Faculty Profiles - TSURUTA Kenji

Papers - TSURUTA Kenji

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Design of multiple-resonant phononic metasurface for sound absorbing and energy harvesting devices

Akira Kojima, Julien Cuau, Yuri Fukaya, Kenji TSURUTA

Japanese Journal of Applied Physics 2025.3

Photoinduced dynamics during electronic transfer from narrow to wide bandgap layers in one-dimensional heterostructured materials Reviewed

Yuri Saida, Thomas Gauthier, Hiroo Suzuki, Satoshi Ohmura, Ryo Shikata, Yui Iwasaki, Godai Noyama, Misaki Kishibuchi, Yuichiro Tanaka, Wataru Yajima, Nicolas Godin, Gaël Privault, Tomoharu Tokunaga, Shota Ono, Shin-ya Koshihara, Kenji Tsuruta, Yasuhiko Hayashi, Roman Bertoni, Masaki Hada

Nature Communications 15 ( 1 ) 2024.5

Publishing type：Research paper (scientific journal) Publisher：Springer Science and Business Media LLC

Abstract

Electron transfer is a fundamental energy conversion process widely present in synthetic, industrial, and natural systems. Understanding the electron transfer process is important to exploit the uniqueness of the low-dimensional van der Waals (vdW) heterostructures because interlayer electron transfer produces the function of this class of material. Here, we show the occurrence of an electron transfer process in one-dimensional layer-stacking of carbon nanotubes (CNTs) and boron nitride nanotubes (BNNTs). This observation makes use of femtosecond broadband optical spectroscopy, ultrafast time-resolved electron diffraction, and first-principles theoretical calculations. These results reveal that near-ultraviolet photoexcitation induces an electron transfer from the conduction bands of CNT to BNNT layers via electronic decay channels. This physical process subsequently generates radial phonons in the one-dimensional vdW heterostructure material. The gathered insights unveil the fundamentals physics of interfacial interactions in low dimensional vdW heterostructures and their photoinduced dynamics, pushing their limits for photoactive multifunctional applications.

DOI： 10.1038/s41467-024-48880-3

Other Link： https://www.nature.com/articles/s41467-024-48880-3

Valley Pseudospin Polarized Evanescent Coupling between Microwave Ring Resonator and Waveguide in Phononic Topological Insulators Reviewed

Daiki Hatanaka, Hiroaki Takeshita, Motoki Kataoka, Hajime Okamoto, Kenji Tsuruta, Hiroshi Yamaguchi

Nano Letters 24 ( 18 ) 5570 - 5577 2024.5

Publishing type：Research paper (scientific journal)

A coupled ring-waveguide structure is at the core of bosonic wave-based information processing systems, enabling advanced wave manipulations such as filtering, routing, and multiplexing. However, its miniaturization is challenging due to momentum conservation issues in rings with larger curvature that induce significant backscattering and radiation leakage and hampering stable operation. Here, we address it by taking an alternative approach of using topological technology in wavelength-scale and microwave ring-waveguide coupled systems built in nanoengineered phononic crystals. Our approach, which leverages pseudospin conservation in valley topological systems, eliminates phonon backscattering and achieves directional evanescent coupling. The resultant hypersonic waves in the tiny ring exhibit robust transport and resonant circulation. Furthermore, the ring-waveguide hybridization enables critical coupling, where valley-dependent ring-waveguide interference blocks the transmission. Our findings reveal the capability of topological phenomena for managing ultrahigh-frequency phonons in nano/microscale structures and pave the way for advanced phononic circuits in classical and quantum signal processing applications.

DOI： 10.1021/acs.nanolett.4c00806

Robust and Reconfigurable Waveguide Design in Valley-Topological Phononic Crystals Reviewed

Md. Shuzon Ali, Yusuke Hata, Motoki Kataoka, Masaaki Misawa, Kenji Tsuruta

Materials Science Forum 1107 141 - 145 2023.12

Authorship：Corresponding author Publishing type：Research paper (scientific journal) Publisher：Trans Tech Publications, Ltd.

As an analogy of topological insulators and superconductors, “topological phononics”, which applies the concept of band topology to acoustic dispersion, has attracted increasing attention in recent years. We present design of topological acoustic/elastic waveguides in phononic crystals. Topological waveguides are designed from the phonon dispersion analyses by finding edge modes appearing at interfaces between phononic crystals with different band topologies. As a prototype model, we first designed the topological waveguides in kHz regimes. Experimental validation of the designed waveguide has been performed in the frequency region via laser-doppler measurements. The robustness of the waveguide propagation against defects, corners, and structural inaccuracy in the waveguide has been quantitatively evaluated. We also introduced a structural transition of local symmetry inversion in the phononic crystal to implement a reconfigurability into the waveguide .Further development toward GHz regime will pave the way to the development of next-generation information devices using the proposed structures as an alternative or complimentary approach.

DOI： 10.4028/p-jt9zkn

Active control of localized mode and transmission in topological phononic waveguides by non-Hermitian modulation Reviewed

Md. Shuzon Ali, Yusuke Hata, Kenji Tsuruta

Applied Physics Express 16 ( 9 ) 2023.9

Reconfigurable waveguide based on valley topological phononic crystals with local symmetry inversion via continuous translation Reviewed

Md. Shuzon Ali, Motoki Kataoka, Masaaki Misawa, Kenji Tsuruta

Japanese Journal of Applied Physics 62 ( SJ ) SJ1002 - SJ1002 2023.7

Authorship：Corresponding author Publishing type：Research paper (scientific journal) Publisher：IOP Publishing

Abstract

We proposed a reconfigurable valley topological acoustic waveguide constructed using a 2D phononic crystal (PnC) with C_3v symmetric arrangement of three rods in the unit cell. An interface between two types of PnCs with differently oriented unit cells exhibits high robustness of the valley transport of acoustic waves via the topologically protected state. Structural reconfiguration was introduced by the continuous translation of rod arrays in the PnCs. The topological phase transition in this translational change was quantitatively identified by the change in the Berry curvature. The translation of the rods leaves a dimer array at the interface, creating a localized/defective mode along the waveguide. Despite the presence of the localized mode, the acoustic wave can propagate along the reconfigurable waveguide the same as the original waveguide. The continuous translation of a rod array can be used to turn on and off the bandgap. This can be a new approach to design a robust acoustic device with a high reconfigurability.

DOI： 10.35848/1347-4065/acae63

Other Link： https://iopscience.iop.org/article/10.35848/1347-4065/acae63/pdf

Acoustic metasurfaces and topological phononics for acoustic/elastic device design Invited Reviewed

Kenji Tsuruta

Japanese Journal of Applied Physics 62 ( SJ ) 2023.7

Intermediate State between MoSe₂ and Janus MoSeS during Atomic Substitution Process Reviewed

Hiroo Suzuki, Yijun Liu, Masaaki Misawa, Chiyu Nakano, Yingzhe Wang, Ryo Nakano, Kentaro Ishimura, Kenji Tsuruta, Yasuhiko Hayashi

Nano Letters 2023.5

Self-Limiting Growth of Monolayer Tungsten Disulfide Nanoribbons on Tungsten Oxide Nanowires Reviewed

Hiroo Suzuki, Misaki Kishibuchi, Masaaki Misawa, Kazuma Shimogami, Soya Ochiai, Takahiro Kokura, Yijun Liu, Ryoki Hashimoto, Zheng Liu, Kenji Tsuruta, Yasumitsu Miyata, Yasuhiko Hayashi

ACS Nano 2023.5

Tracking Optical Properties During Atomic Substitution Process from MoSe2 to Janus MoSeS

Hiroo Suzuki, Masaaki Misawa, Yingzhe Wang, Kenji Tsuruta, Yasuhiko Hayashi

JSAP-Optica Joint Symposia 2023 Abstracts 32 20p_A602_5 - 20p_A602_5 2023

Publishing type：Research paper (international conference proceedings) Publisher：Optica Publishing Group

Janus transition metal dichloride (TMDC) is a TMDC with two different chalcogenide elements on the upper and lower surfaces. This special structure is reported to break the out-of-plane symmetry of the monolayer TMDC and produce out-of-plane polarization. This is expected to lead to the development of new electronic properties, such as Rashba spin splitting and piezoelectricity. There have been several reports on the synthesis of Janus TMDCs, and in recent years, the use of chalcogen spices containing H₂ plasma for atomic substitution on the surface of TMDC has attracted attention since Janus TMDCs can be generated at room temperature [1,2]. However, the generation process of Janus TMDCs with this method has not been well under-stood. In addition, the physical properties in the intermediate state between TMDC and Janus TMDC have also not been clarified, although the control of the intermediate state is important for tuning the physical properties of Janus TMDCs. Thus, elucidating the intermediate partially sub-stituted Janus (PSJ) state between MoSe₂ and Janus MoSeS state is essential for understanding the synthesis dynamics and tuning the electrical properties of TMDCs.

DOI： 10.1364/jsapo.2023.20p_a602_5

Design and Robustness Evaluation of Valley Topological Elastic Wave Propagation in a Thin Plate with Phononic Structure Reviewed

Motoki Kataoka, Masaaki Misawa, Kenji Tsuruta

Symmetry 14 ( 10 ) 2022.10

Authorship：Corresponding author Publishing type：Research paper (scientific journal)

Based on the concept of band topology in phonon dispersion, we designed a topological phononic crystal in a thin plate for developing an efficient elastic waveguide. Despite that various topological phononic structures have been actively proposed, a quantitative design strategy of the phononic band and its robustness assessment in an elastic regime are still missing, hampering the realization of topological acoustic devices. We adopted a snowflake-like structure for the crystal unit cell and determined the optimal structure that exhibited the topological phase transition of the planar phononic crystal by changing the unit cell structure. The bandgap width could be adjusted by varying the length of the snow-side branch, and a topological phase transition occurred in the unit cell structure with threefold rotational symmetry. Elastic waveguides based on edge modes appearing at interfaces between crystals with different band topologies were designed, and their transmission efficiencies were evaluated numerically and experimentally. The results demonstrate the robustness of the elastic wave propagation in thin plates. Moreover, we experimentally estimated the backscattering length, which measures the robustness of the topologically protected propagating states against structural inhomogeneities. The results quantitatively indicated that degradation of the immunization against the backscattering occurs predominantly at the corners in the waveguides, indicating that the edge mode observed is a relatively weak topological state.

DOI： 10.3390/sym14102133

First-principles analysis of stearic acid adsorption on calcite (104) surface Reviewed

Narumi Machida, Masaaki Misawa, Yuki Kezuka, Kenji Tsuruta

e-Journal of Surface Science and Nanotechnology 20 ( 4 ) 261 - 265 2022.8

Surface Diffusion-Limited Growth of Large and High-Quality Monolayer Transition Metal Dichalcogenides in Confined Space of Microreactor. Reviewed International journal

Hiroo Suzuki, Ryoki Hashimoto, Masaaki Misawa, Yijun Liu, Misaki Kishibuchi, Kentaro Ishimura, Kenji Tsuruta, Yasumitsu Miyata, Yasuhiko Hayashi

ACS nano 2022.7

Language：English Publishing type：Research paper (scientific journal)

Transition metal dichalcogenides (TMDCs), including MoS2 and WS2, are potential candidates for next-generation semiconducting materials owing to their atomically thin structure and strong optoelectrical responses, which allow for flexible optoelectronic applications. Monolayer TMDCs have been grown utilizing chemical vapor deposition (CVD) techniques. Enhancing the domain size with high crystallinity and forming heterostructures are important topics for practical applications. In this study, the size of monolayer WS2 increased via the vapor-liquid-solid growth-based CVD technique utilizing the confined space of the substrate-stacked microreactor. The use of spin-coated metal salts (Na2WO4 and Na2MoO4) and organosulfur vapor allowed us to precisely control the source supply and investigate the growth in a systematic manner. We obtained a relatively low activation energy for growth (1.02 eV), which is consistent with the surface diffusion-limited growth regime observed in the confined space. Through systematic photoluminescence (PL) analysis, we determined that a growth temperature of ∼820 °C is optimal for producing high-quality WS2 with a narrow PL peak width (∼35 meV). By controlling the source balance of W and S, we obtained large-sized fully monolayered WS2 (∼560 μm) and monolayer WS2 with bilayer spots (∼1100 μm). Combining two distinct sources of transition metals, WS2/MoS2 lateral heterostructures were successfully created. In electrical transport measurements, the monolayer WS2 grown under optimal conditions has a high on-current (∼70 μA/μm), on/off ratio (∼5 × 108), and a field-effect mobility of ∼7 cm2/(V s). The field-effect transistor displayed an intrinsic photoresponse with wavelength selectivity that originated from the photoexcited carriers.

DOI： 10.1021/acsnano.2c05076

Numerical and experimental analysis of additively manufactured particle dampers at low frequencies Reviewed

Honghu Guo, Kazuo Ichikawa, Hiroyuki Sakai, Heng Zhang, Xiaopeng Zhang, Kenji Tsuruta, Kanjuro Makihara, Akihiro Takezawa

Powder Technology 396 696 - 709 2022.1

Publishing type：Research paper (scientific journal)

Particle damping is an effective method for increasing structural damping and is utilized in many fields. Using laser powder bed fusion (LPBF) additive manufacturing (AM), a new integrated particle damper can be produced by deliberately leaving unfused powder inside the structure. This study focuses on experimentally and numerically investigating the damping mechanism and performance of additively manufactured particle dampers in the low-frequency range (< 100 Hz). A numerical simulation approach based on the discrete element method was developed to predict the damping performance of a particle damper. To reduce the computational cost, a multi-unit particle damper (MUPD) was introduced. A series of particle dampers of 316 L stainless steel with different numbers and sizes of unit cells were built using LPBF. The damping mechanism and performance of additively manufactured MUPDs (AM-MUPD) were studied, the results cross-verified via experiments and simulations, and the effects of unit cell size and number investigated.

