Pairing interactions and Gibbs adsorption at the liquid Bi-In surface: A resonant x-ray reflectivity study

Resonant x-ray reflectivity measurements from the surface of liquid Bi22In7 8 find only a modest surface Bi enhancement, with 35 at.% Bi in the first a tomic layer. This is in contrast to the Gibbs adsorption in all liquid allo ys studied to date, which show surface segregation of a complete monolayer of the low surface tension component. This suggests that surface adsorption in Bi-In is dominated by attractive interactions that increase the number of Bi-In neighbors at the surface. These are the first measurements in whic h resonant x-ray scattering has been used to quantify compositional changes induced at a liquid alloy surface.