Molecular-scale growth of silicon oxide was successfully demonstrated onto a polystyrene (PS) substrate at a relatively low temperature less than the glass transition temperature of PS. Our method consists of three processes. A hydrophobic PS substrate was first photochemically modified using vacuum ultraviolet light (VUV) of 172 nm wavelength from an excimer lamp. Organosilane was then chemisorbed from a precursor vapor of 1,3,5,7-tetramethylcyclotetrasiloxane (TMCTS) onto the VUV-modified PS substrate. Finally, each of our samples was again photoirradiated with the same excimer lamp. Using X-ray photoelectron spectroscopy, we confirmed that the chemisorbed TMCTS was photooxidized and converted to silicon oxide after only 3 min of VUV irradiation. Under atomic force microscopy the resulting oxide surface appeared smooth with its thickness estimated to be less than 1 nm by transmission electron microscopy. Due to the growth of this oxide layer of molecular-scale thickness, the charge density and surface acidity on the PS substrate drastically changed, becoming almost identical to those of native oxide on a Si substrate. (C) 2003 Elsevier Science B.V. All rights reserved.