Influence of sulfur on oxygen adsorption onto a polycrystalline Zr surface

Oxidation of a polycrystalline Zr surface is studied by a time-of-flight electron-stimulated desorption TOF-ESD.method and Auger electron spectroscopy AES.. An S-segregated Zr surface is obtained after heat treatment at 1100 K for 15 min in an ultrahigh-vacuum UHV.chamber. Several cycles of Arq bombardment at 925 K and heating at 1000 K remove sulfur layers, resulting in a nearly clean Zr surface. Although oxygen molecules in dissociative states adsorb onto both types of sample surfaces, the sticking coefficient of the oxygen atoms is considerably decreased on the S-segregated surface. Three different sites for the adsorption of oxygen atoms are noted, namely, the subsurface sites, the hollow sites, and the on-top sites. The S atoms segregate to the Zr surface to occupy the hollow or the on-top site, resulting in the observed decrease of the sticking coefficient of the O atoms. q2000 Published by Elsevier Science B.V.