Nanoscale Au rich dots were deposited on SiO2 and Si3N4 substrates by decomposing an adsorbed organometallic precursor using a focused electron beam. The precursor, dimethyl acetylacetonate gold ((CH3)(2)(C5H7O2)Au), does not react with either substrate without electron irradiation. Deposited feature diameters are larger than that of the electron beam used for deposition by an amount comparable to the secondary electron escape depth. This result suggests that axial secondary electron emission through the surface of a growing feature limits the minimum attainable feature size. Real-time composition analysis during growth using electron energy-loss spectroscopy indicates that mature features entrain significant carbon. (c) 2005 American Vacuum Society.