Electrodeposition of germanium from supercritical fluids

Ke, Jie; Bartlett, Philip N.; Cook, David; Easun, Timothy L.; George, Michael W.; Levason, William; Reid, Gillian; Smith, David C.; Su, Wen-Ta; Zhang, Wenjian

doi:10.1039/c1cp22555c

Cited by 33 publications

(52 citation statements)

References 54 publications

(79 reference statements)

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“…25 In 2012 Ke et al reported the first electrodeposition of germanium thin films from a supercritical fluid. 26 Here, the observed electrochemistry was complex, in contrast to the metal systems studied previously, due to the irreversible reduction of the germanium complexes, slow electron transfer processes and the possible formation of an insulating layer. This study was on the reduction of GeCl 4 in sc-CH 2 − anion was the most readily reduced of the chloride based precursors.…”

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confidence: 68%

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Supercritical Fluid Electrodeposition of Elemental Germanium onto Titanium Nitride Substrates

Cummings

Bartlett

Pugh

et al. 2015

J. Electrochem. Soc.

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We report the electrodeposition of germanium from supercritical difluoromethane (sc-CH 2 F 2 ) at 19 MPa and 358 K using [N n Bu 4 ] [GeCl 3 ]. Voltammetry shows a classic nucleation loop on the first anodic scan with a high nucleation overpotential for germanium on TiN. In all cases the deposition appears to be kinetically limited by a coupled, potential independent, chemical step. Films of germanium were deposited at a range of potentials. At high overpotentials the films were dendritic and poorly adherent. At lower overpotentials, below −2 V vs. Ag|LaF 3 , the films are smoother and more homogeneous. Analysis of the films by energy dispersive X-ray (EDX) spectroscopy shows the presence of germanium with some chloride impurity. Raman spectroscopy confirms the deposition of amorphous germanium. Plating by pulsing to −1.9 V vs. Ag|LaF 3 for 100 ms and then growth at −1.5 V vs. Ag|LaF 3 , was found to produce the best films. On annealing at 700 • C under an Ar atmosphere for 1 hour the as-deposited amorphous germanium film is converted into crystalline germanium, as determined by X-ray diffraction (XRD) and Raman spectroscopy. Since the discovery of semiconductor effects in crystalline germanium over half a century ago, 1 germanium based thin films and structures have received considerable interest. These include a number of advanced applications from doping in optics components 2 to high speed electronics, 3 and from Li-ion batteries 4 to third generation photovoltaics. 5Thin films of germanium are typically formed via vacuum processes such as chemical vapor deposition 6,7 or molecular beam epitaxy. 8 In comparison, the non-aqueous electrodeposition of germanium thin films is an attractive alternative as it has the advantages of high material efficiency, directly templated growth and fine control over the evolving structure. 9Over the previous decade Endres and his colleagues have pioneered the electrodeposition of germanium thin films from ionic liquids. [10][11][12][13][14] In this context ionic liquids have a number of advantages over conventional aqueous based solvents; they are chemically stable, they can be purified to remove impurities such as oxygen and water which can decompose the germanium precursors, and they have a wide electrochemical potential window. Initial work in ionic liquids focused on electrodeposition from the Ge(IV) reagent GeI 4 . The electrodeposition was investigated using in situ scanning tunnelling microscopy (STM) and the plated films were shown to be extremely thin (of the order of 12-16 nm) and the plating rate very slow. This self-limiting electrodeposition was attributed to the low conductivity of the deposited germanium film and complex germanium surface chemistry, possibly involving formation of a hydride, fluoride, iodide or hydroxide surface state.12 Germanium thin films have also been electrodeposited from the corresponding chloride and bromide precursors GeX 4 (X = Cl 11 or Br 10 ) in ionic liquids. Again plating rates were low and only very thin films were produced. A re...

