Room-temperature interaction of ultrathin-film yttrium withSrTiO3(100),LaAlO3(100), and MgO(100) surfaces

The crystallographic and electronic structures of surfaces of the large-gap semiconductors ${\mathrm{SrTiO}}_3$(100) and ${\mathrm{LaAlO}}_3$(100), and of the insulator MgO (100), were followed during the initial stages of a metal-beam deposition of yttrium metal at room temperature. The techniques used are low-energy electron diffraction, Auger-, electron-energy-loss, and ultraviolet photoelectron spectroscopy. Yttrium grows epitaxially 1×1 on the MgO (100) surface and nonepitaxially on the ${\mathrm{LaAlO}}_3$(100) and ${\mathrm{SrTiO}}_3$(100) surfaces. Initially, below monolayer coverage, Y is strongly oxidized by the MgO(100) substrate. Near-monolayer yttrium coverages ${\mathrm{Y}}^{2+}$ is identified, and upon further Y deposition the oxidation state gradually changes further towards a lower value. Oxidation of an yttrium film on 1×1 MgO(100) results in changes around the Fermi level and changes in the core-level binding energies, but no changes in the upper valence band were observed.