Paper SS-TuP7
Effects of Interadsorbate Interactions on Surface Resistivity: Oxygen on Sulfur-Predosed Epitaxial Cu(100)

Tuesday, October 16, 2007, 6:00 pm, Room 4C

Measurements of surface resistivity for oxygen absorbed on sulfur-predosed epitaxial Cu(100) reveal the existence and properties of two types of interadsorbate interactions between sulfur and oxygen: S-O repulsion and scattering suppression. The repulsive interaction causes oxygen atoms to first occupy adsorption sites far from the sulfur atoms. As a result the low-coverage variation of surface resistivity with oxygen coverage is unaffected by predosed sulfur, showing the linear dependence previously observed for oxygen on clean Cu(100).¹ As the oxygen coverage increases, oxygen begins to occupy sites near the sulfur atoms. At these sites the resistivity effect of the oxygen atoms is strongly suppressed, so that the sample resistance levels off, remaining unchanged even as oxygen continues to adsorb on the surface. With increasing sulfur precoverage both the maximum resistivity change and the oxygen coverage at which the leveling occurs decrease, because the number of sites unaffected by sulfur is reduced. Both the S-O repulsion and the scattering suppression have an effective range on the order of about 1.4 lattice spacings, with a rather sharp boundary. Both interactions presumably arise from a through-metal coupling involving the metal’s local density of states.

¹R.G. Tobin, Surf. Sci. 524, 183 (2003).