a commercial 3D printer.
“We did everything on the cheap,” recalls
Forth. “We bought an entry-level 3D
printer for printing plastics. We rippedout the printheads and replaced themwith a syringe pump and some microfluidics tubing. If I could start over, I’d doit all differently, but what we did worked
extremely well, given how little we knew
about printing when we started.”

The new method opens a lot of possibilities. Since liquids can flow throughthese structures, they could be used inall-liquid microfluidic devices. Also, theprinted aqueous shapes are promising
as containers for living matter that can
exchange chemicals across the oil−waterinterface.
“What’s really interesting will be tosee what the global scientific community
can think of to do with a material like
this, which combines soft-matter physics
and nanotech to produce a material
that’s unlike anything else out there,”says Forth.
The team is using their printed liquids
to explore the mechanical properties of
two-dimensional materials. They will
also investigate how the materials behave
when a magnetic field is applied to them.

1. Forth, J., Liu, X., Hasnain, J., Toor, A., Miszta, K.,
Shi, S., Geissler, P. L., Emrick, T., Helms, B. A.
& Russell, T. P. Reconfigurable printed liquids.
Advanced Materials 30, 1707603 (2018).

9

RESEARCH HIGHLIGHTS

Charge density waves:

Metal films mimic
substrate’s waves
The behavior of the electrons within an ultrathin metal film is affectedby the electrons in the substrate it is on

10

Bi

Bi
TaS2
© 2018 Seigo Souma

Electrons in an ultrathin metal layer
sometimes adopt the same behavior
as electrons in the underlying substrate, AIMR researchers have found.
Specifically, electrons in a two-atomthick bismuth layer on tantalum sulfide(1T-TaS2) form a periodic formation
known as charge density waves1. Thisfinding offers a new way to control
electrons in metal films and could have
big implications for the application of
topological materials to devices, such as
field-effect transistors.
Interfaces between materials are ofgreat interest to scientists because theyoften give rise to intriguing phenomena.
In particular, a thin film on a substrate
sometimes exhibits a property that thesubstrate possesses. For example, a metal
film on a superconductor can becomesuperconducting near the interface,and a nonmagnetic metal can become
magnetic near its interface with aferromagnetic material.
Now, Seigo Souma of the AIMR at
Tohoku University and his co-workers
have found that an analogous effectoccurs for charge density waves — regular, wave-like arrangements of electrons
that form in certain materials.
The researchers fabricated ultrathin
films of bismuth on two substrates:
silicon and 1T-TaS2 (charge density waves
form in 1T-TaS2 , but not in silicon). They
then examined the electronic states inthe bismuth films using spectroscopy
and calculations.
The team discovered that electrons
in the bismuth layer on silicon showedno departure from normal behavior; inother words, the substrate did not affectElectrons in an ultrathin bismuth film behave just as in any other metal, with no band gap between conduction
and valence electrons (left). But electrons in a bismuth film on a 1T-TaS2 substrate form charge density waves,which results in the formation of a band gap (right).

the bismuth. In contrast, they foundthat charge density waves formed in the
bismuth layer on the 1T-TaS2 substrate.
Moreover, this resulted in the formationof a gap in the energy levels of conduction and bound electrons (see image)within the bismuth.
This effect may offer electrical engineers a new way to manipulate electrons
in metals. “Our results demonstrate that
this effect can be used to tune the electronic band structure in a bismuth film,”
explains Souma. “Since this effect opens
up a relatively large energy gap, it will be
useful for modifying the electronic statesin films in contact with charge-densitywave materials. For example, this could
be used to switch the energy gap in fieldeffect transistors.”
The team now intends to grow more

complex compounds on 1T-TaS2 . “We
used bismuth in this study because it
is a single element and relatively easy
to grow,” says Souma. “Next, we willgrow films of topological insulatorsand semimetals and study the effect onthem. If it turns out that charge density
waves can be used to tune the band gapof a topological insulator or semimetal,
it will be an important breakthrough forthe application of topological materials
to devices.”

1. Yamada, K., Souma, S., Yamauchi, K., Shimamura, N., Sugawara, K., Trang, C. X., Oguchi,T., Ueno, K., Takahashi, T. & Sato, T. Ultrathin
bismuth film on 1T-TaS2: Structural transitionand charge-density-wave proximity effect. Nano
Letters 18, 3235–3240 (2018).

AIMResearch 2018

RESEARCH HIGHLIGHTS

Block copolymers:

Mussels inspire
magneto-optical film

Inspired by a protein that helps mussels strongly cling to surfaces, AIMR
researchers have devised a way to make apolymer film embedded with two kindsof nanoparticles: one plasmonic andthe other magnetic1. This hybrid film is
promising for imaging magnetic fields
and for use in magneto-optical devices.
Mussels can adhere to a wide variety
of materials due to the strong adhesionof mussel foot proteins. The main functional group of mussel foot proteins is
catechol, which has strong adhesion andchemical reduction properties.
Now, Hiroshi Yabu of the AIMR at
Tohoku University and colleagues haveintroduced this catechol group into a
diblock polymer — a polymer made up
of two alternating two building blocks(i.e., ABABAB…, where A and B are two
chemical groups; for example, poly(vinyl
catechol) and polystyrene in this study).
“Only a few diblock copolymers containing the catechol group were reported
prior to our study as catechol inhibits
radical polymerization,” notes Yabu.
The team next employed a two-stepprocess that cleverly exploits the multifunctional properties of the catecholgroup to first add iron oxide nanoparticles and then silver nanoparticles tothe diblock polymer (see image). The
ability of catechol to include metal atoms
in its structure enables it to incorporate
the iron oxide nanoparticles, whereas
catechol’s reduction properties bring inthe silver nanoparticles.
The combination of silver and ironoxide nanoparticles gives the hybrid
polymer interesting properties. The ironoxide nanoparticles exhibit a phenomenon

AIMResearch 2018

Adapted with permission from Ref. 1. Copyright 2018 American Chemical Society

By exploiting the multifunctional nature of a protein found in mussel feet, researchers
have produced a hybrid film that exhibits useful magneto-optical properties

A diblock polymer developed by Hiroshi Yabu’s team at the AIMR consists of two building blocks poly(vinyl
catechol) (red bands) and polystyrene (navy bands). Two types of nanoparticles — iron oxide nanoparticles(gold spheres) and silver (silver spheres) — incorporated in the poly(vinyl catechol) impart the film withspecial magneto-optical properties.

