Surface analysis techniques in the study of segregation phenomena

Abstract

In general, the chemical composition of surfaces and interfaces is different from that of the bulk due to segregation of alloying elements and impurities. Surface analysis techniques play a decisive role in the quantitative study of segregation phenomena, which is necessary for the understanding and improvement of a variety of materials properties. After an outline of the most important surface analysis techniques, namely Auger Electron Spectroscopy (AES), X-ray Photoelectron Spectroscopy (XPS or ESCA), Ion Scattering Spectroscopy (ISS) and Secondary Ion Mass Spectroscopy (SIMS) and their recent developments, a survey of their specific use in segregation studies is given. Examples of the measurement of the equilibrium segregation at surfaces and interfaces demonstrate the determination of the segregation free energy and its dependence on orientation and of solute-solute interactions leading to site competition or synergetic cosegregation in multicomponent systems. Recent work with Scanning Auger Microscopy on surfaces of fractured nickel-indium bicrystals shows a method to measure surface and grain boundary segregation under identical conditions. Dynamic studies of the segregation kinetics yield the bulk diffusion constant of the solute and allow an interpretation of the in-depth profile obtained in the sputtering of alloys. Mainly due to the results of surface analysis studies, a framework of the understanding of segregation phenomena is available, although many details of the solute-solute and solute-structure interactions still need to be disclosed by further research.