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

液-液界面的生长是当前材料合成的重要研究方向。这些流体界面提供了一个柔软的、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微观生长机制的数据，对这些界面上相形成过程的详细理解受到阻碍。在这个项目中，我们的目标是从根本上澄清在液态金属（汞，镓）和水电解质溶液之间的界面上电化学控制生长的具体情况，使用原位x射线散射。我们之前在汞电极上获得的PbBrF生长过程的第一个原子尺度数据揭示了一种复杂的行为，包括在两种液体之间形成定义明确的超薄晶体前驱体层。这些作为随后3D晶体形成的模板，导致准外延生长。在本项目中，我们将系统地研究这些现象在液态金属-电解质界面沉积过程中的作用，并研究沉积形态随电位变化的时间演变。首先，离子化合物的生长将被研究，采用卤化铅作为模型系统。特别地，我们将关注前驱体层的结构作为卤化物种类和液态金属衬底的函数及其在引导晶体生长中的作用。其次，我们将研究通过电化学液-液-固沉积在这些界面上的半导体锗的生长，这是一种新颖的，技术上有趣的过程。这里特别重要的是澄清界面结构，生长的初始阶段，以及三维沉积的随时间变化的形态。作为这些研究的一部分，我们将确定镓-电解质界面的原子尺度结构，特别是液态金属中与电位和温度相关的表面分层，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，作为液-液界面生长过程的operando研究工具。

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.