title: Low pressure oxidation of ordered Sn/Pd(110) surface alloys.
abstract: The reaction of oxygen at low pressure with the Sn/Pd(110) system has been examined by photoelectron spectroscopy using synchrotron radiation. The c(2 × 2) and (3 × 1) reconstructions of the Sn/Pd(110) surface at 0.5 and 0.7 monolayers (ML) Sn coverage and a 1.75 ML Sn overlayer on the Pd(110) surface after flashing to 470 K were studied. The Sn 4d core level is strongly affected by O(2) adsorption while the Pd 3d core level shows very little change other than a decrease in intensity. Starting with a 10 L dose of oxygen, prominent changes in the spectra were observed for all Sn/Pd(110) surface alloys. Analysis of the Sn 4d core levels indicates that oxidation proceeds with the formation of well-defined states of Sn, which were identified as a Pd-Sn-O interface layer, SnO and SnO(2) oxides. The valence band spectra confirm this assignment. The Sn(2+) and Sn(4+) component signals originate from the topmost surface layer, i.e. tin atoms in more highly oxidized states constitute the topmost surface layer on top of the Pd-Sn-O interface. The presence of a sub-surface PdSn intermetallic alloy facilitates the tin oxide formation; the Sn-O phase formation is accompanied by Pd-Sn bond dissociation.
authors.affiliation: Faculty of Mathematics and Physics, Department of Surface and Plasma Science, Charles University, V Holešovičkách 2, 18000 Prague 8, Czech Republic. National Institute for Materials Science, 3-13, Sakura, Tsukuba 305-0003, Japan.
authors.forename: N
authors.initials: N
authors.lastname: Tsud
authors.forename: T
authors.initials: T
authors.lastname: Skála
authors.forename: F
authors.initials: F
authors.lastname: Sutara
authors.forename: K
authors.initials: K
authors.lastname: Veltruská
authors.forename: V
authors.initials: V
authors.lastname: Dudr
authors.forename: M
authors.initials: M
authors.lastname: Yoshitake
authors.forename: K C
authors.initials: KC
authors.lastname: Prince
authors.forename: V
authors.initials: V
authors.lastname: Matolín