IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Surface Science Tuesday Sessions
       Session SS3-TuP

Paper SS3-TuP25
A LEED Investigation of Xe Adsorbed on Pd(111)

Tuesday, October 30, 2001, 5:30 pm, Room 134/135

Session: Adsorption/Desorption Poster Session
Presenter: J. Zhu, Johannes Kepler Universität Linz, Austria
Authors: J. Zhu, Johannes Kepler Universität Linz, Austria
H. Ellmer, Johannes Kepler Universität Linz, Austria
H. Malissa, Johannes Kepler Universität Linz, Austria
D. Semrad, Johannes Kepler Universität Linz, Austria
P. Zeppenfeld, Johannes Kepler Universität Linz, Austria
Correspondent: Click to Email
Xe adsorption on the Pd(111) surface was investigated by means of low energy electron diffraction (LEED) in a UHV chamber with 1.2x10@super -11@ mbar base pressure. Depending on the Xe coverage and substrate temperature, a large number of different phases were identified, including a 2D gas phase and a 2D liquid phase, a commensurate (@sr@3x@sr@3)R30° solid phase (C), a compressed striped incommensurate phase (SI), ordered multilayer structures, and a clear Xe(111) crystal with sharp spots rotated 30° with respect to the substrate. In addition, a hexagonal incommensurate solid phase (HI) and a hexagonal incommensurate rotated phase (HIR) were observed as well as a C -> SI -> HI -> HIR phase transition. The (@sr@7x@sr@7)R19.2° and (@sr@19x@sr@19)R23.5° commensurate phases reported by Hilgers et al.@footnote 1@ were not obtained after Xe adsorption on the clean surface in the entire temperature and coverage range. However, small amounts of contaminants (CO and/or H@sub 2@) on the Pd(111) surface have a striking influence on the Xe post-adsorption. With ~0.1 L of CO pre-adsorbed at 55 K, a clear (@sr@7x@sr@7)R19.2° commensurate phase is obtained. After pre-adsorption of ~0.1 L of H@sub 2@ at 55 K, a commensurate phase (@sr@19x@sr@19)R23.5° appears in the high Xe coverage region. A combination of 0.1 L H@sub 2@ and 0.1 L CO pre-adsorbed at 55 K leads to a phase transition sequence from (@sr@3x@sr@3)R30° -> (@sr@19x@sr@19)R23.5° -> (@sr@7x@sr@7)R19.2° similar to the one reported for Xe on Pd(111) in Ref. 1. From these observations, therefore, we conclude that the high-order commensurate (@sr@7x@sr@7)R19.2° and (@sr@19x@sr@19)R23.5° phases of Xe are related to CO and H@sub 2@ impurities, respectively. @FootnoteText@ @footnote 1@ G. Hilgers, M. Potthoff, N. Müller and U. Heizmann, Surf. Sci. 322 (1995) 207.