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confidence: 68%

“…Compared to our earlier work using GeCl 4(l) to electrodeposit germanium from sc-CH 2 F 2 , 26 [N n Bu 4 ][GeCl 3 ] is much easier to handle and gives more reproducible and better quality films.…”

Section: Discussionmentioning

confidence: 99%

Supercritical Fluid Electrodeposition of Elemental Germanium onto Titanium Nitride Substrates

Cummings

Bartlett

Pugh

et al. 2015

J. Electrochem. Soc.

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“…These works showed that despite being possible to electrodeposit germanium from ionic liquids, there were several issues: the germanium sources are poorly soluble in the ionic liquids, non-standard experimental setups had to be used to cope with the volatility of the most common germanium compounds and deposition rates are low under standard conditions. In another approach, Bartlett et al electrodeposited amorphous germanium from liquid CH 3 [20,21]. Albeit successful, this approach presents some drawbacks: on the one hand, the need of a high pressure cell, which increases the complexity of the experiment and decreases output.…”

Section: Introductionmentioning

confidence: 99%

Electrodeposition of germanium-containing precursors for Cu2(Sn,Ge)S3 thin film solar cells

Malaquias

Lin

et al. 2017

Electrochimica Acta

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A B S T R A C TCu 2 (Sn,Ge)S 3 has recently emerged as an absorber layer for single junction thin film solar cells, already achieving power conversion efficiencies of up to 6.7%. Electrodeposition of metallic precursors and their subsequent annealing is an attractive synthesis method for such solar cell absorber layers, since it does not require vacuum conditions and little energy is consumed. The aqueous electrodeposition of metallic germanium based on current knowledge is limited to very thin layers, which do not provide the stoichiometric amount of material required for thick semiconductor layers. Therefore we introduce an electrodeposition method for the growth of germanium-containing precursors for Cu 2 (Sn,Ge)S 3 , using propylene-glycol-based electrolytes. These baths do not require additives, give rates of germanium electrodeposition higher than other plating baths and are cheap. The electrochemical behaviour of copper, tin and germanium in propylene glycol was studied and the corresponding deposits were characterised. Smooth and compact layers of each of the pure elements were deposited. Additionally, the co-electrodeposition of copper and germanium was studied as well and thin films containing the alloy Cu 3 Ge and metallic copper were obtained. A constant [Cu]/[Ge] ratio of around 3 was found over a wide potential range, with a higher plating efficiency than that of pure germanium. For these reasons, copper and germanium were incorporated into the precursor via the referred co-deposition method. After thermal annealing in the presence of elemental sulphur, the semiconductor Cu 2 (Sn,Ge)S 3 was successfully formed and it was incorporated in a working solar cell structure with efficiency of 0.7%

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“…36,[41][42][43][44][45][46] Ge electroplating has also been reported on semiconducting substrates such as Si. 47 There are some reports on the formation of thick Ge nanostructures, [48][49][50] which showed that, depending on potential, Ge nanostructures can be grown from aqueous solution by dissolution into and saturation of a liquid Hg electrode.…”

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“…44 Bartlett et al have studied electrodeposition of Ge from various supercritical fluids containing Ge(II) or Ge(IV) compounds. 46 They were able to obtain amorphous Ge films from Ge(IV) and Ge(II) precursors; however, films grown from Ge(II) compounds were heavily contaminated.…”

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Electrochemical Formation of Germanene: pH 4.5

Ledina

Bui

Liang

et al. 2017

J. Electrochem. Soc.

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Germanene is a single layer allotrope of Ge, with a honeycomb structure similar to graphene. This report concerns the electrochemical formation of germanene in a pH 4.5 solution. The studies were performed using in situ Electrochemical Scanning Tunneling Microscopy (EC-STM), voltammetry, coulometry, surface X-ray diffraction (SXRD) and Raman spectroscopy to study germanene electrodeposition on Au(111) terraces. The deposition of Ge is kinetically slow and stops after 2–3 monolayers. EC-STM revealed a honeycomb (HC) structure with a rhombic unit cell, 0.44 ± 0.02 nm on a side, very close to that predicted for germanene in the literature. Ideally the HC structure is a continuous sheet, with six Ge atoms around each hole. However, only small domains, surrounded by defects, of this structure were observed in this study. The small coherence length and multiple rotations domains made direct observation with surface X-ray diffraction difficult. Raman spectroscopy was used to investigate the multi-layer Ge deposits. A peak near 290 cm−1, predicted to correspond to germanene, was observed on one particular area of the sample, while the rest resembled amorphous germanium. Electrochemical studies of germanene showed limited stability when exposed to oxygen.

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Electrodeposition of germanium from supercritical fluids

Cited by 33 publications

References 54 publications

Supercritical Fluid Electrodeposition of Elemental Germanium onto Titanium Nitride Substrates

Supercritical Fluid Electrodeposition of Elemental Germanium onto Titanium Nitride Substrates

Electrodeposition of germanium-containing precursors for Cu2(Sn,Ge)S3 thin film solar cells

Electrochemical Formation of Germanene: pH 4.5

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