Segregation, phase separation and grain boundary diffusion in thin films

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Surface segregation in phase separating binary systems has been calculated in a slab, consisting of atomic plains parallel with the free surface, as the function of the slab thickness, d. A special phase diagram is constructed, which shows the regions where there is a surface phase separation together with the bulk solubility curve: both of them depends on d. At small d values and at low temperatures the surface segregation can initiate the phase separation inside the film. For strongly segregating systems the phase separation from the surfaces develops and two layers of the A-rich phase cover the A-poor central phase in the slab (lamellar structure) and there is an enrichment of A atoms in the near surface layers of the upper phase. For weakly segregating systems at temperatures higher than a critical value Tc, - owning to overlapping of the increased concentrations in near-surface layers - an increased solubility can be observed with decreasing grain size. For T<Tc A-rich and A-poor phases can be in equilibrium with columnar structure. The problem of the existence of a minimum on the Gibbs-free energy versus d curve was also investigated in the mono-layer limit of the generalised Fowler-Guggenheim - approximation and it was shown that such a minimum could exist (i.e. a segregation stabilisation of the nanostructure is possible). Furthermore - because of the non-linearity of the problem - the role of 1/d is found to be similar to the temperature: decreasing the surface fraction (1/d) there is a sharp surface phase transition from a large to a small coverage. Consequences of the above results for the grain-boundary diffusion measurements are also discussed.

Original languageEnglish
Pages (from-to)121-128
Number of pages8
JournalDefect and Diffusion Forum
Publication statusPublished - Jan 1 1998



  • Diffusion
  • Grain Boundary
  • Segregation
  • Thin Films

ASJC Scopus subject areas

  • Radiation
  • Materials Science(all)
  • Condensed Matter Physics

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