Abstract
The surface structure of the liquid phase of the Au{sub 72}Ge{sub 28} 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 Au{sub 82}Si{sub 18} eutectic. Instead, the surface of eutectic Au{sub 72}Ge{sub 28} is liquidlike and the layering can be explained by the distorted crystal model with only slight modifications to the first layer.
Highlights
The surface structure of liquid metals was essentially an unexplored phenomena until slightly more than a decade ago when the first synchrotron x-ray reflectivity studies on liquid metal surfaces were carried out.[1,2] These measurements on liquid HgRef. 1͒ and GaRef. 2͒ confirmed the proposal by Rice and colleagues[3,4,5] that the local order at the free surface was sufficient to induce atomic layering
We report experiments here that reveal that the surface order of the liquid Au72Ge28 eutectic shows no evidence of the anomalous surface-induced order that has been observed for the Au82Si18 eutectic
The principal result from this study is the demonstration that the surface structure of the liquid Au72Ge28 eutectic does not exhibit the same extraordinary properties that were found recently for liquid eutectic Au82Si18, i.e., a strong layering normal to the surface that is accompanied by an in-plane 2D crystalline long-range order
Summary
The surface structure of liquid metals was essentially an unexplored phenomena until slightly more than a decade ago when the first synchrotron x-ray reflectivity studies on liquid metal surfaces were carried out.[1,2] These measurements on liquid HgRef. 1͒ and GaRef. 2͒ confirmed the proposal by Rice and colleagues[3,4,5] that the local order at the free surface was sufficient to induce atomic layering This layering decays within a distance from the surface of the order of the bulk liquid correlation length, i.e., 3–4 atomic layers.[4,5] The layering is observed as a peak in the specular reflectivity at the wave vector transfer vector qz = 2 / d where d is the layering distance. There is no evidence for Gibbs adsorption found in other binary liquid metal alloys with such dissimilar components
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