SURFACE SEGREGATION KINETICS IN BINARY SUBSTITUTIONAL SYSTEMS - A COMPARISON BETWEEN MDE AND KTBTM

Because of its great technological relevance the investigation of the kinetics of interface segregation is gaining increasing interest. During the last few years two successful models describing the kinetics of surface segregation in substitutional systems have been developed, the MDE (modified Darken equations) based on the macroscopic diffusion equation and the KTBIM (kinetic tight-binding Ising model) based on the microscopic jump probabilities of atoms of neighbouring atom planes. The resulting segregation kinetics obtained by these models are compared and discussed. Whereas the results for the long-time segregation behaviour are very similar especially in dilute systems, the predicted segregation kinetics in concentrated systems and during the initial phase of the segregation process strongly depends on the applied model. This discrepancy between the results obtained with the two models in part can be avoided by using the concept of an enhanced subsurface mobility of the segregand in the MDE.