Self-organized antireflecting nano-cone arrays on Si (100) induced by ion bombardment

Self-organized nano-cone arrays are fabricated on Si (100) by means of Ar+ ion bombardment at normal incidence with ion energy of 1.5 keV and current density of 1000 µA cm−2. The nano-structured Si surface appears black as seen by the naked eye. The measured reflectance of the surface is less than 11% over the wavelength range from 350 to 2000 nm as compared to that of >∼30% for the polished Si. An enhancement of more than 25% in absorption is observed in this region. The cones are densely distributed over the surface with an average height of ∼350 nm and base width of ∼250 nm. Incorporation of metal atoms such as Fe and Cr is found to be mandatory for the formation of the nano-structures during ion bombardment. High-resolution electron spectra show that for each cone, the apex is metal-enriched, and the rest is nearly free of metal atoms, showing good crystallinity with the same crystallographic orientation as the substrate.