The University of Tokyo · Engineering
Professor Hiroyasu Yamahara's research lab specializes in advanced functional materials and nanoscale devices for next-generation sensing and spintronic applications. The lab focuses on oxide semiconductors, graphene-based nanomaterials, and magnetic oxides, with key research directions including flexoelectricity in epitaxial oxide films, low-dimensional semiconductor heterostructures, and high-sensitivity gas sensors using suspended graphene and surface acoustic waves. The team integrates advanced thin-film growth techniques such as pulsed laser deposition with cutting-edge characterization methods to develop materials for ultra-sensitive, low-power, and room-temperature operation in healthcare and environmental monitoring.
Figures are computed from collected data and may differ slightly.
Abstract Flexoelectricity is a universal property associated with dielectric materials, wherein they exhibit remanent polarization induced by strain gradient. Rare-earth iron garnets, R 3 Fe 5 O 12 , are ferrimagnetic insulators with useful magnetic properties. However, they are unlikely to show remanent dielectric polarization because of their centrosymmetric structure. Here, to induce flexoelectricity, we investigate various rare-earth iron-garnet thin films deposited on lattice-mismatched sub
We report on the synthesis of gallium oxide nanowires by pulsed laser deposition using a gold catalyst. In the vapor-liquid-solid process, gold thickness was the crucial parameter for deciding the morphology of nanowires. In the case of 1 nm thick gold, homogeneous nanowire growth was confirmed at temperatures of 700°C to 850°C. Transmission electron microscopy and selected area electron diffraction measurements showed that the nanowires were polycrystalline. In the cathode luminescence spectra,
To improve the quality of modern life in the current society, low-power, highly sensitive, and reliable healthcare technology is necessary to monitor human health in real-time. In this study, we fabricated partially suspended monolayer graphene surface acoustic wave gas sensors (G-SAWs) with a love-mode wave to effectively detect ppt-level acetone gas molecules at room temperature. The sputtered SiO<sub>2</sub> thin film on the surface of a black 36°YX-LiTaO<sub>3</sub> (B-LT) substrate acted as
Carrier-type control of spin-glass (cluster spin-glass) is studied in order to engineer basic magnetic semiconductor elements using the memory functions of spin-glass. A key of carrier-polarity control in magnetite is the valence engineering between Fe(II) and Fe(III) that is achieved by Ti(IV) substitution. Single phases of (001)-oriented Fe3−xTixO4 thin films have been obtained on spinel MgAl2O4 substrates by pulsed laser deposition. Thermoelectric power measurements reveal that Ti-rich films
Detection of parts-per-trillion (ppt)-level acetone gas molecules at room temperature using suspended graphene on SiO<sub>2</sub> micropillars has rarely been achieved using solid-state devices or surface acoustic wave (SAW) sensors. This paper presents the effect of SiO<sub>2</sub> micropillars and suspended graphene as a guiding and sensing layer to detect acetone gas. The integration of suspended graphene with SiO<sub>2</sub> micropillars introduces a coupled resonance effect arising from the
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