Ultra violet illumination of the -z face of lithium niobate single crystals, under specific conditions, results in an organized arrangement of submicron etch resistant features that reflect the illuminating intensity distribution. Consequently, spatially resolved illumination can produce periodic structures with submicron periodicity. Furthermore, a size self-adjustment of the submicron etch resistant features was observed which is related to characteristic lengths (e.g. grating period) of the overall structure. The effect occurs for a narrow range of illuminating intensities and is attributed to a photo-induced electrostatic charge distribution, which modifies the electrochemical interaction of the acid with the surface. The size and periodicity of the structures, which can be achieved with this method, are suitable for the fabrication of 2D photonic crystal structures in this electro-optically tunable material. (c) 2005 Elsevier B.V. All rights reserved.