known as the magneto-optical Kerr effect(MOKE), while the silver nanoparticles
enhance this effect by boosting the electromagnetic field in their vicinity. In the
MOKE, the magnetic properties of a material alter the properties of light reflectedfrom the material’s surface, making it apowerful way to probe the local magnetization of materials.
“The MOKE is used in magnetic memory devices and future spintronics devices,” says Yabu. “Our binary nanoparticle
assembly enhanced MOKE signals by coassembly of plasmonic nanoparticles andmagnetic nanoparticles, which opens theway to high density and highly sensitive
magnetic devices.”
The film could have much wider application by incorporating different pairs ofnanoparticles. “This result indicates that
our mussel-inspired diblock copolymer

thin film is a promising platform for developing well-ordered hybrid thin films
containing different nanoparticles,”comments Yabu.
Yabu notes that the interdisciplinary
environment at the AIMR was vital fordeveloping the film. “This work is an
example of the significant results from‘fusion research’ between three laboratories at the AIMR working on polymer
science, inorganic nanoparticles andspintronics,” he says.

1. Komiyama, H., Hojo, D., Suzuki, K. Z., Mizukami,S., Adschiri, T. & Yabu, H. Binary nanoparticles
coassembly in bioinspired block copolymer
films: A stepwise synthesis approach using
multifunctional catechol groups and magnetooptical properties. ACS Applied Nano Materials
1, 1666−1674 (2018).

11

RESEARCH HIGHLIGHTS

Superconductors:

Finding superconductivity
in unexpected places

In an unexpected discovery, AIMR
researchers have found that thin filmsof the compound lanthanum oxide(LaO) superconduct at temperatures
below about 5 kelvin1. This opens up
the possibility of using this oxide as abuilding block in novel superconductors
made of superlattices — periodic
structures consisting of layers of two or
more materials.
Lanthanum oxide is not the mostpromising place to look for superconductivity. Samples made up of randomly
orientated crystals were fabricatedunder high pressures in 1980 and foundto conduct electricity like metals. The
compound was largely forgotten about
until high-temperature superconductivity was discovered in cuprate materials
in the late 1980s. While one of thesesuperconductors contained a molecularlayer of lanthanum oxide, the layer itself
was insulating.
Now, Tomoteru Fukumura of the
AIMR at Tohoku University and hiscolleagues have made single-crystal thinfilms of rocksalt lanthanum oxide — socalled because it has the same crystal
structure as sodium chloride, or common salt (see image) — and found thatthey superconduct.
“This discovery is both a surprise
and a mystery,” says Fukumura. “It is asurprise that such a simple binary monoxide is superconducting — so far, only
two other binary monoxides have beenfound to be superconductors. And it isa mystery because only thin films with asingle-crystalline structure show superconductivity; thin films made up of randomly orientated crystals don’t exhibit12© 2018 Kenichi Kaminaga

Thin films of a binary monoxide have been found to superconduct
at a surprisingly high temperatureThin films of rocksalt lanthanum oxide (lattice of red and green spheres) have been found to superconduct
at temperatures below about 5 kelvin due to electrons forming Cooper pairs (yellow spheres).

superconductivity. We currently don’t
have a good answer for this difference.”
The lanthanum oxide films superconduct at temperatures below about
5 kelvin (or −268 degrees Celsius).
Although this does not sound very high,
it is much higher than its cousins — otherlanthanum monochalcogenides (that is,
LaX, where X is sulfur, selenium or tellurium) all superconduct below 1.5 kelvin.
It also bucks the trend established bythese compounds: the temperature atwhich they start superconducting drops
with decreasing mass, whereas lanthanum oxide, the lightest of them, has
the highest superconducting transition
temperature.
Fukumura’s team also found that lanthanum oxide’s transition temperature
can be tuned by varying the strain in its
crystal lattice.
The team is now trying to synthesize

other binary monoxides and theirsuperlattices, since combining themwith lanthanum oxide promises to open
up exciting possibilities, Fukumura
notes. “For example, europium oxide
is a well-known ferromagnetic semiconductor. By combining lanthanumoxide and europium oxide, we shouldbe able to make new ferromagnetic
superconductors, which could be usefulfor superconducting spintronics.” They
have already succeeded in growing thinfilms of various rocksalt binary oxides,
Fukumura adds. Such oxides could be
used as building blocks for superlattices.

1. Kaminaga, K., Oka, D., Hasegawa, T. &Fukumura, T. Superconductivity of rock-salt
structure LaO epitaxial thin film. Journal of
the American Chemical Society 140,
6754–6757 (2018).

AIMResearch 2018

RESEARCH HIGHLIGHTS

Aromatic hydrocarbons:

Polyacenes offer
electronic surprises

After seven years of systematic study,
AIMR researchers have found that a familyof organic materials boasts some surprising electronic properties1. Their findings
could have implications for research into
high-temperature superconductors.
Carbon-based molecules are increasingly being used in electronic components such as transistors. These organic
materials can be very sensitive to light, or
electric and magnetic fields, and it is relatively easy to fine-tune their properties bychemically modifying them.
Some of these materials are based onhydrocarbons known as polyacenes. Theirstructures consist of benzene molecules
joined in a linear chain. The simplest one,naphthalene, contains two benzene rings;
adding more rings makes anthracene,tetracene and pentacene. Other hydrocarbons, such as picene and phenanthrene,contain similar chains in a zigzag pattern.
Researchers had previously reported
that when metals are added to hydrocarbons like these — a process known as doping — the materials can carry an electricalcurrent with no resistance, a property
called superconductivity. However, there
is considerable debate about this behavior.
Katsumi Tanigaki of the AIMR at
Tohoku University and colleagues investigated the electronic properties of arange of these doped molecules. Yet multiple tests of potassium phenanthrene andpotassium picene uncovered no superconductivity, contradicting earlier findings.
To further understand the behavior ofthese materials, the researchers developed
a method for making doped polyacenesthat produced higher quality crystals
than had previously been available. X-ray

AIMResearch 2018© 2018 Katsumi Tanigaki

Metal polyacene compounds have been surveyed for their magnetic
and electrical properties, including superconductivity

