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 ${\mathrm{Bi}}_{22}{\mathrm{In}}_{78}$ find only a modest surface Bi enhancement, with $35\mathrm{at}.\%$ Bi in the first atomic layer. This is in contrast to the Gibbs adsorption in all liquid alloys 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 which resonant x-ray scattering has been used to quantify compositional changes induced at a liquid alloy surface.