SURFACE SEGREGATION OF PTNI ALLOYS - COMPARING THEORETICAL AND EXPERIMENTAL RESULTS

The PtNi system is an interesting example of orientation-dependent segregation behaviour. Experimental and theoretical results of different authors on surface segregation of PtNi alloys are compared. The quite different results from the various theoretical predictions show that only very few methods (e.g. the tight-binding Ising model with an area-preserving map technique, the embedded atom method, or a thorough thermodynamic description) can be used successfully for describing the PtNi system. A multilayer thermodynamic description is used to study the influence of the different effects (negligible surface free energy difference, and the competition between an ordering and a size effect) on the composition profile. For comparing experimental results, the influence of preferential sputtering and annealing at different temperatures as well as environmental influence (e.g. due to carbon impurities or oxygen exposure), which might considerably change the measured values, are discussed.