In the crystal
structure of a
doped polyacene,
metal atoms(green spheres) lie
between flat organic
molecules.

diffraction measurements revealed thatthe potassium atoms in these compounds
are trapped between flat planes of organic
molecules (see image). This implies thatthe size of the metal atom will significantly affect the structure and properties of
the crystal. Unlike potassium anthracene,
for example, rubidium anthracene shows
a form of magnetism, called paramagnetism, at room temperature.
Tanigaki’s team also found that allof the doped polyacenes they studied
are electrical insulators under normal
conditions. However, while potassium
tetracene and potassium pentacene areclassical insulators, potassium anthracene and potassium naphthalene are Mott
insulators, meaning that they can become
conductors under certain circumstances.
For example, the team found that the electrical resistance of potassium anthracene

gradually declined as they ramped up thepressure. “We’ve succeeded in measuring
intrinsic electrical transport systematically in doped polyacenes for the firsttime,” notes Tanigaki.
The electrons in Mott insulators caninteract in a similar way to how electrons
behave in high-temperature superconductors, so these findings may offer valuable clues for further superconductivity
studies. “Our studies of doped polyacenes
from normal pressure to high pressure
could provide important insights for
future exploratory research of high-temperature superconductors,” says Tanigaki.

1. Heguri, S. & Tanigaki, K. Carrier-doped
aromatic hydrocarbons: a new platform incondensed matter chemistry and physics. Dalton
Transactions 47, 2881−2895 (2018).

13

RESEARCH HIGHLIGHTS

Block copolymers:

How to make virus-like
nanoparticles

A simple but powerful technique for
producing virus-like nanoparticles thathave chemically ‘patchy’ surfaces has
been developed by an AIMR researcher
and collaborators1. Such nanoparticles
promise to be useful for a wide range ofapplications, including cell delivery andphotonic materials.
Viruses range in size from about 20
to 400 nanometers. Scientists have beenable to create artificial nanoparticles inthe same size range, but the surfaces ofsuch nanoparticles are typically chemically uniform. In contrast, the surfacesof viruses are highly variable. Producing
artificial nanoparticles that have chemically variable surfaces would greatly enhance their applicability in many areas.
“Chemicallymodifiedpatchynanoparticles are important not only forcreating functional nanomaterials for efficient catalysts and biosensors, but also
for enabling us to control the nanoscalefeatures of synthetic polymer particles tobe like a virus,” says Hiroshi Yabu of the
AIMR at Tohoku University.
Now, Yabu and colleagues have comeup with a straightforward method
for producing such chemically patchy
nanoparticles. It involves dissolving
molecules consisting of two different
polymers, each with a functional chemical group attached, in an organic solvent.
Since the polymers are hydrophobic,
when water is added and the organic
solvent is evaporated, the polymer molecules are forced together so that they
form nanoparticles made up of the twopolymers. They do this in such a way thatmolecules of the same polymer tend toclump together.
The distribution of the two polymers

14© 2018 Hiroshi Yabu

Nanoparticles that resemble viruses can be made by a facile technique

Nanoparticles consisting of two polymers arranged in a stripy structure.

in the nanoparticles can be controlled
by varying the preparation conditions.
For example, stripy nanoparticles madeup of alternating disks of polymers (seeimage), nanoparticles with circles on
their surfaces, and nanoparticles with anonion-layer structure can be fabricatedby varying the conditions, such as thepolymer concentration.
By attaching a fluorescent dye to one ofthe polymers, the researchers were able
to obtain images of the various nanoparticle structures.
“This method for producing functional nanostructured particles brings
us one step closer to interfacial mimics
of natural nanoparticles, and as such,may give access to interesting materials
for fundamental biological studies orbiotechnological uses,” notes Yabu.
The functional chemical groups
protrude from the surface of thenanoparticles and can be easily modified
through chemical reactions. This opens
up a wide range of exciting possibilities.
The team plans to explore the potentialof these nanoparticles. “We intend tochemically modify nanoparticles withenzymes and antibodies so that they canbe used as biosensors for immunoassays
and as intelligent drug carriers,” says
Yabu. “Furthermore, we hope to usethem as templates for chemical catalysts
that have arrays of different enzymes forrealizing cascade reactions like thosethat occur in living bodies.”

1. Varadharajan, D., Turgut, H., Lahann, J., Yabu,
H. & Delaittre, G. Surface-reactive patchy
nanoparticles and nanodiscs prepared bytandem nanoprecipitation and internal phaseseparation. Advanced Functional Materials 28,
1800846 (2018).

AIMResearch 2018

RESEARCH HIGHLIGHTS

Colloidal nanocrystals:

Mesostructured matter in a jam

A novel form of matter made from nanocrystals with tunable phase-changing
properties at interfaces has been createdby an AIMR researcher and his collaborators1. They used a tailored chemical additive to control the nanocrystal assembly’s
transition between the solid and liquidstates. Applications for these dynamic
materials range from catalysis and allliquid electronics to energy storage.
Although colloidal nanocrystals havebeen used to create many solid structures,nanocrystals that remain in a shape-shifting, liquid-like state have received muchless attention, according to Thomas Russell,
whose affiliations include the AIMRat Tohoku University, and Brett Helms
from the Lawrence Berkeley National
Laboratory, USA, who co-led the research.
“Our motivation was to devise a way
by which two-dimensional assemblies ofnanocrystals at interfaces can undergo
solid-to-liquid phase transformations,”
Helms explains. When nanocrystal assemblies solidify they adopt a fixed shape,whereas nanocrystal liquids remain deformable with interesting dynamic properties. When these assemblies encapsulateliquids and retain their shape-shifting
properties, a host of new applications
become imaginable.
The researchers used positively charged
iron oxide nanocrystals dispersed in apolar organic solvent and drawn into asyringe. They inserted the syringe tip into
a second liquid consisting of amine-terminated poly(dimethylsiloxane) (PDMSNH2) dissolved in poly(dimethylsiloxane)
oil, and then extended a droplet of thenanocrystal dispersion from the syringe
tip to create a well-defined interface between the two liquids.

AIMResearch 2018© 2018 Thomas Russell

Soft magnetic actuators and all-liquid printed electronics are potential applicationsof nanocrystal assemblies that, when at an interface, can be switched between solidand liquid

Small molecules (pink) surround the nanocrystals (purple), competing with amine-terminatedpoly(dimethylsiloxane) (blue) for binding to the nanocrystals.

