A synthetic avenue for the formation of yttrium oxide thin films on Si native oxide surfaces is demonstrated by the reaction of Tris(2,2,6,6-tetramethyl-3,5-heptanedionato) yttrium(III) with inorganic (H(2)O(2)) and organic (tert-butyl and di-tert-amyl) peroxides in supercritical carbon dioxide. The reactions are carried out in a hot wall reactor at temperatures below 130 degrees C and pressures ranging from 13.10 to 22.75 MPa. Spectroscopic Ellipsometry verifies thin film formation and X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy measurements confirm formation of yttrium oxide films and the presence of carbonate and hydroxide species which are removed after high temperature anneals. (C) 2007 Elsevier B.V. All rights reserved.