Anomalous layering at the liquid Sn surface

TL;DR

This study uses X-ray reflectivity to reveal unique surface layering phenomena in liquid tin, including a high-density surface layer and atomic layer contraction, expanding understanding of liquid metal surfaces.

Contribution

It reports the first observation of a high-density surface layer in pure liquid metal, specifically tin, and models the surface structure with a contracted atomic layering.

Findings

Presence of a high-density surface layer in liquid Sn

Surface layering similar to other liquid metals

Atomic layer spacing contraction at the surface

Abstract

X-ray reflectivity measurements on the free surface of liquid Sn are presented. They exhibit the high-angle peak, indicative of surface-induced layering, also found for other pure liquid metals (Hg, Ga and In). However, a low-angle peak, not hitherto observed for any pure liquid metal, is also found, indicating the presence of a high-density surface layer. Fluorescence and resonant reflectivity measurements rule out the assignment of this layer to surface-segregation of impurities. The reflectivity is modelled well by a 10% contraction of the spacing between the first and second atomic surface layers, relative to that of subsequent layers. Possible reasons for this are discussed.