X-ray study of the oxidation of liquid-gallium surfaces

The oxidation of liquid-gallium surfaces has been investigated with surface x-ray scattering techniques. By exposing the liquid-metal surface at room temperature to doses on the order of 180 L of oxygen where 1 L=${10}^{\mathrm{-}6}$ Torr s, a gallium oxide film with a well-defined thickness of ∼5 Å readily forms. The oxide thickness and roughness of the liquid/oxide and oxide/vapor interfaces do not change with oxygen dosage up to 1600 L nor with temperature up to 573 K. This is in contrast to what is observed for the bare liquid-Ga surface, which is roughened significantly by thermally excited capillary waves with temperatures up to only 443 K. This is a good indication that the oxide layer provides rigidity to the liquid surface and is likely a solid; grazing-incidence measurements suggest that the film is amorphous or poorly crystallized. Based on comparisons with known crystal structures, models are suggested for the atomic arrangements in the gallium oxide layer and its interface with the underlying liquid.