Medium energy ion scattering studies of ultrathin epitaxial films

Abstract

Medium energy ion scattering (MEIS) has been used to investigate ultrathin epitaxial films. The depth profiles of V2O3(0001) films grown on Pd(111) were examined. The results from this demonstrated that on this substrate the films grown are highly non-uniform, with a large distribution of thicknesses observed for each prepared sample. V2O3(0001) films grown on Au(111) were found to form films with a much more even range of thicknesses, good enough to yield blocking curves. The experimental blocking curves obtained are not in good agreement with half-metal or vanadyl terminated structures favoured by most previous studies. Assuming that imperfections exist in the grown films produced better fits, however this lost surface sensitivity. The optimal structure found is an oxygen termination, proposed by a previous density functional theory (DFT) study. This structure is also found to be consistent with re-examined photoelectron diffraction (PhD) data. Ag2S films grown on Ag(111) were found to suffer severely from beam-induced damage, limiting quantity of obtained data. Unusually, an He+ beam was found to produce less severe effects than an H+ beam. Energy cuts were used to confirm, as proposed by an early Auger electron spectroscopy (AES) study, that the silver sulphide thickness continues to increase with increasing sulphur deposition onto Ag(111). The backscattered ion yields of the blocking curves increased with increasing film thickness, and no additional blocking features were present. These curves were found to be consistent with the structural model proposed by a previous normal incidence X-ray standing waves (NIXSW) study. p2gg(4 × 2)Mn/Cu(100) films were found to form with thicknesses far greater than the two layers anticipated by previous studies. The thick disordered layer precluded any structural analysis. The copper and manganese peaks could not be resolved, resulting in the only information obtained being about the thickness of the films