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) surface grows in a layer-bylayer 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 1X10 ' and 2X10 ' Torr, oxidation follows first-order Langmuir kinetics, with an initial sticking probability of about 10 Oxidation essentially saturates by 10' L (1 L=10 Torr s). A layer of oxide about 8.5 A 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 1.6X10"atoms/cm, 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 Sb203. These results are compared with earlier work on Pb, Bi, and Sn.