X-ray Studies of Atomic Layering at Liquid Metal Surfaces

Abstract

Surface-induced layering has been observed in liquid gallium and mercury using X-ray reflectivity. The specular reflectivity R((q_z)) has been measured to wavevector transfers as large as (q_z) = 3.0 Å(^{−1}). For Ga, the only major deviations from Fresnel theory (R_f) are near qz = 2.4 Å(^{−1}), where there is a peak in the ratio (R/R_f), For Hg, there is a broad peak near 2.15 Å(^{−1}). The data have been collected on a sputtered clean, ultra-high vacuum Ga surface and on a Hg surface in a reducing atmosphere of hydrogen. The data can be explained with a layered liquid/vapor interface that is roughened by thermally excited capillary waves. The layer spacing is similar to the Ga or Hg atomic dimensions, extending into the bulk with an exponential decay length of 6 Å for Ga and 3 Å for Hg.