INCOMPLETE WETTING OF VERY DILUTE CU(AG) ALLOYS BY SURFACE SEGREGATION

The equilibrium segregation isotherm derived from kinetics experiments on a dilute Cu(Ag) solid solution exhibits at T congruent-to 730 K a surface phase transition from almost pure Cu to almost pure Ag. The energetics of the driving forces being unambiguously defined from the electronic structure (TBIM: tight-binding Ising model), this transition can be easily interpreted in the framework of a simplified (Fowler-Guggenheim type) approach. A more sophisticated statistical treatment (APM: area preserving mapping) shows that this transition should be first of a finite succession of layering transitions leading to an incomplete Ag-wetting of the Cu(Ag) surface.