DOI： 10.1016/j.powtec.2021.11.029

Design of High-efficiency Sound Absorption and Energy Harvesting Devices Using Acoustic Metasurfaces Reviewed

R. Takami, M. Misawa, and K. Tsuruta

Proceedings of Symposium on Ultrasonic Electronics (USE2021) 42 3Pb4-7 2021.10

Design of topological phononic structure for multimode propagation Reviewed

H. Takeshita, M. Misawa, and K. Tsuruta

Proceedings of Symposium on Ultrasonic Electronics (USE2021) 42 3Pb1-2 2021.10

Band Structure Design for a Two-Dimensional Phononic Crystal using Various Optimization Methods Reviewed

K. Akae, M. Misawa, and K. Tsuruta

Proceedings of Symposium on Ultrasonic Electronics (USE2021) 42 2Pa1-3 2021.10

Design and measurement of topological elastic waveguide based on phononic crystal Reviewed

M. Kataoka, M. Misawa, and K. Tsuruta

Proceedings of Symposium on Ultrasonic Electronics (USE2021) 42 1J1-1 2021.10

Photoinduced oxygen transport in cobalt double-perovskite crystal EuBaCo2O5.39 Reviewed

Masaki Hada, Satoshi Ohmura, Tadahiko Ishikawa, Masaki Saigo, Naoya Keio, Wataru Yajima, Tatsuya Suzuki, Daisuke Urushihara, Kou Takubo, Yusuke Masaki, Makoto Kuwahara, Kenji Tsuruta, Yasuhiko Hayashi, Jiro Matsuo, Takayoshi Yokoya, Ken Onda, Fuyuki Shimojo, Muneaki Hase, Sumio Ishihara, Toru Asaka, Nobuyuki Abe, Taka-hisa Arima, Shin-ya Koshihara, Yoichi Okimoto

Applied Materials Today 24 101167 - 101167 2021.9

Low-frequency sound absorbing metasurface using multilayer split resonators Reviewed

Shota Takasugi, Keita Watanabe, Masaaki Misawa, Kenji Tsuruta

Japanese Journal of Applied Physics 60 ( {SD} ) 2021.7

Optimization of molecular characteristics via machine learning based on continuous representation of molecules Reviewed

Kyosuke Sato, Kenji Tsuruta

Materials Science Forum 1016 MSF 1492 - 1496 2021

Authorship：Corresponding author Publishing type：Research paper (international conference proceedings)

We demonstrate an automatic materials design method using continuous representation of molecule and its atomic arrangement via a neural network algorithm. This method is applied to optimizing and predicting the HOMO-LUMO gap within the molecules composed of carbon, oxygen, nitrogen, fluorine, and hydrogen. Adopting the Quantum Machine 9 (QM9) dataset as a training dataset for the molecules, we first established a continuous representation of molecules in a latent space, then predicted molecules that have target values of the HOMO-LUMO gap. In the gap maximization calculation, CF4 with the largest gap value in the QM9 dataset was automatically found despite there is no a priori data for the gap. In the case of a target gap value of 0.10 hartree, we found a new molecule whose gap value is closer to 0.10 hartree than any other molecules in the QM9 dataset.

DOI： 10.4028/www.scientific.net/MSF.1016.1492

A mechanistic investigation of moisture-induced degradation of methylammonium lead iodide Reviewed

Masaki Hada, Md. Abdullah Al Asad, Masaaki Misawa, Yoichi Hasegawa, Ryota Nagaoka, Hiroo Suzuki, Ryuji Mishima, Hiromi Ota, Takeshi Nishikawa, Yoshifumi Yamashita, Yasuhiko Hayashi, Kenji Tsuruta

Applied Physics Letters 117 ( 25 ) 253304 - 253304 2020.12

Parameter optimisation for phononic structure using CMA-ES and S-matrix Reviewed

Hiroshi ISAKARI, Kei MATSUSHIMA, Kenji TSURUTA, Toru TAKAHASHI, Toshiro MATSUMOTO

Transactions of the Japan Society for Computational Methods in Engineering 20 65 - 73 2020.12

Low-frequency sound absorbing metasurface using multiple split resonators Reviewed

S. Takasugi, K. Watanabe, M. Misawa, and K. Tsuruta

Proceedings of Symposium on Ultrasonic Electronics (USE2020) 41 3Pb1-1 2020.11

Reconfigurable valley topological phononic waveguide with local C3v symmetry Reviewed

K. Okuno, M. Misawa, and K. Tsuruta

Proceedings of Symposium on Ultrasonic Electronics (USE2020) 41 3Pa1-2 2020.11

Super-chiral vibrational spectroscopy with metasurfaces for high-sensitive identification of alanine enantiomers Reviewed

Takumi Iida, Atsushi Ishikawa, Takuo Tanaka, Atsuya Muranaka, Masanobu Uchiyama, Yasuhiko Hayashi, Kenji Tsuruta

Applied Physics Letters 117 ( 10 ) 101103 - 101103 2020.9

Topologically robust sound wave transport in two-dimensional phononic crystal with a circular rod arrangement in water Reviewed

Kenshi Okuno, Kenji Tsuruta

Japanese Journal of Applied Physics 59 2020.7

Design of non-circular membranes metasurfaces for broadband sound absorption Reviewed

Keita Watanabe, Mikiya Fujita, Kenji Tsuruta

Japanese Journal of Applied Physics 59 2020.7

Characterization of the Σ5(210) / [001] Grain Boundary of Methyl-Ammonium Lead Triiodide Perovskite using Density Functional Theory Reviewed

Kenji TSURUTA

Transactions of the Materials Research Society of Japan 2020.6

Liquid-like dielectric response is an origin of long polaron lifetime exceeding 10 μs in lead bromide perovskites Reviewed

Kiyoshi Miyata, Ryota Nagaoka, Masaki Hada, Takanori Tanaka, Ryuji Mishima, Taihei Kuroda, Sota Sueta, Takumi Iida, Yoshifumi Yamashita, Takeshi Nishikawa, Kenji Tsuruta, Yasuhiko Hayashi, Ken Onda, Toshihiko Kiwa, Takashi Teranishi

The Journal of Chemical Physics 152 ( 8 ) 084704 - 084704 2020.2

Whitish daytime radiative cooling using diffuse reflection of non-resonant silica nanoshells Reviewed

Suichi, T., Ishikawa, A., Tanaka, T., Hayashi, Y., Tsuruta, K.

Scientific Reports 10 ( 1 ) 2020

Design of Non-circular Membranes Metasurfaces for Broadband Sound Absorption Reviewed

K. Watanabe, M. Fujita, and K. Tsuruta

Proceedings of Symposium on Ultrasonic Electronics (USE2019) 40 2P1-5 2019.11

Topologically robust sound wave transport using phononic crystal in water Reviewed

K. Okuno and K. Tsuruta

Proceedings of Symposium on Ultrasonic Electronics (USE2019) 40 2P1-4 2019.11

Ultrafast isomerization-induced cooperative motions to higher molecular orientation in smectic liquid-crystalline azobenzene molecules Reviewed

M. Hada, D. Yamaguchi, T. Ishikawa, T. Sawa, K. Tsuruta, K. Ishikawa, S. Koshihara, Y. Hayashi, T. Kato

Nature Communications 10 ( 1 ) 4159 - 4159 2019.9

Selective Reduction Mechanism of Graphene Oxide Driven by the Photon Mode versus the Thermal Mode Reviewed

Masaki Hada, Kiyoshi Miyata, Satoshi Ohmura, Yusuke Arashida, Kohei Ichiyanagi, Ikufumi Katayama, Takayuki Suzuki, Wang Chen, Shota Mizote, Takayoshi Sawa, Takayoshi Yokoya, Toshio Seki, Jiro Matsuo, Tomoharu Tokunaga, Chihiro Itoh, Kenji Tsuruta, Ryo Fukaya, Shunsuke Nozawa, Shin-ichi Adachi, Jun Takeda, Ken Onda, Shin-ya Koshihara, Yasuhiko Hayashi, Yuta Nishina

ACS Nano 2019 Vol.13 ( 9 ) 10103 - 10112 2019.8

Language：English Publishing type：Research paper (scientific journal) Publisher：ACS Publications

A two-dimensional nanocarbon, graphene, has attracted substantial interest due to its excellent properties. The reduction of graphene oxide (GO) has been investigated for the mass production of graphene used in practical applications. Different reduction processes produce different properties in graphene, affecting the performance of the final materials or devices. Therefore, an understanding of the mechanisms of GO reduction is important for controlling the properties of functional two-dimensional systems. Here, we determined the average structure of reduced GO prepared via heating and photoexcitation and clearly distinguished their reduction mechanisms using ultrafast time-resolved electron diffraction, time-resolved infrared vibrational spectroscopy, and time-dependent density functional theory calculations. The oxygen atoms of epoxy groups are selectively removed from the basal plane of GO by photoexcitation (photon mode), in stark contrast to the behavior observed for the thermal reduction of hydroxyl and epoxy groups (thermal mode). The difference originates from the selective excitation of epoxy bonds via an electronic transition due to their antibonding character. This work will enable the preparation of the optimum GO for the intended applications and expands the application scope of two-dimensional systems.

DOI： 10.1021/acsnano.9b03060

Unravelling the Effect of Pb Vacancy and Water Intercalated Defect on Structural and Electronic Properties in Methyl Ammonium Lead Iodide (MAPI) Perovskite via First Principles Calculations Reviewed

M.A.A. Asad and K. Tsuruta

MTC Letters 6 198 - 19 2019.6

Rapid and reversible lithiation of doped biogenous iron oxide nanoparticles Reviewed

Masaaki Misawa, Hideki Hashimoto, Rajiv Kalia, Syuji Matsumoto, Aiichiro Nakano, Fuyuki Shimojo, Jun Takada, Subodh Tiwari, Kenji Tsuruta, Priya Vashishta

Scientific Reports 9 ( 1 ) 1828 - 1828 2019.2

First-principles Study on Water Dissociation in Grain Boundary of MAPbI<inf>3</inf> Perovskite Reviewed

Asad, M.A.A., Sato, K., Tsuruta, K.

MRS Advances 4 ( 36 ) 2019

Design and Assessment of Phononic Crystals for Controlling Ultrasonic Wave via Optical Measurement Method Reviewed

Kensuke Manabe, Atsushi Ishikawa, Ken Yamamoto, Takefumi Kanda, Kenji Tsuruta

IEEE International Ultrasonics Symposium, IUS 2018-October 2018.12

Authorship：Corresponding author Publishing type：Research paper (international conference proceedings)

Using an optical visualization technique, we experimentally measure ultrasonic propagation in phononic crystals consisting of a two-dimensional square array of copper wires in the water. Two different phononic crystals are designed and fabricated to exhibit waveguiding property and negative refraction of an ultrasonic wave at 200 kHz. The Fresnel diffraction method is employed to directly visualize intensity profile of the wavefront propagating in the phononic crystals, proving waveguiding and negative refraction of the ultrasonic wave. Non-invasive time-resolved imaging of an ultrasonic wave in artificial acoustic structures is thereby demonstrated, paving the way toward an efficient device design for an advanced ultrasonic wave control.

DOI： 10.1109/ULTSYM.2018.8580129

Design of Non-Reciprocal Lamb Wave Filter by Heterojunction Phononic Crystals Reviewed

Kenji Tsuruta, Shota Asada, Yuhei Iwasaki, Atsushi Ishikawa

IEEE International Ultrasonics Symposium, IUS 2018-October 2018.12

Authorship：Lead author,　Corresponding author Publishing type：Research paper (international conference proceedings)

We designed a new acoustic diode model, based on a one-dimensional structure consisting of piezoelectric ceramic films placed periodically in an epoxy plate. Specifically, the model is designed to exhibit non-reciprocal wave propagation in the audible and ultrasonic range. Our model includes no artificial forces to generate the asymmetry in the system but utilizes a mode-conversion mechanisms of elastic-wave propagation at interfaces. We demonstrate numerically that the model can achieve non-reciprocity at a particular frequency range for both S-mode and A-mode incidence of the Lamb wave. We further attempt to develop an additional model that can suppress unwanted backward propagation due to a large mismatch at the heterojunction interface.

DOI： 10.1109/ULTSYM.2018.8579922

Transferable Analytical Model of Phononic Bandgap in Cross-Hole Phononic Crystals Reviewed

Takahiro Nishino, Kenji Tsturuta, Atsushi Ishikawa

2018 IEEE International Ultrasonics Symposium (IUS) 2018.10

Numerical Simulation of Non-Reciprocal Acoustic Waveguide Based on Indirect Interband Transitions Reviewed

Junyi Ge, Atsushi Ishikawa, Kenji Tsturuta

2018 IEEE International Ultrasonics Symposium (IUS) 2018.10

Performance limit of daytime radiative cooling in warm humid environment Reviewed

Takahiro Suichi, Atsushi Ishikawa, Yasuhiko Hayashi, Kenji Tsuruta

AIP Advances 8 ( 5 ) 2018.5

Language：English Publishing type：Research paper (scientific journal) Publisher：American Institute of Physics Inc.

Daytime radiative cooling potentially offers efficient passive cooling, but the performance is naturally limited by the environment, such as the ambient temperature and humidity. Here, we investigate the performance limit of daytime radiative cooling under warm and humid conditions in Okayama, Japan. A cooling device, consisting of alternating layers of SiO2 and poly(methyl methacrylate) on an Al mirror, is fabricated and characterized to demonstrate a high reflectance for sunlight and a selective thermal radiation in the mid-infrared region. In the temperature measurement under the sunlight irradiation, the device shows 3.4 °C cooler than a bare Al mirror, but 2.8 °C warmer than the ambient of 35 °C. The corresponding numerical analyses reveal that the atmospheric window in λ = 16 ∼ 25 μm is closed due to a high humidity, thereby limiting the net emission power of the device. Our study on the humidity influence on the cooling performance provides a general guide line of how one can achieve practical passive cooling in a warm humid environment.

DOI： 10.1063/1.5030156

Metaheuristic Ab Initio Optimum Search for Doping Effects in Nanocarbons Reviewed

Tsuruta Kenji, Mitani Keiichi, Al Asad, Md. Abdullah, Nishina Yuta, Gotoh Kazuma, Ishikawa Atsushi

THERMEC 2018: 10TH INTERNATIONAL CONFERENCE ON PROCESSING AND MANUFACTURING OF ADVANCED MATERIALS 941 2356 - 2359 2018

Language：English Publishing type：Research paper (international conference proceedings) Publisher：TRANS TECH PUBLICATIONS LTD

We have developed a combined approach of metaheuristic optimization algorithms (MOA), such as the genetic algorithm, with an ab-initio materials simulation engine. Concurrent run of the ab-initio calculations with each different parameter set selected by the MOA searches the optimum condition within a given input-parameter space. Using this methodology, the optimum dopant and its position/structure at a graphene edge are found to be a multiple N-atoms doping at graphitic sites, which predicts to lead to better charging/discharging performance when it is used as an anode material of Li-ion battery.

DOI： 10.4028/www.scientific.net/MSF.941.2356

Structure optimization of metallodielectric multilayer for high-efficiency daytime radiative cooling Reviewed

Takahiro Suichi, Atsushi Ishikawa, Yasuhiko Hayashi, Kenji Tsuruta

Proceedings of SPIE - The International Society for Optical Engineering 10369 2017

Language：English Publishing type：Research paper (international conference proceedings) Publisher：SPIE

Engineered metallodielectric nanostructures offer a new platform for controlling thermal emission in a desired manner, thus promise potential applications in passive cooling devices. Here, we present optimization design of metallodielectric multilayer structures for high-efficiency daytime radiative cooling and experimentally characterize their cooling performance. The device structure consists of alternating layers of SiO2 and PMMA on an Ag mirror, which works as a selective thermal emitter at 8-13 μm with a high reflectance for sunlight. Automated design scheme based on simulated annealing method combined with photonic-thermal analysis is developed and applied to search the optimized number and thickness of the layers. The evaluation function in the optimization process is predefined such that a net emission power would be maximized at the ambient temperature of 27 °C (300 K) under the sunlight irradiation of AM1.5G. The numerical results prove efficient radiative cooling to 3.0 °C lower than the ambient temperature, corresponding to 6.6 °C below the bare Ag mirror temperature. Based on the optimized design, the device is fabricated on an Al mirror by using reactive evaporation and spin-coating process over an area of 25 × 25 mm2. The reflectance and absorption properties of the fabricated device are characterized to demonstrate the selective thermal radiation through an atmospheric window. The equilibrium temperature of the device is also investigated to demonstrate the cooling performance under the direct sunlight irradiation.

