In situ X-ray scattering studies of growth at liquid metal - liquid electrolyte interfaces

液-液界面上的生长对材料合成具有重要的现实意义。这些流体界面提供了柔软、无缺陷的衬底，并允许制备各种不同的纳米材料。由于缺乏关于原子尺度界面结构和基本微观生长机制的数据，阻碍了对这些界面上的相形成过程的详细了解。在这个项目中，我们的目标是利用原位X射线散射，从根本上阐明在液态金属(汞、镓)和水溶液电解质溶液之间的界面上电化学控制生长的特殊情况。我们之前在汞电极上为PbBrF所做的工作中获得的关于这种生长过程的第一个原子尺度数据揭示了一种复杂的行为，涉及在两种液体之间形成定义明确的超薄晶体前驱体层。它们作为后续3D晶体形成的模板，导致准外延生长。在拟议的项目中，我们将系统地研究这些现象在液态金属-电解液界面沉积过程中的作用，并研究沉积形态随所用电势的时间演变。首先，我们将以卤化铅为模型体系，研究离子化合物的生长。特别是，我们将侧重于前驱层的结构作为卤化物物种和液态金属衬底的函数，以及它在指导晶体生长中的作用。其次，我们将通过电化学液-液-固沉积来研究半导体锗在这些界面上的生长，这是一种新的、技术上感兴趣的过程。这里特别重要的是澄清界面结构、生长的初始阶段以及3D矿床的随时间变化的形态。作为这些研究的一部分，我们将确定Ga-电解液界面的原子级结构，特别是液态金属中随电位和温度变化的表面分层，这本身就是一个重要的课题。此外，这些实验将有助于进一步发展X射线散射方法，作为研究液-液界面生长过程的一种工具。

Growth at liquid-liquid interfaces is of substantial current interest for material synthesis. These fluid interfaces provide a soft, defect-free substrate and allow preparation of a wide range of different nanomaterials. Detailed understanding of phase formation processes at these interfaces is hampered by the lack of data on the atomic-scale interface structure and the underlying microscopic growth mechanisms. In this project we aim at fundamentally clarifying those for the specific case of electrochemically controlled growth at the interface between liquid metals (mercury, gallium) and aqueous electrolyte solutions using in situ X-ray scattering. First atomic scale data on such growth processes, obtained in our previous work for PbBrF at Hg electrodes, revealed a complex behavior, involving the formation of well-defined ultrathin crystalline precursor layers in between the two liquids. These serve as a template for the subsequent 3D crystal formation, leading to a quasi-epitaxial growth. In the proposed project we will systematically investigate the role of these phenomena in deposition processes at liquid metal - electrolyte interfaces as well as study the temporal evolution of the deposit morphology as a function of the employed potential. First, the growth of ionic compounds will be studied, employing lead halides as a model system. In particular, we will focus on the structure of the precursor layer as a function of halide species and liquid metal substrate and its role in steering the crystal growth. Secondly, we will investigate the growth of the semiconductor germanium at these interfaces by electrochemical liquid-liquid-solid deposition, a novel, technologically interesting process. Of particular importance here is clarification of the interface structure, the initial stages of growth, and the time-dependent morphology of the 3D deposit. As a part of these studies we will determine the atomic-scale structure of the Ga - electrolyte interface, specifically the potential- and temperature-dependent surface layering in the liquid metal, which in itself is an important topic. In addition, these experiments will help in further developing X-ray scattering methods as a tool for operando studies of growth processes at liquid-liquid interfaces.