Adsorption, diffusion and self-diffusion on tungsten surfaces with adsorbed palladium

Abstract The influence of a Pd adsorption layer on the surface self-diffusion of tungsten has been measured using a field emitter technique. By adsorption of 1.2 × 10 15 Pd atoms/cm 2 — measured by high energy ion backscattering — the surface self-diffusion energy decreases from 70 to 54 kcal/mole, and the diffusivity from 0.95 to about 0.2 cm 2 /s, which corresponds to an increase of the diffusion coefficient by a factor 40 at 1600 K and 80 at 1400 K. Furthermore are determined (1) adsorption lifetimes in adsorption-desorption equilibria, (2) the isosteric adsorption heat (103 kcal/mole), and (3) the coefficient of Pd surface diffusion on W resulting in diffusion energies of 32 kcal/mole around (001) and 17 kcal/mole around (111).