Modeling effects of subsurface tension on segregation:Pt25Rh75(111)oscillatory profile used as a test case

Abstract

Surface induced bond energy variations are incorporated as homoatomic interaction model in the statistical-mechanical free energy concentration expansion method (FCEM) for the prediction of temperature dependent segregation in alloys. This article focuses on the role of subsurface (and outermost) layer tensions in the emergence of oscillatory segregation profiles even in alloys with weak mixing or demixing tendency. As a test case for the proposed approach, surface segregation in ${\mathrm{Pt}}_{25}{\mathrm{Rh}}_{75}(111)$ is computed by FCEM with Naval Research Laboratory (NRL)-tight-binding (TB) data of surface-induced bond energy variations. A distinct two-layer oscillatory profile is obtained in fair agreement with previously reported experimental data. According to TB data, such subsurface bonding effects are anticipated also for some other Pt-based alloys. The FCEM/TB approach can be used also for predicting surface segregation phenomena in alloy nanoclusters.