法人別リリース

MANA Scientists Employ Active Machine Learning to Enhance Thermoelectric Performance of Materials

MANA — Fri, 17 Jan 2025 17:00:00 +0900

TSUKUBA, Japan, Jan. 17, 2025 /Kyodo JBN/ --
Research Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS)
Scientists from the Research Center for Materials Nanoarchitectonics (MANA) have integrated machine learning with traditional materials science to expedite the discovery of kesterite-type thermoelectric materials, paving the way for efficient energy conversion technologies.

Image: https://cdn.kyodonewsprwire.jp/prwfile/release/M105739/202412242233/_prw_PI1fl_kDhuzYc5.jpg

Kesterite-type materials, like Cu2ZnSnS4, are promising thermoelectric (TE) materials that convert waste heat into electricity. These non-toxic materials are composed of abundant, easily accessible elements and exhibit a figure of merit (zT), a quantity level that measures thermoelectric efficiency, of greater than 1 at temperatures between 300 and 800K (26 to 526C). Around 500K, kesterites undergo a transition from an ordered cationic structure to a disordered one, which affects their TE properties significantly. However, identifying optimal manufacturing conditions is time-consuming and requires multiple experiments.

Researchers from MANA used machine learning to accelerate this process. In just four experimental cycles, they optimized the sintering process, improving the thermoelectric performance of Cu2.125Zn0.875SnS4 by 60%. The study was led by Dr. Cedric Bourges from the International Center for Young Scientists, along with Guillaume Lambard from the Center for Basic Research on Materials as well as Naoki Sato, Makoto Tachibana, Satoshi Ishii, and Takao Mori from MANA, NIMS, Japan.

The researchers employed Active Learning with Bayesian Optimization (ALMLBO), which analyzes sintering parameters--such as heating rate, sintering temperature, holding time, cooling rate, and applied pressure--alongside thermoelectric properties obtained from experiments. This approach recommended new experimental conditions, and the process was repeated until the thermoelectric properties improved, indicated by a stabilized zT.

The team began with data from 11 samples prepared using spark plasma sintering, combining copper, zinc, tin, and sulfur powders under partial vacuum. The ALMLBO model predicted sintering conditions that achieved a record maximum zT of 0.44 at 725K. "This method showcases how integrating machine learning with traditional materials science accelerates discovery and optimization in complex material systems," say the authors. This approach has the potential to be extended to other materials, enabling rapid innovations in photovoltaics, batteries, and electronics.

Research Highlights Vol. 92
https://www.nims.go.jp/mana/research/highlights/vol92.html

MANA Research Highlights
https://www.nims.go.jp/mana/ebulletin/index.html

MANA Develops Ferroelectric-ferromagnetic Materials for Next-generation Electronics

MANA — Tue, 07 Jan 2025 17:00:00 +0900

TSUKUBA, Japan, Jan. 7, 2025 /Kyodo JBN/ --
Research Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS)
Researchers at the Research Center for Materials Nanoarchitectonics (MANA) have proposed a method to create ferroelectric-ferromagnetic materials, opening doors to advancing spintronics and memory devices.

Image: https://cdn.kyodonewsprwire.jp/prwfile/release/M105739/202412121557/_prw_PI1fl_8666b1RP.jpg

In 1831, Michael Faraday discovered the fundamental connection between electricity and magnetism, demonstrating that a changing magnetic field induces electric current in a conductor.

In a recent study, MANA researchers have proposed a method for designing ferroelectric-ferromagnetic (FE-FM) materials, which exhibit both ferroelectric and ferromagnetic properties, enabling the manipulation of magnetic properties using electric fields and vice versa. Such materials are highly promising for spintronics and memory devices. The advantage of FE-FM materials, extremely rare in nature, is their ability to achieve the cross-control by relatively low electric and magnetic fields. The study, led by Principal Researcher Igor Solovyev from MANA, NIMS, included contributions from Dr. Ryota Ono from MANA, NIMS, and Dr. Sergey Nikolaev from the University of Osaka, Japan.

Ferroelectric materials possess a permanent electric polarization, usually arising from ion displacement in their crystalline lattice and resulting in the formation of charged electric dipoles, which align in the same direction. The key feature of ferromagnetic materials is the uncompensated magnetic moment produced by electron spins and orbital motion. Combining both properties in a single material is challenging since the ion displacement enabling ferroelectricity can disrupt the magnetic ordering needed for ferromagnetism. Similarly, the ferromagnetic alignment of magnetic moments is not sufficient for breaking the spatial inversion symmetry required for producing ferroelectricity.

The authors of the current study proposed that antiferro orbital ordering, driven by the Kugel-Khomskii mechanism, where electrons tend to occupy alternating orbitals, can promote both ferromagnetic interactions and break the inversion symmetry. When tested on VI3, a van der Waals ferromagnet with a honeycomb structure, this ordering resulted in an FE-FM ground state.

"By properly arranging occupied atomic orbitals in a solid, one can make the material not only ferromagnetic but also ferroelectric," says Dr. Solovyev, highlighting the potential of this approach for developing next-generation electronic devices based on multiferroic materials and ferroelectric ferromagnets.

Research Highlights Vol. 91
https://www.nims.go.jp/mana/research/highlights/vol91.html

MANA Research Highlights
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From Bottleneck to Breakthrough: MANA Achieves New Computing Paradigm ...

MANA — Fri, 23 Aug 2024 17:00:00 +0900

TSUKUBA, Japan, Aug. 23, 2024 /Kyodo JBN/ --
Research Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS)
From Bottleneck to Breakthrough: MANA Achieves New Computing Paradigm with Reconfigurable Logic Circuits

Scientists from the Research Center for Materials Nanoarchitectonics (MANA) developed a reconfigurable logic circuit that switches functions with constant input voltages. This innovation opens doors to novel computing architectures.

Image: https://cdn.kyodonewsprwire.jp/prwfile/release/M105739/202408215159/_prw_PI1fl_m0cY8QdY.jpg

Most computers today are based on the von Neumann architecture, where memory and processing are handled separately. The transfer of data between these two units causes a bottleneck, slowing down operations. In-memory computing aims to fix this issue by integrating logic directly into memory for faster and more power-efficient processing.

In a recent breakthrough, researchers from the Quantum Device Engineering Group at MANA, including group leader Yutaka Wakayama and Yoshitaka Shingaya, along with Junko Aimi from the Research Center for Macromolecules and Biomaterials, NIMS, developed electrically reconfigurable two-input logic circuits that can switch between different logic functions. These circuits also function as artificial synapses, which are crucial for advancing neuromorphic computing systems.

The circuit is based on a dual-gate antiambipolar transistor (AAT), constructed by stacking an n-type semiconductor and a p-type one. The AAT has a unique lambda-shaped response curve where the output current changes with the input gate voltages. By manipulating these gate voltages, specific current values corresponding to logic states "0" and "1" are produced. This allows the AAT to perform various logic functions depending on the chosen combination of gate voltages.

To maintain consistent input voltages while adjusting logic states, a zinc phthalocyanine core (ZnPc) is integrated into the AAT. ZnPc traps carrier charges, shifting the peak voltage position associated with different logic functions. This enables the AAT to switch between logic states, such as from AND to OR and from NAND to NOR, under constant input voltages.

