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An Application of SEXAFS to Sub-Monolayer Complexes on Polycrystalline Surfaces

Norman, D. / Tuck, R. A. / Skinner, H. B. / Wadsworth, R. J. / Gardiner, T. M. / Owen, I. W. / Richardson, C. H. / Thornton, G.

Abstract Most applications of Surface Extended X-ray Absorption Fine Structure (SEXAFS) have studied model adsorption systems on single crystal surfaces. The local nature of the SEXAFS probe means that it should be equally well suited to surface systems without long-range order, provided that the adsorbate occupies a unique site. We have shown that this expectation is correct in our study of the local geometry around barium atoms on the surfaces of thermionic emitting cathodes. On tungsten and tungsten/osmium alloy dispenser cathodes Ba is bonded to oxygen with a well-defined short-range order. The Ba-O distance is similar for both cathodes, with oxygen atoms deduced to occupy hollow sites of the substrate. However, the alloy cathode has Ba bonded to two oxygen near neighbours (compared to one for the tungsten cathode), with a slightly longer Ba-substrate distance: this enhances the surface dipole and thus explains the lower work function.

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An Application of SEXAFS to Sub-Monolayer Complexes on Polycrystalline Surfaces

Norman, D. / Tuck, R. A. / Skinner, H. B. / Wadsworth, R. J. / Gardiner, T. M. / Owen, I. W. / Richardson, C. H. / Thornton, G.

Abstract Most applications of Surface Extended X-ray Absorption Fine Structure (SEXAFS) have studied model adsorption systems on single crystal surfaces. The local nature of the SEXAFS probe means that it should be equally well suited to surface systems without long-range order, provided that the adsorbate occupies a unique site. We have shown that this expectation is correct in our study of the local geometry around barium atoms on the surfaces of thermionic emitting cathodes. On tungsten and tungsten/osmium alloy dispenser cathodes Ba is bonded to oxygen with a well-defined short-range order. The Ba-O distance is similar for both cathodes, with oxygen atoms deduced to occupy hollow sites of the substrate. However, the alloy cathode has Ba bonded to two oxygen near neighbours (compared to one for the tungsten cathode), with a slightly longer Ba-substrate distance: this enhances the surface dipole and thus explains the lower work function.

An Application of SEXAFS to Sub-Monolayer Complexes on Polycrystalline Surfaces

Norman, D. / Tuck, R. A. / Skinner, H. B. / Wadsworth, R. J. / Gardiner, T. M. / Owen, I. W. / Richardson, C. H. / Thornton, G.

Abstract Most applications of Surface Extended X-ray Absorption Fine Structure (SEXAFS) have studied model adsorption systems on single crystal surfaces. The local nature of the SEXAFS probe means that it should be equally well suited to surface systems without long-range order, provided that the adsorbate occupies a unique site. We have shown that this expectation is correct in our study of the local geometry around barium atoms on the surfaces of thermionic emitting cathodes. On tungsten and tungsten/osmium alloy dispenser cathodes Ba is bonded to oxygen with a well-defined short-range order. The Ba-O distance is similar for both cathodes, with oxygen atoms deduced to occupy hollow sites of the substrate. However, the alloy cathode has Ba bonded to two oxygen near neighbours (compared to one for the tungsten cathode), with a slightly longer Ba-substrate distance: this enhances the surface dipole and thus explains the lower work function.

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Titel:

An Application of SEXAFS to Sub-Monolayer Complexes on Polycrystalline Surfaces

Beteiligte:

Norman, D. (Autor:in) / Tuck, R. A. (Autor:in) / Skinner, H. B. (Autor:in) / Wadsworth, R. J. (Autor:in) / Gardiner, T. M. (Autor:in) / Owen, I. W. (Autor:in) / Richardson, C. H. (Autor:in) / Thornton, G. (Autor:in)

Erschienen in:

The Structure of Surfaces II ; 183-188

Springer Series in Surface Sciences ; 11

Erscheinungsdatum:

01.01.1988

Format / Umfang:

6 pages

ISBN:

978-3-642-73345-1 , 978-3-642-73343-7

ISSN:

DOI:

https://doi.org/10.1007/978-3-642-73343-7_30

Medientyp:

Aufsatz/Kapitel (Buch)

Format:

Elektronische Ressource

Sprache:

Englisch

Schlagwörter:

Auger Electron Spectroscopy , Single Crystal Surface , Scatter Phase Shift , Surface Dipole , Daresbury Laboratory Physics , Surface and Interface Science, Thin Films , Surfaces and Interfaces, Thin Films , Crystallography

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