Surface oxidation of liquid Sn

TL;DR

This study uses x-ray scattering to investigate how liquid tin's surface oxidizes, revealing a new crystalline SnO phase that forms under specific conditions and differs from known Sn oxide structures.

Contribution

It reports the discovery of a previously unreported crystalline phase of SnO at the liquid Sn surface and details its unique structural properties.

Findings

Oxidation occurs above an activation pressure of ~5.0×10^-6 Torr.

A new crystalline SnO phase with a face-centered cubic structure was observed.

The lattice parameters of the new phase are about 9% smaller than known high-pressure Sn oxides.

Abstract

We report the results of an x-ray scattering study that reveals oxidation kinetics and formation of a previously unreported crystalline phase of SnO at the liquid-vapour interface of Sn. Our experiments reveal that the pure liquid Sn surface does not react with molecular oxygen below an activation pressure of \~5.0*10-6 Torr. Above that pressure a rough solid Sn oxide grows over the liquid metal surface. Once the activation pressure has been exceeded the oxidation proceeds at pressures below the oxidation pressure threshold. The observed diffraction pattern associated with the surface oxidation does not match any of the known Sn oxide phases. The data have an explicit signature of the face-centred cubic structure, however it requires lattice parameters that are about 9% smaller than those reported for cubic structures of high-pressure phases of Sn oxides. Keywords: X-ray scattering, diffraction, and reflection; Oxidation; Surface chemical reaction; Surface structure, morphology, roughness, and topography; Tin; Tin oxides; Liquid surfaces; Polycrystalline thin films