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

Abstract

Room-temperature electrodeposition of Ge crystallites was investigated by the electrochemical liquid–liquid–solid (ec-LLS) process using a family of Hg1–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 In1–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 Hg1–x In x /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.

Understanding and Expanding the Prospects for Electrosynthesis with Liquid Metal Electrodes

“…We posited that the interfacial structure would be quite different in contact with Ge crystals since molten In more readily wets Ge wafers than Hg . The surface tension for In/Ge is 0.58 N m –1 at T = 25 °C while for Hg/Ge it is >1.1 N m –1 . In this case, In should accumulate at this interface.…”

“…P.MurphyB.MagnussenO.MaldonadoS. Pattadar, D. Cheek, Q. Sartori, A. Zhao, Y. Giri, R. P. Murphy, B. Magnussen, O. Maldonado, S. 10.1021/acs.cgd.0c0148520212116451656 …”

“…ec-LLS is natively simple to execute since heating/cooling and vacuum equipment are not required. ec-LLS is not specific to just the common liquid metals in electrochemistry (i.e., Hg), having been performed with other pure liquid metals and molten alloys. ,− ec-LLS is agnostic toward electrolyte type, i.e,. both molecular and ionic electrolyte solvents are suitable. , ec-LLS can be performed with large or minute volumes of liquid metals. , …”

Detection of Ge-Containing Adlayers at the Liquid Hg/Water Interface by In Situ X-ray Reflectivity in Aqueous Borate Electrolytes Containing Dissolved GeO2

“…Two more recent sets of studies have illustrated the value of XRR in studying electrodeposition processes at water/liquid metal interfaces. XRR measurements combined with grazing incidence X-ray diffraction elucidated the initial steps in the nucleation and growth of lead halide crystals at liquid Hg electrolyte interfaces. , Other XRR data have separately identified the surface composition and structure of liquid Hg–In alloy electrodes used to grow Ge crystals …”

“…8,28 Other XRR data have separately identified the surface composition and structure of liquid Hg−In alloy electrodes used to grow Ge crystals. 29 This study utilizes XRR to determine in situ the interface between liquid Hg and aqueous Na 2 B 4 O 7 containing dissolved GeO 2 . This electrolyte is of interest since electrodeposition of Ge nanowires, 14 microwires, 30 and epitaxial films 31 is possible with a variety of liquid metals.…”