X-ray Photoelectron Spectroscopy Study of Interfacial Reactions between Metal and Ultrathin Ge Oxide

After evaporation of four different metal films (Al, Ti, Ni, and Au) on thermally-grown Ge oxide/Ge(100), the chemical bonding features in the region near the metal/oxide interfaces were investigated by high-resolution X-ray photoelectron spectroscopy (XPS). From the analysis of core-line spectra, we found that a part of thermally-grown GeO 2 was reduced with Ni, Ti, and Al evaporation. The reduction of GeO 2 layer becomes insignificant in the increasing order of metal oxide formation energy metals as predicted from the calculation of Gibbs free energy change in each metal oxidation. For Al that is mostly reactive with GeO 2 , not only the oxygen transfer from GeO 2 to Al, but also the formation of Al–Ge bonds in the region near the Al/GeO 2 interface occurs with Al evaporation on thermally grown GeO 2 .