Initial oxidation of ultrathin antimony films on Au(111) and of polycrystalline antimony.

Abstract

It has been shown previously that antimony evaporated onto a Au(111) surface grows in a layer-by-layer mode. The present work compares the initial, fast-oxidation stage of these films with that on bulk polycrystalline antimony. Measurements were carried out in an ultrahigh-vacuum environment using Auger electron spectroscopy, low-energy electron diffraction, electron-energy-loss spectroscopy, and work-function change measurements. At 300 K and for oxygen pressures between 1\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}5}$ and 2\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}3}$ Torr, oxidation follows first-order Langmuir kinetics, with an initial sticking probability of about ${10}^{\mathrm{\ensuremath{-}}5}$. Oxidation essentially saturates by ${10}^{7}$ L (1 L=${10}^{\mathrm{\ensuremath{-}}6}$ Torr s). A layer of oxide about 8.5 \AA{} thick is formed in this initial stage, both for Sb films and for bulk antimony. An initial antimony film on Au(111) of about 1.7 monolayers, or 1.6\ifmmode\times\else\texttimes\fi{}${10}^{15}$ atoms/${\mathrm{cm}}^{2}$, is required to complete this oxide layer, for saturation oxidation. The chemical composition of the oxidized films and the oxidized surface of bulk antimony is ${\mathrm{Sb}}_{2}$${\mathrm{O}}_{3}$. These results are compared with earlier work on Pb, Bi, and Sn.