The interesting chemistry happened at
this interface, where the PDMS-NH2 fromone liquid would bind to the charged
nanocrystals in the other to form a stable
nanocrystal monolayer (see image) spanning the interface. When the monolayer
was compressed by slightly retracting thedroplet into the syringe, it ‘jammed’ into asolid state, creating a permanent wrinkled
surface on the suspended droplet.
But the material’s properties changed
when the researchers added a charged small
molecule to the polar organic phase, which
could reversibly bind to the nanocrystals
and compete with the binding of PDMSNH2 to the nanocrystals. When the droplet
was retracted, the wrinkles appeared,
but then disappeared, showing that thenanocrystal monolayer reconfigured backinto its dynamic, liquid-like state. Thanks
to the use of iron-based nanocrystals, thedroplet also transiently deformed when an
external magnetic field was applied.

“In essence, we have created a soft
magnetic actuator,” Helms says. “Infuture schemes, the use of catalytically
active nanocrystals would allow molecules encapsulated in the fluids to undergo chemical reactions.” Such a system
could function like a battery, allowing
energy to be stored chemically and later
released.
The team is continuing to explore thesystem’s novel dynamic properties, Helmssays. “Our next step is to translate theapproach to three-dimensional printed
objects from two immiscible fluids.”

1. Zhang, Z., Jiang, Y., Huang, C., Chai, Y., Goldfine,E., Liu, F., Feng, W., Forth, J., Williams, T.
E., Ashby, P. D., Russell, T. P. & Helms, B. A.
Guiding kinetic trajectories between jammed andunjammed states in 2D colloidal nanocrystalpolymer assemblies with zwitterionic ligands.
Science Advances 4, eaap8045 (2018).

15

RESEARCH HIGHLIGHTS

Metal oxide nanoparticles:

Scrutinizing cerium oxidefrom all angles

By using state-of-the-art analysis techniques, AIMR researchers have mapped
the distribution of valence states insidecerium oxide (CeO2) nanocubes1 andimaged single surfactant molecules on thesurfaces of cerium oxide nanocrystals2.
These findings will help make moreefficient catalysts and pave the way todesign new functional materials.
Cerium oxide is an extremely versatileceramic, being used in applications asdiverse as solid oxide fuel cells, catalytic
antioxidants for treating oxidative stressrelated diseases, and catalytic converters
for cleaning vehicle exhaust gas. Mostof its interesting properties, including
its extraordinarily high capacity to store
oxygen, stem from the fact that the cerium
cation has two stable valence states, Ce4+
and Ce3+, and can be repeatedly converted
between them.
To gain insights into the mechanism
behind the high oxygen storage capacity ofcerium oxide nanocrystals, Yuichi Ikuhara
and Tadafumi Adschiri of the AIMR at
Tohoku University and colleagues usedscanning transmission electron micro­
scopy (STEM) and electron energy loss
spectroscopy (EELS) to analyze the distribution of the two valence states within
nanocubes of cerium oxide with sizes
between about 5 and 12 nanometers. They
discovered that, Ce3+ ions are concentrated near the surface of larger nanocubes
but are almost absent in the center, where
the Ce4+ valence state predominates. In
contrast, nanocubes smaller than about
6 nanometers contain a significant amountof Ce3+ ions at their centers.
These findings will inform both
fundamental and applied studies. “Our16

© 2018 Kazutoshi Inoue

High-resolution analyses reveal the internal composition of cerium oxide
nanoparticles and their interaction with individual surfactant molecules

AIMR researchers have succeeded in imaging single surfactant molecules on the surfaces of metal oxide nanoparticles.

quantitative analysis of the valence state
distribution, combined with local structural transformation, provides a basis
for understanding the intrinsic featuresof cerium oxide nanocrystals,” notes
Adschiri. “It will also provide critical guidance for designing and fabricating novel
oxygen-storage materials that can be used
as catalysts and solid electrolytes.”
In a related study, the researchers used
STEM and EELS to examine how surfactants interact with cerium oxide nanoparticles. This is important since surfactants,
which lower the nanocrystals’ surface
energy, are indispensable for synthesizing
metal oxide nanoparticles with controllable sizes and desired morphologies and arethought to play a key role in applications.
The team succeeded in imaging single surfactant molecules on the surfaces of metaloxide nanoparticles — the first time such ahigh resolution has been achieved.

“We found direct evidence that surfactant coverage ensures the synthesisof well-dispersed ultrafine nanocrystals
that do not clump together,” comments
Ikuhara. “The direct characterizationof single surfactant molecules of an organic surfactant on the surfaces of metaloxide nanocrystals will advance ourunderstanding of the surface chemistry of
surfactant-modified nanocrystals.”
The team will investigate the effect ofadding dopants on the distribution of thevalence state in ultrafine nanocrystals.

1. Hao, X., Yoko, A., Chen, C. et al. Atomic‐-scale
valence state distribution inside ultrafine CeO2
nanocubes and its size dependence. Small 14,1802915 (2018).
2. Hao, X., Chen, C., Saito, M. et al. Direct imaging
for single molecular chain of surfactant on CeO2
nanocrystals. Small 14, 1801093 (2018).

AIMResearch 2018

RESEARCH HIGHLIGHTS

Superconductivity:

A potential hide-out
for Majorana fermions

A system created by AIMR researchersconsisting of an ultrathin metal film ona high-temperature superconductor isa promising host for elusive particles
known as Majorana fermions1. Such aplatform could lead to new applicationsin spintronics and quantum computing.
Matter is made up of protons, neutronsand electrons, which are all examples offermions — particles that have half-integer
spins (for example, spins of 1/2 and 3/2).
Every fermion has an antiparticle, which
has the same mass as the particle but the
opposite sign for one of its quantum properties (such as its charge). For instance,
the antiparticle of the negatively charged
electron is the positively charged positron.
Over eight decades ago, Italian
theoretical physicist Ettore Majorana predicted the existence of a special fermionthat is its own antiparticle, the so-called
Majorana fermion. While Majorana
fermions have yet to be observed as elementary particles, they could appear as
quasiparticles — excitations in materials
that behave as particles — in some special
material systems.
So-called topological superconductors
are particularly promising systems forsupporting Majorana fermions. “The lowest energy state of topological superconductors has been theoretically predicted
to form a superconducting gap in the electronic state of the bulk and gapless stateat surfaces and edges, which should leadto the emergence of Majorana fermions,”
explains Katsuaki Sugawara of the AIMRat Tohoku University. “Consequently,
many researchers are intensively studying
topological superconductors with the goalof finding Majorana fermions.”

