X-ray Reflectivity Studies of the Surface Structure of Liquid Metals

Abstract

Extensive theoretical predictions of atomic layering at the surfaces of liquid metals have remained unconfirmed due to the limited range of wave vector transfer qz that has been previously measured. We report here on X-ray reflectivity studies from the surfaces of liquid mercury to qz greater-than or equivalent to 2.8 Å−1, and gallium to qz greater-than or equivalent to 3.0 Å−1, that show peaks which clearly demonstrate atomic layering with spacing on the order of the atomic diameter. The exponential decay of layer penetration into the bulk for Ga (6.5 Å) is larger than for Hg (3–3.5 Å). The prominent features of the layering remain unchanged under self-assembled monolayers of thiols. The Ga layering shows an unexpected strong temperature dependence. Differences between the reflectivity from Ga and Hg at small qz indicate fundamental differences in the surface structure for these two liquid metals.