DOI： 10.1117/12.2273640

Selective electroless plating of 3D-printed plastic structures for three-dimensional microwave metamaterials Reviewed

Ishikawa, A., Kato, T., Takeyasu, N., Fujimori, K., Tsuruta, K.

Applied Physics Letters 111 ( 18 ) 2017

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER INST PHYSICS

A technique of selective electroless plating onto PLA-ABS (Polylactic Acid-Acrylonitrile Butadiene Styrene) composite structures fabricated by three-dimensional (3D) printing is demonstrated to construct 3D microwave metamaterials. The reducing activity of the PLA surface is selectively enhanced by the chemical modification involving Sn2+ in a simple wet process, thereby forming a highly conductive Ag-plated membrane only onto the PLA surface. The fabricated metamaterial composed of Ag-plated PLA and non-plated ABS parts is characterized experimentally and numerically to demonstrate the important bi-anisotropic microwave responses arising from the 3D nature of metallodielectric structures. Our approach based on a simple wet chemical process allows for the creation of highly complex 3D metal-insulator structures, thus paving the way toward the sophisticated microwave applications of the 3D printing technology. Published by AIP Publishing.

DOI： 10.1063/1.4986203

Automated Design of Infrared Digital Metamaterials by Genetic Algorithm Reviewed

Yuya Sugino, Atsushi Ishikawa, Yasuhiko Hayashi, Kenji Tsuruta

METAMATERIALS, METADEVICES, AND METASYSTEMS 2017 10343 2017

Language：English Publishing type：Research paper (international conference proceedings) Publisher：SPIE-INT SOC OPTICAL ENGINEERING

We demonstrate automatic design of infrared (IR) metamaterials using a genetic algorithm (GA) and experimentally characterize their IR properties. To implement the automated design scheme of the metamaterial structures, we adopt a digital metamaterial consisting of 7 x 7 Au nano-pixels with an area of 200 nm x 200 nm, and their placements are coded as binary genes in the GA optimization process. The GA combined with three-dimensional (3D) finite element method (FEM) simulation is developed and applied to automatically construct a digital metamaterial to exhibit pronounced plasmonic resonances at the target IR frequencies. Based on the numerical results, the metamaterials are fabricated on a Si substrate over an area of 1 mm x 1 mm by using an EB lithography, Cr/Au (2/20 nm) depositions, and liftoff process. In the FT-IR measurement, pronounced plasmonic responses of each metamaterial are clearly observed near the targeted frequencies, although the synthesized pixel arrangements of the metamaterials are seemingly random. The corresponding numerical simulations reveal the important resonant behavior of each pixel and their hybridized systems. Our approach is fully computer-aided without artificial manipulation, thus paving the way toward the novel device design for next-generation plasmonic device applications.

DOI： 10.1117/12.2273607

Design of non-reciprocal acoustic waveguides by indirect interband transitions Reviewed

Ishikawa, A., Tsuruta, K.

Japanese Journal of Applied Physics 56 ( 7 ) 2017

Language：English Publishing type：Research paper (scientific journal) Publisher：IOP PUBLISHING LTD

We numerically demonstrate a non-reciprocal acoustic waveguide by utilizing the indirect interband transition between two guided modes. The waveguide, consisting of a water core sandwiched between parallel steel plates, is designed to support symmetric and asymmetric guided modes with different frequencies and wavevectors. Dynamic mode conversion is then achieved by applying spatio-temporal density modulation in the core of the waveguide to induce both frequency and wavevector shifts of the incident guided wave. Numerical simulations prove that the phase matching condition is satisfied only for the forward propagation, not for the backward one, thus realizing the non-reciprocal acoustic waveguide. Our approach based on a linear dynamic system may achieve wide-band tunable operation with a low-energy consumption, paving the way toward the sophisticated acoustic diode applications. (C) 2017 The Japan Society of Applied Physics.

DOI： 10.7567/JJAP.56.07JB01

Performance Improvement of HfS2 Transistors by Atomic Layer Deposition of HfO2 Reviewed

Kanazawa, T., Amemiya, T., Upadhyaya, V., Ishikawa, A., Tsuruta, K., Tanaka, T., Miyamoto, Y.

IEEE Transactions on Nanotechnology 16 ( 4 ) 582 - 587 2017

Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

Hafnium disulfide (HfS2) is one of the transition metal dichalcogenides which is expected to have the high electron mobility and the finite bandgap. However, the fabrication process for HfS2 = based electron devices is not established, and it is required to bring out the superior transport properties of HfS2. In this report, we have investigated the effects of the atomic layer deposited HfO2 passivation on the current properties of HfS2 transistors. HfO2 passivation of the HfS2 surface enhanced the drain current and significantly reduced the hysteresis. Moreover, HfO2 passivation allows the use of a higher annealing temperature and further improvement of the drain current.

DOI： 10.1109/TNANO.2017.2661403

Cross-Polarized Surface-Enhanced Infrared Spectroscopy by Fano-Resonant Asymmetric Metamaterials Reviewed

Ishikawa, A., Hara, S., Tanaka, T., Hayashi, Y., Tsuruta, K.

Scientific Reports 7 ( 1 ) 2017

Language：English Publishing type：Research paper (scientific journal) Publisher：NATURE PUBLISHING GROUP

Plasmonic metamaterials have overcome fundamental limitations in conventional optics by their capability to engineer material resonances and dispersions at will, holding great promise for sensing applications. Recent demonstrations of metamaterial sensors, however, have mainly relied on their resonant nature for strong optical interactions with molecules, but few examples fully exploit their functionality to manipulate the polarization of light. Here, we present cross-polarized surface-enhanced infrared absorption (SEIRA) by the Fano-resonant asymmetric metamaterial allowing for strong background suppression as well as significant field enhancement. The metamaterial is designed to exhibit the controlled Fano resonance with the cross-polarization conversion property at 1730 cm(-1), which spectrally overlaps with the C=O vibrational mode. In the cross-polarized SEIRA measurement, the C=O mode of poly(methyl methacrylate) molecules is clearly observed as a distinct dip within a Fano-resonant transmission peak of the metamaterial. The vibrational signal contrast is then improved based on the cross-polarized detection scheme where only the light interacting with the metamaterial-molecular coupled system is detected by totally eliminating the unwanted background light. Our metamaterial approach achieves the zeptomole sensitivity with a large signal-to-noise ratio in the far-field measurement, paving the way toward the realization of ultrasensitive IR inspection technologies.

DOI： 10.1038/s41598-017-03545-8

Robust plasmonic hot-spots in a metamaterial lattice for enhanced sensitivity of infrared molecular detection Reviewed

Ishikawa, A., Hara, S., Tanaka, T., Zhang, X., Tsuruta, K.

Applied Physics Letters 111 ( 24 ) 2017

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER INST PHYSICS

High-density and long-lived plasmonic hot-spots are an ideal system for high-sensitive surface-enhanced infrared absorption (SEIRA), but these conditions arc usually incompatible due to unwanted near-field coupling between the adjacent unit structures. Here, by fully controlling plasmonic interference in a metamaterial lattice, we experimentally demonstrate densely packed long-lived quadrupole plasmons for high-sensitive SEIRA. The metamaterial consists of a strongly coupled array of super-and sub-radiant plasmonic elements to exhibit an electromagnetic transparency mode at 1730 cm(-1), which spectrally overlaps with the C=O vibrational mode. In the SEIRA measurement, the C=O mode of poly(methyl methacrylate) molecules is clearly observed as a distinct dip within a transmission peak of the metamaterial. The corresponding numerical simulations reveal that constructive interference uniformly forms coherent quadrupole plasmons over the metamaterial lattice, leading to a stronger molecular signal from the system. Our metamaterial approach provides a robust way to construct ideal hot-spots over the sample, paving the way toward a reliable sensing platform of advanced infrared inspection technologies. Published by AIP Publishing.

DOI： 10.1063/1.5004703

Effect of the HfO2 passivation on HfS2 Transistors Reviewed

T. Kanazawa, T. Amemiya, V. Upadhyaya, A. Ishikawa, K. Tsuruta, T. Tanaka, Y. Miyamoto

2016 IEEE 16TH INTERNATIONAL CONFERENCE ON NANOTECHNOLOGY (IEEE-NANO) 865 - 867 2016

Language：English Publishing type：Research paper (international conference proceedings) Publisher：IEEE

Hafnium Disulfide (HfS2) is one of the transition metal dichalcogenides which is expected to have high electron mobility and finite bandgap. However, the fabrication process for HfS2 based electron devices has not been established, and it is required to bring out the superior transport properties of HfS2. In this report, we have investigated the effects of ALD HfO2 passivation on the current properties of HfS2 Transistors. HfO2 passivation of HfS2 surface achieved the improvement in drain current and significant reduction of hysteresis. The charge trapping at the outermost surface seems to be the dominant factor for degradation of the current stability.

Rectification of Lamb wave propagation in thin plates with piezo-dielectric periodic structures Reviewed

Iwasaki, Y., Tsuruta, K., Ishikawa, A.

Japanese Journal of Applied Physics 55 ( 7 ) 2016

Language：English Publishing type：Research paper (scientific journal) Publisher：IOP PUBLISHING LTD

Based on a heterostructured plate consisting of piezoelectric-ceramic/epoxy-resin composites with different periodicities, we design a novel acoustic diode for the symmetrical/asymmetrical (S/A) mode of Lamb wave at audible ranges. The acoustic diode is constructed with two parts, i.e., the mode conversion part and the mode selection part, and the mode conversion mechanism at the interface is applied to the mode hybridization from S to S+A and for the mode conversion from A to S. The phonon band structures for each part are calculated and optimized so that the mode selection is realized for a specific mode at the junction. Finite-element simulations prove that the proposed acoustic diode achieves efficient rectification at audio frequency ranges for both S and A mode incidences of the Lamb wave. (C) 2016 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.55.07KB02

Controlled Fano Resonances via Symmetry Breaking in Metamaterials for High-Sensitive Infrared Spectroscopy Reviewed

Shuhei Hara, Atsushi Ishikawa, Takuo Tanaka, Yasuhiko Hayashi, Kenji Tsuruta

METAMATERIALS, METADEVICES, AND METASYSTEMS 2016 9918 2016

Language：English Publishing type：Research paper (international conference proceedings) Publisher：SPIE-INT SOC OPTICAL ENGINEERING

A high-sensitive polarized surface-enhanced infrared absorption (polarized SEIRA) is proposed and demonstrated by utilizing the resonant coupling of Fano-resonant mode of the asymmetric metamaterials and IR vibrational mode of a polymer nano-film. The asymmetric metamaterials consisting of an Au nano-rod pair with a coupling nano-antenna were fabricated and characterized to demonstrate the controlled Fano resonances at 1730 cm(-1), which spectrally overlapped with the C=O stretching vibrational mode. In the co-polarized SEIRA measurement, the C=O mode of the PMMA nano-film was clearly observed as a conventional anti-resonant peak within the Fano line-shape of the metamaterial. For the cross-polarized case, on the other hand, a distinctive dip appeared within a cross-polarized transmission peak of the metamaterial. Since the unwanted background is strongly suppressed in the cross-polarized detection scheme, the signal contrast was dramatically improved, allowing for the attomole detection of the C=O bond in the far-field measurement. Our metamaterial approach achieves the significant improvement of signal-to-background ratio in the far-field measurement, thus paving the way toward the high-sensitive analysis of functional group in direct IR spectroscopy.

DOI： 10.1117/12.2237559

Doping effect on photoabsorption and charge-separation dynamics in light-harvesting organic molecule Reviewed

Ohmura, Satoshi, Tsuruta, Kenji, Shimojo, Fuyuki, Nakano, Aiichiro

Aip Advances 6 ( 1 ) 2016

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER INST PHYSICS

Using ab-initio theoretical methods, we demonstrate possible enhancement of photo-conversion efficiency of an organic solar cell via intentional doping in molecular graphene-fullerene heterojunction [the hexabenzocoronene (HBC)-triethylene glycol (TEG)-C-60 molecule]. Photoabsorption analysis indicates oxygen substitution into HBC leads to an extension of the spectra up to an infrared regime. A quantum-mechanical molecular dynamics simulation incorporating nonadiabatic electronic transitions reveals that a dissociated charge state (D+ and A(-)) in the O-doped system is more stable than the pristine case due to the presence of an effective barrier by the TEG HOMO/LUMO level. We also find that oxygen doping in HBC enhances the intermolecular carrier mobility after charge separation. On the other hand, the pristine molecule undergoes rapid recombination between donor and acceptor charges at the interface. These analyses suggest that the graphene oxidation opens a new window in the application of organic super-molecules to solar cells. (C) 2016 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.

DOI： 10.1063/1.4939848

Few-layer HfS2 transistors Reviewed

Kanazawa, Toru, Amemiya, Tomohiro, Ishikawa, Atsushi, Upadhyaya, Vikrant, Tsuruta, Kenji, Tanaka, Takuo, Miyamoto, Yasuyuki

Scientific Reports 6 2016

Language：English Publishing type：Research paper (scientific journal) Publisher：NATURE PUBLISHING GROUP

HfS2 is the novel transition metal dichalcogenide, which has not been experimentally investigated as the material for electron devices. As per the theoretical calculations, HfS2 has the potential for well-balanced mobility (1,800 cm(2)/V.s) and bandgap (1.2 eV) and hence it can be a good candidate for realizing low-power devices. In this paper, the fundamental properties of few-layer HfS2 flakes were experimentally evaluated. Micromechanical exfoliation using scotch tape extracted atomically thin HfS2 flakes with varying colour contrasts associated with the number of layers and resonant Raman peaks. We demonstrated the I-V characteristics of the back-gated few-layer (3.8 nm) HfS2 transistor with the robust current saturation. The on/off ratio was more than 10(4) and the maximum drain current of 0.2 mu A/mu m was observed. Moreover, using the electric double-layer gate structure with LiClO4: PEO electrolyte, the drain current of the HfS2 transistor significantly increased to 0.75 mA/mu m and the mobility was estimated to be 45 cm(2)/V.s at least. This improved current seemed to indicate superior intrinsic properties of HfS2. These results provides the basic information for the experimental researches of electron devices based on HfS2.

DOI： 10.1038/srep22277

First-principles calculation of amorphization of Si and P co-doped α-Fe₂O₃

Mitani K., Tsuruta K., Ishikawa A.

Meeting Abstracts of the Physical Society of Japan 71 1504 - 1504 2016

Terahertz wavefront control by tunable metasurface made of graphene ribbons Reviewed

Takumi Yatooshi, Atsushi Ishikawa, Kenji Tsuruta

APPLIED PHYSICS LETTERS 107 ( 5 ) 2015.8

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER INST PHYSICS

We propose a tunable metasurface consisting of an array of graphene ribbons on a silver mirror with a SiO2 gap layer to control reflected wavefront at terahertz frequencies. The graphene ribbons exhibit localized plasmon resonances depending on their Fermi levels to introduce abrupt phase shifts along the metasurface. With interference of the Fabry-Perot resonances in the SiO2 layer, phase shift through the system is largely accumulated, covering the 0-to-2 pi range for full control of the wavefront. Numerical simulations prove that wide-angle beam steering up to 53 degrees with a high reflection efficiency of 60% is achieved at 5 THz within a switching time shorter than 0.6 ps. (C) 2015 AIP Publishing LLC.

