Adsorption of sulfur on TiO2(110) studied with STM, LEED and XPS:: temperature-dependent change of adsorption site combined with O-S exchange

We have studied the adsorption of elemental sulfur on TiO2(110) for exposure at room temperature and at 300 degrees C. Depending on the substrate temperature we found different adsorption sites with scanning tunneling microscopy (STM). At room temperature sulfur adsorbs on the titanium rows with a high mobility along the [001] direction. At 300 degrees C sulfur adsorbs at the position of the bridging oxygen rows and forms short chains along the [1 (1) over bar 0] direction at low coverages. High coverages result in the formation of a (3 x 1) superstructure. X-ray photoelectron spectroscopy (XPS) shows a 2 eV shift of the sulfur 2p peak to lower binding energy concurrently with the change of adsorption site from the titanium to the oxygen rows. For the (3 x 1) structure a distinct Ti3+ shoulder appears at the Ti 2p(3/2) peak. Based on these measurements we present a model where sulfur replaces every third bridging oxygen atom of the substrate and the other bridging oxygens are completely removed. (C) 2000 Elsevier Science B.V. All rights reserved.