The device also functions like an artificial synapse. Adjusting the readout voltage modifies its synaptic response or current, similar to how brain synapses strengthen or weaken signals. As Dr. Wakayama highlights, "We have developed a non-von Neumann type device architecture by integrating the nonvolatile memory function with the dual-gate AAT, which is not achievable in conventional CMOS architectures."

Research Highlights Vol. 90
https://www.nims.go.jp/mana/research/highlights/vol90.html

MANA Research Highlights
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Powering Future Night and Day: MANA Develops Cutting-edge Thermoelectric Generator

MANA — Thu, 27 Jun 2024 17:00:00 +0900

TSUKUBA, Japan, June 27, 2024 /Kyodo JBN/ --
Research Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS)
Researchers from the Research Center for Materials Nanoarchitectonics (MANA) have developed a thermoelectric generator that can use both radiative cooling and solar heating to produce electricity, opening doors to applications in powering small off-grid sensors.

Image: https://cdn.kyodonewsprwire.jp/prwfile/release/M105739/202406212511/_prw_PI1fl_b15ClD6X.jpg

Daytime radiative cooling is typically used to cool surfaces that face the sky, like the roof of a building. Since these devices thermally radiate towards the sky, they also generate a slight temperature difference with respect to their surroundings. This difference in temperature can be leveraged to produce electricity using a thermoelectric generator.

However, most radiative cooling materials also reflect sunlight, limiting the solar energy that can be utilized for generating electricity.

This limitation was addressed in a recent study, where a research team from MANA, including Dr. Satoshi Ishii, Dr. Cedric Bourges, Nicholaus K. Tanjaya, and Dr. Takao Mori, developed a mostly transparent thermoelectric device that is capable of harnessing both radiative cooling and solar heating to generate power.

The device consists of a top transparent plate that acts as a radiative cooler and a bottom plate coated in blackbody paint which absorbs incoming sunlight. Separated by a transparent thermoelectric junction, the innovative “co-planar” design of the device allows sunlight to reach the bottom plate for solar absorption, unlike previous versions with separate solar absorbing and radiative cooling regions.

Through several experiments, the researchers demonstrated the ability of this thermoelectric generator to produce power during daytime via radiative cooling and solar heating, and through radiative cooling during nighttime. “The ability of our device to continuously generate thermoelectric voltage day and night makes it an ideal standalone power supply for off-grid sensors, which have become increasingly common in recent years,” remarks Dr. Ishii.

Replacing batteries in remote devices can be inconvenient and expensive. This innovative thermoelectric generator offers a reliable power solution, eliminating the need for frequent battery changes and paving the way for the operation of critical devices even in off-grid locations.

Research Highlights Vol. 89
https://www.nims.go.jp/mana/research/highlights/vol89.html

MANA Research Highlights
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Advancing Organic Circuits: MANA Study Changes Current Computing Architecture

MANA — Thu, 22 Feb 2024 17:00:00 +0900

TSUKUBA, Japan, Feb. 22, 2024 /Kyodo JBN/ --
Research Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS)
Researchers from the Research Center for Materials Nanoarchitectonics (MANA) have developed a novel organic logic inverter circuit capable of handling four logical states. This advancement improves the data processing capabilities of organic integrated circuits.

Image: https://cdn.kyodonewsprwire.jp/prwfile/release/M105739/202402156623/_prw_PI1fl_3PVnyta8.jpg

Organic integrated circuits, constructed with small molecules or polymers, show great potential for human-friendly interactive mobile applications. These circuits are lightweight, flexible, biocompatible, and cost-effective. As a result, they are important for the development of radio-frequency identification tags, smart displays, and healthcare sensors. However, traditional organic circuits are incompatible with modern lithographic techniques and thus suffer from low integration density and poor data-processing capability. To address this issue, ongoing efforts are focused on developing multivalued logic circuits based on antiambipolar transistors (AATs).

In a recent breakthrough, a research team from MANA, including principal researcher Ryoma Hayakawa, group leader Yutaka Wakayama, and JSPS fellow Debdatta Panigrahi, has successfully created an organic quaternary logic inverter circuit that can handle four logical states, a notable advancement beyond the traditional three found in ternary logic circuits. The organic quaternary logic inverter circuit was constructed by connecting an AAT, comprising two "n"-type organic semiconductors and a "p"-type organic semiconductor, to a double-layered "n"-type transistor in series.

Dr. Hayakawa explains: "We have developed an organic AAT, which exhibited two distinct negative differential transconductance (NDT) characteristics. The bi-NDT characteristics were achieved via the incorporation of two lateral organic heterojunctions. Each heterojunction could generate an NDT characteristic, which instigated the bi-NDT behavior in the AATs." This unique bi-NDT feature enabled the team to produce a quaternary inverter that can handle four logic states without increasing the number of transistors. This innovation can, thus, significantly improve the data-processing capability of organic integrated circuits.

This quaternary inverter achieves the four distinguishable logic states of "1," "2/3," "1/3" and "0" at a relatively low driving voltage of 14 V, making it suitable for energy-efficient logic applications. The proposed circuit thus advances the capabilities of organic circuits for more demanding computing applications.

Research Highlights Vol. 88
https://www.nims.go.jp/mana/research/highlights/vol88.html

Official website:
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MANA Scientists Usher in Advances in Thermoelectric Materials

MANA — Fri, 16 Feb 2024 17:00:00 +0900

TSUKUBA, Japan, Feb. 16, 2024 /Kyodo JBN/ --
Research Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS)
Scientists from the Research Center for Materials Nanoarchitectonics (MANA) have now enhanced Mg3(Sb, Bi)2-based alloys with molybdenum, paving the way for materials that efficiently harness heat energy.

Image: https://cdn.kyodonewsprwire.jp/prwfile/release/M105739/202402086375/_prw_PI1fl_PFe1hPJC.jpg

Thermoelectric (TE) materials convert heat into electricity and can contribute to compensating for the global fossil fuel shortage. Their conversion mechanism relies on factors such as electron and vibrational wave (phonon) scattering at grain boundaries (GB) that form between different crystal orientations in a material. Notably, some kinds of doping can show potential to optimize thermoelectric performance and enhance the heat-to-electricity conversion efficiency.

Among promising TE materials are alloys containing magnesium and antimony or bismuth, denoted as Mg3(Sb, Bi)2. Since reducing GB scattering can enhance their performance, it is worth probing how certain kinds of doping can affect these alloys.

Now, in a recent study led by Dr. Takao Mori, Group Leader of the Thermal Energy Materials Group at MANA, at the National Institute for Materials Science (NIMS), along with first author Mr. Longquan Wang, Mg3(Sb, Bi)2-based alloys were enhanced by the addition of molybdenum (Mo). The team discovered that Mo aids electron movement by regulating the grain size and band structure (allowed energy levels for electrons in a solid). They also optimized the Sb to Bi ratio to restrain phonon transport by introducing structural defects, reducing phonon group velocity and increasing atomic disorder. A single-leg device achieved close to 12% conversion efficiency.

