Liquid-Gas Interfacial Chemistry of Gallium-Indium Eutectic in the Presence of Oxygen and Water Vapor

Gallium-indium eutectic (eGaIn) is a liquid metal being explored in a number of applications because of its high thermal/electrical conductivity and favorable deformability. A key function regulating the mechanical properties of eGaIn is the ability to rapidly form a passivating oxide layer, which is known to occur upon exposure to air under ambient conditions. Nevertheless, little is known about the molecular level surface reactivity of eGaIn toward oxygen and water vapor under in situ conditions. Herein we present ambient pressure X-ray photoelectron spectroscopy results examining the liquid-gas interface of eGaIn in the presence of oxygen and water vapor. By examining each gas independently, results reveal that both oxygen and water vapor react with Ga in eGaIn to form the same oxidized products: Ga3+ oxide (Ga2O3) as an outer layer and Ga1+ oxide (Ga2O) as an interlayer. Despite similar product formation, stark differences are observed in pressure-dependence and adsorbate-induced binding energy shifts. The results herein suggest both oxygen and water vapor uniquely contribute to the oxidative passivation of eGaIn under ambient conditions.