Characterization of Metal Surfaces by Secondary Ion Mass Spectrometry and X-ray Photoelectron Spectroscopy

The techniques of XPS and SIMS have been combined in the same ultra-high vacuum system for the study of surface reactions. Using a mass spectrometer capable of detecting high molecular weight clusters, we have investigated the behavior of clusters up to Ag5+ and In4+ ejected from polycrystalline Ag and In surfaces under low flux argon ion bombardment. For lattice-oxide formation on Pb and In surfaces cleaned by ion bombardment, the O 1s peak areas directly relate to the PbO+ and InO+ intensities allowing calibration of surface coverages for SIMS studies. The fact that PbO2+ emission begins at higher oxygen exposure than PbO+ suggests that oxygen incorporation into the lattice occurs directly. For In, however, the fact that InO2+ emission increases in roughly the same fashion as InO+ indicates that indium oxide islands grow outward from one or more nucleating sites, allowing for the existence of oxygen-oxygen next-nearest neighbors at low coverage for InO2+ formation.