Electrochemical Liquid-Liquid-Solid Deposition of Ge at Hg Microdroplet Ultramicroelectrodes

Zhang, Tim; Fahrenkrug, Eli; Maldonado, Stephen

doi:10.1149/2.0691609jes

Cited by 10 publications

(11 citation statements)

References 29 publications

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“…Using electrochemical gradients rather than thermal gradients, the electrochemical liquid–liquid–solid (ec-LLS) strategy mirrors the nucleation and crystal growth aspects of VLS and LPE but without any heating or extensive support apparatus. Simply, a liquid metal acts as the working electrode where oxidized species can be reduced and then dissolved into the liquid metal at rates dictated by the electrochemical reduction reaction, surface chemistry, and rates of dissolution. − Recent studies have shown that the liquid metal alloy composition affects the resultant crystal size and morphology, , but clear design rules for the liquid metal have yet to be identified.…”

Section: Introductionmentioning

confidence: 99%

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

Pattadar

Cheek

Sartori

et al. 2021

Crystal Growth & Design

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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.

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Section: Introductionmentioning

confidence: 99%

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

Pattadar

Cheek

Sartori

et al. 2021

Crystal Growth & Design

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“…Prior electrochemical studies of Ge ec-LLS on Hg microdroplets support a complicated mechanism for the reduction of GeO 2 where adsorbed species may be involved. 57 If a rate-determining intermediate is surface bound and at too low of a surface coverage to result in the formation and dissolution of Ge 0 into the liquid metal, then Ge nanowire growth will not occur. The role of at least one surface-bound species in the electrochemical process is further in line with separate observation that Ge nanowire growth was never observed when the liquid metals were exposed to saturating levels of citrate ligands.…”

Section: Resultsmentioning

confidence: 99%

“…This point suggests that the formal concentration in solution did not directly relate to the rate of reduction (as would be expected for the reduction of a diffusion limited species in solution). Prior electrochemical studies of Ge ec-LLS on Hg microdroplets support a complicated mechanism for the reduction of GeO 2 where adsorbed species may be involved . If a rate-determining intermediate is surface bound and at too low of a surface coverage to result in the formation and dissolution of Ge 0 into the liquid metal, then Ge nanowire growth will not occur.…”

Section: Resultsmentioning

confidence: 99%

In Situ Transmission Electron Microscopy Measurements of Ge Nanowire Synthesis with Liquid Metal Nanodroplets in Water

et al. 2020

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The growth of Ge nanowires in water inside a liquid transmission electron microscope (TEM) holder has been demonstrated at room temperature. Each nanowire growth event was stimulated by the incident electron beam on otherwise unsupported liquid Ga or liquid In nanodroplets. A variety of conditions were explored, including liquid metal nanodroplet surface condition, liquid metal nanodroplet size and density, formal concentration of dissolved GeO2, and electron beam intensity. The cumulative observations from a series of videos recorded during growth events suggested the following points. First, the conditions necessary for initiating nanowire growth at uncontacted liquid metal nanodroplets in a liquid TEM cell indicate the process was governed by solvated electrons generated from secondary electrons scattered by the liquid metal nanodroplets. The attained current densities were comparable to those achieved in conventional electrochemical liquid–liquid–solid (ec-LLS) growths outside of a TEM. Second, the surface condition of the liquid metal nanodroplets was quite influential on whether nanowire growth occurred and surface diffusion of Ge adatoms contributed to the rate of crystallization. Third, the Ge nanowire growth rates were limited by the feed rate of Ge to the crystal growth front rather than the rate of crystallization at the liquid metal/solid Ge interface. Estimates of an electrochemical current for the reduction of dissolved GeO2 were nominally in line with currents used for Ge nanowire growth by ec-LLS outside of the TEM. Fourth, the Ge nanowire growths in the liquid TEM cell occurred far from thermodynamic equilibrium, with supersaturation values of 104 prior to nucleation. These collective points provide insight on how to further control and improve Ge nanowire morphology and crystallographic quality by the ec-LLS method.

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“…The basic observation that all of the e-BiIn caps had smooth shapes and surfaces devoid of Ge crystallites suggested that, under the conditions employed here, nucleation and crystallization of Ge at the e-BiIn/Si interface was energetically more favorable than homogeneously within e-BiIn and heterogeneously at the electrolyte/e-BiIn interface. Accordingly, we consider the solvation properties of e-BiIn for Ge more akin to Ga-based liquid metals , than pure Hg, where the former supports heterogeneous nano- and microwire growth while the latter does not. In this work, definitive evidence of epitaxial Ge micro- or nanowire growth was not collected.…”

Section: Discussionmentioning

confidence: 99%

“…Our group has previously identified mercury (Hg), gallium (Ga), indium (In), and a eutectic alloy of Ga and In (e-GaIn) as metals that can operate as electrodes and growth solvents in ec-LLS. ,,, Metals without either Hg or Ga are particularly desirable since the former has high volatility and the latter tends to incorporate strongly in group IV semiconductor crystals . A potentially interesting alternative liquid metal is eutectic bismuth indium (21.3 at.…”

Section: Introductionmentioning

confidence: 99%

Eutectic-Bismuth Indium as a Growth Solvent for the Electrochemical Liquid-Liquid-Solid Deposition of Germanium Microwires and Coiled Nanowires

DeMuth

Lancaster

et al. 2017

Crystal Growth & Design

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Crystalline germanium (Ge) micro-and nanowires have been grown from aqueous electrolytes through an electrochemical liquid-liquid-solid (ec-LLS) process using eutectic bismuth indium (e-BiIn) alloy as the liquid metal electrode. This alloy represents the first non-Hg or non-Ga containing liquid metal to be used for the growth of a group IV semiconductor crystal below the boiling point of water. The electrochemical stability of e-BiIn in aqueous electrolyte was assessed through cyclic voltammetry, which showed the metal alloy was destabilized either by anodic oxidation at potentials more positive than −1.0 V vs E(Ag/AgCl) or by cathodic reduction of Bi to BiH 3 at potentials more negative than −1.4 V vs E(Ag/AgCl). Within this potential window, ec-LLS produced Ge micro-and nanowires that were evaluated with scanning electron microscopy, high resolution transmission electron microscopy, and selected area electron diffraction. The cumulative analyses showed pronounced crystallinity in the as-prepared Ge microwires and nanowires, with nanowires showing an unexpected coiled morphology. Atom probe tomography data showed some incorporation of In and Bi at 6 and 3 at. %, respectively. The tomography data further demonstrated that the distribution of the metals was not uniform, as In-rich clusters were observed. A high doping character in the as-prepared Ge nanowires was separately confirmed with two-terminal resistivity measurements. In total, this work not only identifies a new liquid metal type that is amenable for ec-LLS but also suggests strongly that the composition of the liquid metal influences the resultant crystal size, shape, and purity.

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Electrochemical Liquid-Liquid-Solid Deposition of Ge at Hg Microdroplet Ultramicroelectrodes

Cited by 10 publications

References 29 publications

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

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

In Situ Transmission Electron Microscopy Measurements of Ge Nanowire Synthesis with Liquid Metal Nanodroplets in Water

Eutectic-Bismuth Indium as a Growth Solvent for the Electrochemical Liquid-Liquid-Solid Deposition of Germanium Microwires and Coiled Nanowires

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