Surface spectroscopies and transmission electron microscopy (TEM) techniques have been used to investigate the influence of interfacial oxide (<50 A) on chemical bonding and reaction at Pt/ Si (111) and Ti/Si (111) interfaces. In both cases the deposited metal undergoes reaction even at room temperature, but the nature of this reaction is very different for Pt vs Ti. Ti reduces a Si02 surface layer, producing Ti-O bonds; cross-sectional TEM shows that the as-deposited interface is smooth and continuous, a consequence of the Ti-SiO2 interfacial reaction. In contrast, Pt reacts with Si from the substrate, presumably through pinholes, thereby forming silicide. Aggregation of Pt on the Si02 is observed, confirming the absence of Pt-SiO2 reaction. The disappearance of Si-O bonding features in photoemission spectra is found to be strongly correlated to the morphology of the metal overlayer. © 1985, American Vacuum Society. All rights reserved.