Investigation of mass transfer surface self-diffusion on palladium

Abstract

Growth of voids in thin palladium layers (8–20 nm) on alumina and silica substrates has been investigated by Auger electron spectroscopy and atomic force microscopy. Using the Brandon–Bradshaw’s model, based on capillarity forces, the surface self-diffusion coefficients of palladium have been evaluated in the temperature range of 583–823 K. We have found that the results are independent of the substrate, in agreement with the assumption that the growth of voids is controlled by surface self-diffusion on the metal. The mass transfer surface self-diffusion coefficients are expressed by D s ( m 2/ s)=1.1×10 −7 exp[−97±13 ( kJ/mol) /RT] . These new results are compared with literature data. The experimental and theoretical values for intrinsic diffusion coefficients on oriented surfaces disclose much lower activation energies than that found in the present work, and the differences are related to the formation energy of the defects responsible for surface diffusion.