DOI： 10.1063/1.4927824

Other Link： http://orcid.org/0000-0002-1447-2530

Terahertz acoustic wave on piezoelectric semiconductor film via large-scale molecular dynamics simulation Reviewed

Ryo Hikata, Kenji Tsuruta, Atsushi Ishikawa, Kazuhiro Fujimori

JAPANESE JOURNAL OF APPLIED PHYSICS 54 ( 7 ) 2015.7

Language：English Publishing type：Research paper (scientific journal) Publisher：IOP PUBLISHING LTD

By atomistic simulation, we investigate an acoustic wave at THz frequencies in nanoscale thin films of aluminum-nitride piezoelectric material. A mode analysis reveals that the thickness longitudinal mode along the [0001] direction exists stably at the atomic level. To control the acoustic wave, we introduce a phononic crystal (PC) structure in the films. We determine the band-gap frequency in the phonon dispersion of the PC structure and confirm via molecular dynamics simulation that the acoustic wave within the band-gap frequency can be confined by a waveguide structure with a PC. The possibility of designing and controlling a THz acoustic wave in a nanoscale thin film with a PC is thereby demonstrated. (C) 2015 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.54.07HB07

Fabrication of Thin-Film HfS2 FET Reviewed

T. Kanazawa, T. Amemiya, A. Ishikawa, V. Upadhyaya, K. Tsuruta, T. Tanaka, Y. Miyamoto

2015 73RD ANNUAL DEVICE RESEARCH CONFERENCE (DRC) 2015-August 217 - 218 2015

Terahertz wavefront control by graphene metasurface Reviewed

Takumi Yatooshi, Atsushi Ishikawa, Kenji Tsuruta

Materials Research Society Symposium Proceedings 1788 37 - 42 2015

Language：English Publishing type：Research paper (international conference proceedings) Publisher：Materials Research Society

We propose and numerically investigate a tunable metasurface made of an array of graphene ribbons to dynamically control terahertz (THz) wavefront. The metasurface consists of graphene micro ribbons on a silver mirror with a SiO2 gap layer. The graphene ribbons are designed to exhibit localized plasmon resonances depending on their Fermi levels to introduce abrupt phase shifts along the metasurface. With interference of the Fabry-Perot resonances in the SiO2 layer, phase shift through the system is largely accumulated, covering up to 2jt range for full control of the THz wavefront. Numerical simulations prove that wide-angle reflected THz beam steering from -53° to +53° with a high reflection efficiency as high as 60% is achieved at 5 THz while the propagation direction of THz beam could be switched within 0.6 ps.

DOI： 10.1557/opl.2015.730

Other Link： http://orcid.org/0000-0002-1447-2530

A density functional study of vacancy formation in grain boundaries of undoped alpha-alumina Reviewed

Takafumi Ogawa, Akihide Kuwabara, Craig A. J. Fisher, Hiroki Moriwake, Katsuyuki Matsunaga, Kenji Tsuruta, Satoshi Kitaoka

ACTA MATERIALIA 69 365 - 371 2014.5

Language：English Publishing type：Research paper (scientific journal) Publisher：PERGAMON-ELSEVIER SCIENCE LTD

Recent oxygen permeation experiments with cc-alumina have shown that the two major diffusing species at the grain boundaries, i.e. oxygen and aluminum vacancies, switch over in terms of their dominance depending on the oxygen partial pressure at high temperatures (the so-called p-n transition). In order to investigate this transition behavior the formation energies of charged oxygen and aluminum vacancies at Al2O3 grain boundaries were evaluated using density functional theory. The electronic structures affecting the carrier concentrations are assessed for three types of grain boundaries. The ratios of the grain boundary band gaps relative to the bulk value lie in the range of 0.6-0.85 depending on the degree of grain boundary misorientation. From the formation energies we find that, at band gaps around 60% compared to the bulk value, the dominant vacancy alters depending on the pressure, consistent with the oxygen permeation experiments. Our results suggest that the band bap narrowing occurring at grain boundaries enhances the creation of oxygen vacancies and conduction electrons, facilitating the observed transition. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.actamat.2014.01.059

Core structure and dissociation energetics of basal edge dislocation in alpha-Al2O3: A combined atomistic simulation and transmission electron microscopy analysis Reviewed

Kenji Tsuruta, Eita Tochigi, Yuki Kezuka, Kazuaki Takata, Naoya Shibata, Atsutomo Nakamura, Yuichi Ikuhara

ACTA MATERIALIA 65 76 - 84 2014.2

Language：English Publishing type：Research paper (scientific journal) Publisher：PERGAMON-ELSEVIER SCIENCE LTD

Using large-scale molecular dynamics (MD) simulations, we investigate the energetics and local structures/stresses of partial dislocations, 1/3 < 01 (1) over bar0 > and 1/3 < 10 (1) over bar0 >, dissociated from the 1/3 < 11 (2) over bar0 > perfect basal edge dislocation in alpha-Al2O3. The validity of the model adopted in the simulation is confirmed by comparing with theoretical stress/strain distributions and with those experimentally obtained from a high-resolution transmission electron microscopy (HRTEM) observation. Partial dislocation pairs have a stable inter-core distance (similar to 2 nm), which is also a phenomenon that is observed in the HRTEM experiments. The distance between the partials can be explained quantitatively by the balance between an elastic core core repulsion and an effective attractive force against the extension of stacking faults (SFs). A comparison is made for two types of core structures of partial dislocations: a pair of partials with Al-terminated/O-terminated extra-half planes and that with Al-/Al-terminated ones. The overall tendency of the inter-core interaction and the equilibrium distances are the same in both cases, whereas the Al-O-terminated pair is slightly favourable in energy at the equilibrium distance. A residual shear stress on the SF plane is observed in the MD results, which can be attributed to local atomic structure in the SF. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.actamat.2013.11.035

Phononic-Crystal Acoustic Lens by Design for Energy-Transmission Devices Reviewed

Yusuke Kanno, Kenji Tsuruta, Kazuhiro Fujimori, Hideki Fukano, Shigeji Nogi

ELECTRONICS AND COMMUNICATIONS IN JAPAN 97 ( 1 ) 22 - 27 2014.1

Language：English Publishing type：Research paper (scientific journal) Publisher：WILEY-BLACKWELL

The lens effect of acoustic waves in a two-dimensional (2D) phononic crystal is studied by numerical simulation based on the finite-difference time-domain (FDTD) method. We calculate the phonon band structure of 2D phononic crystals, consisting of metal/ceramic cylinders placed periodically in water. The lens effect is observed for the far-field wave in phononic crystals with two-layered and graded-index structure. We compare the focal intensity and the energy transmission efficiency in these numerical experiments, and show that a novel energy-transmission device can be designed using phononic crystals. (c) 2013 Wiley Periodicals, Inc. Electron Comm Jpn, 97(1): 22-27, 2014; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ecj.11491

DOI： 10.1002/ecj.11491

Graphene metasurface for THz wavefront control Reviewed

Yatooshi T, Ishikawa A, Tsuruta K

JSAP-OSA Joint Symposia, JSAP 2014 2014

Effect on acoustic wave propagation by the interior structure of waveguide filled up with water

Tsubouchi Kazuya, Tadokoro Masaaki, Fujimori Kazuhiro, Ishikawa Atsushi, Tsuruta Kenji, Fukano Hideki

The Proceedings of The Computational Mechanics Conference 2014.27 325 - 326 2014

Optically Powered Voltage Supply Device for Effective Utilization of Optical Energy in the Fiber-to-the-Home Network Reviewed

Hideki Fukano, Takeshi Shinagawa, Kenji Tsuruta

ELECTRONICS AND COMMUNICATIONS IN JAPAN 96 ( 10 ) 37 - 42 2013.10

Language：English Publishing type：Research paper (scientific journal) Publisher：WILEY-BLACKWELL

SUMMARYAn optically powered device using an InGaAs photodiode has been developed. This study aims to harvest light energy (2.8 to 500 mu W) from the FTTH (fiber-to-the-Home) network and to utilize it for operating remote sensors without an external energy source. We designed the booster circuit and evaluated its characteristics, confirming that it could boost an input voltage of 0.3 V to 3.0 V. We also evaluated the characteristics of an InGaAs photodiode and confirmed that it could output a voltage over 0.3 V using 10-mu W input light. We demonstrate that a ready-made sensor can be operated with an input optical power as low as 10 mu W. (c) 2013 Wiley Periodicals, Inc. Electron Comm Jpn, 96(10): 37-42, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ecj.11472

DOI： 10.1002/ecj.11472

Design and development of highly ecient transducer for ultrasonic wireless power transmission system Reviewed

Yuki Hori, Kazuhiro Fujimori, Kenji Tsuruta, Shigeji Nogi

ELECTRICAL ENGINEERING IN JAPAN 184 ( 3 ) 27 - 35 2013.8

Language：English Publishing type：Research paper (scientific journal) Publisher：WILEY-BLACKWELL

In this paper, a transducer that is suitable for the ultrasonic wireless power transmission system is discussed. The transducer is designed based on Mason's equivalent circuit theory, basically. The transducer was developed using design parameters optimized by multiphysics analysis. As a result, it is confirmed that the transmission eciency is drastically improved to more than 50%. This result suggests that wireless power transmission by acoustic wave is feasible. (c) 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 184(3): 2735, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22406

DOI： 10.1002/eej.22406

Interaction between Atomic Vacancies in Crystalline Si Wafer: A Tight-binding Molecular Dynamics Study Reviewed

K. Takata, K. Tsuruta, T. Ogawa, H. Iyetomi

Trans. Meter. Res. Soc. J 37 ( 2 ) 143 - 146 2012.4

Language：English Publisher：The Materials Research Society of Japan

Vacancy interaction in crystalline Si wafer is studied by numerical simulation based on the Tight-Binding Molecular Dynamics (TBMD) method. We evaluate an effective interaction between vacancy pair in bulk and in a thin slab as model systems of a Si wafer. In the case of vacancy pair in bulk crystal, results reveal that there is an effective "capture radius" of the vacancies to form a divacancy at around 8Å at 300K and 13Å at 600K. Surface structure involving vacancies in Si slab undergoes a reconstruction accompanying dimer-rows in [110] direction initiated by the vacancies. The capture radius is also found to exist in the slab and binding energy of the divacancy has depth dependence due to the surface effect.

DOI： 10.14723/tmrsj.37.143

Experimental Analysis of Optical Fiber Multimode Interference Structure and its Application to Refractive Index Measurement Reviewed

Shuji Taue, Yoshiki Matsumoto, Hideki Fukano, Kenji Tsuruta

JAPANESE JOURNAL OF APPLIED PHYSICS 51 ( 4 ) 2012.4

Language：English Publishing type：Research paper (scientific journal) Publisher：IOP PUBLISHING LTD

We investigated a fiber-based multimode interference phenomenon in the wavelength domain by using a white light source and an optical spectrum analyzer. This phenomenon was produced by a larger-core optical fiber joined at both ends with smaller-core optical fibers. We examined the variation of interference wavelength with changes in the length of the larger-core fiber. The interference wavelengths were blue-shifted and the interference signals were sharpened with an increase in the length of the larger-core fiber. The calculated results agreed well with the measured results. Next, we investigated how the input and output fibers with a small core influence the interference signal characteristics. By comparing the amplitude differences of the interference signal we find the conditions of input and output (I/O) fibers for higher sensitivity. In addition, an interference-signal shift was observed by changing the medium surrounding an multimode interference (MMI) structure. The amount of shift increased at a longer wavelength. This leads to the sensitive detection of the refractive index. Finally, a demonstration of the optical fiber refractometer with a multimode interference structure was given by refractive-index measurements of ethanol/water solutions. (C) 2012 The Japan Society of Applied Physics

DOI： 10.1143/JJAP.51.04DG14

An investigation for optimum design of matching circuit in highly efficient RF-DC conversion circuit by genetic algorithm Reviewed

Kondo Y, Fujimori K, Tsuruta K

IEEE Antennas and Propagation Society, AP-S International Symposium (Digest) 194 - 197 2012

Characteristics of RF-DC conversion circuit for wireless power transmission using the low resistance GaN schottky barrier diode Reviewed

Fujimori K, Wagi T, Tsuruta K, Nogi S, Ozawa Y, Furukawa M, Fujiwara T

IEEE Antennas and Propagation Society, AP-S International Symposium (Digest) 190 - 193 2012

Design and development of highly efficient transducer for ultrasonic wireless power transmission system Reviewed

Yuki Hori, Kazuhiro Fujimori, Kenji Tsuruta, Shigeji Nogi

IEEJ Transactions on Electronics, Information and Systems 132 ( 3 ) 1 - 343 2012

Language：English Publishing type：Research paper (scientific journal) Publisher：Institute of Electrical Engineers of Japan

In this paper, the transducer that is suitable for the ultrasonic wireless power transmission system is discussed. The transducer is designed based on the Mason's equivalent circuit theory, basically. Design parameters of the transducer are optimized for by using the multi physics analysis and developed. As results, it is confirmed that the transmission efficiency is drastically improved to more than 50%. This result suggests that the WPT by acoustic wave is practicable. © 2012 The Institute of Electrical Engineers of Japan.

