Atomic-scale surface demixing in a eutectic liquid BiSn alloy

TL;DR

This study uses resonant x-ray reflectivity to reveal atomic-scale surface demixing in a liquid BiSn alloy, showing multilayer composition modulation driven by Bi-Sn interactions.

Contribution

It provides the first quantitative analysis of atomic-scale surface demixing in a liquid alloy using multilayer Gibbs models.

Findings

Atomic-scale demixing extends over three layers.

Bi-Sn interactions dominate near-surface composition.

Multilayer models accurately describe the surface structure.

Abstract

Resonant x-ray reflectivity of the surface of the liquid phase of the Bi$_{43}$Sn$_{57}$ eutectic alloy reveals atomic-scale demixing extending over three near-surface atomic layers. Due to the absence of underlying atomic lattice which typically defines adsorption in crystalline alloys, studies of adsorption in liquid alloys provide unique insight on interatomic interactions at the surface. The observed composition modulation could be accounted for quantitatively by the Defay-Prigogine and Strohl-King multilayer extensions of the single-layer Gibbs model, revealing a near-surface domination of the attractive Bi-Sn interaction over the entropy.