Synchrotron Studies of Liquid Metal Surfaces

该研究计划的目标是利用同步辐射对液态金属和合金表面的原子结构进行基本的了解。结合x射线反射率、非镜面漫射散射和掠入射衍射，可以完整地描述表面平面和表面法向平面上的原子结构。重点研究了较早发现的液态共晶Au82Si18表面存在二维晶相的物理起源，但目前尚无理论解释。我们考虑过的一个想法是，晶体表面相是由Au和Si之间的大量负混合热产生的，这导致了体积液体Au82Si18中已经存在的高度的化学和拓扑短程有序。对于目前所研究的所有金属液体，表面诱导平行于表面的原子分层，并且认为对于Au82Si18，这可能导致平面内二维长程晶体秩序。因此，其他系统，如Pd-Si， Pd-Ge，显示出类似的混合焓和相图，如Au-Si，到目前为止，在奖学金的生命周期内进行了研究。此外，液态金属表面的研究扩展到具有与金属液体明显不同的大块液体结构的纯Ge等新型材料，以及多组分大块金属玻璃形成液体。由于APS的束线Chem- MatCARS上的新仪器的可用性，液体Au82Si18的表面结构的细节测量以前无法研究的液体Au82Si18的表面结构允许对表面相进行更连贯和物理上更现实的理解

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