The practical implications of this study could have substantial real-world effects. Moreover, Mg3(Sb, Bi)2-based materials use abundant and low-cost elements, unlike alloys such as PbTe and GeTe, which contain rare and toxic elements. According to Dr. Mori: “With the intensifying energy consumption and environmental issues, recovering waste heat from industry, transportation, and daily life is an important issue. Thermoelectric devices can directly convert heat into electricity, thereby providing a potential solution for the energy crisis and environmental issues.”

In summary, MANA scientists have achieved improved thermoelectric performance in Mg3(Sb, Bi)2-based materials, opening possibilities for developing materials capable of harvesting heat effectively.

Research Highlights Vol. 87
https://www.nims.go.jp/mana/research/highlights/vol87.html

Official website: https://www.nims.go.jp/mana/index.html

New Leap in Flexible Electronics: MANA's Breakthrough Doping Innovation

MANA — Tue, 06 Feb 2024 17:00:00 +0900

TSUKUBA, Japan, Feb. 6, 2024 /Kyodo JBN/ --
Research Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS)
Researchers from the Research Center for Materials Nanoarchitectonics (MANA) have introduced a doping method to achieve accurate and consistent conductivity for organic semiconductors.

Image: https://cdn.kyodonewsprwire.jp/prwfile/release/M105739/202401295845/_prw_PI1fl_B5KMh4cs.jpg

Organic semiconductors consisting of polymers are important for the development of flexible electronic devices. However, achieving consistent conductivity using current doping methods is challenging. Doping involves the addition of dopants to the semiconductor via a redox reaction to increase the density of charge carriers. However, the process is sensitive to the reaction atmosphere and impurities, particularly water, which deactivates the dopants.

In a new study, a research team led by Dr. Yu Yamashita from MANA, in collaboration with Dr. Masaki Ishii (first author) from MANA, has now developed a simple doping method capable of producing organic semiconductors of desired conductivity levels. The method is based on the proton-coupled electron transfer reaction (PCET) observed in biochemical processes.

In PCET, protons and electrons are simultaneously transferred between two molecules. This reaction provides a way to convert an organic semiconductor into a p-type doped state by encouraging a molecule to accept electrons from the semiconductor. For the doping process, the researchers immersed PBTTT, an organic semiconductor, in an aqueous solution containing benzoquinone (BQ), hydroquinone (HQ), and hydrophobic molecular anions. BQ receives protons from the aqueous solution along with electrons from PBTTT. The electron transfer from the organic semiconductor increases the number of holes in the organic semiconductor, changing its conductivity.

The advantage of this method lies in its reproducibility and pH-dependent controllability. Adjusting the solution's pH allows precise control over the doping amount and, subsequently, the conductivity. "The Fermi level of the semiconductors was precisely and reproducibly tuned by the pH of the doping solution," says Dr. Yamashita. Moreover, such precise doping was conducted in ambient air for the first time, demonstrating unprecedented scalability suitable for device manufacturing.

This innovative doping method offers a cost-effective approach for developing flexible and stable electronics, such as wireless sensors, energy-harvesting modules, biomolecular devices, displays, and solar cells.

Research Highlights Vol. 86
https://www.nims.go.jp/mana/research/highlights/vol86.html

Official website: https://www.nims.go.jp/mana/index.html

MANA Researchers Realize High-performance Physical Reservoir Computing with Multi-detection ...

MANA — Tue, 03 Oct 2023 17:00:00 +0900

TSUKUBA, Japan, Oct. 3, 2023 /Kyodo JBN/ --
Research Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS)
MANA Researchers Realize High-performance Physical Reservoir Computing with Multi-detection Chaotic Spin Wave Interference

Researchers from the Research Center for Materials Nanoarchitectonics (MANA) present the first experimental demonstration of a physical reservoir computing system based on spin wave interference.

Image:
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Novel technologies are shaping the modern world, and artificial intelligence (AI) systems are expected to play an important role in this transformation. Accordingly, demand for compact AI devices with low power consumption and high computational performance is growing rapidly. Recently, physical reservoir computing, which relies on a physical system to efficiently process information, has emerged as a promising technology for ubiquitous AI implementation. To be considered suitable for reservoir computing, the physical system must possess nonlinearity, short-term memory, and the ability to map in high dimensions. Notably, spin wave interference in ferromagnetic materials satisfies all three criteria and is considered a promising candidate for efficient reservoir computing. However, its experimental realization has remained elusive so far.

Now, a research team led by Principal Investigator Kazuya Terabe from MANA has experimentally demonstrated a reservoir computing system based on multi-detection nonlinear spin wave interference for the first time. Their study involved Dr. Wataru Namiki as the first author and Dr. Takashi Tsuchiya as the corresponding author.

The team utilized an yttrium iron garnet single crystal with multi-antennas, which excited and detected multi-spin waves. The physical reservoir computing system showed excellent performance for a hand-written digit recognition task, second-order nonlinear dynamical tasks, and nonlinear autoregressive moving average (NARMA); specifically, a maximum testing accuracy rate of 89.6% for hand-written digit recognition and normalized mean square errors (MSEs) of 8.37 x 10 to the power of minus 5 and 1.81 x 10 to the power of minus 2 for the nonlinear dynamical tasks and NARMA2, respectively. Notably, the MSEs are the best figures reported for any experimental physical reservoir.

"The high performance can be attributed to a high nonlinearity and a large memory capacity of the multi-detection chaotic spin wave interference system. It can thus contribute to the implementation of integrated physical reservoir systems with real-world applications," concludes Dr. Tsuchiya.

Research Highlights Vol. 85
https://www.nims.go.jp/mana/research/highlights/vol85.html

MANA Research Highlights
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MANA Researcher Realizes Plasmaron Quasiparticles in Cuprate Superconductors

MANA — Thu, 31 Aug 2023 17:00:00 +0900

TSUKUBA, Japan, Aug. 31, 2023 /Kyodo JBN/ --
Research Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS)
A team led by a researcher at Research Center for Materials Nanoarchitectonics (MANA) delved into the interplay of plasma oscillations and electrons in cuprate superconductors, shedding light on the emergence of plasmarons--distinct quasiparticles driven by charge fluctuations within the system.

Image: https://cdn.kyodonewsprwire.jp/prwfile/release/M105739/202308288564/_prw_PI1fl_p9M5a59h.jpg

Metallic systems exhibit plasmons--quanta of collective electron oscillation--as elementary charge excitations. Recently, this behavior was confirmed even in high-temperature cuprate superconductors, materials with potential to revolutionize next-generation electronics. However, studying the interplay of plasmons and electrons in such materials presents unique challenges due to their strongly correlated nature and layered structure.

Recently, a research team, including Principal Researcher Hiroyuki Yamase at MANA in Japan, and Dr. Matias Bejas and Prof. Andres Greco from UNR-CONICET in Rosario, Argentina, focused on understanding the influence of plasmons on electron dispersion in cuprates, leading to the discovery of intriguing quasiparticles called "plasmarons" in these materials.

