We present an approach for the generation of metallic Ga dots and In nano-crystallites which. in contrast to conventional bottorn-up, or top-down processes. is based on a subtractive self-oroganization process relying on material decomposition induced by focused ion beam exposure. The diameters of the Ga dots ran-e from 120 to 850 nm with an aspect ratio of about 0.4 at a dot density of up to 7 X 10(7)/cm(2). Two-dimensional ordered arrays of freestanding dots were fabricated by a site control technique relying on prepatterned holes and an irradiation mediated migration and agglomeration. By the analogous technique we generated indium nanocrystallites on the (100) InAs surface with sizes ranging g from about 50 nm to a few microns obviously due to a preferential loss of arsenic atoms during Ga+ focused ion beam irradiation. The influence of the ion dose, the beam energy, and the dose rate on the surface evolution was investigated by atomic force microscopy. scanning, electron microscopy, Auger electron spectroscopy, and x-ray diffraction measurements. (C) 2004 American Vacuum Society.