Surface Phases in Binary Liquid Metal Alloys: An X-ray Study

Holger Tostmann, Elaine DiMasi, Oleg G. Shpyrko, Peter S. Pershan, Benjamin M. Ocko, and Moshe Deutsch Division of Applied Sciences and Department of Physics, Harvard University, Cambridge MA 02138 Department of Physics, Brookhaven National Laboratory, Upton NY 11973-5000 Department of Physics, Bar-Ilan University, Ramat-Gan 52100, Israel Abstract Surface sensitive x-ray scattering techniques with atomic scale resolution are employed to investigate the microscopic structure of the surface of three classes of liquid binary alloys: (i) Surface segregation in partly miscible binary alloys as predicted by the Gibbs adsorption rule is investigated for Ga-In. The first layer consists of a supercooled In monolayer and the bulk composition is reached after about two atomic diameters. (ii) The Ga-Bi system displays a wetting transition at a characteristic temperature Tw ≈ 220 C. The transition from a Bi monolayer on Ga below Tw to a thick Bi-rich wetting film above Tw is studied. (iii) The effect of attractive interactions between the two components of a binary alloy on the surface structure is investigated for two Hg-Au alloys.