Spectral Emissivity of Anti-Reflective Moth-Eye Surfaces

In this work, the spectral (blackbody) emissivity of highly transmissive, micro-structured ‘moth-eye’ surfaces is explored. Because such surfaces are highly transparent to infrared light, it stands to reason that moth-eye structures should also affect the thermal radiation balance at surface interfaces. Measurements of this effect have not been previously conducted. An apparatus to measure relative spectral emissivity of transmissive materials was developed and measurements of moth-eye structured silicon were conducted using Fourier transform infrared spectroscopy. The moth-eye silicon was compared against an unstructured silicon wafer and a reference blackbody. Moth-eye structured surfaces were found to increase emission of thermal radiation; certain wavelengths were emitted differently than others, showing that previously established effects of structure size and shape on wavelength-dependent transmittance are also exhibited in spectral emissivity. These findings suggest that surfaces with tunable thermal radiation may be achievable, potentially yielding improvements in imaging technologies, passive radiative cooling, and lighting efficiency.