"Unlike phonons and magnetic fluctuations, plasmons in cuprates do not manifest themselves as kinks in the electron dispersion. Instead, they give rise to plasmarons, which are generated by bosonic fluctuations associated with the local constraint imposed by strong electron correlations rather than the usual charge-density fluctuations," explains Dr. Yamase. This finding highlights the distinct nature of plasmarons in cuprate superconductors.

The researchers found that the optical plasmon is responsible for the emergence of plasmarons, forming an additional band in the one-particle excitation spectrum. Remarkably, the plasmarons predicted in cuprates exhibit similarities to those discussed in other metallic systems, including alkali metals, graphene, monolayer transition-metal dichalcogenides, semiconductors, diamond, and SrIrO3 films. This suggests the general applicability of the concept of plasmarons in metallic systems beyond cuprates, meaning the findings could be applied to a plethora of new metallic quantum systems.

"The insights gained from this research will have significant implications for engineering the band structure in metallic quantum materials," highlights Dr. Yamase.

In conclusion, understanding the interplay between plasmons and electrons, particularly the emergence of plasmarons, can provide valuable knowledge for manipulating and tailoring the properties of metallic systems and designing new materials for novel applications.

Research Highlights Vol. 84
https://www.nims.go.jp/mana/research/highlights/vol84.html

MANA Research Highlights
https://www.nims.go.jp/mana/ebulletin/index.html

MANA Develops Novel "Drycell" Microdroplets to Make Handling Single Cell Easier

MANA — Thu, 03 Aug 2023 17:00:00 +0900

TSUKUBA, Japan, Aug. 3, 2023 /Kyodo JBN/ --
Research Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS)
Scientists at the Research Center for Materials Nanoarchitectonics (MANA) have developed micrometer-sized "liquid marbles" that can encapsulate single to several living cells, thereby aiding single-cell studies.

To analyze individual cells, the desired number of cells must be isolated spatially. This often requires extensive training and use of expensive laboratory equipment. MANA scientists have recently overcome this hurdle using nanotechnology. They coated cell-suspension microdroplets with superhydrophobic nanoparticles -- tiny particles that possess surfaces with exceptional water-repellent properties -- and created spherical structures known as "drycells," with customizable sizes ranging from one to several hundred micrometers, which can be handled and picked up with ease. This will make cell picking easier and greatly facilitate single-cell analysis.

Image: https://cdn.kyodonewsprwire.jp/prwfile/release/M105739/202307147139/_prw_PI1fl_vc765eK8.jpg

To achieve this, the research team hand-sprayed suspended cells to create a cellular "mist." Upon coming into contact with a vibrating nanoparticle bed, the cell-containing mist droplets instantly got coated with superhydrophobic-fumed silica nanoparticles, thus producing liquid marble-like drycells with a dry powder-like outer layer surrounding an inner liquid core. In fact, the scientists could create drycells with >95% inner aqueous content surrounded by a dry outer layer. These droplets exhibited powder-like smooth flow and could easily be picked up with a pair of tweezers without suffering any damage or spilling the inner liquid. Moreover, the superhydrophobic silica nanoparticles in the surface coating prevented the droplets from merging.

The scientists could sort the drycells according to size through sieving. They were also able to simultaneously encapsulate normal and cancerous cells as well as creating several cell colonies inside these drycells. Further, they could introduce liquids into, as well as withdraw, the liquid from these droplets with ease. Finally, they observed that centrifugation could separate the nanoparticles from the cell-suspension layers, which makes the process recyclable.

"Our method of drycell production efficiently facilitates cell picking and lowers the barrier for single-cell studies and will greatly improve the accessibility and productivity of single-cell analysis," concludes Dr. Koichiro Uto, speaking on behalf of study co-authors Mizuki Tenjimbayashi and Shota Yamamoto.

Research Highlights Vol. 83
https://www.nims.go.jp/mana/research/highlights/vol83.html

MANA Research Highlights
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WPI-MANA Demystifies Conductivity of Ruthenate Nanosheets, Moving Towards Next-generation ...

MANA — Fri, 17 Feb 2023 15:00:00 +0900

TSUKUBA, Japan, Feb. 17, 2023 /Kyodo JBN/ --
International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science (NIMS)
WPI-MANA Demystifies Conductivity of Ruthenate Nanosheets, Moving Towards Next-generation Electronics

A research team at the International Center for Materials Nanoarchitectonics (WPI-MANA) has shed light on how electrical conduction in oxide nanosheets can be markedly affected by small changes in their atomic arrangement.

(Image: https://kyodonewsprwire.jp/prwfile/release/M105739/202302032657/_prw_PI1fl_8t5iT34J.jpg)

The physical properties of a material are dictated by the arrangement of its atoms. This holds true not only for classical three-dimensional crystals but also for two-dimensional structures such as atomically thin nanosheets that are quickly becoming the cornerstone of many next-generation technologies.

However, the detailed atomic arrangement of certain nanosheets has not been fully elucidated, which limits experts' understanding of the origin of their desirable properties. This problem is also encountered when investigating ruthenate nanosheets, conductive oxides with promising applications in electronics and energy storage.

The mystery underlying the conduction mechanisms in ruthenate nanosheets motivated a team of researchers at WPI-MANA, led by Dr. Satoshi Tominaka, to further investigate their atomic structure. In a recent study, they analyzed how the possible structural symmetries in ruthenate nanosheets altered their conducting properties.

The researchers employed a pair distribution function (PDF), which described the probability of finding two atoms at a certain distance apart inside a material. Using PDF, they found that ruthenate nanosheets with the same atomic composition can adopt two different atomic arrangements, leading to differences in their symmetry. "Although the structural difference was not large, symmetry changes resulted in remarkably different properties, with ruthenate nanosheets behaving either as a graphene-like semimetal or a semiconductor as confirmed by our calculations," explains Dr. Tominaka. "This highlights the importance of symmetry analysis, even in low-dimensional materials."

Overall, this study paves the way to a better understanding of oxide nanosheets, which could be a game changer in the development of future electronic and electrochemical devices.

Research Highlights Vol. 82
https://www.nims.go.jp/mana/research/highlights/vol82.html

MANA Research Highlights
https://www.nims.go.jp/mana/research/highlights/

Towards Inexpensive and Highly Conductive Anion-Exchange Membranes: WPI-MANA

MANA — Wed, 15 Feb 2023 15:00:00 +0900

TSUKUBA, Japan, Feb. 15, 2023 /Kyodo JBN/ --
International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science (NIMS)
An international research team at the International Center for Materials Nanoarchitectonics (WPI-MANA) has worked to improve the ionic conductivity of anion-exchange membranes (AEMs) made from layered double hydroxides (LDHs), laying the foundation for their use in many electrochemical applications.

(Image: https://kyodonewsprwire.jp/prwfile/release/M105739/202302032656/_prw_PI1fl_5tT8FF5G.jpg)

LDHs are inorganic compounds that can be made into extremely thin "nanosheets." These flexible sheets are well-suited to serve as AEMs, which have a wide range of applications, including the manufacture of batteries, water treatment, and electrolysis.

