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Interaction of cesium and oxygen on W(110) I. Cesium adsorption on oxygenated and oxidized W(110)
A48 Hume-Rothery, is used for analysing some aspects of the surface structures reported by LEED crystallography for S adsorbed on the (110) surfaces of nickel and rhodium, and for O adsorbed on the (110) surfaces of nickel and iridium. The main objectives are to rationalise the different adsorption sites adopted by S and O, and to assess the measured bond lengths. For the latter, use is made of a bond length-bond order relationship given by Pauling. Surface Science 92 (1980) 88 96 © North-Holland Publishing Company A D S O R P T I O N SITES OF CO ON M o ( 1 0 0 ) H. N I E H U S
[nstitut ffir Grenzfldchenforschung und Vakuumphysik, Kernforschungsanlage Jalich GmbH, D-5170 Jfilich, Germany Received 14 June 1979; accepted for publication 22 August 1979 The angular distribution of electron stimulated desorption (ESDIAD) in combination with LEED has been used in order to determine the geometrical arrangement of carbon monoxide on a clean Mo(100) surface. The desorption of oxygen ions upon electron bombardment occurs preferentially from molecularly adsorbed CO (a-CO). a-CO adsorbs either in four-fold "hollow" or two-fold "bridge" positions between the Mo substrate atoms and produces a cross pattern in ESDIAD showing streaks in the (001) and (010) directions. Suppression of the streaks occurs as the a-CO coverage increases.
Surface Science 92 (1980) 97-118 © North-Holland Publishing Company I N T E R A C T I O N O F CESIUM A N D O X Y G E N ON W(110) t I. Cesium a d s o r p t i o n o n o x y g e n a t e d and o x i d i z e d W(110) J.-L. D E S P L A T * and C.A. P A P A G E O R G O P O U L O S **
Stanford/NASA Ames Joint Institute/or Surface and Microstructural Research, NASA-Ames, Moffett Field, California 94035, USA Received 18 June 1979; accepted for publication 14 September 1979 Cesium adsorption on oxygenated and oxidized W(110) is studied by Auger electron spectroscopy, LEED, thermal desorption and work function measurements. For oxygen coverages up to 1.5 × 101 s cm-2 (oxygenated surface), preadsorbed oxygen lowers the cesiated work function minimum, the lowest (~1 eV) being obtained on a two-dimensional oxide structure with 1.4 X 1015 oxygen atoms per cm 2. Thermal desorption spectra of neutral cesium show that the oxygen adlayer increases the cesium desorption energy in the limit of small cesium coverages, by the same amount as it increases the substrate work function. Cesium adsorption destroys the p(2 X 1) and p(2 X 2) oxygen structures, but the 2D-oxide structure is left nearly unchanged. Beyond 1.5 X 101 s cm-2 (oxidized surface), the work function minimum rises very rapidly with the oxygen coverage, as tungsten oxides begin to form. On bulk tungsten oxide layers, cesium appears to diffuse into the oxide, possibly forming a cesium tungsten bronze, characterized by a new desorption state. The thermal stability of the 2D-oxide structure on W(110) and the facetting of less dense tungsten planes suggest a way to achieve stable low work functions of interest in thermionic energy conversion applications.
[nstitut ffir Grenzfldchenforschung und Vakuumphysik, Kernforschungsanlage Jalich GmbH, D-5170 Jfilich, Germany Received 14 June 1979; accepted for publication 22 August 1979 The angular distribution of electron stimulated desorption (ESDIAD) in combination with LEED has been used in order to determine the geometrical arrangement of carbon monoxide on a clean Mo(100) surface. The desorption of oxygen ions upon electron bombardment occurs preferentially from molecularly adsorbed CO (a-CO). a-CO adsorbs either in four-fold "hollow" or two-fold "bridge" positions between the Mo substrate atoms and produces a cross pattern in ESDIAD showing streaks in the (001) and (010) directions. Suppression of the streaks occurs as the a-CO coverage increases.
Surface Science 92 (1980) 97-118 © North-Holland Publishing Company I N T E R A C T I O N O F CESIUM A N D O X Y G E N ON W(110) t I. Cesium a d s o r p t i o n o n o x y g e n a t e d and o x i d i z e d W(110) J.-L. D E S P L A T * and C.A. P A P A G E O R G O P O U L O S **
Stanford/NASA Ames Joint Institute/or Surface and Microstructural Research, NASA-Ames, Moffett Field, California 94035, USA Received 18 June 1979; accepted for publication 14 September 1979 Cesium adsorption on oxygenated and oxidized W(110) is studied by Auger electron spectroscopy, LEED, thermal desorption and work function measurements. For oxygen coverages up to 1.5 × 101 s cm-2 (oxygenated surface), preadsorbed oxygen lowers the cesiated work function minimum, the lowest (~1 eV) being obtained on a two-dimensional oxide structure with 1.4 X 1015 oxygen atoms per cm 2. Thermal desorption spectra of neutral cesium show that the oxygen adlayer increases the cesium desorption energy in the limit of small cesium coverages, by the same amount as it increases the substrate work function. Cesium adsorption destroys the p(2 X 1) and p(2 X 2) oxygen structures, but the 2D-oxide structure is left nearly unchanged. Beyond 1.5 X 101 s cm-2 (oxidized surface), the work function minimum rises very rapidly with the oxygen coverage, as tungsten oxides begin to form. On bulk tungsten oxide layers, cesium appears to diffuse into the oxide, possibly forming a cesium tungsten bronze, characterized by a new desorption state. The thermal stability of the 2D-oxide structure on W(110) and the facetting of less dense tungsten planes suggest a way to achieve stable low work functions of interest in thermionic energy conversion applications.