In-situ X-ray scattering studies of growth at liquid metal-electrolyte interfaces
Electrochemical growth at liquid-metal electrolyte interfaces was investigated with in-situ X-ray scattering techniques. Three studies of different combinations of liquid metal working electrodes and electrolytes are presented. In the first, a liquid mercury electrode immersed in a solution of NaX + PbX2 (X= Br, Cl, F) was probed by X-ray reflectivity and grazing incidence X-ray diffraction as a function of applied potential. In this study, PbBr2 and PbCl2 containing solutions showed a defined layer formation at a potential close to the de-amalgamation region of Pb from Hg. For more positive potential, the systems exhibited quasi-epitaxial growth of bulk crystals of Pb(OH)Y (Y=Br, Cl) oriented with the c-axis of the precursor layer along the surface normal direction. On the contrary, growth in the F-containing solution resulted in a powder-like deposit. This study reveals how the ad-layer can act as a template and determine the orientation of the bulk crystals. In the second, the interface between Hg-Na2B4O7 and Hg-Na2B4O7 + GeO2 was also investigated in-situ with X-ray reflectivity studies. The data suggested an enriched H2GeO3 and/or HGeO3- at the working electrode's surface. At positive potentials, an ultrathin film was observed at the Hg-electrolyte interface, likely formed by condensation reaction driven by the concentration of HGeO3- at the liquid Hg/electrolyte interface. In the third, deposition of crystalline Ge on different working electrode compositions Hg(1-x)In(x) (for x= 0, 0.3, 0.5, 0.7, 1) was investigated. Changes were observed in the Ge crystals shape, both as a function of potential and composition. X-ray reflectivity indicates that the very first layer of the liquid electrode is Hg. Thus, nucleation and growth must occur underneath the surface of the substrate. The crystalline grain morphology is mainly affected by In as a liquid metal component due to the strong affinity between In and Ge.