AIMResearch 2018

Adapted with permission from Ref 1. Copyright 2018 American Chemical Society.

A hybrid material could be a good place to look for an elusive particle
first predicted 80 years ago

A scanning tunneling micrograph of a candidate topological superconductor consisting of an ultrathin bismuth
film on a high-temperature superconductor.

Now, Sugawara and colleagues haveproduced a hybrid material that theystrongly suspect is a topological superconductor. They grew a six-atom-thick filmof bismuth on top of a bismuth strontium
calcium copper oxide superconductor
and analyzed it using electron microscopy
and spectroscopy techniques. Their analysis suggests that the hybrid material is acandidate topological superconductor. If
it does turn out to be topological superconductor, there is a high chance it could
be used to produce Majorana fermions.
Unlike other superconducting systems
explored in previous studies, the one fabricated by Sugawara and his team superconducts at a high temperature and has arelatively large superconducting gap, bothof which are advantageous for establishing it is a topological superconductor andfor looking for Majorana fermions.
“We believe our new platform could
harborlong-sought-after
Majorana
fermions that are stable at high temperatures,” says Sugawara. “And it could help
realize novel applications in spintronics
and quantum computing.”
The researchers are doing further experiments that will definitively show whether
the system is a topological superconductor
and can host Majorana fermions.

1. Shimamura, N., Sugawara, K., Sucharitakul, S.,
Souma, S., Iwaya, K., Nakayama, K., Trang, C. X.,
Yamauchi, K., Oguchi, T., Kudo, K. et al. Ultrathin
bismuth film on high-temperature cuprate
superconductor Bi2Sr2CaCu2O8+δ as a candidateof a topological superconductor. ACS Nano 12,
10977–10983 (2018).

17

IN THE SPOTLIGHT

IN THE SPOTLIGHT
INTERNATIONAL WORKSHOPS

Published online on 25 September 2018

Deepening existing connections
with Europe and Asia
The AIMR has been actively pursuing collaboration with researchers and institutions in both Europe and AsiaTo enhance global awareness ofthe World Premier International
Research Center Initiative (WPI)
and four WPI materials-related centers,
researchers from the Advanced Institutefor Materials Research (AIMR) attended
the 2018 European Materials ResearchSociety (E-MRS) Spring Meeting in
June, where they helped manage a boothand run a workshop. This was the thirdtime that the four centers — the AIMR,
the International Center for Materials
Nanoarchitectonics (MANA), the Institutefor Integrated Cell-Material Sciences(iCeMS) and the International Institutefor Carbon-Neutral Energy Research(I2CNER) — have jointly participated in
the E-MRS Spring Meeting, which thisyear was held in Strasbourg, France.
The WPI exhibition booth provided
an important platform to promote
the activities of the WPI and the four
centers to attendees of the 2018 E-MRS
Spring Meeting. Over the three days thatthe booth was open, it attracted many
European researchers, who browsed its
posters and brochures while enjoying
some traditional Japanese food andbeverages. A wide range of researchersvisited the booth — senior researchers
who had stayed i n Japa n or had
collaborated with Japanese researchers;
young researchers interested in working
at Japanese institutions; and participantsfrom other booths who were curious
about Japanese academic institutions.
Outreach staff members from the four
WPI centers managed the booth andwere joined by WPI researchers between
sessions. Such face-to-face dialog between
WPI members and European researchers
was very valuable for enhancing the
profile of WPI and the four centers.

18Top: Susumu Ikeda, director of the AIMR Research Support Division, introducing the workshop and the WPIat the STAM–WPI Joint Workshop. Bottom: The WPI exhibition booth at the 2018 E-MRS Spring Meeting in
Strasbourg, France.

Also this year, the WPI centers helda joint workshop with the open-accessmaterials science journal Science andTechnology of Advanced Materials(STAM) about future developments at thefrontiers of materials science. This joint

AIMResearch 2018

IN THE SPOTLIGHT

workshop was born out of discussions
held two years ago between members of
WPI and STAM about the possibility ofcollaborating to highlight the activities ofthe entire material science community inJapan. At the beginning of the workshop,
AIMR’s Susumu Ikeda explained the
purpose of the workshop and introduced
the framework of the WPI. His talk was
followed by an introduction to STAM by
its editor-in-chief, Shu Yamaguchi of the
University of Tokyo. This was followedby five presentations about how materials
science can contribute to realizing asustainable society by researchers fromfour WPI centers and Swiss Federal
Laboratories for Materials Science andTechnology (Empa).
H i rosh i Yabu of A I M R t a l ked
about experimental and theoretical
approaches for controlling the shapesof nanostructured particles made frompolymers. His team has developed asimple method for fabricating block
copolymer particles that have a varietyof nanostructures by simple solvent
evaporation from polymer solutions
containing poor solvents. The uniquephase-separated structures they obtained
can be described by a mathematicalmodel that was developed with the helpof AIMR’s mathematicians. This method
can be used to create new nanostructured
materials that will help address medical
and environmental issues.
The four WPI centers have jointly
participated in E-MRS Meetings every
other year since 2014 as it is proving to bean effective way to promote international
exchange and collaboration
Strengthening ties with
Tsinghua University
Changing continents, the Tohoku−
Tsinghua Joint Workshop on Materials
and Spintronics Sciences is a good
example of the effectiveness of promoting
collaboration through long-standing
efforts and mutual exchange withinternational partners.
The relationship between Tohoku
University and Tsinghua University has
been deepening over many years throughactive personnel exchanges — the two
universities signed their first academic
exchange agreement back in 1998. As partof Tohoku University, the AIMR has also
cooperated with Tsinghua University. In

AIMResearch 2018

Shin-ichi Orimo, principal investigator at the AIMR, giving a keynote speech at the Tohoku-Tsinghua Joint
Workshop on Materials and Spintronics Sciences in Sendai.

