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Oxidation of Cs2Te with superficial Te clusters studied by XPS
A377 Surface Science 251/252 (1991) 1075-1080 North-Holland
1075
Oxidation of Cs2Te with superficial Te clusters studied by XPS L. Soriano, L. Galfin and F. Rueda Departamento Fisica Aplicada C-XII, Universidad Aut6noma de Madrid, E-28049 Madrid, Spain Received 8 October 1990; accepted for publication 7 December 1990 The oxidation of alkali-metal (Cs, K) tellurides at room temperature and low oxygen pressure has been studied by X-ray photoelectron and Auger electron spectroscopies (XPS, XAES). The oxidation kinetics is faster than logarithmic and does not saturate for the exposures studied, while a migration of alkali ions to the surface is detected. These effects are strongly enhanced in a sample of overcaesiated telluride with elemental Te dusters on the surface. A strong gradient of the oxidation state (Te 2-, Te °, Te 4+, Te 6+) is formed in a depth of the order of the XPS analysis depth. The oxygen concentration shows a similar gradient. Cs202 is formed too. The surface layer remains as Cs2Te; the Te clusters also remain unreactive at the surface; they only transform into telluride when heavy oxidation of the Cs2Te film is reached.
Surface Science 251/252 (1991) 1081-1085 North-Holland
1081
Acido-basic properties of specific surface sites of magnesium oxide Sophie Russo and Claudine Noguera Laboratoire de Physique des Solides, Universitd de Paris Sud, 91405 Orsay, France Received 1 October 1990; accepted for publication 30 November 1990 We report a self consistent tight binding calculation of the electronic structure of (100) and (110) perfect MgO surfaces, as well as a rough (100) surface. The local charges and electronic gap are discussed with special attention borne on the value of the Madelung field. Acido-basic properties of various sites at these surfaces are further analyzed through the adsorption energy of H + and O H species.
1086
Surface Science 251/252 (1991) 1086-1090 North-Holland
Oxygen adsorption on Pt(lll) covered by an incomplete Cs(2 x 2) overlayer R. Riwan, C. Papageorgopoulos 1 and J. Cousty D PhG / PA S, Centre d'Etudes Nucldaires de Saclay F, 91191 Gif-sur- Yvette, France Received 1 October 1990; accepted for publication 15 January 1991 Adsorption of oxygen on an incomplete Cs(2 X 2) layer adsorbed on Pt(11) at 300 K has been studied by WF changes LEED and ARUPS. Upon increasing oxygen exposures, a gradual desordering is observed while the WF increases from 2 eV up to 3.2 eV for 50 L. Depending on the oxygen exposures, two oxygen molecular species have been detected from ARUP spectra. The thermal behaviour of these Cs-O compounds has been probed.
1075
Oxidation of Cs2Te with superficial Te clusters studied by XPS L. Soriano, L. Galfin and F. Rueda Departamento Fisica Aplicada C-XII, Universidad Aut6noma de Madrid, E-28049 Madrid, Spain Received 8 October 1990; accepted for publication 7 December 1990 The oxidation of alkali-metal (Cs, K) tellurides at room temperature and low oxygen pressure has been studied by X-ray photoelectron and Auger electron spectroscopies (XPS, XAES). The oxidation kinetics is faster than logarithmic and does not saturate for the exposures studied, while a migration of alkali ions to the surface is detected. These effects are strongly enhanced in a sample of overcaesiated telluride with elemental Te dusters on the surface. A strong gradient of the oxidation state (Te 2-, Te °, Te 4+, Te 6+) is formed in a depth of the order of the XPS analysis depth. The oxygen concentration shows a similar gradient. Cs202 is formed too. The surface layer remains as Cs2Te; the Te clusters also remain unreactive at the surface; they only transform into telluride when heavy oxidation of the Cs2Te film is reached.
Surface Science 251/252 (1991) 1081-1085 North-Holland
1081
Acido-basic properties of specific surface sites of magnesium oxide Sophie Russo and Claudine Noguera Laboratoire de Physique des Solides, Universitd de Paris Sud, 91405 Orsay, France Received 1 October 1990; accepted for publication 30 November 1990 We report a self consistent tight binding calculation of the electronic structure of (100) and (110) perfect MgO surfaces, as well as a rough (100) surface. The local charges and electronic gap are discussed with special attention borne on the value of the Madelung field. Acido-basic properties of various sites at these surfaces are further analyzed through the adsorption energy of H + and O H species.
1086
Surface Science 251/252 (1991) 1086-1090 North-Holland
Oxygen adsorption on Pt(lll) covered by an incomplete Cs(2 x 2) overlayer R. Riwan, C. Papageorgopoulos 1 and J. Cousty D PhG / PA S, Centre d'Etudes Nucldaires de Saclay F, 91191 Gif-sur- Yvette, France Received 1 October 1990; accepted for publication 15 January 1991 Adsorption of oxygen on an incomplete Cs(2 X 2) layer adsorbed on Pt(11) at 300 K has been studied by WF changes LEED and ARUPS. Upon increasing oxygen exposures, a gradual desordering is observed while the WF increases from 2 eV up to 3.2 eV for 50 L. Depending on the oxygen exposures, two oxygen molecular species have been detected from ARUP spectra. The thermal behaviour of these Cs-O compounds has been probed.