Evidence for Facilitated Surface Transport during Ge Crystal Growth by Indium in Liquid Hg–In Alloys at Room Temperature

Room-temperature electrodeposition of Ge crystallites was investigated by the electrochemical liquid–liquid–solid (ec-LLS) process using a family of Hg$_{1–x}$In$_x$ alloys. The objective was to determine whether different liquid metal alloys with nominally the same bulk solubility toward Ge but potentially different surface character would yield any differences in the resultant Ge crystallites. Variation of the In fraction in these alloys was the control variable. The following details were ascertained from the cumulative data. First, in accordance with thermodynamic predictions, the surface of Hg$_x$In$_{1–x}$ alloys was strongly enriched with Hg according to X-ray specular reflectivity data. These data further indicated that the surface enrichment was confined exclusively to a single atomic layer at the liquid metal surface. These properties of the Hg$_{1–x}$Inx/electrolyte interface structure facilitated the first two steps of the ec-LLS process. Second, the presence of In influenced the morphology of the resultant Ge crystallites from ec-LLS, in accordance with mediated transport of the Ge upon initial electroreduction. Specifically, X-ray diffraction, Raman, and microscopy data suggest that a strong affinity between In and Ge that affects the crystal morphology. This study thus motivates further exploration of both In as a component in liquid metal solvents to facilitate grain size and more general studies detailing how the surface structure and composition of liquid metals influence crystal growth. These findings significantly advance the prospect for preparing technologically relevant inorganic crystalline semiconductors at low temperatures