LDHs have ultrahigh ionic conductivity towards hydroxide ions, which facilitates the flow of current. Although LDH nanosheets can reach high levels of ionic conductivity of 10 to the power of minus 1 S/cm, this value only affects ions moving in the in-plane direction; that is, along the nanosheet. In contrast, their ionic conductivity through the nanosheet --in the cross-plane direction-- is about 10 to the power of minus 6 S/cm, which is five orders of magnitude lower. This hinders fast ionic conduction across AEMs comprising restacked LDH nanosheets.

Fortunately, a research team from WPI-MANA, led by Prof. Renzhi Ma, has now found a solution to this problem. They used a simple vacuum-assisted filtration process to combine LDH nanosheets with LDH nanoparticles, producing a hybrid composite membrane. This membrane exhibited high ionic conductivity in both the in-plane and cross-plane directions.

The researchers proposed that introducing nanoparticles reduced the restacking order of the nanosheets. This created diverse ion-conducting pathways in the composite membrane, ultimately boosting its ionic conductivity. "By changing the orientation of the nanosheets, their ultrahigh conductivity along the in-plane was leveraged to achieve fast transmembrane ionic transport," explains Prof. Ma. The composite membrane achieved a conductivity level of 10 to the power of minus 2 S/cm (about 10,000 times higher than pure LDH nanosheets) in the cross-plane direction.

Prof. Ma says, "The excellent conductivity of our composite membranes will unlock their potential use as competitive AEMs for platinum-free electrochemical energy storage and conversion." The team's efforts will accelerate the development of less expensive AEMs for next-generation energy and environmental technologies.

Research Highlights Vol. 81
https://www.nims.go.jp/mana/research/highlights/vol81.html

MANA Research Highlights
https://www.nims.go.jp/mana/research/highlights/

Novel, Biocompatible UV Light Absorber: WPI-MANA

MANA — Fri, 28 Oct 2022 15:00:00 +0900

TSUKUBA, Japan, Oct. 28, 2022 /Kyodo JBN/ --
International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science (NIMS)
An International research team at the International Center for Materials Nanoarchitectonics (WPI-MANA) has developed a biocompatible ultraviolet (UV) light-shielding compound from naturally occurring aqueous iron(III), hereinafter aqua-Fe(III), complexes stabilized inside a layered silicate scaffold.

(Image:
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UV-absorbing materials are important to many industries, spanning healthcare, cosmetics, and material protection, among others. Their low environmental impact has made titanium dioxide (TiO2) nanoparticles the most commonly used UV absorber in sunscreens and cosmetics. However, many health concerns -- including its toxicity to cells and carcinogenic potential -- surround the use of TiO2. This has triggered the search for alternative safer, biocompatible, yet affordable UV-shielding compounds.

Now, researchers at WPI-MANA have prepared a new UV-absorbing material using biocompatible and readily available aqua-Fe(III) complexes. These complexes, which are widely available in biological systems, are naturally biocompatible. However, they are difficult to isolate and stabilize.

The WPI-MANA team, led by Dr. Yusuke Ide, used a layered silicate to stabilize the dimeric state of aqua-Fe(III) complexes. "The issue with aqua-Fe(III) complexes is that they are only stable in extremely acidic solutions, which presents a health hazard and is not feasible for use in products requiring UV shields. We use a material that has gaps, or pores, that are the size of the iron complex dimer. The aqua-Fe(III) dimer is imbedded into the silica pores and 'stuck' inside, thereby remaining stable even outside an acidic environment," explains Ide.

The silica itself is flexible, biocompatible, and affordable, and doesn’t react with UV light, meaning it doesn’t interfere with the UV-shielding properties of aqua-Fe(III). Moreover, when mixed with a natural oil, it forms a UV-absorbing material which could be interesting to the art and manufacturing industries. "UV damage to paintings and other goods is a standard problem, and our material could be used as a protective layer. It is more transparent than -- and functions just as well as -- conventional TiO2 coatings," concludes Ide.

With a variety of silicate frameworks available, this new method of manufacturing UV-shielding materials provides a clear blueprint for developing future applications of the same.

Research Highlights Vol. 80
https://www.nims.go.jp/mana/research/highlights/vol80.html

MANA Research Highlights
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Insight into Organic Antiambipolar Transistors: WPI-MANA

MANA — Tue, 25 Oct 2022 15:00:00 +0900

TSUKUBA, Japan, Oct. 25, 2022 /Kyodo JBN/ --
International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science (NIMS)
International Center for Materials Nanoarchitectonics (WPI-MANA) researchers have elucidated the mechanism behind organic antiambipolar transistors (OAATs), a new class of transistors with possible applications in artificial intelligence and neuromorphic devices.

(Image:
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Transistors are one of the basic building blocks of modern technology and electronics. The emergence of artificial intelligence and brain-like devices has brought about a need for multiple logic gate operations to be conducted on the same transistor chip. Even the gold standard, complementary metal-oxide semiconductor (CMOS) transistors, cannot handle such a large load of operations. Hence, the search is on for technologies that can.

Researchers from WPI-MANA, led by Dr. Ryoma Hayakawa, have been investigating a new class of transistors, OAATs. OAATs can support multiple logic gate operations owing to a unique property called negative differential transconductance (NDT). The research team’s extensive work, directed by Dr. Yutaka Wakayama, has looked to first elucidate the charge-carrier mechanism in these devices, and then also apply them to multiple logic gate operations. "We needed to know how OAATs work so that they could then be improved upon. So, we directly visualized the electron flow in an OAAT, using a technique called operando photoemission electron microscopy (PEEM). We were then able to understand where the transistor junction gets its exciting switchable property," explains Wakayama.

The PEEM experiments showed that a depletion layer is formed at the lateral p-n interface; this generates a large potential difference, enhancing electron conduction in the transistor. Armed with this knowledge, the research team looked at its applicability. "By adjusting input voltages across OAATs, we could achieve five different logic gate operations on the same device. We could even switch between two logic gates with a given set of inputs," explains Wakayama.

OAATs are stable and reliable, operating for months. They can surpass CMOS devices for many applications. Keeping this in mind, the work done at WPI-MANA could lead to a massive reduction in the number of transistors required in current integrated circuits and improve their processing ability, enabling the development of more advanced technology that can handle large amounts of operations.

Research Highlights Vol. 79
https://www.nims.go.jp/mana/research/highlights/vol79.html

MANA Research Highlights
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New Diamond Transistor Exhibits High Hole Mobility: WPI-MANA

MANA — Fri, 29 Jul 2022 14:00:00 +0900

TSUKUBA, Japan, July 29, 2022 /Kyodo JBN/ --
International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science (NIMS)
A research team at the International Center for Materials Nanoarchitectonics (WPI-MANA), using a new fabrication technique, has developed a diamond field-effect transistor with high hole mobility, which can lead to reduced conduction loss and higher operational speeds.

(Image: https://kyodonewsprwire.jp/prwfile/release/M105739/202207153906/_prw_PI1fl_1IRPNuNx.jpg)

Field-effect transistors (FETs) are semiconductor devices that can switch electric power and amplify electric signals. FETs made of wide-bandgap semiconductors can handle high power efficiently and are useful for power electronics and communications. The use of SiC and GaN is therefore growing, but diamond has a wider bandgap and more desirable properties that could boost device performance.

