Experimental evidence for equilibrium surface segregation in a CoPd alloy

Abstract

The surface concentration of a polycrystalline Co-Pd(30 at%) alloy was investigated over a wide temperature range by Auger electron spectroscopy. Reversible changes of surface composition were observed at temperatures of 800-1080 K. Above 1100 K, irreversible depletion of palladium in the surface region occurred. Auger transitions of different energies were used for depth profile characterization. Variation of the palladium concentration with temperature at the surface-bulk equilibrium showed palladium segregation with a heat of segregation of Q=27 kJ mol ^–1 .