Model calculations of surface phase transitions in Ga–Bi alloys: adsorption,wetting, surface freezing and melting

Abstract

Thermodynamic model calculations of the surface phase transitions inGa–Bi alloys are performed, which account in particular for the finitethickness of the adsorption films. The excess chemical potential of bismuth inthe films is calculated by employing a screened Coulomb potential. Thecalculated dependence of the liquid film thickness predicts adsorption andcomplete wetting transitions, which are in qualitative agreement with theexperimental data. On the basis of surface tension calculations the surfacefreezing–melting transition is modelled and the results coincide with experimentalobservations via second harmonic generation and surface light scattering. Usingan appropriate description of the nucleation mechanism in liquid filmsthe line tension between the liquid and solid films is determined by afit of experimental data. A complete diagram of the surface liquid–solidphase transitions on the vapour/liquid Ga–Bi interface is derived.