OXYGEN REACTION ON THE NB(110) SURFACE AFTER EXPOSING TO H2O AND O-2 UNDER ELECTRON-BOMBARDMENT

The reaction of oxygen on the Nb (110) surface at 240 K after exposure to H2O and O2 under e-bombardment has been investigated by using AES and EELS techniques. The uptake of oxygen atoms is much more efficient when the surface is exposed to H2O than to O2. The chemistry of the oxygen adatoms is analysed on the basis of the AES Nb(M45N23V) and EELS structures. At the highest H2O exposure the oxygen atoms are in the form of Nb2O5 oxide, while for O2 the final state is an oxide of less valence. Initial sticking coefficients of approximately 1 and 0.41 for oxygen and water respectively, at 240 K adsorption temperature, have been determined. A model based on dissociative adsorption and electron stimulated desorption processes is presented to explain the differences between both molecules.