Surface chemistry of liquid bismuth under oxygen and water vapor studied by ambient pressure X-ray photoelectron spectroscopy

Highlights: • Liquid-gas interface of Bi examined at 550 K via ambient pressure XPS. • Water vapor remained unreactive over the entire pressure range. • Oxygen unreactive up to 10⁻⁴ Torr, above this pressure Bi₂O₃ forms at surface. • Oxygen exposure onset for liquid Bi significantly higher than for solid Bi. Bismuth (Bi) has a fairly low melting point of 544 K making it practical as a liquid metal medium in a number of applications. Under ambient atmospheric conditions the surface of solid Bi oxidizes. While the solid Bi interface has been fairly well characterized with surface science studies upon exposure to oxygen, to date little is known about the molecular level reactivity of the liquid interface. Using ambient pressure X-ray photoelectron spectroscopy the liquid–gas interfacial chemistry of Bi was examined upon exposure to oxygen gas and water vapor at 550 K up to a maximum pressure of 0.5 Torr. Water vapor remained unreactive towards the liquid interface over the entire pressure range. Oxygen remined unreactive up to 10⁻⁴ Torr, whereas above this pressure oxidation was observed forming Bi₂O₃. The oxidation exposure onset was > 5 × 10⁵ Langmuirs, significantly higher than what is required for solid Bi interfaces.