particular, Qikun Xue, vice-president andprofessor at the Department of Physics
of Tsinghua University and principal
investigator at the AIMR, has made avital contribution by playing a leadingrole in the collaboration. He is alsochair of the Tohoku University Alumni
Association in China and has acted as abridge between the universities as well as
the AIMR.
An important way to strengthen
collaboration is to establish common
research themes with partners, whichleads to two-way exchange of information
and researchers. To build closer ties
with partners in this way, the AIMR
has established joint research centers at
the University of Cambridge in the UK
and the University of Chicago in theUSA, and it is now in discussions with
Tsinghua University to create anotherjoint laboratory in Beijing, China.
In December 2017, the first joint
workshop on materials and spintronics
sciences was held at Tsinghua University
as part of Tohoku University Day. Some
AIMR researchers participated in theworkshop and took the opportunity to
discuss a plan to establish a new joint
research center at Tsinghua University.
This year, the AIMR organized thesecond inter-university event: The
Tohoku−Tsinghua Joint Workshop on
Materials and Spintronics Sciences. This
was a key event in Tohoku University’s
new materials science research center,
which is being established as part of theuniversity’s new status as a DesignatedNational University.

O n 2 6 J u l y, a f t e r s i g n i n g amemor a ndu m of u nder s t a nd i ng ,plenary lectures, and a tour of Takashi
Takahashi’s laboratory, the workshop washeld at the Westin Hotel in Sendai. Bothuniversities gave opening remarks, whichwere followed by two keynote speeches.
Shin-ichi Orimo, of the AIMR and theInstitute of Materials Research, Tohoku
University, gave a talk on advanced
hydride research for energy device
applications, while Ke He of Tsinghua
University described the search for
intrinsic magnetic insulator materials.
Workshop participants then went
to one of two parallel sessions: Novel
Electronic Materials and Spintronics,
and A New Stream of Structural andFunctional Materials. Both sessions
highlighted close interactions between
the researchers at the two universities.
Sometimes interactions went beyond
research. For example, Jing-Feng Li of
Tsinghua University obtained his PhDfrom Tohoku University in 1991 andworked at Tohoku University’s School ofEngineering until 2002. He has playeda key role as a mediator in the exchange
between researchers from the two
universities. Several Tsinghua University
researchers have also conducted researchat Tohoku University.
Through these international events,
AIMR is strengthening its global networkand enhancing its internationalization,
which is a key mission of the WPI centers.
The AIMR is aiming for even greater
heights, namely to become a dynamic hub
for global brain circulation. ■19

IN THE SPOTLIGHT

Hirano-Iwata in discussion with her laboratory staff. She finds the research environment at AIMR conducive to cooperative research.

FEATURED RESEARCHERS

Published online on 25 December 2018

Transcending research boundaries
Drawing inspiration from Marie Curie and Japanese female scientists, AIMR principal investigator Ayumi HiranoIwata is exploring networks made from rat neurons as well as artificial cell membranes for detecting drug side effects

A

IMResearch talks to Ay umi
H i ra no -Iwat a , a lead i ng
researcher at the Advanced
Institute for Materials Research (AIMR) at
Tohoku University. Her research straddles
many fields, including bioelectronics
and nanobiotechnology; she has also
recently started collaborating withmathematicians. Hirano-Iwata joined
Tohoku University in 2006, and in 2016
she became a principal investigator at the
AIMR, which encourages researchers likeher who want to overcome the boundaries

20

between research fields by adopting aninterdisciplinary approach.
AIMResearch: It is not easy pursuing acareer as female researcher in Japan. What
led you to become a scientist?
H i r a n o - I w a t a : I remember being
inspired after reading a book aboutMarie Curie when I was a middle school
student. I struggled a bit when I started
doing research as a university student as
there were many things I didn’t know.
But after clearing that initial hurdle, I

started to really enjoy generating myown conjectures — and the feeling ofgratification when they turned out tobe correct. It was hard to find researchjobs after graduating. At first, I was justdoing analytical chemistry and finding
it a bit narrow and restrictive. I wanted
to get into technologies that are more
physics based. It was then that I joined
Tohoku University, where I started doing
research involving microfabrication andpharma-materials. And that researchreally took off.

AIMResearch 2018

IN THE SPOTLIGHT

AIMResearch: What has been one of yourcareer highlights?
Hirano-Iwata: I’ve been working on
developing artificial cell-membranesensors that mimic actual heart cell
membranes with a view to using them todetect potential side effects of drugs on theheart. Our artificial cell membranes were
initially very fragile, making them almost
impossible to use as sensors. So we triedstabilizing them using microfabrication
techniques, and it worked very well. That
was certainly one highlight.
We’re continuing to work on them.
Since drug side effects vary from person
to person, we’d like to extend thisapproach for personalized medicine. If
we can use microfabrication techniques
to develop side-effect sensors tailored forindividual patients, it will demonstrate
the potential of using microfabrication for
personalized medicine.
AIMResearch: What other projects are you
working on?
Hirano-Iwata: I’m also leading a project inwhich we make circuits by taking neurons
from rat brains and arranging them onsmall glass chips. These circuits are likeminiature brains and they have functions
that are beginning to resemble those of
actual brains. In some cases, the circuits
consist of just a few neurons, whereas inother cases we use about 100.
A I M R e s e a r c h : Yo u r re s e a rc h i sinterdisciplinary. What fields does it cover?
Hirano-Iwata: My research involves
microfabrication, biomaterials, chemistry,electronic engineering, neuroscienceand physiology. And I’m just starting acollaboration with mathematicians at the
AIMR, including Hiroshi Suito, the leaderof the Mathematical Science Group.
AIMResearch: Have you encounteredany challenges in doing interdisciplinary
research?
Hirano-Iwata: Initially, it was difficult
to communicate with each other. But
sometimes even miscommunication canadvance research. For example, when wewere making the artificial cell membranes,
the researchers responsible for fabricating
microapertures didn’t fully understand thebiological aspects of the membranes. As aresult, they made small tapered apertures.
This ‘mistake’ turned out to be very

AIMResearch 2018

do you have beyond Tohoku University?
Hirano-Iwata: I’m collaborating with amicrofabrication scientist at Yamagata
University and a protein researcher
at Saitama University. A scientist at
Toyohashi University of Technology is
helping us characterize the artificial cell
membranes. Overseas collaborations
include one with Jordi Soriano at Barcelona
University. He’s an expert in the nervous
system and is very good at analyzing thecomplex data generated by the neuralcircuits we make. Also, Tay Netoff of the
University of Minnesota in the US is a
specialist in small neural networks andwe’re working with him in constructing
artificial networks of neurons.

