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°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°C sulfur adsorbs at the position of the bridging oxygen rows and forms short chains along the [11̄0] direction at low coverages. High coverages result in the formation of a (3×1) 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 (3×1) structure a distinct Ti3+ shoulder appears at the Ti 2p3/2 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.