arXiv subjects

Satoshi Ishii

Publications and source records attributed to Satoshi Ishii.

14 recordsLinked to original sources

arXiv2024

Metasurface-Enabled Multifunctional Single-Frequency Sensors without External Power

IoT sensors are crucial for visualizing multidimensional and multimodal information and enabling future IT applications/services such as cyber-physical space, digital twins, autonomous driving, smart cities, and virtual/augmented reality (VR or AR). However, IoT sensors need to be battery-free to realistically manage and maintain the growing number of available sensing devices. Here, we provide a novel sensor design approach that employs metasurfaces to enable multifunctional sensing without requiring an external power source. Importantly, unlike existing metasurface-based sensors, our metasurfaces can sense multiple physical parameters even at a fixed frequency by breaking classic harmonic oscillations in the time domain, making the proposed sensors viable for usage with limited frequency resources. Moreover, we provide a method for predicting physical parameters using the machine learning-based approach of random forest regression. The sensing performance was confirmed by estimating temperature and light intensity, and excellent determination coefficients larger than 0.96 were achieved. Our study affords new opportunities for sensing multiple physical properties without relying on an external power source or needing multiple frequencies, which markedly simplifies and facilitates the design of next-generation wireless communication systems.

eess.SP↗

arXiv2023

Transmission ERDA of ubiquitous deuterium in H-containing materials

Transmission-type elastic recoil detection analysis (T-ERDA) using 8.02 MeV He has been successfully applied to determine the concentration of ubiquitous deuterium in mylar and PPS films, both containing hydrogen as a component. The determined D/H ratios of $(1.60\pm 0.08) \times 10^{-4}$ and $(1.23\pm 0.08) \times 10^{-4}$ for mylar and PPS, respectively, are only slightly deviated from the Standard Mean Ocean Water value of $1.55\cdots \times 10^{-4}$. These results indicate potential sensitivity of T-ERDA for analysis of the variation of ubiquitous deuterium in hydrogen-containing materials. Such deuterium analysis might be useful for unique characterization of not only natural, but also synthesized hydrogen-containing materials.

cond-mat.mtrl-sci↗

arXiv2022

Determination of hydrogen concentration in solids by transmission ERDA under nuclear-elastically enhanced recoiling of H by 8 and 9 MeV He

Hydrogen concentrations in thin self-supporting samples of polyphenylene sulfide and muscovite have been determined by nuclear-elastic recoil detection analysis of transmission layout. The analysis procedure is based only on the database of stopping power and recoil cross section for material analysis, without using any reference sample of known H content. For the polyphenylene sulfide sample, the determined value of $(2.87\pm 0.26)\times 10^{22}\,{\rm H}/$cm$^{3}$ is in good agreement with the calculated value of $3.01 \times 10^{22}\,{\rm H}/$cm$^{3}$. For the muscovite sample, the H concentration originating each from bound water and absorbed water is uniform over the entire thickness of the sample. The determined concentration $(9.43 \pm 0.75) \times 10^{21}$ H$/$cm$^{3}$ of the muscovite agrees excellently with the value of $9.36 \times 10^{21}$ H$/$cm$^{3}$ obtained from other quantitative analyses typically applied for minerals. The present results demonstrate the capability of accurate determination of H contents in materials and minerals by transmission ERDA.

cond-mat.mtrl-sci↗

arXiv2019

An On-Chip Quad-Wavelength Pyroelectric Sensor for Spectroscopic Infrared Sensing

Merging photonic structures and optoelectronic sensors into a single chip may yield a sensor-on-chip spectroscopic device that can measure the spectrum of matters. In this work, we propose and realize an on-chip concurrent multi-wavelength infrared (IR) sensor. The fabricated quad-wavelength IR sensors exhibit four different narrowband spectral responses at normal incidence following the pre-designed resonances in the mid-wavelength infrared region that corresponds to the atmospheric window. The device can be applied for practical spectroscopic applications such as non-dispersive IR sensors, IR chemical imaging devices, pyrometers, and spectroscopic thermography imaging.

physics.app-ph↗

arXiv2018

Inversion-induced orbital and exchange disorders in antiferromagnetic A-site spinel CoAl2O4