The team used a new fabrication technique to develop the FET, wherein it fabricated the transistor with hexagonal boron nitride as a gate insulator and without exposing the diamond’s surface to air. The advantage is that it can reduce the density of negative charges on the diamond surface. If there are negative charges, they produce random Coulomb potential, which scatters the holes when they conduct near the diamond surface. This degrades the effectiveness of hole conduction and decreases the mobility of the holes.

Also, with the negative charges, even if no gate voltage is applied, there are holes, and so the transistor is "normally on," and this is not suitable for power electronics applications.

"In contrast, in our new technique, we can reduce the density of negative charges on the diamond surface. So the holes are less scattered, and therefore we can obtain higher mobility," said team leader Dr. Takahide Yamaguchi. "This also results in 'normally-off’ operation, which is desirable for power electronics."

Dr. Yamaguchi pointed to some possible applications of this breakthrough. "Our new approach for fabricating diamond transistors could be used to make low-loss switches for power electronics and high-frequency high-output amplifiers for communications."

Research Highlights Vol. 78
https://www.nims.go.jp/mana/research/highlights/vol78.html

MANA Research Highlights
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New TEM Technique Creates 2.8nm Transistor: WPI-MANA

MANA — Tue, 26 Jul 2022 14:00:00 +0900

TSUKUBA, Japan, July 26, 2022 /Kyodo JBN/ --
International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science (NIMS)
An international research team at the International Center for Materials Nanoarchitectonics (WPI-MANA) has used a transmission electron microscope (TEM) to create a 2.8nm transistor consisting of nanochannels embedded in metallic carbon nanotubes (CNTs), which exhibits quantum transport at room temperature.

(Image: https://kyodonewsprwire.jp/prwfile/release/M105739/202207043388/_prw_PI1fl_r2SG7I16.jpg)

One major aim of nanotechnology research is to control the helical structure of a CNT. This structure determines the nanotube’s properties, and altering it can result in drastic changes, such as turning it from a metal to a semiconductor. To achieve this, the focus has been on growing nanotubes to control the structure, but this has been very difficult due to their extremely small size, only one or two nanometers in diameter.

To address this difficulty, researchers at WPI-MANA have developed a technique to precisely manipulate individual CNTs and alter their helical structure inside a TEM.

The WPI-MANA team used nanoprobes to apply tension and heat to the CNT. This deformed a section of the nanotube, altering its structure and changing it from a metal into a semiconductor.

The section of the altered nanotube was very short, and formed a semiconductor embedded in a metallic nanotube. The researchers believe this can be used as a semiconductor channel, and with the original metallic nanotube as the source and drain, the effect is like a molecular transistor embedded inside the nanotube.

Dr. Dai-Ming Tang, leading member of the team, said, "This transistor is extremely small, only 2.8nm in channel length, shorter than any current silicon-based transistors. In fact, this is among the world’s smallest transistors, and we created it by using our new technique."

Another exciting aspect of this work relates to the behavior of materials on such tiny scales. "Because we can make such a very small transistor, other effects appear," Dr. Tang said. "For example, we have seen quantum transport at room temperature, which is usually observed only at extremely low temperatures."

This could allow the density of transistors on a computer chip to be much higher, leading to more powerful and faster electronics.

Research Highlights Vol. 77
https://www.nims.go.jp/mana/research/highlights/vol77.html

MANA Research Highlights
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Making Fuel from Sunlight and CO2: WPI-MANA

MANA — Fri, 18 Mar 2022 17:00:00 +0900

TSUKUBA, Japan, Mar. 18, 2022 /Kyodo JBN/ --
International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science (NIMS)
Since joining the International Center for Materials Nanoarchitectonics (WPI-MANA) in 2007, Dr. Jinhua Ye has focused on research and development of photo-functional materials and their applications in the fields of environment preservation and new energy production. In addition to her position at WPI-MANA, she is an adjunct professor of Hokkaido University, and a fellow of the Royal Society of Chemistry. Dr. Ye is a highly cited researcher, having published over 600 papers in high-quality research journals, which have been cited more than 50,000 times.

(Image:https://kyodonewsprwire.jp/prwfile/release/M105739/202203017972/_prw_PI1fl_mycpE4H4.jpg)

Q: Thank you for meeting with us today. To start with, could you give us a rundown of your current research?

“Basically, I am studying photo-functional materials and their applications in the fields of environment preservation and new energy production. I’m developing catalysts for converting CO2 into hydrocarbons, using sunlight to power the reactions. For this I am focusing on finding materials to act as catalysts for the reactions, and broadening our understanding of how to make these reactions more efficient and selective.

It’s a three-step process. First we ask, ‘How can we absorb more light?’ In particular visible light and infrared, not just UV. To do that, we need to tune the band gap of the material. If it’s too wide, it will only absorb a small part of the UV light. But if it’s too narrow, the generated electron hole reduction activity or oxidation activity will be limited. So we need to find some kind of compromise.

And then also, if it is to help the reaction, we need the reduction energy of this conduction band to be more negative than some reaction. On the other hand, we also need to adjust the valence band position. So we think about all these things, and then we can have a guideline for what kind of electronic structure or element is better, or what kind of crystallinity or conductivity it should have...”

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Selective Hybrid Photocatalyst Allows Oxidative Coupling of Methane to Ethane with ...

MANA — Wed, 16 Mar 2022 17:00:00 +0900

TSUKUBA, Japan, Mar. 16, 2022 /Kyodo JBN/ --
International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science (NIMS)
Selective Hybrid Photocatalyst Allows Oxidative Coupling of Methane to Ethane with Dioxygen: WPI-MANA

A team at the International Center for Materials Nanoarchitectonics (WPI-MANA) has demonstrated that methane can be efficiently and selectively oxidized to ethane with oxygen under light irradiation over an Au-ZnO/TiO2 hybrid. This achievement opens the door to cheaper and more efficient production of valuable chemicals using methane as a feedstock.

(Image: https://kyodonewsprwire.jp/prwfile/release/M105739/202203017971/_prw_PI1fl_OzJ4zJPV.jpg)

Methane (CH4), the main component of natural gas and shale gas, is not only an abundant and low-cost fuel, but also a powerful greenhouse gas with a potential 28-34 times that of CO2. Directly and selectively converting methane to value-added higher hydrocarbons or oxygenates has been attracting substantial interest from both academia and industry, and could reduce society’s reliance on crude oil and contribute to carbon neutrality.

However, the high C-H bond dissociation energy and non-polar nature of methane, along with the higher reactivity of the desired products, make selective activation and conversion of methane challenging.

The WPI-MANA group designed an Au-ZnO/TiO2 hybrid photocatalyst for selectively oxidizing CH4 to ethane (C2H6) with oxygen (O2). This showed a high C2H6 production rate with high selectivity and excellent durability, which were more than one order of magnitude higher than the state-of-the-art photocatalytic systems.

Mechanistic studies showed that the formation of ZnO/TiO2 heterojunctions by precisely controlling the ratio and interface structure of ZnO/TiO2 led to enhanced activity, while maintaining high selectivity owing to the weak overoxidation ability of the main component ZnO. Moreover, using Au nanoparticles as the cocatalyst not only promotes charge separation, but also facilitates methyl (CH3) species desorption to form methyl radicals, which promotes the formation of C2H6 and inhibits the overoxidation of CH4 to CO2.

