Microscopic surface structure of liquid alkali metals

We report an x-ray scattering study of the microscopic structure of the sur face of a liquid alkali metal. The bulk liquid structure factor of the eute ctic K67Na33 alloy is characteristic of an ideal mixture, and so shares the properties of an elemental liquid alkali metal. Analysis of off-specular d iffuse scattering and specular x-ray reflectivity shows that the surface ro ughness of the K-Na alloy follows simple capillary wave behavior with a sur face structure factor indicative of surface-induced layering. Comparison of the low-angle tail of the K67Na33 surface structure factor with the one me asured for liquid Ga and In previously suggests that layering is less prono unced in alkali metals. Controlled exposure of the liquid to H-2 and O-2 ga s does not affect the surface structure, indicating that oxide and hydride are not stable at the liquid surface under these experimental conditions.