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Reactivity and Structural Aspects of Cesium and Oxygen States at Cu(110) Surfaces: An XPS and STM Investigation

Carley, Albert Frederick, Davies, Philip Rosser, Harikumar, K. R., Jones, Rhys Vaughan and Roberts, Meirion Wyn 2004. Reactivity and Structural Aspects of Cesium and Oxygen States at Cu(110) Surfaces: An XPS and STM Investigation. Journal of Physical Chemistry B 108 (38) , pp. 14518-14526. 10.1021/jp049469x

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Abstract

Structural and reactivity aspects of Cu(110)−Cs and Cu(110)−Cs/O overlayers have been investigated by XPS and STM. The development of cesium-induced structures at a Cu(110)−Cs overlayer has been followed as a function of cesium coverage at 295 K and the reactivity of the overlayer first to oxygen and subsequently to ammonia and carbon dioxide studied. For cesium concentrations up to 1.3 × 1014 cm-2 an incommensurate pseudo square structure is observed which is in registry with the copper substrate in the 100 direction. This coexists, at 1.3 × 1014 Cs adatoms cm-2, with a structure consisting of 11̄0-orientated rows which are not atomically resolved but have a spacing in the 100 direction of 1.1 nm. At a cesium concentration of 1.5 × 1014 cm-2, patches of structure with an inter-row spacing of 0.7 nm are present, and at a cesium concentration of 1.9 × 1014 cm-2, only the latter spacing is observed. An increase in cesium concentration to 2.1 × 1014 cm-2 results in an increase in the inter-row spacing to 1.1 nm. Exposure of cesium-modified surfaces to oxygen results in the development of new terraces superimposed upon the cesium-modified surface with the latter structurally unchanged by the formation of the oxygen adlayer, although there is a change in the XP binding energy of the Cs(3d) peaks. The new terraces consist of 100-orientated chains similar to those observed at unmodified Cu(110) surfaces; however, at low cesium concentrations these chains are arranged in (3 × 1) as well as (2 × 1) domains and at high cesium concentrations a c(6 × 2)O structure develops with an exposure of oxygen as low as 10 L. The adsorption of cesium at partially preoxidized surfaces results in the formation of a c(2 × 4) structure and also structures which have no simple relationship with the substrate lattice and which we assign to strained Cu−O (2 × 1) structures. At a surface with a complete monolayer of oxygen present the cesium forms 11̄0 chains with a minimum interchain spacing of 0.5 nm and alternate chains showing well-resolved maxima with a spacing of 0.5 nm. The adatoms in between the chains are less well-defined suggesting a degree of mobility in the 11̄0 direction. In comparison with oxygen at unmodified Cu(110) surfaces, oxygen states at the cesium-modified surface are unreactive to ammonia at 295 K, reaction only occurring after exposures of 300 L at 490 K. However, the cesium surface is reactive to carbon dioxide chemisorption at 295 K resulting in a surface carbonate with extensive migration of cesium and the emergence of areas of the underlying copper surface.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Chemistry
Cardiff Catalysis Institute (CCI)
Subjects: Q Science > QD Chemistry
Publisher: ASC Publications
ISSN: 1520-6106
Last Modified: 03 Nov 2017 01:41
URI: http://orca.cf.ac.uk/id/eprint/10380

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