Ayumi Hirano-Iwata started her research life as ananalytical chemist but is now doing research thatstraddles microfabrication, biomaterials, chemistry,electronic engineering, neuroscience and physiology.

effective in stabilizing the membranes. It
was truly serendipitous.
AIMResearch: How does the AIMR
encourage interdisciplinary research?
Hirano-Iwata: There are many researchmeetings that bring together scientists
from different f ields. For example,
before joining the AIMR, I’d never been
to a symposium by a mathematician.
While working on fabricating artificial
cell membranes at the AIMR, I was
wrestling with how to figure out the best
structure for our microfabricated chips toenhance the stability of the membranes,and I was beginning to despair that I’dever be able to do it. But then I heard apresentation by a mathematician at aninternational symposium organized by
the AIMR and I thought: “This person
could solve the problem.” So I spoke tohim after the presentation, and he wasvery enthusiastic about collaborating withme. I’ve found that mathematicians at the
AIMR are all eager to help, which is a real
boon to researchers such as myself who
are working on materials and devices.
It really makes it easy to collaborate.
Other AIMR researchers, such as juniorprincipal investigator Hiroshi Yabu, arealso working on the collaborative project
to fuse biomaterials with mathematics.
AIMResearch: What kind of collaborations

AIMResearch: As a female researcher, how
do you find the research environment at the
AIMR and Tohoku University?
Hirano-Iwata: The situation has changed
considerably since I was a student. I was
lucky to become a PhD student as some
professors wouldn’t take women as PhD
candidates. But the environment haschanged to the point that sometimes
being female can almost be advantageous.
Tohoku University was the first university
in Japan to admit female students, and it
has developed a system for supporting
female researchers and nurturing female
leaders throughout the university.
AIMResearch: Did you have any rolemodels?
Hirano-Iwata: Of course, Marie Curie
was a big inspiration. In Japan, there wasalso Maki Kawai, who went to the same
university as me. She has gone on to
become a top researcher. She developed
spat ia l ly select ive sing le-molecu lespectroscopy, and, in 2018, she became
the first woman to become president of
the Chemical Society of Japan. I aspire
to be like her. Kaoru Tamada at Kyushu
University who is a well-regarded professor
was another good role model for me. Closer
to home, there is Motoko Kotani, wholeads the AIMR. It’s a big encouragement
having a female director at the institute
who is also a top mathematician. She
does a great job of leading the AIMR,
while making efforts to create a research
environment that is attractive for women,
in keeping with Tohoku University’s strong
tradition of promoting female involvementin science. ■21

IN THE SPOTLIGHT

Professor at the University of Wisconsin−
Madison, John Perepezko (right; AIMR adjunctprofessor) posing a question to Chris Pickard,
professor of the University of Cambridge, UK(AIMR principal investigator), at the Q&A
session of the AIMR Workshop 2018.

INTERNATIONAL SYMPOSIUM

Published online on 26 March 2018

New beginnings in materials scienceand spintronics
A special symposium marked the commencement of an exciting new era in materials and spintronics researchat Tohoku University

F

ollowing Tohoku University’s
select ion by t he Japa nesegovernment as a DesignatedNationa l Universit y in June 2017,plans are afoot to create world-leading
research centers that will enhance
the university’s already formidable
reputation in four vital areas: materials
science, spintronics, next-generation
medical care and disaster science.
In collaboration with several otherinstitutes and depar t ments at t heuniversity, the Advanced Institute for22

Materials Research (AIMR) will play a
key role in developing the new materials
science center.
To s t i mu l at e i nt e rd i s c ipl i n a r y
dialogue and idea sharing, the Kick-off
Symposium for World Leading ResearchCenters — the first event of its kind,being jointly organized by materials
science and spintronics groups — washeld in Sendai on 19–20 February 2018. It
brought together top minds from Tohoku
University and internationally, as well as
industry partners.

In his welcome address, Susumu
Satomi, president of Tohoku University,
spoke of the honor of being selected
as a Designated National University
alongside the University of Tokyo andKyoto University. He highlighted theimportance of strengthening researchunder this new framework and providing
the best possible working conditions in
the light of increasing global competition.
Engineering a social revolution
Represent i ng Japa n’s Mi nist r y of

AIMResearch 2018

IN THE SPOTLIGHT

Education, Culture, Sports, Scienceand Technology (MEXT), Masanori
Shinano, deputy director-general of theHigher Education Bureau, conveyed
his aspirations for “advancing researchthat will be a force for innovation andactualization of Society 5.0.” Outlined
in Japan’s Fifth Science and Technology
Basic Plan in 2016, Society 5.0 aims totransform society through the widespread
adoption of artificial intelligence, big data,
robotics and the Internet of Things (IoT).
C o nt i nu i n g o n t h e t h e m e o fSociety 5.0, Kazuo Kyuma, an executive
member of Japan’s Council for Science,
Technology and Innovation, explainedthat “integrating cyberspace and physicalspace will be key to creating new values
in industry and social systems” and novel
materials will be indispensable to realizing
this so-called Super Smart Society.
Ky uma expressed his conf idence
in the AIMR under the leadership of
Director Motoko Kotani, highlighting its
accomplishments in the areas of metallic
glasses, porous materials and spintronics
materials. He commended the impressive
advances in spintronics by Hideo Ohno,
director of the Research Institute ofElectrical Communication (RIEC) as wellas principal investigator at the AIMR,
and Tetsuo Endoh, director of the Center
for Innovative Integrated Electronic
Systems (CIES).
Building on a proud legacy
In her opening remarks, Kotani referredto Tohoku Universit y’s more thancentury-long history of excellence inresearching materials. It extends backto the founding of the Institute forMaterials Research (IMR) in 1916 andthe work of the institute’s first director
Kotaro Honda, who is renowned for his
development of permanent magnet steels.
It also includes the establishment of theInstitute of Multidisciplinary Research
for Advanced Materials (IMRAM) in2001 and the AIMR in 2007.
Building on this rich histor y ofresea rch, t he A I M R is ex plor i ng
materials science by harnessing thepower of mathematics, Kotani noted. She
emphasized the importance of “forging
strong international ties through a global
alliance network, consolidating researchcapabilities at a university-wide level,focusing on research that addresses

