Oxidation of ultra-thin Ti films on Mo(100): Soft X-ray photoelectron spectroscopy study

Abstract

Titanium oxide films grown on Mo(100) have been investigated by low-energy electron diffraction (LEED) and soft X-ray photoelectron spectroscopy (PES). The film was grown by Ti deposition on Mo(100) and subsequent oxidation of the film by 12L of O2 exposure at room temperature. As the film was annealed at 700–1000°C, the film in which the Ti atoms were in a Ti3+ oxidation state was formed. As the film was annealed at 1100–1500°C, the oxidation state of Ti in the film was converted to Ti2+. The valence electronic structure of the film was measured under the condition that the emission from the Mo substrate was minimized due to a Cooper minimum of the Mo 4d photoionization cross sections (hν=100eV). It was found that the Ti 3d band in normal-emission spectra was increased in intensity when the film was annealed at 1100–1500°C. As the film was annealed at 1300°C for 10s and 20s, the film-covered Mo(100) gave (2×2) and (4×1) LEED patterns, respectively. The two-dimensional band structure of the (2×2) system was investigated by angle-resolved PES, and it was found that the film with a (1×1) periodicity with respect to the Mo(100) substrate existed in the (2×2) system.