DOI： 10.1541/ieejeiss.132.337

Other Link： http://orcid.org/0000-0002-1447-2530

Frequency characteristic of transmission efficiency depended on matching condition of transducer in ultrasonic wireless power transmission system Reviewed

Fujimori K, Tominaga S, Tanda K, Tsuruta K, Nogi S

IEEE Antennas and Propagation Society, AP-S International Symposium (Digest) 166 - 169 2012

An ab initio analysis of electronic states associated with a silicon vacancy in cubic symmetry Reviewed

OGAWA Takafumi, TSURUTA Kenji, IYETOMI Hiroshi

Solid State Communications 151 ( 21 ) 1605 - 1608 2011.11

Negative Refraction and Energy-Transmission Efficiency of Acoustic Waves in Two-Dimensional Phononic Crystal: Numerical and Experimental Study Reviewed

Yuuki Kasai, Kenji Tsuruta, Kazuhiro Fujimori, Hideki Fukano, Shigeji Nogi

JAPANESE JOURNAL OF APPLIED PHYSICS 50 ( 6 ) 2011.6

Language：English Publishing type：Research paper (scientific journal) Publisher：JAPAN SOC APPLIED PHYSICS

The negative refraction of acoustic waves in a two-dimensional phononic-crystal slab is studied by numerical simulation based on the finite-difference time-domain (FDTD) method and by ultrasonic measurement. The incident-angle dependences of energy-transmission efficiency in the simulation and experiment are in good agreement in the frequency range of approximately 1.2 MHz. Using the FDTD method, we optimize the efficiency by varying structural parameters such as filling fraction and slab thickness. The effect of deviation from the ideal crystallinity is also evaluated quantitatively via the simulation. These results indicate that an energetically efficient acoustic lens can be fabricated by carefully optimizing the structure of the phononic crystal. (C) 2011 The Japan Society of Applied Physics

DOI： 10.1143/JJAP.50.067301

Structures and Local Electronic States of Dislocation Loop in 4H-SiC via a Linear-Scaling Tight-Binding Study Reviewed

Fusanori Hamasaki, Kenji Tsuruta

MATERIALS TRANSACTIONS 52 ( 4 ) 672 - 676 2011.4

Language：English Publishing type：Research paper (scientific journal) Publisher：JAPAN INST METALS

The atomic- and electronic-level structures of a dislocation loop and a stacking fault in 4H-SiC crystal are investigated by using large-scale tight-binding (TB) molecular-dynamics simulation. We employ a linear-scaling TB method implemented on a parallel computer in order to accelerate the 9,600-atoms calculation which is required for such a nanoscale simulation. We find that the initial configuration that involves unstable C-C networks around the dislocation loop is relaxed to a structure having six-membered rings, and that the distribution of electron populations is inhomogeneous on the loop. The local electronic density of states shows two peaks in the bulk band gap, where one of these peaks may correspond to the defect state observed in EBIC and CL experiments. [doi:10.2320/matertrans.MBW201024]

DOI： 10.2320/matertrans.MBW201024

Design of Anti-Resonance Transducer and Its Abilities for Efficient Ultrasonic Wireless Power Transmission System Reviewed

Yuki Hori, Yusuke Shigeta, Kazuhiro Fujimori, Kenji Tsuruta, Shigeji Nogi

2011 41ST EUROPEAN MICROWAVE CONFERENCE 67 - 70 2011

Language：English Publishing type：Research paper (international conference proceedings) Publisher：IEEE

We developed a fundamental testbed and investigated the suitable transducer for the wireless power transmission (WPT). We also had reported experimental results of the transmission efficiency in water by using the commercial transducer (COM) which only designed to match to the acoustic impedance of water by its structure and the electric impedance of the transmitter and receiver by matching networks. In this paper, we investigate the transducer (DEV) for improving the transmission efficiency based on the Mason's equivalent circuit. For deciding a structure and materials of the transducer, we used ANSYS well-known as the multi-physics simulator.
In this result, it is confirmed that the transmission efficiency is drastically improved from less than 1% to 60% compared to our previous report. In addition, we manufactured designed transducer, and confirmed the system's efficiency is about 50 % experimentally. This result also suggests that WPT by the acoustic wave be practicable.

Other Link： http://orcid.org/0000-0002-1447-2530

The Influences of Diode Parameters on Conversion Efficiency of RF-DC Conversion Circuit for Wireless Power Transmission System Reviewed

Kazuhiro Fujimori, Sho-ichi Tamaru, Kenji Tsuruta, Shigeji Nogi

2011 41ST EUROPEAN MICROWAVE CONFERENCE 57 - 60 2011

Language：English Publishing type：Research paper (international conference proceedings) Publisher：IEEE

RF-DC conversion circuit is one of the most important components in the wireless power transmission technologies. For realizing highly efficient wireless power transmission, it is necessary to design the RF-DC conversion circuit with high conversion efficiency, and the designing method of the circuit is actively studied. In this paper, the influences of diode parameters, such as its resistance, junction capacitance, parasitic reactance, and so on, on the conversion efficiency of the RF-DC conversion circuit are investigated to clarify the characteristic of the diode for obtaining highly efficient RF-DC conversion circuit.

Other Link： http://orcid.org/0000-0002-1447-2530

Development of highly efficient transducer for wireless power transmission system by ultrasonic Reviewed

Yusuke Shigeta, Yuki Hori, Kazuhiro Fujimori, Kenji Tsuruta, Shigeji Nogi

2011 IEEE MTT-S International Microwave Workshop Series on Innovative Wireless Power Transmission: Technologies, Systems, and Applications, IMWS-IWPT 2011 - Proceedings 171 - 174 2011

Language：English Publishing type：Research paper (international conference proceedings)

We developed a fundamental testbed and investigated the suitable transducer for the wireless power transmission (WPT). We also reported experimental results of the transmission efficiency in water by using the commercial transducer (COM) which only designed to match to the acoustic impedance of water and the electric impedance of the transmitter and receiver. In this paper, we investigate the transducer for improving the efficiency based on the Mason's equivalent circuit. For deciding a structure and materials of the transducer, we used ANSYS well-known as the multi-physics simulator. In this result, it is confirmed that the transmission efficiency is drastically improved from less than 1% to 60%. In addition, we made designed transducer, and confirmed the systems' efficiency is about 50 %. This result suggests that the WPT by acoustic wave is practicable. © 2011 IEEE.

DOI： 10.1109/IMWS.2011.5877115

Other Link： http://orcid.org/0000-0002-1447-2530

Initial Stage of Consolidation of Silicon-Carbide Nanocrystals under Pressure: A Tight-Binding Molecular-Dynamics Study Reviewed

Kenji Tsuruta

JOURNAL OF NANOMATERIALS 2011

Language：English Publishing type：Research paper (scientific journal) Publisher：HINDAWI PUBLISHING CORPORATION

Tight-binding molecular-dynamics (TBMDs) simulations are performed to study atomic and electronic structures during high-temperature consolidation processes of nanocrystalline silicon carbide under external pressure. We employ a linear-scaling method (the Fermi-operator expansion method) with a scalable parallel algorithm for efficient calculations of the long time-scale phenomena. The results show that microscopic processes of the consolidation depend strongly on initial orientations of the nanocrystals. It is observed that an orientational rearrangement of the nanocrystals initially misaligned is induced by an instantaneous shearing force between nanocrystals, whereas the aligned system undergoes densification without shearing. Analysis on an effective-charge distribution and an average bond-order distribution reveals electronic-structure evolutions during these processes.

DOI： 10.1155/2011/308495

Molecular Dynamics Study on Dielectric Properties of Silicon Oxynitride: Composition and Microstructure Dependence Reviewed

Munemasa Tomita, Kenji Tsuruta

ELECTROCERAMICS IN JAPAN XIV 485 287 - 290 2011

Language：English Publishing type：Research paper (international conference proceedings) Publisher：TRANS TECH PUBLICATIONS LTD

Extra-long molecular-dynamics simulations are performed to study the interplay between dielectric properties and microstructures of silicon oxynitride. We quantitatively obtained the ionic permittivity and its linear dependence on nitrogen concentration. Analyses on microstructure of the oxynitride show that, as the N concentration increases, N atoms enter Si-O networks creating smaller-sized rings. While overall tendency of dielectric constant is monotonic increase on the N concentration, microscopic characteristics, such as local displacement of atoms, are strongly depend on local bonding environments.

DOI： 10.4028/www.scientific.net/KEM.485.287

Acoustic lens using sonic crystal for energy-transmission application Reviewed

Y. Kanno, Y. Kasai, K. Tsuruta, K. Fujimori, H. Fukano, S. Nogi

2011 IEEE MTT-S International Microwave Workshop Series on Innovative Wireless Power Transmission: Technologies, Systems, and Applications, IMWS-IWPT 2011 - Proceedings 207 - 210 2011

Language：English Publishing type：Research paper (international conference proceedings)

We design and characterize a two-dimensional sonic crystal (SC) to manipulate the propagation of acoustic waves by numerical simulation based on the finite-difference time-domain (FDTD) method and by ultrasonic measurement. Two types of SC for an acoustic lens effect are studied. One is a homogeneous periodic structure exhibiting negative refraction, and the other has a hetero-structure. Negative refraction behavior in the simulation is good agreement with the experiment in the frequency range around 1.2MHz. We also observe a lens effect for far-field wave in the hetero-structured SC. These results indicate that a novel energy-transmission/harvesting device can be designed using SCs. © 2011 IEEE.

DOI： 10.1109/IMWS.2011.5877131

Density-Functional Analysis on Vacancy Orbital and its Elastic Response of Silicon Reviewed

Takafumi Ogawa, Kenji Tsuruta, Hiroshi Iyetomi, Hiroshi Y. Kaneta, Terutaka Goto

RELIABILITY AND MATERIALS ISSUES OF SEMICONDUCTOR OPTICAL AND ELECTRICAL DEVICES AND MATERIALS 1195 2010

Language：English Publishing type：Research paper (international conference proceedings) Publisher：MATERIALS RESEARCH SOC

Recent experiments on ultrasonic measurements of non-doped and boron-doped silicon indicate that vacancies in crystalline silicon can be detected through the elastic softening at low temperature. This is attributed to enhanced response of electronic quadrupole localized at the vacancies to the elastic strain. In the present work, the electronic quadrupole moment of the vacancy orbital in silicon and their strain susceptibility are evaluated quantitatively by using the density-functional method. We show the orbital of gap state is localized around vacancy but extended over several neighbors. The effect of applied magnetic field on the vacancy orbital and its multipole structures are also investigated. We find that the results obtained from these calculations are consistent with the ultrasonic experiments.

DOI： 10.1557/PROC-1195-B08-11

Classical and Hybrid Density-Functional/Classical Molecular Dynamics Study of Dislocation Core in Alumina Ceramic Reviewed

Kenji Tsuruta, Toshiyuki Koyama, Shuji Ogata

MATERIALS TRANSACTIONS 50 ( 5 ) 1015 - 1018 2009.5

Language：English Publishing type：Research paper (scientific journal) Publisher：JAPAN INST METALS

We perform molecular-dynamics simulation,, to investigate the atomic and electronic structures of a basal edge dislocation it) alpha-Al2O3. The core structure consisting of two non-stoichiometric partial dislocations, which has been recently proposed by an experiment, is examined by an empirical interatomic-potential model and by a hybrid quantum/classical approach. The atomic rearrangements in the full and in the partial dislocation cores are analyzed. The local electronic structure in the full dislocation core is evaluated by the density-functional method applied for a quantum-cluster region in the hybrid simulations. Interaction potentials between partial dislocations are investigated by the classical model. Results preliminarily obtained show that the partials aligned normal to a basal plane ({10001}) has a short-ranged repulsive nature approximately within 8 angstrom. [doi: 10.2320/matertrans.MC200833]

DOI： 10.2320/matertrans.MC200833

An FDTD Analysis of Nanostructured Electromagnetic Metamaterials Using Parallel Computer Reviewed

Ryosuke Umeda, Chieko Totsuji, Kenji Tsuruta, Hiroo Totsuji

MATERIALS TRANSACTIONS 50 ( 5 ) 994 - 998 2009.5

Language：English Publishing type：Research paper (scientific journal) Publisher：JAPAN INST METALS

Metamaterial with negative permittivity and permeability is studied by means of computer simulations. We analyze the electromagnetic response of nanostructured metamaterials to evanescent waves at optical frequency via the finite-difference time-domain simulations on parallel computer. Effects of the nanostructure on dielectric and magnetic properties are taken into account by introducing the Drude-Lorentz model in the materials dispersion. Size effect on the dispersion is examined by comparing the model with that of a noble metal particle. A re-focusing and an amplification of the evanescent waves propagating through a metamaterial, consisting of metal slabs/vacuum stacking, are demonstrated for the frequency range at 614-744 THz. By properly treating the materials dispersion, we show that the nanostructured metamaterial may behave as a left-handed material in the optical range. [doi:10.2320/matertrans.MC200822]

DOI： 10.2320/matertrans.MC200822

Negative Refraction of Acoustic Waves in a Two-Dimensional Phononic Crystal via FDTD Simulation Reviewed

Tomoyuki Kurose, Kenji Tsuruta, Chieko Totsuji, Hiroo Totsuji

MATERIALS TRANSACTIONS 50 ( 5 ) 1004 - 1007 2009.5

Language：English Publishing type：Research paper (scientific journal) Publisher：JAPAN INST METALS

Negative refraction of acoustic waves in a two-dimensional (2D) phononic crystal is studied by numerical simulation based on the finite-difference time-domain (FDTD) method. We calculate the phonon band structure of 2D phononic crystals, consisting of metal cylinders placed periodically in a liquid. By comparing several combinations of materials for metal cylinder and liquid, we analyze the dependence of the band structures on sound speed and density of liquid media. The negative refraction of the acoustic waves is observed at the interfaces between the phononic crystal slab and the liquid. We find that an acoustic "lens effect" with the slab appears due to the negative refractions. The relationship between the focal intensity in the lens effect and the band structure of the phononic crystal is quantitatively discussed. [doi: 10.2320/matertrans.MC200823]

DOI： 10.2320/matertrans.MC200823

A classical-map simulation of two-dimensional electron fluid: an extension of classical-map hypernetted-chain theory beyond the hypernetted-chain approximation Reviewed

Chieko Totsuji, Takashi Miyake, Kenta Nakanishi, Kenji Tsuruta, Hiroo Totsuji

JOURNAL OF PHYSICS-CONDENSED MATTER 21 ( 4 ) 2009.1

Language：English Publishing type：Research paper (scientific journal) Publisher：IOP PUBLISHING LTD

A method for numerically simulating quantum systems is proposed and applied to the two-dimensional electron fluid at T = 0. This method maps quantum systems onto classical ones in the spirit of the classical-map hypernetted-chain theory and performs simulations on the latter. The results of the simulations are free from the assumption of the hypernetted-chain approximation and the neglect of the bridge diagrams. A merit of this method is the applicability to systems with geometrical complexity and finite sizes including the cases at finite temperatures. Monte Carlo and molecular dynamics simulations are performed corresponding to two previous proposals for the 'quantum' temperature and an improvement in the description of the diffraction effect. It is shown that one of these two proposals with the improved diffraction effect gives significantly better agreement with quantum Monte Carlo results reported previously for the range of 5 <= r(s) <= 40. These results may serve as the basis for the application of this method to finite non-periodic systems like quantum dots and systems at finite temperatures.

