Work function changes with sulfur coverage on Pt(111)

Work function changes (Δφ) with sulfur coverage have been measured on Pt(111). The sulfur overlayer has been also characterized by LEED, AES and TDS techniques. An unexpected Δφ decrease, which correlates with the growth of a p(2 × 2) structure, has been recorded. At higher sulfur coverage, a reverse in the sign of Δφ has been observed with a $\text{(}\text{3}\text{×}\text{3}\text{)R30 °}$ structure. It is proposed that the recent model of Shustorovich and Baetzold could account for these sulfur-induced Δφ changes. It is also concluded that the sulfur adsorption bond on platinum must be essentially covalent.