Faculty Profiles - TSURUTA Kenji

Papers - TSURUTA Kenji

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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

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