Using a forest of gold nanowires to reduce the reflectivity of silicon

The optical reflectivity of polished silicon covered by a forest of vertically standing gold nanowires (grown inside the pores of an anodic alumina matrix) is found to be considerably smaller than that of bare polished silicon and strongly influenced by scattering of light by the nanowires. We propose a phenomenological modification to the Maxwell–Garnett effective medium theory formula to account for this effect. We also find that the gold nanowire/alumina film has interesting optical properties, such as transparency in the mid-infrared and high absorbance in the visible, and may be used as a low reflectivity coating and a low-pass filter.