AN XPS STUDY OF CARBON SEGREGATION ON POLYCRYSTALLINE SILVER

X-ray photoelectron spectroscopy (XPS) was used to measure the surface concentration of carbon on a high-purity polycrystalline foil of silv er between 300 and 800 K. In the range from 300 to 450 K a reversible transport of impurity level carbon occurs between the surface and the bulk. Above 450 K a near-monolayer carbidic-like state is observed whi ch exhibits a C ls binding energy of 284.5 eV. Below 450 K this state coexists with a precipitated dense amorphous state at 284.8 Ev which g rows with decreasing temperature. Both the equilibrium surface concent ration and the kinetics of carbon accumulation on the surface were mea sured at various temperatures. The equilibrium data were fitted with a simple precipitation model from which a 17 kJ/mol enthalpy of solutio n for carbon in silver was obtained. The analysis of the kinetic data yielded the diffusion coefficient for carbon precipitation at various temperatures from which a 19 kJ/mol activation energy for diffusion wa s derived.