DOI： 10.1088/0953-8984/21/4/045502

Spin polarization of two-dimensional electron system in parabolic potential Reviewed

Takashi Miyake, Chieko Totsuji, Kenta Nakanishi, Kenji Tsuruta, Hiroo Totsuji

PHYSICS LETTERS A 372 ( 40 ) 6197 - 6201 2008.9

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

We analyze the ground state of the two-dimensional quantum system of electrons confined in a parabolic potential with the system size around 100 at 0 K. We map the system onto a classical system on the basis of the classical-map hypernetted-chain (CHNC) method which has been proven to work in the integral-equation-based analyses of uniform systems and apply classical Monte Carlo and molecular dynamics simulations. We find that, when we decrease the strength of confinement keeping the number of confined electrons fixed, the energy of the spin-polarized state with somewhat lower average density becomes smaller than that of the spin-unpolarized state with somewhat higher average density. This system thus undergoes the transition from the spin-unpolarized state to the spin polarized state and the corresponding critical value of r(s) estimated from the average density is as low as r(s) similar to 0.4 which is much smaller than the r(s) value for the Wigner lattice formation. When we compare the energies of spin-unpolarized and spin-polarized states for given average density, our data give the critical r(s) value for the transition between unpolarized and polarized states around 10 which is close to but still smaller than the known possibility of polarization at r(s) similar to 27. The advantage of our method is a direct applicability to geometrically complex systems which are difficult to analyze by integral equations and this is an example. (C) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physleta.2008.08.036

Vibrational Properties of Si Crystal with Vacancy: A Tight-Binding Study

Takafumi Ogawa, Kenji Tsuruta, Chieko Totsuji, Hiroo Totsuji, Hiroshi Iyetomi

Memoirs of the Faculty of Engineering, Okayama University 42 ( 1 ) 44 - 47 2008.1

Nickel-related defect in diamond: A tight-binding molecular-dynamics study Reviewed

Kenji Tsuruta, Satoshi Emoto, Chieko Totsuji, Hiroo Totsuji

COMPUTATIONAL MATERIALS SCIENCE 38 ( 4 ) 873 - 882 2007.2

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Structural, electronic, and magnetic properties of isolated Ni impurities at point defects and a dislocation core in diamond are investigated using tight-binding molecular-dynamics simulations. The results show the structural stabilization associated by lowering local symmetry in the cases of point defects. The segregation energies of Ni impurity for a substitutional site and for an interstitial site in the dislocation core are estimated to be in the same order within 0.2 eV. The local electronic density-of-states reveals that the gap states appeared by the insertion of Ni impurity are strongly localized around the Ni sites. Magnetic moments on neighboring C atoms are induced so as to screen the moment on the Ni atom except for the case of interstitial Ni impurity in which the total magnetic moment remains non-zero. Analyses indicate that localized atomic d states on the Ni atom and the p-d coupling between Ni and neighboring C atoms are responsible for the residual magnetic moment in the system with an interstitial Ni defect. In the other systems investigated, on the other hand, the bonding states between Ni impurity and its neighboring C atoms are dominated by the s-p coupling. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.commatsci.2006.06.003

Two-step melting of spherical Yukawa and Coulomb clusters Reviewed

Takafumi Ogawa, Hiroo Totsuji, Chieko Totsuji, Kenji Tsuruta

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 75 ( 12 ) 2006.12

Language：English Publishing type：Research paper (scientific journal) Publisher：PHYSICAL SOC JAPAN

By extensive Monte Carlo simulations, two separate peaks are found in the specific heat of relatively small spherical clusters of particles with 100 < N < 400, interacting via the Yukawa and Coulomb potentials and confined in the external field. The analyses of the diffusion and positional fluctuations show that these peaks at lower and higher temperatures reflect the loss of intrashell two-dimensional ordering and of the radial ordering, respectively. The magnitudes of the fluctuations in the outermost shell are consistent with the conventional Lindemann criterion. The results can be verified by experiments in ion traps and in dusty plasmas under microgravity or equivalent isotropic environments.

DOI： 10.1143/JPSJ.75.123501

Structure of spherical Yukawa clusters Reviewed

Hiroo Totsuji, Takafumi Ogawa, Chieko Totsuji, Kenji Tsuruta

Journal of Physics A: Mathematical and General 39 ( 17 ) 4545 2006.4

Dynamics of melting of spherical Yukawa and Coulomb clusters Reviewed

Takafumi Ogawa, Hiroo Totsuji, Chieko Totsuji, Kenji Tsuruta

NON-NEUTRAL PLASMA PHYSICS VI 862 242 - 247 2006

Language：English Publishing type：Research paper (international conference proceedings) Publisher：AMER INST PHYSICS

Spherical Yukawa and Coulomb clusters are composed of charged particles interacting via the Yukawa and Coulomb potential and confined by the external potential. Melting transitions of these clusters are analyzed by Monte Carlo (MC) and molecular dynamics (MD) simulations. By MC simulations, it is found that the specific heat of relatively small clusters (100 <= N <= 400) has two peaks. The diffusion analyses by MC and MD simulations and the fluctuation analyses related to the Lindemann criteria indicate that two peaks at lower and higher temperatures reflect the losses in ordering in azimuthal and radial directions, respectively.

DOI： 10.1063/1.2387929

Structure and thermodynamics of spherical Yukawa and Coulomb clusters Reviewed

Hiroo Totsuji, Takafumi Ogawa, Chieko Totsuji, Kenji Tsuruta

NON-NEUTRAL PLASMA PHYSICS VI 862 232 - 241 2006

Language：English Publishing type：Research paper (international conference proceedings) Publisher：AMER INST PHYSICS

Structures in the ground state and thermodynamics related to melting of spherical Yukawa and Coulomb clusters confined in external fields of less than 103 particles are discussed on the basis of molecular dynamics and Monte Carlo simulations and theoretical methods. At low temperatures, particles form concentric shell structures which are expressed by simple formulas and insensitive to the strength of screening. Structures are reproduced by the shell model when the intrashell cohesive energy is properly taken into account. The specific heat of clusters of relatively small sizes 100 <= N-d <= 400 has two peaks as a function of temperature. By analyses of diffusions, it is shown that the peaks at lower and higher temparatures corresponds to the loss of ordering in the azimuthal and radial (and therefore total) ordering, respectively. Magnitudes of fluctuations in the outermost shell are consistent with the conventional Lindemann criterion.

DOI： 10.1063/1.2387928

Structure of finite two-dimensional systems of dust particles at finite temperatures Reviewed

H Totsuji, C Totsuji, MS Liman, K Tsuruta

PHYSICS OF PLASMAS 12 ( 10 ) 2005.10

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER INST PHYSICS

The structure of confined two-dimensional systems of dust particles in dusty plasmas is analyzed at finite temperatures by numerical simulations and theoretical approaches. The finite Yukawa system is adopted as a model for these systems and the variational method which has been successful in reproducing structures at low temperatures is extended to finite temperatures through replacement of the cohesive energy by the Helmholtz free energy recently given in the form of simple interpolation formulas. The results are compared with those of numerical simulations and their satisfactory agreement has been obtained. Finite-temperature structures presented here will be useful to evaluate the physical parameters of the two-dimensional systems of dust particles often formed near the boundary between the plasma bulk and the sheath.

DOI： 10.1063/1.2116827

Structure of spherical Yukawa clusters: A model for dust particles in dusty plasmas in an isotropic environment Reviewed

Hiroo Totsuji, Takafumi Ogawa, Chieko Totsuji, Kenji Tsuruta

Physical Review E 72 ( 3 ) 036406 2005.9

Ordering of dust particles in dusty plasmas under microgravity Reviewed

Hiroo Totsuji, Chieko Totsuji, Takafumi Ogawa, Kenji Tsuruta

Physical Review E 71 ( 4 ) 045401 2005.4

Thermodynamics of a two-dimensional Yukawa fluid Reviewed

H Totsuji, MS Liman, C Totsuji, K Tsuruta

PHYSICAL REVIEW E 70 ( 1 ) 2004.7

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER PHYSICAL SOC

Thermodynamic quantities of a two-dimensional Yukawa system, a model for various systems including single-layered dust particles observed in dusty plasmas, are obtained and expressed by simple interpolation formulas. In the domain of weak coupling, the analytical method based on the cluster expansion is applied and, in the domain of intermediate and strong coupling, numerical simulations are performed. Due to reduced dimensionality, the treatment based on the mean field fails at the short range and exact behavior of the binary correlation is to be taken into account even in the case of weak coupling.

DOI： 10.1103/PhysRevE.70.016405

Thermodynamics of a two-dimensional Yukawa fluid Reviewed

Hiroo Totsuji, M. Sanusi Liman, Chieko Totsuji, Kenji Tsuruta

Physical Review E - Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics 70 ( 1 ) 7 2004

Language：English Publishing type：Research paper (scientific journal)

Thermodynamic quantities of a two-dimensional Yukawa system, a model for various systems including single-layered dust particles observed in dusty plasmas, are obtained and expressed by simple interpolation formulas. In the domain of weak coupling, the analytical method based on the cluster expansion is applied and, in the domain of intermediate and strong coupling, numerical simulations are performed. Due to reduced dimensionality, the treatment based on the mean field fails at the short range and exact behavior of the binary correlation is to be taken into account even in the case of weak coupling. © 2004 The American Physical Society.

DOI： 10.1103/PhysRevE.70.016405

Estimation of screening length and electric charge on particles in single-layered dusty plasma crystals (vol 68, art no. 017401, 2003) Reviewed

C Totsuji, MS Liman, K Tsuruta, H Totsuji

PHYSICAL REVIEW E 68 ( 4 ) 2003.10

Estimation of screening length and electric charge on particles in single-layered dusty plasma crystals Reviewed

C Totsuji, MS Liman, K Tsuruta, H Totsuji

PHYSICAL REVIEW E 68 ( 1 ) 499011 2003.7

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER PHYSICAL SOC

Single-layered two-dimensional crystals of dust particles are often observed in dusty plasma experiments and the data on their structure can be obtained by analyzing the images usually taken by charge-cupled device cameras. We give here some formulas for practical purposes of estimating the screening length and the electric charge on a dust particle from the surface density and the radius of such finite two-dimensional dust crystals. The formulas are derived on the basis of our theoretical approach which has been successful in reproducing results of molecular-dynamics simulations on dusty plasmas. An example of application is also shown.

DOI： 10.1103/PhysRevE.68.017401

Other Link： http://orcid.org/0000-0002-1447-2530

Estimation of screening length and electric charge on particles in single-layered dusty plasma crystals Reviewed

Chieko Totsuji, M. Sanusi Liman, Kenji Tsuruta, Hiroo Totsuji

Physical Review E - Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics 68 ( 1 ) 4 2003

Language：English Publishing type：Research paper (scientific journal)

Single-layered two-dimensional crystals of dust particles are often observed in dusty plasma experiments and the data on their structure can be obtained by analyzing the images usually taken by charge-cupled device cameras. We give here some formulas for practical purposes of estimating the screening length and the electric charge on a dust particle from the surface density and the radius of such finite two-dimensional dust crystals. The formulas are derived on the basis of our theoretical approach which has been successful in reproducing results of molecular-dynamics simulations on dusty plasmas. An example of application is also shown. © 2003 The American Physical Society.

DOI： 10.1103/PhysRevE.68.017401

Competition between two forms of ordering in finite Coulomb clusters Reviewed

H Totsuji, T Kishimoto, C Totsuji, K Tsuruta

PHYSICAL REVIEW LETTERS 88 ( 12 ) 2002.3

Language：English Publishing type：Research paper (scientific journal) Publisher：AMERICAN PHYSICAL SOC

The lowest-energy state of spherical clusters made up of single-species charged particles in a three-dimensional confining potential is investigated by molecular dynamics simulations for a system size of 5 x 10(3) to 1.2 x 10(5). The energy per particle is compared between shell-structured clusters and spherical finite-bcc lattices with relaxed surfaces. The shell structure in the interior is the lowest-energy configuration for ion numbers lower than about 10(4), while for higher ion numbers, an interior with bcc ordering surrounded by a few shells on the outside has lower energy. The formation of a small bcc lattice (nucleation) in the shell-structured cluster of 2 x 10(4) ions is observed.

DOI： 10.1103/PhysRevLett.88.125002

Structure and Madelung energy of coulomb clusters Reviewed

H Totsuji, T Kishimoto, C Totsuji, K Tsuruta

NON-NEUTRAL PLASMA PHYSICS IV 606 181 - 190 2002

Language：English Publishing type：Research paper (international conference proceedings) Publisher：AMER INST PHYSICS

The ground state of the system of charged particles of one species confined by the three-dimensional, isotropic, and parabolic potential is investigated by molecular dynamics simulations. It is shown that, with the increase of the system size or the number of particles in the system N, the ground state changes from the shell-structured system to the finite bee lattice with reconstructed surface. The critical value of the transition is estimated to be between N = 10(4) and N = 2 x 10(4). The nucleation of the bee lattice in the she I I- structured cluster of 2 x 10(4) ions is observed.

Dusty plasmas under microgravity Reviewed

H Totsuji, C Totsuji, T Kishimoto, K Tsuruta

NON-NEUTRAL PLASMA PHYSICS IV 606 201 - 206 2002

Language：English Publishing type：Research paper (international conference proceedings) Publisher：AMER INST PHYSICS

The structures of Yukawa systems spherically confined under the condition of micro-gravity are analyzed by molecular dynamics simulations. It is shown that the system is separated into the outer and the inner parts and well-developed shells appear in the outer part at low temperatures. In the case of Yukawa mixtures, there occurs the separation of species according to the magnitude of charges.

Collaborative Simulation Grid: Multiscale Quantum-Mechanical/Classical Atomistic Simulations on Distributed PC Clusters in the US and Japan Reviewed

H. Kikuchi, R. K. Kalia, A. Nakano, P. Vashishta, H. Iyetomi, S. Ogata, T. Kouno, F. Shimojo, K. Tsuruta, S. Saini

Proceedings of the IEEE/ACM Supercomputing (SC) 2002 Conference (IEEE Computer Society, Los Alamitos, CA, 2002) 63 - 70 2002

Structure of finite two-dimensional Yukawa lattices: Dust crystals Reviewed

H Totsuji, C Totsuji, K Tsuruta

PHYSICAL REVIEW E 64 ( 6 ) 2001.12

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER PHYSICAL SOC

Dust particles in plasmas are often confined near the boundary between the plasma bulk and the sheath where the gravitation is balanced by electrostatic force. To keep dust particles from running away horizontally, an electrostatic potential is usually applied to the electrode surrounding these dusty plasmas and, under appropriate conditions. we have finite two-dimensional lattices of dust particles. Modeling the interaction between dust particles as the isotropic Yukawa interaction, structures of finite two-dimensional Yukawa systems at low temperatures have been analyzed both by numerical simulations and variational methods. The effect of the correlation energy between dust particles is shown to play an important role in the formation of the one-body distribution in these systems.

DOI： 10.1103/PhysRevE.64.066402

Parallel tight-binding molecular dynamics for high-temperature neck formation processes of nanocrystalline silicon carbide Reviewed

K Tsuruta, H Totsuji, C Totsuji

MATERIALS TRANSACTIONS 42 ( 11 ) 2261 - 2265 2001.11

Language：English Publishing type：Research paper (scientific journal) Publisher：JAPAN INST METALS

Tight-binding molecular dynamics (TBMD) simulations are performed to investigate atomic and electronic structures during neck formation processes of nanocrystalline silicon carbide at high temperature. For calculating the electronic energy and forces we use a linear-scaling method (the Fermi-operator expansion method) with a scalable parallel algorithm. The TBMD simulations of collision of SiC nanospheres show that processes of neck formation depend strongly on contact angles between the two grains. Electronic populations at grain boundaries are rather uniform, even in a disordered structure of the grain boundary between misaligned nanospheres, Atomic diffusions at elevated temperature are, on the other hand, quite different in the necks formed with different orientations of particles.

Neck formation processes of nanocrystalline silicon carbide: a tight-binding molecular dynamics study Reviewed

K Tsuruta, H Totsuji, C Totsuji

PHILOSOPHICAL MAGAZINE LETTERS 81 ( 5 ) 357 - 366 2001.5

Language：English Publishing type：Research paper (scientific journal) Publisher：TAYLOR & FRANCIS LTD

Atomistic and electronic structures in the process of intergranular neck formation of nanocrystalline silicon carbide (SiC) have been investigated by a tight-binding molecular dynamics method. An order-N parallel algorithm is employed for efficient calculations of electronic energy and forces. We find that a defect-free neck is formed between SIC nanocrystals aligned along [11 (2) over bar] axis at T = 1000 K. In the case of neck formation between tilted nanocrystals (with an orientation equivalent to a {122}, Sigma = 9 grain boundary), surface reconstruction before sintering, that is Si-Si bond formation, significantly affects the grain-boundary formation. The spatial distribution of the electronic population and the electronic density of states show that structural defects, accompanied by gap states, are formed around the reconstructed regions after the sintering.

