Surface structure of the liquid Au72Ge28 eutectic phase: X-ray reflectivity

The surface structure of the liquid phase of the Au72Ge28 eutectic alloy has been measured using resonant and nonresonant x-ray reflectivity and grazing incidence x-ray diffraction. In spite of the significant differences in the surface tension of liquid Ge and Au the Gibbs adsorption enhancement of Ge concentration at the surface is minimal. This is in striking contrast to all the other binary alloys with large differences in the respective surface tensions measured up to date. In addition there is no evidence of the anomalous strong surface layering or in-plane crystalline order that has been reported for the otherwise quite similar liquid Au82Si18 eutectic. Instead, the surface of eutectic Au72Ge28 is liquidlike and the layering can be explained by the distorted crystal model with only slight modifications to the first layer.