モハメッド シュルズ ミヤ

Self-sustained electrical oscillations (SEOs) in VO2 films have attracted considerable attention owing to their potential to emulate spiking pulses in neuromorphic circuits. However, triggering stable SEOs and the controlling oscillation frequency remain challenging because the details of circuit operation with VO2-based devices are not yet well understood. In this study, we propose a method to observe SEOs stably in a VO2-based planar device with Au/Ti facing electrodes by introducing a 50 Hz sinusoidal voltage from a curve tracer. The transient aspects, including the onset and collapse of the SEO, were captured, providing clarity on the oscillation frequency range and circuit conditions for the SEOs, which are closely correlated with the device temperature. It became clear that the parallel capacitance not only determined the oscillation frequency but also controlled the current through VO2 just after the insulator–metal transition of VO2, playing a role in triggering stable oscillations. We also successfully observed the transient aspects from in-phase to anti-phase synchronized oscillations in the coupled oscillations. This study advances the experimental procedures and applications of SEOs in VO2-based planar devices.

Amorphous tungsten oxide films are prepared on indium tin oxide/glass substrates using reactive magnetron sputtering and their electrochromic (EC) properties are investigated. To achieve the densely colored films, samples of 500 and 1000 nm thickness are deposited with different pumping speeds and oxygen flow rates at Ar 3 Pa atmosphere. The as‐deposited films are similarly transparent (≈80%), but their EC properties vary depending on the deposition conditions and strongly on film thickness. The 500 nm‐thick samples have a transmittance of 4–8% in the colored state, which recover well in the bleached state. In contrast, the 1000 nm‐thick films have very low transmittance (<1%) in the colored state but are not completely recovered. Among 1000 nm‐thick films, large pumping speed and a large oxygen flow rate condition result in comparatively better recoverability. The cyclic voltammograms of 500 nm films show small and balanced charge transfer, while those of 1000 nm films reveal large and unbalanced charge transfer. These indicate that more ions are intercalated into the 1000 nm samples but are not completely deintercalated. These findings contribute to the development of EC applications for light shielding.

<title>Abstract</title> The present work investigates a tin-based highly efficient perovskite solar cell (PSC) by a solar cell capacitance simulator in one dimension. Molybdenum disulfide is introduced as hole transport layer in the proposed solar cell device structure. The photovoltaic performances of the proposed solar cell are investigated by varying thickness, doping concentration, and bulk defect density of various layers. Furthermore, the operating temperature and the series and shunt resistances are analyzed systematically. A higher conversion efficiency of 25.99% is obtained at the absorber thickness of 2000 nm. The optimum doping density of 10¹⁷ cm⁻³ is estimated for the absorber, electron transport layer (ETL), and hole transport layer (HTL), respectively. The optimum thicknesses of 50 nm, 1000 nm, and 60 nm are also found for the titanium dioxide as ETL, methylammonium tin triiodide (CH₃NH₃SnI₃) as absorber layer, and molybdenum disulfide as HTL, respectively. The efficiency of the proposed lead-free CH₃NH₃SnI₃-based solar cell with the alternative molybdenum disulfide HTL is calculated to be 24.65% with open-circuit voltage of 0.89 V, short-circuit current density of 34.04 mA/cm², and fill-factor of 81.46% for the optimum parameters of all layers. These findings would contribute to fabricate low-cost, non-toxic, stable, and durable lead-free PSCs for the next generation.

<title>Abstract</title>In this study, copper bismuth oxide (CuBi₂O₄) absorber-based thin film heterojunction solar cell structure consisting of Al/FTO/CdS/CuBi₂O₄/Ni has been proposed. The proposed solar cell device structure has been modeled and analyzed by using the solar cell capacitance simulator in one dimension (SCAPS-1D) software program. The performance of the proposed photovoltaic device is evaluated numerically by varying thickness, doping concentrations, defect density, operating temperature, back metal contact work function, series and shunt resistances. The current density–voltage behaviors at dark and under illumination are investigated. To realize the high efficiency CuBi₂O₄-based solar cell, the thickness, acceptor and donor densities, defect densities of different layers have been optimized. The present work reveals that the power conversion efficiency can be enhanced by increasing the absorber layer thickness. The efficiency of 26.0% with open-circuit voltage of 0.97 V, short-circuit current density of 31.61 mA/cm², and fill-factor of 84.58% is achieved for the proposed solar cell at the optimum 2.0-μm-thick CuBi₂O₄ absorber layer. It is suggested that the p-type CuBi₂O₄ material proposed in the present study can be employed as a promising absorber layer for applications in the low cost and high efficiency thin-film solar cells.

© 2020 Author(s). In this study, we studied how to connect a thermoacoustic engine (TAE) and an impulse turbine to construct a thermoacoustic generator for converting thermal energy into electric power. The thermoacoustic generator was separated into two sub-systems: (1) system A, which consisted of a looped-tube TAE and a branch tube, and (2) system B, which consisted of an impulse turbine loop and a branch tube. The sub-systems were evaluated individually using an acoustic driver to determine the driving conditions such as branch length, driving frequency, and temperature for the connected system. In system A, which included the TAE, the change in specific acoustic impedance was small with respect to the velocity amplitude. However, in system B, which included the impulse turbine, the change in specific acoustic impedance with respect to the velocity amplitude was nonlinear. The sub-systems were connected by branch pipes, whose lengths were determined from the individual sub-system evaluation results, and the device was confirmed to self-oscillate at the driving temperature. When the device was operated at the driving conditions, the frequency, velocity amplitude, and specific acoustic impedance with self-oscillation were the same as those of the individual sub-systems. This also confirms the validity of evaluating the TAE and impulse turbine separately.

反応性高周波マグネトロンスパッタ法を用いて、ガラス基板上へ酸化亜鉛(ZnO)薄膜を堆積した後、二酸化バナジウム(VO2)薄膜の成膜を行った。ZnOは透明性が高く、透明基板上へVO2薄膜を堆積させることにより、光学センサーやスマートウィンドウなどの光学的応用が期待される。本研究では、ZnO薄膜の結晶性及びZnO/glass上へのVO2薄膜の結晶成長について報告する。

反応性スパッタ法による酸化物薄膜堆積において、絶縁性基板へ高周波バイアス電圧を印加して成膜を行った。高周波バイアス印加に伴う-50～-300Vの自己バイアス電圧発生によって、高エネルギーイオンの基板入射を促進できる。本発表では、高エネルギーイオン入射と結晶成長、膜表面モフォロジーとの関連について報告する。金属―絶縁体転移を示す酸化バナジウム薄膜及び酸化亜鉛薄膜への適用結果を示す。

VO₂は、68℃付近の温度において絶縁的な状態から金属的な状態へ相転移を起こすことから様々な応用が期待されている。近年、低電圧スイッチングが期待される導電層上へのVO₂薄膜の成長が盛んに研究されており、我々は今まで導電性TiN層上へのVO₂薄膜の多結晶成長について報告した。本研究では、RFマグネトロンスパッタ法により導電性TiN層へのVO₂薄膜の配向成長と転移特性に成功したので報告する。