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Deuterium uptake in titanium thin films: t ssc00621 the effect of oxide, and metal (Ti and Fe) overlayers
A498 Surface Science 160 (1985) 235-252 North-Holland, Amsterdam
235
DEUTERIUM UPTAKE IN TITANIUM THIN FILMS: t ssc00621THE EFFECT OF OXIDE, AND METAL (Ti AND Fe) OVERLAYERS M i c h a e l C. B U R R E L L
* and Neal R. ARMSTRONG
**
Department of Chemistry, University of Arizona, Tucson, Arizona 85721, USA Received 3 December 1984; accepted for publication 5 April 1985 Titanium thin films prepared in UHV were reacted with deuterium (PD2 < 1 × 10 -5 Torr) to various loadings, as determined by microgravimetry using a quartz crystal microbalance. The kinetics of deuterium absorption favor a mechanism in which an a-phase surface deuteride forms on the film during the early stages of the reaction, resulting in a constant rate of deuterium uptake during most of the reaction. Surface characterization by AES and ELS, however, demonstrated spectral changes which were dependent on the bulk film stoichiometry. Electron-beam decomposition of the surface deuteride during AES analysis is postulated to explain this result. Oxidation of the titanium film surface caused a decrease in the deuterium absorption rate, completely inhibiting the reaction when oxides of thickness 20 A or greater were formed. Fresh titanium layers on top of the oxide renewed the ability of the Ti film to take up D 2 at the previous rate. Iron adlayers were found to accelerate the D 2 absorption rate of Ti films, or to likewise reactivate oxidized Ti surfaces.
Surface Science 160 (1985) 253-270 North-Holland, Amsterdam
253
THE BONDING STATE OF CARBON SEGREGATED TO at-IRON SURFACES AND ON IRON CARBIDE SURFACES STUDIED BY ELECTRON SPECTROSCOPY G. PANZNER
* and W. DIEKMANN
**
Max- Planck- Institut ff~r Eisenforschung GmbH, Max. Planck- Strasse 1, D- 4000 Df~sseldorf 1, Fed. Rep. of Germany Received 11 February 1985; accepted for publication 15 April 1985 Segregated carbon on the Fe(100) surface has been studied by means of X-ray and ultraviolet photoelectron (XPS, UPS), Auger electron (AES) and electron energy loss spectroscopy (ELS). For comparison, the surfaces of polycrystaUine graphite and of iron carbides stabilized by chromium or manganese additions have been investigated. On the iron surface, carbon exists as a chemisorbed state or a graphitic multilayer. The two states exhibit different energy positions in XPS, and are different in energy positions and lineshapes in AES and ELS. During the transition of graphitic carbon to chemisorbed carbon on Fe(100) a novel coverage-dependent Auger feature is reported. The spectra of graphitic carbon on the iron surface always coincide with those of solid graphite. The carbon Auger transitions of chemisorbed carbon and of iron carbides exhibit very similar lineshapes, but the energy position§ of both states differ in AES as well as XPS.
235
DEUTERIUM UPTAKE IN TITANIUM THIN FILMS: t ssc00621THE EFFECT OF OXIDE, AND METAL (Ti AND Fe) OVERLAYERS M i c h a e l C. B U R R E L L
* and Neal R. ARMSTRONG
**
Department of Chemistry, University of Arizona, Tucson, Arizona 85721, USA Received 3 December 1984; accepted for publication 5 April 1985 Titanium thin films prepared in UHV were reacted with deuterium (PD2 < 1 × 10 -5 Torr) to various loadings, as determined by microgravimetry using a quartz crystal microbalance. The kinetics of deuterium absorption favor a mechanism in which an a-phase surface deuteride forms on the film during the early stages of the reaction, resulting in a constant rate of deuterium uptake during most of the reaction. Surface characterization by AES and ELS, however, demonstrated spectral changes which were dependent on the bulk film stoichiometry. Electron-beam decomposition of the surface deuteride during AES analysis is postulated to explain this result. Oxidation of the titanium film surface caused a decrease in the deuterium absorption rate, completely inhibiting the reaction when oxides of thickness 20 A or greater were formed. Fresh titanium layers on top of the oxide renewed the ability of the Ti film to take up D 2 at the previous rate. Iron adlayers were found to accelerate the D 2 absorption rate of Ti films, or to likewise reactivate oxidized Ti surfaces.
Surface Science 160 (1985) 253-270 North-Holland, Amsterdam
253
THE BONDING STATE OF CARBON SEGREGATED TO at-IRON SURFACES AND ON IRON CARBIDE SURFACES STUDIED BY ELECTRON SPECTROSCOPY G. PANZNER
* and W. DIEKMANN
**
Max- Planck- Institut ff~r Eisenforschung GmbH, Max. Planck- Strasse 1, D- 4000 Df~sseldorf 1, Fed. Rep. of Germany Received 11 February 1985; accepted for publication 15 April 1985 Segregated carbon on the Fe(100) surface has been studied by means of X-ray and ultraviolet photoelectron (XPS, UPS), Auger electron (AES) and electron energy loss spectroscopy (ELS). For comparison, the surfaces of polycrystaUine graphite and of iron carbides stabilized by chromium or manganese additions have been investigated. On the iron surface, carbon exists as a chemisorbed state or a graphitic multilayer. The two states exhibit different energy positions in XPS, and are different in energy positions and lineshapes in AES and ELS. During the transition of graphitic carbon to chemisorbed carbon on Fe(100) a novel coverage-dependent Auger feature is reported. The spectra of graphitic carbon on the iron surface always coincide with those of solid graphite. The carbon Auger transitions of chemisorbed carbon and of iron carbides exhibit very similar lineshapes, but the energy position§ of both states differ in AES as well as XPS.