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 mu A 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 >similar to 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 similar to 350 nm and base width of similar to 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. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3560539]