Sn segregation to the low index surfaces of a copper single crystal

The kinetics of the surface segregation to the low index surfaces of a Cu(111) 0.121 at% Sn, Cu(110) 0.072 at% Sn and a Cu(100) 0.099 at% Sn single crystal was investigated by means of Auger electron spectroscopy and low energy electron diffraction (LEED) in the temperature range 660 to 840 K. The data was fitted with a modified Darken model which describes the concentration-time dependence from time zero to equilibrium using equilibrium coverage values deduced from the LEED measurements. The diffusion coefficients for the bulk diffusion in the three directions are: D-(111) = 9 x 10(-5) exp(-172/RT), D-(110) = 5 x 10(-5) exp(-178/RT) and D-(100) = 7 x 10(-6) exp(-168/RT) m(2)/s. The surface segregation energies are also found from the fits and are Delta G((111)) = 76 +/- 5, Delta G((110)) = 72 +/- 5 and Delta G((100)) = 64 +/- 5, respectively.