title: An STM investigation of sulfur and alkoxide adsorption on Ni(100).
abstract: The effect of sulfur on alkoxide formation and decomposition on the Ni(100) surface has been investigated with STM and LEED. At low coverage sulfur adsorbs into a p(2 x 2) structure, in agreement with LEED measurements and previous STM results. With increasing sulfur coverage, the p(2 x 2) structure saturates the surface and scattered domains of c(2 x 2) appear. Further increases in sulfur coverage affect increases in c(2 x 2) domain sizes; the state of the sulfur-covered surface up to 0.43 ML is characterized by p(2 x 2) and c(2 x 2) domains. STM measurements of the evolution of the sulfur-covered surface with D(2)S(g) adsorption are suggestive of sulfur nucleation and growth at multiple sites on the surface. Alkoxide formation on these surfaces was studied following exposure to ROH (R = CH(3), CH(3)CH(2), CH(3)CH(2)CH(2), and C(6)H(5)). The alkoxy surface intermediates adsorbed in p(2 x 2)-S vacancies and, in the case of phenoxy, between hollow sites. Agreement between the methoxy coverage determined by XPS and the fraction of the surface covered with p(2 x 2)-S, as determined by STM, suggests that the p(2 x 2) vacancies are the sites of methoxy adsorption, and hence the active sites for selective poisoning.
authors.affiliation: Department of Chemical Enineering, Stanford University, Stanford, California 94305-5025, USA.
authors.forename: Ali R
authors.initials: AR
authors.lastname: Alemozafar
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Madix