Monolayer and multilayer & mixed OH/water on Pd(111)



Cummings, Linda
Monolayer and multilayer & mixed OH/water on Pd(111). [Unspecified]

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Abstract

An extensive amount of literature can be found containing experimental and theoretical studies of water adsorption on metal surfaces, yet an understanding of the water – metal interface remains far from complete. The binding energy of the water – metal interface determines whether water wets a metal surface to form a complete hydrogen bonded network, forms 3-dimensional ice clusters on a non-wetting surface or dissociates to form hydroxyl, hydrogen and sometimes oxygen on the surface. All of these structures are seen depending on the growth conditions and reactivity of the metal surface. In this thesis it is shown that submonolayer water adsorbs intact on Pd(111) to form a structure with (√3×√3)R30° periodicity. As the first layer saturates the spots in the √3 position split due to the formation of dense domain boundaries. Although the first layer of water covers the Pd surface, subsequent layer-by-layer growth does not occur. Instead, an extended superstructure forms by attaching 3D clusters of ice and areas of bare monolayer remain exposed. The formation of an ordered oxygen network results in detection of an intense LEED pattern, even at a coverage of 80 layers. As the first layer of water compresses, it stabilises the growth of the larger superstructure. Further investigation shows the hydrogen network formed during multilayer growth is weakly bonded and helium atom scattering shows that there is disorder on a local scale. Co-adsorption of oxygen alters the structure and stability of water overlayers and on Pd(111) a stable mixed (OH + H2O) layer forms with (√3×√3)R30° periodicity but is unreactive towards hydrogen, therefore the low temperature reaction between hydrogen and oxygen cannot be catalysed.

Item Type: Unspecified
Additional Information: Date: 2013-01 (completed)
Subjects: Q Science > QD Chemistry
Divisions: Fac of Science & Engineering > School of Chemistry
Depositing User: Symplectic Admin
Date Deposited: 07 Aug 2013 10:31
Last Modified: 18 May 2019 00:10
URI: http://livrepository.liverpool.ac.uk/id/eprint/9533
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