An AES study of Sn surface segregation in Cu single crystals

Quantitative treatment of Sn segregation data in the three low-index planes of Cu(111), Cu(110) and Cu(100) was carried out. Auger electron spectroscopy (AES) was used to acquire the data by heating the sample linearly with time (positive linear temperature ramp, PLTR) from 450 to 900 K and immediately cooling it linearly with time (negative linear temperature ramp, NLTR) from 900 to 650 K. The experimental data were fitted using the Darken model for the PLTR profiles. Two supportive models - Fick's integral and the Bragg-Williams equations - were used to extract the starting segregation parameters for the Darken model. Fick's integral was used to fit part of the data for the PLTR profile and the Bragg-Williams equations were used for the NLTR profile, which accounts for an extended equilibrium segregation region. The Sn segregation parameters, namely the interaction energy Omega(Cu-Sn), the diffusion coefficient D and the segregation energy Delta G, were found as: D-(111) = 9.2 x 10(-4) exp(-205/RT)m(2) s(-1); Delta G((111)) = 70 kJ mol(-1); Omega(Cu-Sn) = 3.8 kJ mol(-1) D-(110) = 2.7 X 10(-6) exp(-168/RT)m(2) s(-1); Delta G((110)) = 62 kJ mol(-1); Omega(Cu-Sn) = 3.8 kJ mol(-1) D-(100) = 6.2 X 10(-6) exp(-189/RT)m(2) s(-1); Delta G((100)) = 65 kJ mol(-1); Omega(Cu-Sn) = 3.9 kJ mol(-1) Copyright (c) 2005 John Wiley & Sons, Ltd.