Bias-reference X-Ray photoelectron spectroscopy of sapphire and yttrium aluminum garnet crystals

Abstract

An XPS technique which uses a biased gold dot as a reference marker was used to measure the A12p, the 01s, and the Y 3d bond energies in single crystals of sapphire and in Ce-doped and Ca-doped crystals of yttrium aluminum garnet. The observed A12p and the Ols binding energies were shifted in the various specimens, but the aluminum and the oxygen peaks in each sample were shifted in the same direction by the same voltages. It is postulated that these apparent chemical shifts were caused by changes in the Fermi energy levels rather than by changes in the binding energies. The Fermi energy of one of the materials was used as a standard, and the Fermi levels of all of the crystals were determined relative to it. The Fermi energy level of the sapphire crystal was measured at 3.7 eV above the top of the valence band, and that of a YAG crystal annealed in an oxidizing atmosphere at 1.9 eV.