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

• Applicant: Professor Dr. Olaf Magnussen
• Subject Area: Physical Chemistry of Solids and Surfaces, Material Characterisation ; Experimental Condensed Matter Physics
• Term: from 2014 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 266661790

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.

• DFG Programme: Research Grants
• Co-Investigator: Privatdozentin Dr. Bridget Murphy