The initial sticking coefficient and the saturation coverage in the chemisorption region for oxygen on evaporated nickel films, polycrystalline nickel foils and various nickel single crystals, have been determined quantitatively. The oxygen coverage was measured by calibration of the oxygen Auger signal with a quartz crystal microbalance. For absolute pressure measurements in the ultrahigh vacuum region, the ionization gauge was calibrated with a gas friction manometer. On very rough surfaces the value of the initial sticking coefficient is nearly 1, whereas on the flat Ni(111) plane it only reaches the value 0.12. Interestingly on Ni(111), the adsorption probability increases with increasing coverage up to 0.2 monolayers of oxygen. An adsorption model involving non-zero dissociation probability at an occupied adsorption site is used to explain this unusual behaviour.
Treatment code (Nähere Zuordnung)
- Basic - Fundamental (Grundlagenforschung)