M Schurmans

ON THE CONSPICUOUS SEGREGATION BEHAVIOR AT Pt–Rh SURFACES

Phase demixing is evaluated as a possible explanation for the anomalous temperature dependence of the Pt segregation at the Pt50Rh50(511), Pt25Rh75(110) and Pt25Rh75(100) surfaces. Calculations are performed in the quasichemical approximation and a broken bond scheme. Although the calculations based on systematic demixing tend to overestimate the surface enrichment, the qualitative agreement appears to be rather good.

Synergy between material, surface science experiments and simulations

This chapter examines the link between bulk alloys and surfaces and the necessary conditions that effective simulation techniques must meet in order to properly describe, in a consistent manner, the varied phenomena that characterize each field of research. After a brief description of the thermodynamics of alloy formation and surface segregation in ordered and disordered alloys, model calculations combining the Monte Carlo method and suitable energy models are presented as fully complementary to experiments in order to gain insight in segregation and other surface phenomena, deployed by materials in order to minimize their surface free energy and hence their total Gibbs free energy. In the confrontation between experiments and modeling, it is assumed that the surface, as observed experimentally, corresponds to the equilibrium situation of minimal Gibbs free energy. The entropy part is modeled by the stochastic nature of Monte Carlo simulations, while the energy part is taken into account by appropriate energy models. In this chapter, we describe the (modified) embedded atom method, the derivation of its parameters, and its applications to several cases of interest.