COVERAGE OF FOREIGN ATOMS ON SURFACES AS A FUNCTION OF ADSORPTION, SPUTTERING, AND DIFFUSION RATES

During sputtering of a surface the coverage of foreign atoms may be changed by diffusion from the bulk to the surface and by adsorption from the gas phase. Assuming sufficiently high negative surface segregation enthalpy i.e. high ratios of surface to bulk concentration in equilibrium, simple expressions of the coverage time function for finite and semi-infinite samples are derived. The equations were applied to experimental results of oxygen coverage on a niobium surface where the three processes mentioned above were active. From the comparison with these results the diffusion coefficients of O in Nb D = 2 × 10-13 m2/s at 520°C and D = 9 × 10-13 m2/s at 600°C were evaluated. © 1979.