Synchrotron Studies of Liquid Metal Surfaces

该研究提案的目标是通过同步辐射发展对液态金属和合金表面原子结构的基本了解。X射线反射率、非镜面漫反射和掠入射衍射的组合使得能够完整地描述表面平面内和垂直于表面的原子结构。重点讨论了液态共晶Au82Si18表面存在2D晶相的物理原因，并对其进行了理论上的解释。我们考虑的一个观点是，晶面相是由于Au和Si之间的大的负混合热而导致体液Au82Si18中已经有了高度的化学和拓扑短程有序化。对于目前所研究的所有金属液体，表面诱导了平行于表面的原子分层，人们认为，对于Au82Si18，这可能导致平面内2D长程结晶有序。因此，到目前为止，还研究了其他体系，如Pd-Si，Pd-Ge，它们表现出类似的混合热容和相图，如Au-Si。此外，对液态金属表面的研究扩展到了新的材料类别，如具有与金属液体明显不同的体液结构的纯Ge，以及多组分的大块金属玻璃形成液。由于在APS的光束线化学MatCARS上有新的仪器可用，液体Au82Si18的表面结构的测量允许对表面相的更连贯和物理上的真实了解，这是以前无法研究的液体Au82Si18的表面结构的细节

The goal of the research proposal was to develop basic understanding of the atomic structure of the surfaces of liquid metals and alloys by means of synchrotron radiation. The combination of x-ray reflectivity, off-specular diffuse scattering and grazing incidence diffraction allows for a complete description of the atomic structure in the plane of the surface and normal to the surface. Special focus was laid on the physical origin of the existence of 2D crystalline phases at the surface of liquid eutectic Au82Si18 that was discovered earlier and for which yet no theoretical explanation exists.One idea that we had considered is that crystalline surface phases arise from the large negative heat of mixing between Au and Si that leads to a high degree of chemical and topological short range order already in the bulk liquid Au82Si18. For all metallic liquids investigated so far the surface induces atomic layering parallel to the surface and the thought is that for Au82Si18 this might lead to in-plane 2D long-range crystalline order. Consequently other systems like Pd-Si, Pd-Ge that show comparable mixing enthalpies and phase diagrams like Au-Si were so far investigated within the lifetime of the fellowship. Furthermore, the study of liquid metal surfaces was extended to new classes of material like pure Ge that has a distinctly different bulk liquid structure than metallic liquids and to multicomponent bulk metallic glass forming liquids.Because of the availability of new instrumentation at the beamline Chem- MatCARS at APS the surface structure of liquid Au82Si18 measurements of details of the surface of structure of liquid Au82Si18 that could not previously be studied allowed a much more coherent and physically realistic understandinig of the surface phases.1