Quasi-two-dimensional freezing and melting at the liquid/vapour interface of a Ga–Pb alloy

We have studied the quasi-two-dimensional freezing and respective melting at the liquid/vapour interface of a dilute lead-in-gallium alloy (0.52 at.% Pb) for the first time by XPS and AES spectroscopy at different temperatures below and above the transition temperature of 183.5 °C. Pb-rich wetting films of roughly 1 monolayer have been determined. At the onset of surface freezing (SF) the film thickness rises to a value of ∼2 monolayers and reaches a maximum of ∼4 monolayers of nearly pure Pb at ∼1 K below the SF temperature. These film characteristics are reproducible in different heating and cooling cycles.