Nanomaterials - 17

Abstract

The refractive index of a thermal radiation medium plays a role in the magnitude of heat flux. However, the refractive index is often omitted because those of air and vacuum are unity. Here we investigated whether silicon (Si) micropyramids, which has a high refractive index in the mid-infrared region, can be used as thermal extractors into vacuum. The purpose of introducing micropyramids is to reduce total internal refraction, where a hemisphere dome was used previously whose height increases with increasing area.[1]
Fig. 1. (a) shows the numerically simulated thermal extraction enhancement factor of Si micropyramids into vacuum against planar Si surface. The result shows that Si micropyramids can enhance thermal extraction by 64.6% with the optimized pyramid width. In experiments, micro-sized pyramids were fabricated by wet etching a 500 µm thick Si substrate (Fig. 1. (b)),[2] and the thermal extraction was evaluated by a heat flux sensor in vacuum. The measured heat flux of the Si micropyramids was greater than that of the planar Si substrate or without Si substrate. These numerical and experimental results indicate that the Si micropyramids can enhance thermal radiation by thermal extraction despite their reduced thickness.