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.
Highlights
Chemical reactions at interfaces are of the fundamental and practical scientific interest
The oxidation of Al is rather rapid in the presence of even trace amounts of molecular oxygen, the formation of a relatively thin surface oxide layer effectively passivates the bulk from further oxidation [4]
In addition to these reflectivity scans the reflected signal at the point corresponding to the specular condition at qz = 0.5 A À1 was continuously monitored during the entire oxidation process even when the Sn surface was heavily oxidized and the specular signal was smeared out
Summary
Chemical reactions at interfaces are of the fundamental and practical scientific interest. In spite of the fact that the free surfaces of liquid metals have recently attracted considerable attention because of the atomic ordering at the liquid–vapor interface [5,6,7] there have been very few studies of their reactive properties [8,9,10,11]. Oxidation of such surfaces are of particular interest because they lack the types of defects at which homogeneous nucleation occurs on solid surfaces namely steps, pits and dislocations [1]. JUðqzÞj2 exp1⁄2ÀrðqzÞ2q2z ; ð1Þ rðqzÞ2 1⁄4 r2int: þ rcwðqzÞ2; where Rf(qz) is the Fresnel reflectivity that can be calculated from classical optics for a flat and structureless surface, U(qz) is the surface structure factor, and r(qz) is the effective surface roughness consisting of the intrinsic roughness rint and the
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