On the Madelung energy of spherical Coulomb clusters Reviewed

T Kishimoto, C Totsuji, K Tsuruta, H Totsuji

PHYSICS LETTERS A 281 ( 4 ) 256 - 259 2001.3

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

We perform large-scale molecular dynamics (MD) simulations of Coulomb clusters in a spherical trapping field. The fast multipole method have been employed to simulate clusters of up to 5 x 10(4) particles while previous investigations are limited to clusters of less than 5000 particles, It is found that the Madelung energy of bce clusters with reconstructed surfaces is substantially smaller than the extrapolated values based on the previous results for smaller multilayered icosahedral clusters. (C) 2001 Elsevier Science B.V. All rights reserved.

Structure of finite two-dimensional Yukawa lattices: Dust crystals Reviewed

Hiroo Totsuji, Chieko Totsuji, Kenji Tsuruta

Physical Review E - Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics 64 ( 6 ) 7 2001

Language：English Publishing type：Research paper (scientific journal)

Dust particles in plasmas are often confined near the boundary between the plasma bulk and the sheath where the gravitation is balanced by electrostatic force. To keep dust particles from running away horizontally, an electrostatic potential is usually applied to the electrode surrounding these dusty plasmas and, under appropriate conditions, we have finite two-dimensional lattices of dust particles. Modeling the interaction between dust particles as the isotropic Yukawa interaction, structures of finite two-dimensional Yukawa systems at low temperatures have been analyzed both by numerical simulations and variational methods. The effect of the correlation energy between dust particles is shown to play an important role in the formation of the one-body distribution in these systems. © 2001 The American Physical Society.

DOI： 10.1103/PhysRevE.64.066402

Yukawa mixtures with and without gravity Reviewed

H Totsuji, T Kishimoto, C Totsuji, K Tsuruta

PHYSICA SCRIPTA T89 117 - 121 2001

Language：English Publishing type：Research paper (scientific journal) Publisher：ROYAL SWEDISH ACAD SCIENCES

The structures of systems of particles with repulsive Yukawa interactions are analyzed by molecular dynamics simulations with emphasis on the behavior of Yukawa mixtures. To keep the density of particles with mutual repulsion at finite values, we need some confining mechanism and the latter has strong effects on the structure formation. Under the gravity, the confinement is one-dimensional and we have layered structures. In this case, Yukawa mixtures are separated by the difference in the charge to mass ratios. In the case without gravity, we may have three-dimensional confinement and the behavior of the system may be analyzed by assuming spherical symmetry. We show that there also occurs a separation of species according to the magnitude of charges under the condition of no gravity and we have well-organized structures when the temperature is sufficiently low.

Other Link： http://orcid.org/0000-0002-1447-2530

Initial stages of sintering of TiO<inf>2</inf>nanoparticles: Variable-charge molecular dynamics simulations Reviewed

Ogata S, Iyetomi H, Tsuruta K, Shimojo F, Nakano A, Vashishta P, Kalia R.K, Loong C.-K

Materials Research Society Symposium - Proceedings 634 B7.6.1 - B7.6.6 2001

Yukawa Mixtures with and without Gravity

Hiroo Totsuji, Tokunari Kishimoto, Chieko Totsuji, Kenji Tsuruta

Physica Scripta T89 ( 1 ) 117 - 117 2001

A scalable molecular-dynamics algorithm suite for materials simulations: design-space diagram on 1024 Cray T3E processors Reviewed

F Shimojo, TJ Campbell, RK Kalia, A Nakano, P Vashishta, S Ogata, K Tsuruta

FUTURE GENERATION COMPUTER SYSTEMS-THE INTERNATIONAL JOURNAL OF ESCIENCE 17 ( 3 ) 279 - 291 2000.11

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

A suite of scalable molecular-dynamics (MD) algorithms has been developed for materials simulations. The linear scaling MD algorithms encompass a wide spectrum of physical reality: (i) classical MD based on a many-body interatomic potential model; (ii) environment-dependent, variable-charge MD: (iii) quantum mechanical MD based on the tight-binding method; and (iv) self-consistent quantum MD based on the density functional theory. Benchmark tests on 1024 Gray T3E processors including 1.02-billion-atom many-body and 22 500-atom density functional MD simulations demonstrate that these algorithms are highly scalable. A design-space diagram spanning seven decades of system size and computational time is constructed for materials scientists to design an optimal MD simulation incorporating maximal physical realism within a given computational budget. (C) 2000 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0167-739X(00)00087-X

Other Link： http://orcid.org/0000-0002-1447-2530

Role of atomic charge transfer on sintering of TiO2 nanoparticles: Variable-charge molecular dynamics Reviewed

S Ogata, H Iyetomi, K Tsuruta, F Shimojo, A Nakano, RK Kalia, P Vashishta

JOURNAL OF APPLIED PHYSICS 88 ( 10 ) 6011 - 6015 2000.11

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER INST PHYSICS

The stability of surface structure and space-charge distribution in free TiO2 nanoparticles are investigated for both rutile and anatase phases using a variable-charge interaction potential in which atomic charges vary dynamically depending on their environment. We find the dynamic charge transfer: (i) enhances atomic diffusion at surfaces of the spherical nanoparticles at high temperatures; and (ii) creates additional repulsive force between the two nanospheres through formation of a double-charge surface layer in each nanosphere. The surface diffusion due to the charge transfer clearly distinguishes the two nanospheres with different underlying crystalline structures; the surface diffusion constant of the anatase sphere is almost three times as great as that of the rutile sphere. Variable-charge molecular dynamics simulations are then applied to sintering of two TiO2 nanospheres. It turns out that the enhanced surface diffusion in the anatase nanosphere at high temperatures significantly promotes neck formation between the two spheres. (C) 2000 American Institute of Physics. [S0021-8979(00)08323-7].

DOI： 10.1063/1.1321785

Other Link： http://orcid.org/0000-0002-1447-2530

Sintering, structure, and mechanical properties of nanophase SiC: A molecular-dynamics and neutron scattering study Reviewed

A Chatterjee, RK Kalia, A Nakano, A Omeltchenko, K Tsuruta, P Vashishta, CK Loong, M Winterer, S Klein

APPLIED PHYSICS LETTERS 77 ( 8 ) 1132 - 1134 2000.8

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER INST PHYSICS

Structure, mechanical properties, and sintering of nanostructured SiC (n-SiC) are investigated with neutron scattering and molecular-dynamics (MD) techniques. Both MD and the experiment indicate the onset of sintering around 1500 K. During sintering, the pores shrink while maintaining their morphology: the fractal dimension is similar to 2 and the surface roughness exponent is similar to 0.45. Structural analyses reveal that interfacial regions in n-SiC are disordered with nearly the same number of three- and fourfold coordinated Si atoms. The elastic moduli scale with the density as similar to rho(mu), where mu=3.4 +/- 0.1. (C) 2000 American Institute of Physics. [S0003-6951(00)04334-5].

Strongly coupled nonneutral plasmas: Equilibrium and relaxation in two-component plasmas in Penning-Malmberg trap Reviewed

H Totsuji, K Tsuruta, C Totsuji, K Nakano, T Kishimoto, K Kamon

JOURNAL DE PHYSIQUE IV 10 ( P5 ) 271 - 274 2000.3

Language：English Publishing type：Research paper (scientific journal) Publisher：E D P SCIENCES

The relaxation processes and the equilibrium distribution of two-component nonneutral plasmas in the Penning-Malmberg trap are analyzed by molecular dynamics simulations and theoretical approaches. As an example, mixtures of antiprotons and electrons for antiproton cooling experiments are considered. The relaxation of antiproton energy is calculated based on the rate equations and it is shown that the slow energy transfer between parallel and perpendicular components of strongly magnetized electrons does not affect the whole relaxation process seriously. The equilibrium distribution of each species are obtained by extensive molecular dynamics simulations for various values of parameters and the results are reproduced by theoretical calculations to a good accuracy. The condition for the centrifugal separation is obtained.

DOI： 10.1051/jp4:2000549

Large scale quantum simulations of strongly coupled plasmas on a PC cluster Reviewed

H Totsuji, K Tsuruta, C Totsuji

JOURNAL DE PHYSIQUE IV 10 ( P5 ) 267 - 270 2000.3

Language：English Publishing type：Research paper (scientific journal) Publisher：E D P SCIENCES

As a method of quantum simulation for large systems with surfaces and inhomogenieties, the density functional molecular dynamics is applied to the hydrogen plasma in the domain of liquid metallic hydrogen and the performance of a PC cluster is measured. Usefulness of relatively small scale PC cluter is shown even without much efforts in tuning the programs for parallel computation.

Other Link： http://orcid.org/0000-0002-1447-2530

Structure and dynamics of Yukawa dusty plasmas and dusty plasma mixtures Reviewed

C. Totsuji, H. Totsuji, K. Tsuruta, K. Kamon, T. Kishimoto, T. Sasabe

Le Journal de Physique IV 10 ( PR5 ) Pr5 - 425 2000.3

Structures and structural transitions in strongly-coupled Yukawa dusty plasmas and mixtures Reviewed

H Totsuji, C Totsuji, K Tsuruta

FRONTIERS IN DUSTY PLASMAS 141 - 146 2000

Language：English Publishing type：Research paper (international conference proceedings) Publisher：ELSEVIER SCIENCE BV

Regarded as Yukawa systems in external confining potentials, structures and transitions in dusty plasmas have been analyzed theoretically and by numerical simulations. The one-dimensional confinement in three dimensions and the radial confinement in two dimensions are considered. The results of simulations have been reproduced to a good accuracy in both cases. It is shown that the inclusion of the correlation energy or the effect of strong coupling is of essential importance in the theory. A crossover from the surface freezing of Coulomb system to surface melting of systems of short-ranged interactions is observed.

Intercluster interaction of TiO2 nanoclusters using variable-charge interatomic potentials Reviewed

S Ogata, H Iyetomi, K Tsuruta, F Shimojo, RK Kalia, A Nakano, P Vashishta

NANOPHASE AND NANOCOMPOSITE MATERIALS III 581 667 - 672 2000

Language：English Publishing type：Research paper (international conference proceedings) Publisher：MATERIALS RESEARCH SOCIETY

A new interatomic potential has been developed for molecular-dynamics simulations of TiO2 based on the formalism of Streitz and Mintmire [J. Adhesion Sci. Technol. 8, 853 (1994)], in which atomic charges vary dynamically according to the generalized electronegativity-equalization principle. The present potential reproduces various quantities of rutile crystal including vibrational density of states, static dielectric constants, melting temperature, elastic moduli, and surface relaxation. Calculated cohesive-energy and dielectric constants for anatase crystal agree well with experimental data The potential is applied to TiO2 nanoclusters (size 60-80 Angstrom) for both anatase and rutile phases to analyze their equilibrium configuration and space-charge distribution. Stable double-charge layer is found in the surface region of a spherical nanocluster for both rutile and anatase, resulting in enhanced Coulomb-repulsion between the nanoclusters at close proximity.

Other Link： http://orcid.org/0000-0002-1447-2530

Variable-charge interatomic potentials for molecular-dynamics simulations of TiO2 Reviewed

S Ogata, H Iyetomi, K Tsuruta, F Shimojo, RK Kalia, A Nakano, P Vashishta

JOURNAL OF APPLIED PHYSICS 86 ( 6 ) 3036 - 3041 1999.9

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER INST PHYSICS

An interatomic potential model has been developed for molecular-dynamics simulations of TiO2 (rutile) based on the formalism of Streitz and Mintmire [J. Adhes. Sci. Technol. 8, 853 (1994)], in which atomic charges vary dynamically according to the generalized electronegativity equalization principle. The present model potential reproduces the vibrational density of states, the pressure-dependent static dielectric constants, the melting temperature, and the surface relaxation of the rutile crystal, as well as the cohesive energy, the lattice constants, and the elastic moduli. We find the physical properties of rutile are significantly affected by dynamic charge transfer between Ti and O atoms. The potential allows us to perform atomistic simulations on nanostructured TiO2 with various kinds of interfaces (surfaces, grain boundaries, dislocations, etc.). (C) 1999 American Institute of Physics. [S0021-8979(99)07618-5].

DOI： 10.1063/1.371165

Other Link： http://orcid.org/0000-0002-1447-2530

Parallel molecular dynamics simulations of high temperature ceramics Reviewed

A Chatterjee, T Campbell, RK Kalia, A Nakano, A Omeltchenko, K Tsuruta, P Vashishta, S Ogata

JOURNAL OF THE EUROPEAN CERAMIC SOCIETY 19 ( 13-14 ) 2257 - 2264 1999

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCI LTD

'Grand Challenge' atomistic simulations of high-temperature structural materials ave performed on multiple, parallel platforms. The simulations focus on sintering of ceramic nanoclusters, structure and mechanical properties of nanophase ceramics, and hypervelocity impact damage in diamond coatings. (C) 1999 Elsevier Science Ltd. All rights reserved.

Structures and dynamics of dusty plasmas and dusty plasma mixtures Reviewed

H Totsuji, C Totsuji, K Tsuruta, K Kamon, T Kishimoto, T Sasabe

NON-NEUTRAL PLASMA PHYSICS III 498 389 - 394 1999

Language：English Publishing type：Research paper (international conference proceedings) Publisher：AMER INST PHYSICS

Dusty plasmas can be regarded as assemblies of Yukawa particles in a one-dimensional potential well. We extend the analyses on dusty plasmas in two directions: the two-dimensional Yukawa system and Yukawa mixtures. (1) Under appropriate conditions at low temperatures, dust particles sit in a plane which is perpendicular to the gravitational field. When they are also confined laterally by an electrode, we have a finite two-dimensional system of Yukawa particles. The low temperature structures are obtained by molecular dynamics simulations and the results are reproduced by theoretical analyses. Through these analyses we show that the correlation energy of the Yukawa system plays an essential role in structure formations. As for dynamics of this system, a crossover from the surface freezing of Coulomb system to surface melting of systems of short-ranged interactions is observed. (2) In the case of mixtures, we have an extra parameter characterizing the difference in the gravity on each species. We obtain the low temperature structures of this system and compare them with theoretical predictions based on the results for the case of one component.

Two-component nonequilibrium nonneutral plasma in Penning-Malmberg trap Reviewed

H Totsuji, K Tsuruta, C Totsuji, K Nakano, K Kamon, T Kishimoto

NON-NEUTRAL PLASMA PHYSICS III 498 77 - 82 1999

Language：English Publishing type：Research paper (international conference proceedings) Publisher：AMER INST PHYSICS

The behavior of the two-component nonneutral plasma in the Penning Malmberg trap is analyzed by simulations and theoretical approaches. The parameters expected in experiments of antiproton cooling by electrons are assumed. The relaxation of antiproton energy is followed by the rate equation with proper account taken into account for the slow transfer of energy between parallel and perpendicular components of strongly magnetized electrons. The equilibrium distribution of each species are obtained by molecular dynamics simulations for various Values of parameters and the results are reproduced by theoretical calculations to a good accuracy. The condition for the centrifugal separation is obtained.

