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 × 10−5exp(−172/RT), D(110) = 5 × 10−5exp(−178/RT)andD(100) = 7 × 10−6exp(−168/RT)m2/s. The surface segregation energies are also found from the fits and areΔG(111) = 76 ± 5, ΔG(110) = 72 ± 5andΔG(100) = 64 ± 5, respectively.