The growth of voids in 8 to 20nm Pd layers, on alumina or silica substrates, was investigated by means of Auger electron spectroscopy and atomic force microscopy. By using the Brandon-Bradshaw model, based upon capillary forces, the Pd surface self-diffusion coefficient was determined at 583 to 823K. It was found that the results were independent of the substrate; in agreement with the assumption that void growth was controlled by surface self-diffusion on the metal. The mass transfer surface self-diffusion could be described by,

D (m2/s) = 1.1 x 10-7 exp[-97(kJ/mol)/RT]

Previous experimental and theoretical values, for intrinsic diffusion coefficients on oriented surfaces, indicated much lower activation energies than those found here. The differences were attributed to the formation energy of the defects that were responsible for surface diffusion.

I.Beszeda, E.G.Gontier-Moya, D.L.Beke: Surface Science, 2003, 547[1-2], 229-38