Structural correlations and mechanical behavior in nanophase silica glasses Reviewed

T. J. Campbell, R. K. Kalia, A. Nakano, F. Shimojo, K. Tsuruta, P. Vashishta, S. Ogata

Physical Review Letters 82 ( 20 ) 4018 - 4021 1999

Structure and dynamics of consolidation and fracture in nanophase ceramics via parallel molecular dynamics Reviewed

K Tsuruta, JH Wang, A Omeltchenko, A Nakano, RK Kalia, P Vashishta

COMPUTER-AIDED DESIGN OF HIGH-TEMPERATURE MATERIALS 323 - 332 1999

Structural correlations and stress distribution at silicon/silicon nitride interface Reviewed

ME Bachlechner, A Omeltchenko, K Tsuruta, A Nakano, RK Kalia, P Vashishta, Ebbsjo, I, A Madhukar

COMPUTER-AIDED DESIGN OF HIGH-TEMPERATURE MATERIALS 244 - 255 1999

Dynamic fracture in nanophase ceramics and diamond films: Multimillion atom parallel molecular-dynamics simulations Reviewed

A Omeltchenko, K Tsuruta, A Nakano, R Kalia, P Vashishta, O Shenderova, DW Brenner

COMPUTER-AIDED DESIGN OF HIGH-TEMPERATURE MATERIALS 81 - 104 1999

Atomistic simulation of nanostructured materials Reviewed

A Nakano, ME Bachlechner, TJ Campbell, RK Kalla, A Omeltchenko, K Tsuruta, P Vashishta, S Ogata, Ebbsjo, I, A Madhukar

IEEE COMPUTATIONAL SCIENCE & ENGINEERING 5 ( 4 ) 68 - 78 1998.10

Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE COMPUTER SOC

Materials and devices with microstructures on the nanometer scale are revolutionizing technology, but until recently simulation at this scale has bean problematic. Developments in parallel computing are now allowing atomistic simulation using multiresolution algorithms, such as fast multipole methods. With these algorithms, researchers may soon be able to simulate applications up to one billion atoms.

DOI： 10.1109/99.735897

Dynamics of consolidation and crack growth in nanocluster-assembled amorphous silicon nitride Reviewed

K Tsuruta, A Nakano, RK Kalia, P Vashishta

JOURNAL OF THE AMERICAN CERAMIC SOCIETY 81 ( 2 ) 433 - 436 1998.2

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER CERAMIC SOC

Consolidation and fracture dynamics in nanophase amorphous Si3N4 are investigated using 10(6)-atom molecular-dynamics simulations. At a pressure of 15 GPa and 2000 K, the nanophase system is almost fully consolidated within a fraction of a nanosecond. The consolidation process is well-described by the classical theory of sintering. Under an applied strain the consolidated system develops several cracks which propagate parallel to each other, causing failure at multiple sites. The critical strain at which the nanophase system fractures is much larger than that for crystalline Si3N4.

Oxidation dynamics of nanophase aluminum clusters: A molecular dynamics study Reviewed

S Ogata, TJ Campbell, K Tsuruta, A Nakano, RK Kalia, P Vashishta, CK Loong

PHASE TRANSFORMATIONS AND SYSTEMS DRIVEN FAR FROM EQUILIBRIUM 481 625 - 630 1998

Language：English Publishing type：Research paper (international conference proceedings) Publisher：MATERIALS RESEARCH SOCIETY

Oxidation of an aluminum nanocluster (252,158 atoms) of radius 100 Angstrom placed in gaseous oxygen (530,727 atoms) is investigated by performing molecular-dynamics simulations on parallel computers. The simulation takes into account the effect of charge transfer between Al and O based on the electronegativity equalization principles. We find that the oxidation starts at the surface of the cluster and the oxide layer grows to a thickness of similar to 28 Angstrom. Evolutions of local temperature and densities of Al and O are investigated. The surface oxide melts because of the high temperature resulting from the release of energy associated with Al-O bondings. Amorphous surface-oxides are obtained by quenching the cluster. Vibrational density-of-states for the surface oxide is analyzed through comparisons with those for crystalline Al, Al nanocluster, and alpha-Al2O3.

Other Link： http://orcid.org/0000-0002-1447-2530

Role of ultrafine microstructures in dynamic fracture in nanophase silicon nitride Reviewed

RK Kalia, A Nakano, A Omeltchenko, K Tsuruta, P Vashishta

PHYSICAL REVIEW LETTERS 78 ( 11 ) 2144 - 2147 1997.3

Language：English Publishing type：Research paper (scientific journal) Publisher：AMERICAN PHYSICAL SOC

Using 10(6)-atom molecular-dynamics simulations, we investigate dynamic fracture in nanophase Si3N4. The simulations reveal that intercluster regions are amorphous, and they deflect cracks and give rise to local crack branching. As a result, the nanophase system is able to sustain an order-of-magnitude larger external strain than crystalline Si3N4. We also determine the morphology of fracture surfaces: For in-plane fracture surface profiles the roughness exponent zeta = 0.57 and for out-of-plane profiles the exponents zeta(perpendicular to) = 0.84 and zeta(parallel to) = 0.75 are in excellent agreement with experiments.

Morphology of pores and interfaces and mechanical behavior of nanocluster-assembled silicon nitride ceramic Reviewed

RK Kalia, A Nakano, K Tsuruta, P Vashishta

PHYSICAL REVIEW LETTERS 78 ( 4 ) 689 - 692 1997.1

Language：English Publishing type：Research paper (scientific journal) Publisher：AMERICAN PHYSICAL SOC

Million atom molecular-dynamics simulations are performed to investigate the structure, dynamics, and mechanical behavior of cluster-assembled Si3N4. These solids contain highly disordered interfacial regions with 50% undercoordinated atoms. Systems sintered at low pressures have percolating pores whose surface morphologies are well characterized by two values of the roughness exponent, 0.46 and 0.86; these are close to the experimental values found by Bouchaud et al. for fracture surfaces. Results for elastic moduli are consistent with a three-phase model for heterogeneous materials.

Structure, mechanical properties, and dynamic fracture in nanophase silicon nitride via parallel molecular dynamics Reviewed

K Tsuruta, A Omeltchenko, A Nakano, RK Kalia, P Vashishta

NANOPHASE AND NANOCOMPOSITE MATERIALS II 457 205 - 210 1997

Language：English Publishing type：Research paper (international conference proceedings) Publisher：MATERIALS RESEARCH SOCIETY

Million-atom molecular-dynamics (MD) simulations are performed to study the structure, mechanical properties, and dynamic fracture in nanophase Si3N4. We find that intercluster regions are highly disordered: 50% of Si atoms in intercluster regions are three-fold coordinated. Elastic moduli of nanophase Si3N4 as a function of grain size and porosity are well described by a multiphase model for heterogeneous materials. The study of fracture in the nanophase Si3N4 reveals that the system can sustain an order-of-magnitude larger external load than crystalline Si3N4. This is due to branching and pinning of the crack front by nanoscale microstructures.

Other Link： http://orcid.org/0000-0002-1447-2530

Million atom molecular dynamics simulation of nanophase silicon nitride Reviewed

RK Kalia, A Nakano, A Omeltchenko, K Tsuruta, P Vashishta

CHEMISTRY AND PHYSICS OF NANOSTRUCTURES AND RELATED NON-EQUILIBRIUM MATERIALS 89 - 96 1997

Language：English Publishing type：Research paper (international conference proceedings) Publisher：MINERALS, METALS & MATERIALS SOC

Structural correlations and dynamic fracture in nanocluster-assembled silicon nitride are investigated with molecular-dynamics (MD) simulations involving 1.08 million particles. These simulations reveal that the consolidated nanophase Si3N4 has highly disordered intercluster regions that contain 50% under-coordinated atoms. Amorphous interfacial regions deflect cracks and give rise to local crack branching. These dissipative mechanisms enable the nanophase system to sustain an order-of-magnitude larger external strain than crystalline Si3N4. The morphology of fracture surfaces in nanophase Si3N4 is also determined. The MD results for roughness exponents are very close to experimental values even though the materials and length scales are very different.

Other Link： http://orcid.org/0000-0002-1447-2530

Fracture of nanophase ceramics: A molecular-dynamics study Reviewed

A Nakano, RK Kalia, A Omeltchenko, K Tsuruta, P Vashishta

NANOPHASE AND NANOCOMPOSITE MATERIALS II 457 187 - 192 1997

Language：English Publishing type：Research paper (international conference proceedings) Publisher：MATERIALS RESEARCH SOCIETY

New multiscale algorithms and a load-balancing scheme are combined for molecular-dynamics simulations of nanocluster-assembled ceramics on parallel computers. Million-atom simulations of the dynamic fracture in nanophase silicon nitride reveal anisotropic self-affine structures and crossover phenomena associated with fracture surfaces.

Other Link： http://orcid.org/0000-0002-1447-2530

Million atom molecular dynamics simulations of materials on parallel computers Reviewed

P Vashishta, RK Kalia, W Li, A Nakano, A Omeltchenko, K Tsuruta, JH Wang, Ebbsjo, I

CURRENT OPINION IN SOLID STATE & MATERIALS SCIENCE 1 ( 6 ) 853 - 863 1996.12

Language：English Publisher：CURRENT SCIENCE LTD

Recent advances in computing technology - parallel computer architectures, portable software and development of robust O(N) algorithms - have revolutionized the field of computer simulation. Using the space-time multiresolution molecular dynamics algorithms it is possible to carry out multimillion atom simulations of materials in different ranges of density, temperature and uniaxial strain.

DOI： 10.1016/S1359-0286(96)80113-6

Early stages of sintering of silicon nitride nanoclusters: A molecular-dynamics study on parallel machines Reviewed

K Tsuruta, A Omeltchenko, RK Kalia, P Vashishta

EUROPHYSICS LETTERS 33 ( 6 ) 441 - 446 1996.2

Language：English Publishing type：Research paper (scientific journal) Publisher：EDITIONS PHYSIQUE

Sintering of Si3N4 nanoclusters is investigated With the molecular-dynamics approach. At 2000 K thermally rough nanocrystals develop an asymmetric neck in 100 picoseconds. The neck contains more fourfold than threefold coordinated Si atoms, Amorphous nanoclusters develop a symmetric neck which has nearly equal number of threefold and fourfold coordinated Si atoms. In both cases, sintering is driven by surface diffusion of Si and N atoms. The diffusion is much more rapid in the neck joining amorphous nanoclusters than in the neck region of nanocrystals.

DOI： 10.1209/epl/i1996-00359-2

Early stages of sintering of Si3N4 nanoclusters via parallel molecular dynamics Reviewed

K Tsuruta, A Omeltchenko, RK Kalia, P Vashishta

MATERIALS THEORY, SIMULATIONS, AND PARALLEL ALGORITHMS 408 181 - 186 1996

Sintering of amorphous Si3N4 nanoclusters: A molecular dynamics study of stress analysis Reviewed

JH Wang, K Tsuruta, A Omeltchenko, RK Kalia, P Vashishta

MATERIALS THEORY, SIMULATIONS, AND PARALLEL ALGORITHMS 408 573 - 578 1996

Dense plasma as a statistical ensemble of Coulomb clusters: A new paradigm Reviewed

K TSURUTA, S ICHIMARU

NON-NEUTRAL PLASMA PHYSICS II ( 331 ) 252 - 261 1995

Erratum: Short-range screening potentials for classical Coulomb fluids: Monte Carlo sampling and cluster model studies (Physical Review E (1995) 51, 4, (3788)) Reviewed

Ichimaru S, Ogata S, Tsuruta K

Physical Review E 51 ( 4 ) 3788 - 3788 1995

SHORT-RANGE SCREENING POTENTIALS FOR CLASSICAL COULOMB FLUIDS - MONTE-CARLO SAMPLING AND CLUSTER MODEL STUDIES Reviewed

S ICHIMARU, S OGATA, K TSURUTA

PHYSICAL REVIEW E 50 ( 4 ) 2977 - 2985 1994.10

Language：English Publishing type：Research paper (scientific journal) Publisher：AMERICAN PHYSICAL SOC

Screening potential, the balance between the bare Coulomb repulsion and the potential of mean force in a charged liquid, plays an essential role in the theoretical estimation of enhancement for the nuclear reaction rates in dense stellar matter. For the accurate assessment of the screening potential at short interparticle separations, we revisit the first-principles calculations for the coefficients of the Widom expansion and undertake extra-long Monte Carlo samplings in specifically designed binary-ionic systems. The results are compared with those obtained from an approximate estimation based on extrapolation from intermediate distances. We also present model calculations of the screening potential with two-ion clusters, which shed light on the relation between the short- and intermediate-range behaviors.

BINDING-ENERGY, MICROSTRUCTURE, AND SHELL-MODEL OF COULOMB CLUSTERS Reviewed

K TSURUTA, S ICHIMARU

PHYSICAL REVIEW A 48 ( 2 ) 1339 - 1344 1993.8

Language：English Publishing type：Research paper (scientific journal) Publisher：AMERICAN PHYSICAL SOC

By computer-simulation and analytic studies for binding energies and microscopic shell structures, it is shown that Coulomb clusters assume particularly stable configurations at certain ''magic numbers'' of particles. Through analyses with the spherical Voronoi numbers, a special role that the icosahedral geometry plays in shaping the particle configurations on the spherical surfaces is elucidated. Gross features in the cluster structures, such as the shell radii and intershell partition of particles, are well accounted for by an appropriate shell model.

DOI： 10.1103/PhysRevA.48.1339

Collisional equipartition rate for a magnetized pure electron plasma Reviewed

Michael E. Glinsky, Thomas M. O'Neil, Marshall N. Rosenbluth, Kenji Tsuruta, Setsuo Ichimaru

Physics of Fluids B 4 ( 5 ) 1156 - 1166 1992

Language：English Publishing type：Research paper (scientific journal)

The collisional equipartition rate between the parallel and perpendicular velocity components is calculated for a weakly correlated electron plasma that is immersed in a uniform magnetic field. Here, parallel and perpendicular refer to the direction of the magnetic field. The rate depends on the parameter κ̄ = (b̄/rc)/√2, where rc = √T/m/Ωc is the cyclotron radius and b̄ = 2e 2/T is twice the distance of closest approach. For a strongly magnetized plasma (i.e., κ̄ ≫ 1), the equipartition rate is exponentially small (v∼exp[ -5(3πκ̄)2/5/6]). For a weakly magnetized plasma (i.e., κ̄ ≪ 1), the rate is the same as for an unmagnetized plasma except that rc/b̄ replaces λD/b̄ in the Coulomb logarithm. (It is assumed here that rc &lt
λD
for rc &gt
λD, the plasma is effectively unmagnetized.) This paper contains a numerical treatment that spans the intermediate regime κ̄∼1, and connects onto asymptotic results in the two limits κ̄ ≪ 1 and κ̄ ≫ 1. Also, an improved asymptotic expression for the rate in the high-field limit is derived. The present theoretical results are in good agreement with recent measurements of the equipartition rate over eight decades in κ̄ and four decades in the scaled rate v/nv̄b̄2, where n is the electron density and v̄ = √2T/m. © 1992 American Institute of Physics.

DOI： 10.1063/1.860124

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