INITIAL OXIDATION OF ULTRATHIN ANTIMONY FILMS ON AU(111) AND OF POLYCRYSTALLINE ANTIMONY

It has been shown previously that antimony evaporated onto a Au(111) s urface grows in a layer-by-layer mode. The present work compares the i nitial, fast-oxidation stage of these films with that on bulk polycrys talline antimony. Measurements were carried out in an ultrahigh-vacuum environment using Auger electron spectroscopy, low-energy electron di ffraction, electron-energy-loss spectroscopy, and work-function change measurements. At 300 K and for oxygen pressures between 1 X 10(-5) an d 2 X 10(-3) Torr, oxidation follows first-order Langmuir kinetics, wi th an initial sticking probability of about 10(-5). Oxidation essentia lly saturates by 10(7) L (1 L = 10(-6) Torr s). A layer of oxide about 8.5 angstrom 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 X 10(15) atoms/cm2, is required to complete this oxide layer, for saturation oxidation. The chemical composition of th e oxidized films and the oxidized surface of bulk antimony is Sb2O3. T hese results are compared with earlier work on Pb, Bi, and Sn.