Tuning of the thermal radiation spectrum in the near-infrared region by metallic surface microstructures

This paper reviews our recent research on thermal radiation from metallic surface microstructures to develop selective radiators for thermophotovoltaic generation. Numerical simulation showed that two different peaks appeared on the emissivity spectra of metallic gratings. One was originated from surface plasmon polaritons, which was dependent on the grating period and angle. The other peak was explained by the microcavity effect which arose from each microcavity on a grating surface. The microcavity effect became dominant with deepening gratings, and showed suitable properties for selective radiators in thermophotovoltaic generation: a high emissivity within the visible and near-infrared regions, and angle independence. We developed two kinds of two-dimensional metallic gratings based on Si and W with the period of 1.0-2.0 νm. The W gratings composed of rectangular microcavities displayed a high emissivity in the near-infrared region as expected from the calculation results. It was confirmed experimentally that the W selective radiators have advantages for high-power and high-efficiency thermophotovoltaic systems.