THE ADSORPTION OF H2O VS O-2 ON BERYLLIUM

The adsorption mechanism and initial oxidation of sputtered beryllium exposed to H2O and to O-2 were studied using a combination of the DRS, AES and XPS techniques. For both cases, the ''clustering'' Langmuir t ype mechanism was found to fit the adsorption kinetics, The initial st icking coefficients, estimated from these fits, are S-O(H2O) approxima te to 1 and S-O(O2) approximate to 0.07. Oxide islands, similar to 3 m onolayers thick, are formed in both cases, spreading laterally till a full layer is formed. For O-2 the oxidation stops at this stage, while for H2O it continues at a lower rate, reaching a saturation level of about six monolayers. Observation of significant broadening of the AES O KW peak in the stage of thickness growth for the H2O exposure, and DRS H depth profiling indicate that hydrogen is trapped in the oxide m atrix. Possible hydrogen-enhanced-diffusion of ions through the oxide seems to enable the further growth. (C) 1997 Elsevier Science B.V.