These findings could guide the future design of photocatalysts that could transform methane to ethane with high activity and selectivity. This, along with other technologies such as new reactor designs, could provide an economically viable way to directly convert methane into ethane.

This research was conducted by Jinhua Ye (MANA Principal Investigator, Group Leader, Photocatalytic Materials Group, WPI-MANA, NIMS) and her collaborators.

Research Highlights Vol. 76
https://www.nims.go.jp/mana/research/highlights/vol76.html

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Exfoliation of Zeolites into Solution Produces Porous Monolayers: WPI-MANA

MANA — Mon, 14 Mar 2022 17:00:00 +0900

TSUKUBA, Japan, Mar. 14, 2022 /Kyodo JBN/ --
International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science (NIMS)
A pioneering study at the International Center for Materials Nanoarchitectonics (WPI-MANA) has resulted in the first direct exfoliation of zeolites into a liquid suspension of monolayers. This breakthrough provides proof of the presence of monolayers, and could lead to their use in the creation of catalysts, nanodevices, drug delivery systems and other products with tailored properties.

(Image: https://kyodonewsprwire.jp/prwfile/release/M105739/202203017970/_prw_PI1fl_ikk290hZ.jpg)

Some two-dimensional (2D) materials, such as graphene, exhibit a variety of unique properties thanks to their molecular thinness and large size, as well as their 2D anisotropy. Catalysts and electrode materials that take advantage of nanosheets’ high surface area are a promising field, but the 2D anisotropy prevents efficient transfer of ions and molecules within the materials. Therefore, 2D materials with through-holes are attracting attention, but so far there have been few examples of them.

Zeolites are typical porous materials and some of them have a layered structure. So exfoliating them in a single 2D layer could result in nanosheets with a regular pore structure. Although there have been reports of the synthesis of zeolite nanosheets in trace yields, large quantities of the substance have not been obtained at a usable level.

A WPI-MANA group succeeded in synthesizing zeolite nanosheets (MWW and FER types) by exfoliating them into a single layer by greatly swelling the layered zeolite in a solution containing organic ammonium ions.

Dispersing the zeolites into liquids provides the most effective approach to their practical exploitation to fabricate materials with particular activity and functionality. The suspended layers can be deposited on supports or restacked into hierarchical structures alone or in combination with other 2D materials to produce solids with useful properties.

The exfoliation and proof of the presence of monolayers in the colloids open new possibilities of synthesizing functional hybrid and hierarchically structured materials. The researchers also made predictions about potential applications of zeolite monolayer colloids based on the anisotropic physical properties of 2D materials.

This research was conducted by Takayoshi Sasaki (MANA Principal Investigator, Group Leader, Soft Chemistry Group, WPI-MANA, NIMS) and his collaborators.

Research Highlights Vol. 75
https://www.nims.go.jp/mana/research/highlights/vol75.html

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Artificial Retinal Device Mimics Human Optical Illusions: WPI-MANA

MANA — Thu, 10 Mar 2022 17:00:00 +0900

TSUKUBA, Japan, Mar. 10, 2022 /Kyodo JBN/ --
International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science (NIMS)
A team at the International Center for Materials Nanoarchitectonics (WPI-MANA) has developed the first-ever artificial retinal device that increases the edge contrast between lighter and darker areas of an image, using ionic migration and interaction within solid. The device has the potential for use in developing compact, energy-efficient visual sensing and image-processing hardware systems capable of processing analog signals.

(Image: https://kyodonewsprwire.jp/prwfile/release/M105739/202203017969/_prw_PI1fl_p63mh2x3.jpg)

Recently artificial intelligence (AI) system developers have shown much interest in research on various sensors and analog information-processing systems inspired by the human senses. Most AI systems require sophisticated software and complex circuit configurations, including custom-designed processing modules. The problem with these systems is that they are large and consume much power.

The team built a multiple ionic device system, each of which had a lithium cobalt oxide channel arranged on a common lithium phosphorus oxynitride electrolyte. Because of the migration of Li-ions between the channels through the electrolyte, the devices were highly interactive, similar to human retinal neurons such as photoreceptors, and horizontal and bipolar cells. Input voltage pulses caused ions within the electrolyte to migrate across the channels, which changed the output channel current.

The device was able to process input image signals and produce an image with increased edge contrast between darker and lighter areas. This is similar to the human visual system’s ability to increase edge contrast between brightness differences by means of visual lateral inhibition.

The human eye produces various optical illusions associated with tilt angle, size, color and movement, in addition to darkness/lightness, and this process is believed to play a crucial role in the visual identification of different objects. The artificial retinal device the team created could be used to reproduce these types of optical illusions. They hope to develop visual sensing systems capable of performing human retinal functions by integrating their device with other components, including photoreceptor circuits.

This research was conducted by Tohru Tsuruoka (Chief Researcher, Nanoionic Devices Group, WPI-MANA, NIMS), Kazuya Terabe (MANA Principal Investigator, Group Leader, Nanoionic Devices Group, WPI-MANA, NIMS) and their collaborator.

Research Highlights Vol. 74
https://www.nims.go.jp/mana/research/highlights/vol74.html

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WPI-MANA Probing Potential of Quantum Materials

MANA — Mon, 22 Nov 2021 17:00:00 +0900

TSUKUBA, Japan, Nov. 22, 2021 /Kyodo JBN/ --
International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science (NIMS)
The NIMS Quantum Materials Project is WPI-MANA’s newly formed group for research into creating and exploiting quantum materials. Recently the Japanese government selected a number of priority research projects and has directed funds toward them. One of the fields of interest is quantum technology -- quantum computing, quantum information and so on -- related to the very small physical world, the quantum domain. WPI-MANA spoke to two scientists of the NIMS project:

Kazunari Yamaura, Group Leader, Nano-Materials Field, Quantum Solid State Materials Group, WPI-MANA; and Taichi Terashima, Group Leader, Nano-System Field, Quantum Material-Properties Group, WPI-MANA.

(Image: https://kyodonewsprwire.jp/prwfile/release/M105739/202111163421/_prw_PI1fl_jcHaZPFQ.jpg)

Q: First of all, could you describe your research for us?
Yamaura: I am focusing on developing quantum materials using high-temperature and high-pressure synthesis methods. These methods are advantageous to develop materials and properties in general. One target is to develop the quantum properties of polarized metals.
Since joining WPI-MANA, I have been researching polar metals, a kind of dielectric material. They were discovered a long time ago, and were considered as an unusual theoretical material. But recently they are sparking interest again and now we are thinking that they could be a new category of quantum material. The polarization can be controlled, oriented this way or that, using conventional electric techniques. And this polarization is connected to the surface state, the quantum state.
Terashima: My research involves finding ways to determine the Fermi surface of metals by quantum oscillation measurements and magnetotransport properties in magnetic fields. The Fermi surface, also known as the “face” of a metal, is a straightforward example of the nature of conduction electrons in a metal. The Fermi surface gives us a picture of how electrons will behave if some external stimuli are applied.
I have been working mainly on iron-based superconductors and rare-earth/uranium compounds, but since moving to WPI-MANA, I have been researching the Fermi surfaces of topological materials…
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Electrons Move in Preferred Direction in Cuprate Superconductors: WPI-MANA

MANA — Thu, 18 Nov 2021 17:00:00 +0900

TSUKUBA, Japan, Nov 18, 2021 /Kyodo JBN/ --
International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science (NIMS)
A team at the International Center for Materials Nanoarchitectonics (WPI-MANA) has gleaned important insights into the properties of Lanthanum-based cuprate superconductors, the highest-temperature superconducting family yet discovered under ambient pressure.