AIMResearch 2018

Four plenary speakers at the symposium (clockwise from top left: David Awschalom, Alfio Quarteroni, Tetsuya
Tsurumaru and Masato Sagawa).

the needs of society, and working
toward the United Nations’ Sustainable
Development Goals.”
Speaking in his capacity as RIEC
director, Hideo Ohno, who will become
the president of Tohoku University
from April 2018, also ref lected on theuniversity’s rich past. He drew attention
to the work of Junichi Nishizawa, apioneer in semiconductor research,and Shunichi Iwasaki, the inventor of
perpendicular magnetic recording, atechnology used globally in hard disks.
“Spintronics is a field that inherits andcombines these early achievements,” hesaid. Now spanning materials science,
condensed-mat ter physics, dev ice
engineering and system applications,spintronics will be foundational for
realizing Society 5.0, he added.
Diverse technologies
In a special message, Dan Shechtman,
who was awarded the Nobel Prizein chemistry in 2011 for his workon quasicr ysta ls, ex tended his
congratulations to Tohoku University
and expressed his hopes for young

scientists to continue contributing to theuniversity’s outstanding achievements.
Presentations in six sessions began withplenary talks covering an array of new
developments in spintronic technologies,
mathematics, and computational andmaterials science.
David Awschalom of the Universityof Chicago explained that, in contrast to
the conventional goal of removing defects
from devices, his team is “putting defects
back into quantum systems to explore
new electronic and optical technologies.”
For example, embracing defects in siliconcarbide to achieve a new level of control
over spin dynamics could profoundly
impact quantum information processing
and medical imaging.
In his talk titled ‘Taking Mathematics
to Heart’, Alfio Quarteroni of Politecnico
d i M i l a no, It a ly, a nd t he É c ole
Polytechnique Fédérale de Lausanne(EPFL), Switzerland, described how
numerical simulations can be used tomodel systems even as complex as thehuman heart. Running simulationsof healthy and unhealthy hearts, hesaid, could help doctors diagnose

23

IN THE SPOTLIGHT

cardiovascular disease and determine
better treatment plans. He added thatmathematical models are providing
insig hts into f ields as d iverse as
seismology and sports science.
Representative director and chairmanof Renesas Electronics Corporation,
Tetsuya Tsurumaru, stated: “Spintronics
has the highest possibility of providing
solutions to emerging technologicaldemands.” Acknowledging the top-level
spintronics research conducted at Tohoku
University, he stressed the importanceof strengthening mutual cooperation.
“Semiconductors have the power tochange the world,” Tsurumaru said. The
challenges ahead will be to “cultivate
global human resources and encourage
open innovation,” he added.
Renowned inventor Masato Sagawa,
now a consu lta nt at Da ido Steel
Co, Ltd, presented his work on thedevelopment of neodymium−iron−boron sintered magnets, for which he
was awarded the Japan Prize in 2012.
Referring to his studies at and latercollaborations with Tohoku University,
he noted that “the contribution of
Tohoku University, especially that of the
IMR, was overwhelmingly importantin the evolution of the world’s strongest
permanent magnets.” He indicatedthat the most promising applications
for these magnets will be robots andelectric vehicles, and concluded byproposing that the coming era of cleaner
technologies based on light rare-earth
elements such as neodymium be termed
the Rare-Earth Iron Age.
Projecting into the future
In her presentation, a f ter a brief
introduction to the World Leading
Research Center for Materials Science,
Kotani gave an overview of the AIMR’s
activities so far and described her own
expertise in geometrical analysis. She
shared her vision for a collaborative
way forward, which will be critical toachieving “new research objectives withincreasing global relevance, including the

Researchers interacting at the symposium’s poster session.

development of highly efficient energy
conversion and storage systems basedon functional materials, and reliablesocial infrastructure systems based on
structural materials.”
Kotani explained that the AIMR’s
three target projects have already proved
fruitful, and said that mathematics
as a common language is “helping tovisualize, quantify and conceptualize
data” to deepen our understanding ofmaterials science.
On the university’s new status, Kotani
commented: “We are proud to be selected
as a focus research center and more than
happy to be a role model to transfer theknow-how we have developed to achieve
world premier status in the WPI program
to other research centers.” The AIMR,
she adds, will aim to “maintain top-levelresearch in its capacity as a member of the
newly established WPI Academy and playa central role in Tohoku University’s new
materials science research center.”
Unleashing the potential of spintronics
As the final plenary speaker, Ohnopresented his work on nanospintronics“Semiconductors have thepower to change the world.”
24

devices for artificial intelligence andvery large-scale integration. The ideal
technology for working memory, hesuggested, is a “non-volatile memorythat is scalable and fast and has virtually
infinite endurance.” Spintronic memory
devices, he averred, are the only ones
k nown to be capable of achieving
this ideal.
Ohno noted that scalability is oneof the top priorities for industry torealize a wide variety of applications for
artificial intelligence and that this aspectmakes materials so crucial. The coming
challenges, he said, will be to “deepen
knowledge and transfer it to the realworld and provide an R&D platform for
cutting-edge technologies.”
In total, 373 people took part in thetwo-day symposium, including 15 invited
speakers, and 183 posters were displayed
at Sendai International Center.
The symposium was followed by the
AIMR Workshop 2018 on 21 February,which provided another opportunity
for resea rchers at t he A I M R , its
joint research centers and overseas
partner institutions to interact. Heldannually since 2008, the workshop is acontinuation of the AIMR International
Symposium (AMIS), which aims tostimulate further research exchange
and international networking at the
AIMR through providing a forum fordiscussions from various angles. ■AIMResearch 2018

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

wpi-aimr.tohoku.ac.jp/en/aimresearch/
AIMResearch is published by the Advanced Institute for Materials Research (AIMR)at Tohoku University in collaboration with the Partnership and Custom Media unitof Nature Research, a division of Nature Japan KK.
© 2019 AIMR, Tohoku University. This publication may be reproduced in its
original form for personal use only. Modification or commercial use without priorpermission from the copyright holder is prohibited.

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