Aluminium oxide ultrathin-film growth on the Mo(110) surface: a work-function study

Submonolayer-to-multilayer films deposited onto the surface of Mo(110) crystal by thermal evaporation of bulk aluminium oxide in ultrahigh vacuum have been studied by Auger electron spectroscopy, low-energy electron diffraction and work-function measurements (the Anderson method). The Auger spectra of the films at all coverages studied are composed of the lines characteristic for the bulk oxide; no evidence of a metallic Al signal is found. The layer-by-layer growth mode occurs up to two monolayers. Increase of the reflectivity of the low-energy electrons (1 to 4 eV) as the film grows indicates that the film has a reduced density of states, which probably resembles the band gap of the bulk alumina. The films deposited on a substrate held at room temperature are amorphous, whereas deposition at 1300 K results in a hexagonal superstructure.