The adsorption mechanism and initial oxidation of sputtered beryllium exposed to H2O and to O2 were studied using a combination of the DRS, AES and XPS techniques. For both cases, the "clustering" Langmuir type mechanism was found to fit the adsorption kinetics. The initial sticking coefficients, estimated from these fits, are S0(H2O) ≈ 1 S0(O2) ≈ 0.07. Oxide islands, ∼ 3 monolayers thick, are formed in both cases, spreading laterally till a full layer is formed. For O2 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 KVV peak in the stage of thickness growth for the H2O exposure, and DRS H depth profiling indicate that hydrogen is trapped in the oxide matrix. Possible hydrogen-enhanced-diffusion of ions through the oxide seems to enable the further growth.
- Adsorption kinetics
- Auger electron spectroscopy