The inversion and volume effects on magnetism in a spinel-type magnetically frustrated compound, CoAl2O4, and its gallium-substituted system, CoAl2-xGaxO4, were investigated. Magnetically frustrated Co2+ with spin S = 3/2 on the tetrahedral site formed a diamond lattice in CoAl2O4 located in the vicinity of the magnetic phase boundary between Neel and spin-spiral states. In the Ga-substituted system, the number of Co ions, the so-called inversion h dominating the octahedral site, increased with increasing x. From comprehensive crystallographic, magnetic, and thermal measurements, increments of both volume and inversion strongly reduced the Neel point, while the latter also induced a spin-glass state above the critical value of hc = 0.09. In the spin glass state, h > hc, the orbital degree of freedom of Co2+ ions in the octahedral site appeared in the magnetic entropy, which couples strongly with that of spin, even above the magnetic transitions. Above h ~ hc, the field-induced quenched magnetic moment appeared above the transitions. Therefore, a short range ordered state emerged among the paramagnetic, antiferromganetic, and spin-glass states in the magnetic phase diagram.

cond-mat.str-el↗

arXiv2015

Examining the performance of refractory conductive ceramics as plasmonic materials: a theoretical approach

The main aim of this study is to scrutinize promising plasmonic materials by understanding their electronic structure and correlating them to the optical properties of selected refractory materials. For this purpose, the electronic and optical properties of the conductive ceramics TiC, ZrC, HfC, TaC, WC, TiN, ZrN, HfN, TaN, and WN are studied systematically by means of first-principles density functional theory. A full ab initio procedure to calculate plasma frequency from the electronic band structure is discussed. The dielectric functions are calculated by including electronic interband and intraband transitions. Our calculations confirm that transition metal nitrides, such as TiN, ZrN, and HfN, are the strongest candidates, exhibiting performance comparable to that of conventional noble metals in the visible to the near-infrared regions. On the other hand, carbides are not suitable for plasmonic applications because they show very large losses in the same regions. From our calculated dielectric functions, the scattering and absorption efficiencies of nanoparticles made of these refractory materials are evaluated. It is revealed that TiN and TaC are the best candidate materials for applications in photothermal energy conversion over a broad spectral region. Furthermore, quality factors for localized surface plasmon resonance and surface plasmon polaritons are calculated to compare quantitative performances, and ZrN and HfN are found to be comparable to conventional plasmonic metals such as silver and gold

physics.comp-ph↗

arXiv2015

Band engineering of ternary metal nitride system Ti1-x ZrxN for plasmonic applications

Chemical composition is the primary factor that determines the electronic band structure and thus also influences the optical properties of plasmonic ceramics including nitrides and oxides. In this work, the optical and plasmonic properties of TiN, ZrN and their hypothetical intermediate alloys Ti1-xZrxN (x= 0, 0.25, 0.50, 0.75, and 1), are studied by using first-principles density functional theory. We demonstrate the effects of electronic band structure tuning (band engineering) on the dielectric properties by varying the concentration of metallic constituents. Our calculations reveal that bulk plasma frequency, onset of interband transitions, width of bulk plasmon resonance and cross-over frequency, can be tuned flexibly in visible spectrum region by varying the amount of Zr concentration in Ti1-xZrxN alloy system. We found that low threshold interband energy onset (~1.95 eV) leads to high losses in Ti rich compounds than that of ZrN which points to lower losses.

physics.comp-ph↗

arXiv2015

Multistage ordering and critical singularities in Co1-xZnxAl2O4 (0 < x < 1):Dilution and pressure effects in a magnetically frustrated system

We report comprehensive studies of the crystallographic,magnetic, and thermal properties of a spinel-type magnetically frustrated compound, CoAl2O4, and a magnetically diluted system,Co1-xZnxAl2O4. These studies revealed the effects of dilution and disorder when the tetrahedral magnetic Co ion was replaced by the nonmagnetic Zn ion. Low-temperature anomalies were observed in magnetic susceptibility at x < 0.6. A multicritical point was apparent at T = 3.4 K and x = 0.12, where the antiferromagnetic, spin glass-like, and paramagnetic phases met. At that point, the quenched ferromagnetic component induced by a magnetic field during cooling was sharply enhanced and was observable below x = 0.6. Around x = 0.6, magnetic susceptibility and specific heat were described by temperature power laws, chi ~ C/T ~ T-d, in accord with the site percolation threshold of the diamond lattice. This behavior is reminiscent of a quantum critical singularity. We propose an x-temperature phase diagram in the range 0 < x < 1 for Co1-xZnxAl2O4. The transition temperature of CoAl2O4 determined from magnetic susceptibility measured under hydrostatic pressure increased with increasing pressure.

