Growth morphology and electronic structure of ultra-thin TaOx films on Ag(100)

A study of the growth morphology and electronic structure of TaOx films on the Ag(100) substrate has been performed to determine the properties of ultra-thin TaOx films without the influence of a mixed interfacial oxide (i.e., a disordered SiO2/TaOx interface for growth on Si). The TaOx films were grown by thermal evaporation of Ta in an oxygen atmosphere of 1 x 10(-6) Torr. Growth on a Ag(100) surface held at room temperature results in an amorphous TaOx overlayer, as determined by low energy electron diffraction. The onset of ordering of these films occurs for a post-anneal at similar to 500 degreesC. A diffraction pattern that corresponds to a multi-domain overlayer structure is observed for anneals at similar to 550 degreesC. Deposition of Ta without oxygen results in the formation of Ta islands. These results indicate that there is a very weak adsorbate-substrate interaction. Photoemission measurements of the TaOx films show the formation of a band gap with the valence band maximum residing at 3.5 eV below the Fermi level. Core level shifts of similar to3.5 eV are observed for the Ta with no indication of metallic Ta at the surface.