掲載種別：研究論文（学術雑誌）  

© 2020 Elsevier Ltd Near-field radiation transfer between a metal–insulator–metal (MIM)-structured emitter and receiver was investigated through numerical simulation using a finite difference time domain (FDTD) method. Both the emitter and receiver consist of a squared-island-type metal array composed of nickel (Ni), an insulator layer composed of silicon dioxide (SiO2), and a metal substrate composed of nickel (Ni). The emitter and receiver were set up with a vacuum gap of a few hundred nanometers. The results showed that the near-field radiation flux was enhanced by a factor of approximately four, when compared to that between blackbody surfaces. Simultaneously, the enhancement was spectrally controlled over frequencies ranging from 9 × 1014 to 20 × 1014 rad/s (approximating to a wavelength range of 0.9 to 2.1 μm) depending on the size of the squared island. Images of the magnetic field in both the emitter and receiver clarified that the spectrally enhanced radiation flux was caused by the magnetic polariton (MP)) generated in the insulator between the squared-island metal and the substrate metal when the frequency of the MP coincided with that of the near-field radiation. Moreover, the resonance mode between the frequencies of the MP and near-field radiation was predicted by an impedance model that considered the capacitance between the islands in the emitter and receiver, in addition to the conventional circuit of a MIM structure.

DOI： 10.1016/j.applthermaleng.2020.116041

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掲載種別：研究論文（学術雑誌）  

© 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement. Spectral absorptance of a metal-semiconductor-metal (MSM) thin-multilayer structured thermo-photovoltaic cell was experimentally investigated. A MSM consists of a thin GaSb-semiconductor sandwiched between a top fishnet-type electrode and a flat backside electrode made of gold. A thin GaSb layer was grown on a substrate made of InAs using molecular beam epitaxy, and then all of the InAs substrate was removed using wet etching. The GaSb film was bonded on a surface of gold, which was sputtered on a Si substrate, using a van der Waals bonding method. The top fishnet-type electrode was made using electron beam lithography and a lift-off process. In the case of a 115 nm thick GaSb layer and a square fishnet aperture of a 300 nm × 310 nm size, the spectral absorptance of MSM reached a local peak (95%) at a wavelength of 1.66 µm, which is similar to spectra predicted by numerical simulation. Moreover, the equivalent resonance cavity model and LC circuit model functioned well to indicate the wavelength of several distinct peaks of absorptance.

DOI： 10.1364/OE.410828

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掲載種別：研究論文（学術雑誌）  

© 2019 Elsevier Ltd The electromagnetic field around a thermophotovoltaic (TPV) cell made of a metal–semiconductor–metal (MSM) multilayer with a square-grid electrode layer, referred to as a fishnet layer, was numerically calculated using a three-dimensional finite difference time domain method to obtain the absorptance of the MSM multilayer. In this study, gold and gallium antimony assumed to be materials of the metal and semiconductor layer, respectively. Even if there was no top metal layer, several peaks of absorptance were observed because of the optical interference inside the gallium antimony thin film. Here, the peak wavelength shifted to a shorter wavelength region by placing a fishnet layer on the gallium antimony layer. Moreover, the wavelength of the first peak of the optical interference could be adjusted at the active range of wavelength from 0.8 um to 1.8 um for the TPV cell made of gallium antimony for a practical power generation system. As a result, even in a several hundred nanometers thickness of semiconductor, a 60% of radiant energy absorbed could be concentrated in the active range of wavelength that is defined as a spectral efficiency. From the simulation results with an equivalent waveguide model, the shift of the first peak using the fishnet layer could be described using a dispersion relation of the waveguide, which was fulfilled with gallium antimony. Moreover, the superposition of different resonant modes originated from the waveguide-like structure and strip-wired structure affected the spectral absorption of the MSM multilayer when the wall of the fishnet structure was expanded.

DOI： 10.1016/j.ijheatmasstransfer.2019.01.087

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掲載種別：研究論文（国際会議プロシーディングス）  

© Begell House Inc. 2020. Electromagnetic fields around metal-semiconductor-metal (MSM) multilayers with a squared island top layer were calculated numerically, and their spectral absorptances were evaluated. The top and bottom metal layers were set to be gold; however, the intermediate semiconductor layer was set to be gallium antimony (GaSb). With a squared island top gold layer, the first peak shifted to a longer wavelength range. Uncharted second peaks emerged from 1.0 to 2.0 μm when the island width was longer than 300 nm. By observing the distributions of the z-directional electric fields at the wavelength of the absorptance peak, it was clarified that the second peak of absorptance was generated by horizontal directional Fabry-Perot interference inside GaSb layer depending on the width of the island. Moreover, the first peak could be described using the LC equivalent circuit model in the condition with wide distance between two islands. However, it was indicated that the LC circuit model needed a correction about capacitance between the upper and ground layer in the condition with narrow distance between two islands.

DOI： 10.1615/RAD-19.410

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掲載種別：研究論文（学術雑誌）  

© 2017 Elsevier Ltd This study shows that near-field radiation transfer is spectrally enhanced using nanometer-sized square pillar array structured surfaces, which are faced toward each other with a vacuum gap of a few hundred nanometers. In this case, the emitter exhibits a temperature of 1000 K, while the receiver exhibits a temperature of 300 K. Moreover, the pillar array structured surfaces made of aluminum-doped zinc oxide (AZO) were assumed. The electromagnetic fields inside AZO and in the vacuum gap were calculated using the finite difference time domain numerical simulation method, which uses a spherical emission source with a sinusoidal modulated Gaussian pulse distributed inside the AZO. As a result, there are local maximum radiation fluxes at the fundamental frequency originating from the Fabry–Pèrot interference between the fundamental wavelength and the pillar height, at its second and third harmonic frequencies, and at the asymptote frequency of the surface wave relating to the plasma frequency. The most striking feature is that the radiation flux at the fundamental frequency becomes more than 30 times higher than that for the far-field blackbody radiation transfer by using a pillar width and a channel width of 80 nm, because the electromagnetic energy emitted spherically is collimated in the direction from the emitter to the receiver.

DOI： 10.1016/j.ijheatmasstransfer.2017.07.075

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