cond-mat.str-el↗

arXiv2014

Unidirectional light propagation through two-layer nanostructures based on optical near-field interactions

We theoretically demonstrate direction-dependent polarization conversion efficiency, yielding unidirectional light transmission, through a two-layer nanostructure by using the angular spectrum representation of optical near-fields. The theory provides results that are consistent with electromagnetic numerical simulations. This study reveals that optical near-field interactions among nanostructured matter can provide unique optical properties, such as the unidirectionality observed here, and offers fundamental guiding principles for understanding and engineering nanostructures for realizing novel functionalities.

physics.optics↗

arXiv2014

Plasmonic waveguides with hyperbolic multilayer cladding

Engineering plasmonic metamaterials with anisotropic optical dispersion enables us to tailor the properties of metamaterial-based waveguides. We investigate plasmonic waveguides with dielectric cores and multilayer metal-dielectric claddings with hyperbolic dispersion. Without using any homogenization, we calculate the resonant eigenmodes of the finite-width cladding layers, and find agreement with the resonant features in the dispersion of the cladded waveguides. We show that at the resonant widths, the propagating modes of the waveguides are coupled to the cladding eigenmodes and hence, are strongly absorbed. By avoiding the resonant widths in the design of the actual waveguides, the strong absorption can be eliminated.

physics.optics↗

arXiv2014

Plasmonic waveguides cladded by hyperbolic metamaterials

Strongly anisotropic media with hyperbolic dispersion can be used for claddings of plasmonic waveguides. In order to analyze the fundamental properties of such waveguides, we analytically study 1D waveguides arranged of a hyperbolic metamaterial (HMM) in a HMM-Insulator-HMM (HIH) structure. We show that hyperbolic metamaterial claddings give flexibility in designing the properties of HIH waveguides. Our comparative study on 1D plasmonic waveguides reveals that HIH-type waveguides can have a higher performance than MIM or IMI waveguides.

physics.optics↗

arXiv2011

Fabrication of submicron La$_{2-x}$Sr$_{x}$CuO$_{4}$ intrinsic Josephson junction stacks

Intrinsic Josephson junction (IJJ) stacks of cuprate superconductors have potential to be implemented as intrinsic phase qubits working at relatively high temperatures. We report success in fabricating submicron La$_{2-x}$Sr$_{x}$CuO$_{4}$ (LSCO) IJJ stacks carved out of single crystals. We also show a new fabrication method in which argon ion etching is performed after focused ion beam etching. As a result, we obtained an LSCO IJJ stack in which resistive multi-branches appeared. It may be possible to control the number of stacked IJJs with an accuracy of a single IJJ by developing this method.

cond-mat.supr-con↗

arXiv2010

Searching for Better Plasmonic Materials

Plasmonics is a research area merging the fields of optics and nanoelectronics by confining light with relatively large free-space wavelength to the nanometer scale - thereby enabling a family of novel devices. Current plasmonic devices at telecommunication and optical frequencies face significant challenges due to losses encountered in the constituent plasmonic materials. These large losses seriously limit the practicality of these metals for many novel applications. This paper provides an overview of alternative plasmonic materials along with motivation for each material choice and important aspects of fabrication. A comparative study of various materials including metals, metal alloys and heavily doped semiconductors is presented. The performance of each material is evaluated based on quality factors defined for each class of plasmonic devices. Most importantly, this paper outlines an approach for realizing optimal plasmonic material properties for specific frequencies and applications, thereby providing a reference for those searching for better plasmonic materials.

physics.optics↗

arXiv2008

Resistivity reduction of boron-doped multi-walled carbon nanotubes synthesized from a methanol solution containing a boric acid

Boron-doped multi-walled carbon nanotubes (MWNTs) were synthesized using a methanol solution of boric acid as a source material. Accurate measurements of the electrical resistivity of an individual boron-doped MWNT was performed with a four-point contact, which was fabricated using an electron beam lithography technique. The doped boron provides conduction carriers, which reduces the resistivity of the MWNT.

cond-mat.mtrl-sci↗