Optical Properties of Silicon and Germanium Nanowire Fabric

The optical properties of free-standing nonwoven silicon (Si) and germanium (Ge) nanowire fabrics, including diffuse and specular reflectance, diffuse and direct transmittance, and absorptance spectra, were measured using an integrating sphere to account fully for all incident photons. Very thin, 50 μm thick, sheets with ∼90% void volume have extremely high optical densities. They are optically opaque across nearly all wavelengths from ultraviolet to near-infrared, and only minimal light penetrates when photon energies are below the band gap. The high optical density arises from a combination of scattering and absorption due to their high aspect ratio and narrow diameter as well as surface effects due to their very high surface area to volume ratio.