Evidence for Pd Bonding with Si Intermediate Oxidation-States

The bonding of Pd atoms evaporated on a thin layer of silicon intermediate oxidation states has been studied by core level and valence band photoemission spectroscopy. The particular substrate was obtained by controlled exposure of a cleaved Si surface to oxygen in order to have few angstroms of silicon oxidation states with a small percentage Of SiO2. The deposition of Pd on this substrate was investigated studying the Pd 3d and Si 2p core level spectra as well as the valence band as, a function of the metal coverage. Our results indicate evidence that the pristine Si intermediate oxidation states modify their configuration and bind metal atoms. In fact in the Si 2p spectrum changes in the chemical shift are observed for these states, and new peaks arise whose areas increase with metal coverage. The three-dimensional growth characteristics of the metal are deduced from the behavior of the relative intensity for the different components of the Si 2p core spectrum. Furthermore, the shifts of the Pd 3d core level and of the Fermi edge towards higher binding energies at low coverage confirm the formation of metal islands on a nonconducting substrate.