(Image: https://kyodonewsprwire.jp/prwfile/release/M105739/202111052920/_prw_PI1fl_xUCB97EN.jpg)

The team’s results imply that, in contrast to common belief among researchers for the last 35 years, electrons have a preferred direction along either the x or the y axis in each CuO2 plane, and the preferred direction alternates between the planes.

High-temperature cuprate superconductors have continued to generate keen interest for more than 30 years due to the various phenomena they exhibit with changes in carrier doping and temperature, such as the pseudogap phase, nematic order, charge-density wave and spin-density wave, as well as superconductivity.

The Fermi surface is fundamental in condensed matter physics for understanding metallic properties. Its shape directly reflects the electron motion inside the material and as such it is the key to understanding materials’ properties.

High-temperature cuprate superconductors are characterized by stacks of copper–oxygen (CuO2) planes, a fact that has convinced many researchers that electrons exhibit two-dimensional motion in CuO2 planes.

The WPI-MANA team, led by Hiroyuki Yamase, applied the high-resolution X-ray Compton scattering technique to a sample of La(2-x)Sr(x)CuO4 and imaged the momentum distribution of electrons.

The results provide new understanding of the electronic properties of cuprate superconductors. Compton scattering can be a powerful tool to elucidate electronic properties in materials and sometimes works beyond other widely employed techniques. The researchers said it will be exciting to see the technique employed as a complement to other methods.

This research was carried out by Hiroyuki Yamase of WPI-MANA and his collaborators.

“Fermi Surface in La-Based Cuprate Superconductors from Compton Scattering Imaging”
Yamase, H., Sakurai, Y., Fujita, M. et al. Nat Commun 12, 2223 (2021)
https://doi.org/10.1038/s41467-021-22229-6

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“On-Surface Shapeshifters” Exhibit Oxidation-State-Dependent Conformational and Self-assembly ...

MANA — Tue, 16 Nov 2021 17:00:00 +0900

TSUKUBA, Japan, Nov. 16, 2021 /Kyodo JBN/ --
International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science (NIMS)
“On-Surface Shapeshifters” Exhibit Oxidation-State-Dependent Conformational and Self-assembly Behaviors: WPI-MANA

A team at the International Center for Materials Nanoarchitectonics (WPI-MANA) has found that substances known as pyrazinacenes exhibit on-surface oxidation-state-dependent conformational and self-assembly behaviors. This “shape-shifting” could result in a variety of applications.

(Image: https://kyodonewsprwire.jp/prwfile/release/M105739/202111052919/_prw_PI1fl_GTdhG33d.jpg)

The team’s broad experimental and theoretical study revealed that pyrazinacenes containing decaazapentacene are stable against oxidation but unstable against reduction.

Pyrazinacenes represent an unusual class of redox-active chromophores, and represent an emerging class of highly nitrogenous heteroacenes with unique properties. They have excellent potential for use based on their special supramolecular properties, including interactions in biological systems. They lie at the core of molecular materials’ applications because of their important optical and electronic features.

The team determined that the already established structure-function relationships of molecular materials known from solution now need to be re-evaluated to predict and understand the interface-specific chemical, electronic, optical and mechanical properties of any newly synthesized molecules.

The research was completed by David Miklik (WPI-MANA) and S. Fatemeh Mousavi (Department of Physics, University of Basel, Switzerland) under the leadership of Thomas Jung (Laboratory of Micro- and Nanotechnology, Paul Scherrer Institute, Switzerland) and Jonathan P. Hill (WPI-MANA).

“We suggest the term 'on-surface shapeshifter’ to describe these compounds, based on their oxidation-state-coupled on-surface molecular morphology variations,” the scientists said in their paper.

The substances’ chemical complexity, they said, motivates further investigations comparing in-solution and interfacial reactivity, in particular toward tunable photo-redox compounds or the generation of synthetically inaccessible molecules.

This research was carried out by David Miklik of the Functional Chromophores Group of WPI-MANA and S. Fatemeh Mousavi of the University of Basel, Switzerland, and their collaborators.

“Pyrazinacenes Exhibit On-Surface Oxidation-State-Dependent Conformational and Self-Assembly Behaviours”
Miklik, D., Fatemeh Mousavi, S., Buresova, Z. et al. Commun Chem 4, 29 (2021).
https://doi.org/10.1038/s42004-021-00470-w

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WPI-MANA: Harvesting Energy at Nanoscale with Triboelectric Nanogenerators (TENG)

MANA — Fri, 12 Nov 2021 17:00:00 +0900

TSUKUBA, Japan, Nov. 12, 2021 /Kyodo JBN/ --
International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science (NIMS)
New research at the International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science (NIMS), advances the field of triboelectric nanogenerators (TENG), devices that hold promise in wireless charging of energy storage devices such as batteries and capacitors. This could pave the way for new ways to harvest mechanical energy without the need for any external amplification and boosters, and wirelessly transmit the generated energy for storage.

(Image: https://kyodonewsprwire.jp/prwfile/release/M105739/202111052918/_prw_PI1fl_63WHglS5.jpg)

A triboelectric nanogenerator is an energy-harvesting device that converts external mechanical energy at nanoscale into electricity. These devices can be used to utilize all kinds of mechanical energy that is available but wasted in daily life, such as human motion, walking, vibration and mechanical triggering.

The technology has been generating avid interest worldwide. The first papers on TENG were published only recently, in 2012, by Prof. Zhong Lin Wang’s group at the Georgia Institute of Technology, and since then the performance and efficiency of the devices have improved dramatically. Early on, it was found that adding nanostructures to the surfaces of the active materials improved their efficiency, as it increases the surface area and thus the amount of charge transfer.

A MANA team, led by Ken C. Pradel of MANA and Naoki Fukata, Principal Investigator and Group Leader of MANA’s Nanostructured Semiconducting Materials Group, devised a simple geometric model showing how arrays of hemispheres can interlock and increase the amount of surface contact.

They correlated this with a polyamide and polyvinylidene fluoride model system, TENG. They found that by tuning the spacing between the pattern features, the output voltage and current can be greatly improved.

“By deepening our understanding of the surface interactions in these devices, we can optimize them in smarter ways to reduce cost and improve performance,” they said.

This research was carried out by Ken C. Pradel, JSPS Fellow at the time of research (WPI-MANA), and his collaborator.

“Systematic Optimization of Triboelectric Nanogenerator Performance Through Surface Micropatterning”
Ken C. Pradel et al., Nano Energy Volume 83 (May 2021)
https://doi.org/10.1016/j.nanoen.2021.105856

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