Step-edge segregation of bimetallic alloys - A LEIS study of Pt25Rh75(410)

We demonstrate that low energy ion scattering can be used to study the step -edge composition on vicinal single crystal surfaces. Employing the shadowi ng and focusing effects inherent to ion scattering, it is possible to perfo rm site-specific composition measurements on single crystal surfaces over a wide temperature range. By combining these measurements with ion trajector y simulations we have extracted quantitative information concerning the ste p-edge composition. This technique has been applied to the Pt25Rh75(4 1 0) surface in the temperature range between 400 degreesC and 700 degreesC, The experiments reveal a much stronger Pt enrichment of the step edges than at the terrace sites. This difference between the step-edge composition and t he terrace site composition is significantly larger than predicted by simpl e segregation models based on bond breaking. (C) 2001 Elsevier Science B.V. All rights reserved.