Nanopatterning of a silicon surface by near-field enhanced laser irradiation

We report on a method that allows direct, massively parallel nanopatterning of a silicon Surface using ultraviolet (UV) lasers. Silica or polystyrene nanospheres with diameters of the order of the laser wavelength were deposited on the silicon surface. Spheres arranged themselves into hexagonally close-packed form due to capillary force. The nanosphere array was irradiated with 248 and 355 nm UV lasers. The silicon surface was locally melted due to enhancement of the optical field between the nanosphere and the substrate. Redistribution of molten material due to surface tension forces leads to the formation of a nanodent array. These nanodents vary their shape from bowl-like to 'sombrero-like' with the increase of laser energy as a result of competition between the thermocapillary force and the chemicapillary force.