Wetting Phase Transition at the Surface of Liquid Ga-Bi alloys: An X-ray Reflectivity Study

TL;DR

This study uses X-ray reflectivity to investigate surface structural changes in liquid Ga-Bi alloys across the monotectic temperature, revealing a wetting film with unexpected properties.

Contribution

It provides the first detailed structural characterization of the wetting transition at the surface of liquid Ga-Bi alloys using high-resolution X-ray reflectivity.

Findings

Presence of a Bi monolayer at all temperatures.

Formation of a thick, Bi-rich wetting film above the monotectic temperature.

Observation of a concentration gradient within the wetting film.

Abstract

X-ray reflectivity measurements of the binary liquid Ga-Bi alloy reveal a dramatically different surface structure above and below the monotectic temperature $T_{mono}=222^{\circ}$ C. A Gibbs-adsorbed Bi monolayer resides at the surface at both regimes. However, a 30 {\AA} thick, Bi-rich wetting film intrudes between the Bi monolayer and the Ga-rich bulk for $T > T_{mono}$. The internal structure of the wetting film is determined with {\AA} resolution, showing a theoretically unexpected concentration gradient and a highly diffuse interface with the bulk phase.