Fabrication electrodeposition

Continuous plating of wire and strip is, unlike the preceding techniques, a prefabrication process. The production of tinplate is the largest scale continuous operation, but any electrodeposit may be applied this way. Subsequent fabrication processes arc likely to damage the coating, so that pre-coating is best reserved for ductile coatings which are anodic to the substrate in service, as is the case for tin. 

Electrodeposition This method of paint application is basically a dipping process. The paint is water-based and is either an emulsion or a stabilised dispersion. The solids of the paint are usually very low and the viscosity lower than that used in conventional dipping. The workpiece is made one electrode, usually the cathode, in a d.c. circuit and the anode can be either the tank itself or suitably sized electrodes sited to give optimum coating conditions. The current is applied for a few minutes and after withdrawal and draining the article is rinsed with de-ionised water to remove the thin layer of dipped paint. The deposited film is firmly adherent and contains a minimum of water and can be stoved without any flash-off period. This process is used for metal fabrications, notably car bodies. Complete coverage of inaccessible areas can be achieved and the corrosion resistance of the coating is excellent (Fig. 14.1). 

Chemical vapor deposition (CVD) has grown very rapidly in the last twenty years and applications of this fabrication process are now key elements in many industrial products, such as semiconductors, optoelectronics, optics, cutting tools, refractory fibers, filters and many others. CVD is no longer a laboratory curiosity but a maj or technology on par with other maj or technological disciplines such as electrodeposition, powder metallurgy, or conventional ceramic processing. 

Conventional electrodeposition from solutions at ambient conditions results typically in the formation of low-grade product with respect to crystallinity, that is, layers with small particle size, largely because it is a low-temperature technique thereby minimizing grain growth. In most cases, the fabricated films are polycrystalline with a grain size typically between 10 and 1,000 nm. The extensive grain boundary networks in such polycrystalline materials may be detrimental to applications for instance, in semiconductor materials they increase resistivity... 

Electrodeposition has been attempted also on flexible substrates within the scope of fabricating flexible solar cells. Huang et al. [177] investigated the electrodeposition of CIS on Au-coated plastic substrate from aqueous acidic (pH 1.65) solutions of millimolar CuCh, InCb, Se02, containing triethanolamine and sodium citrate. Stoichiometric, semiconductive CIS films (Eg = 1.18 eV) were obtained after annealing at 150 °C in nitrogen. 

Electrodeposition of copper indium disulfide (CulnS2) has been reported [180-182], In a typical instance, single-phase polycrystalline CuInS2 thin films composed of 1-3 fim sized crystallites were grown on Ti by sulfurization of Cu-ln precursors prepared by sequentially electrodeposited Cu and In layers [183]. In this work, solar cells were fabricated by electrodepositing ZnSe on CuInS2. Cyclic... 

The optical properties of electrodeposited, polycrystalline CdTe have been found to be similar to those of single-crystal CdTe [257]. In 1982, Fulop et al. [258] reported the development of metal junction solar cells of high efficiency using thin film (4 p,m) n-type CdTe as absorber, electrodeposited from a typical acidic aqueous solution on metallic substrate (Cu, steel, Ni) and annealed in air at 300 °C. The cells were constructed using a Schottky barrier rectifying junction at the front surface (vacuum-deposited Au, Ni) and a (electrodeposited) Cd ohmic contact at the back. Passivation of the top surface (treatment with KOH and hydrazine) was seen to improve the photovoltaic properties of the rectifying junction. The best fabricated cell comprised an efficiency of 8.6% (AMI), open-circuit voltage of 0.723 V, short-circuit current of 18.7 mA cm, and a fill factor of 0.64. 

Aqueous cathodic electrodeposition has been shown to offer a low-cost route for the fabrication of large surface n-CdS/p-CdTe solar cells. In a typical procedure, CdTe films, 1-2 xm thick, are electrodeposited from common acidic tellurite bath over a thin window layer of a CdS-coated substrate under potential-controlled conditions. The as-deposited CdTe films are stoichiometric, exhibit strong preferential (111) orientation, and have n-type conductivity (doping density typically... 

McGregor SM, Dharmadasa IM, Wadsworth 1, Care CM (1996) Growth of CdS and CdTe by electrochemical technique for utilisation in thin film solar cells. Opt Mater 6 75-81 Morris GC, Das SK (1992) Some fabrication procedures for electrodeposited CdTe solar cells. Int J Sol Energy 12 95-108... 

Duffy NW, Lane DW, Ozsan ME, Peter LM, Rogers KD, Wang RL (2000) Structural and spectroscopic studies of CdS/CdTe heterojunction cells fabricated by electrodeposition. Thin Sohd Films 361 314-320... 

Non-aqueous electrolytes have been used for the preparation of CdS, CdSe, and CdTe nanowire arrays by dc electrodeposition in porous AAO templates of various pore diameters [155, 156]. For instance, CdSe NW arrays with uniform wurtzite crystal structure were fabricated from a non-aqueous DMSO solution containing CdCl2 and elemental Se. The NWs were shown to be of uniform length (2-15 p.m) and diameter (about 20 nm). The c-axis, [00.2], of the grown... 

Let us add here that the fabrication of polycrystalline semiconductive films with enhanced photoresponse and increased resistance to electrochemical corrosion has been attempted by introducing semiconductor particles of colloidal dimensions to bulk deposited films, following the well-developed practice of producing composite metal and alloy deposits with improved thermal, mechanical, or anti-corrosion properties. Eor instance, it has been reported that colloidal cadmium sulfide [105] or mercuric sulfide [106] inclusions significanfly improve photoactivity and corrosion resistance of electrodeposited cadmium selenide. 

Fig. 8. Schematic representation of a vertical media fabricated by electrodeposition of a ferromagnetic metal into the pores of alumina cells formed by anodization of an Al disk [107]. (Reprinted by permission of The Electrochemical Society).

A.L. Crumbliss, S.C. Perine, J. Stonehuerner, K.R. Tubergen, Junguo Zhao, R.W. Henkens, and J.P. O Daly, Colloidal gold as a biocompatible immobilization matrix suitable for the fabrication of the enzyme electrode by electrodeposition. Biotechnol. Bioeng. 40, 483-490 (1992). 

Simultaneous and continuous measurements of extracellular pH, potassium K+, and lactate in an ischemic heart were carried out to study lactic acid production, intracellular acidification, and cellular K+ loss and their quantitative relationships [6, 7], The pH sensor was fabricated on a flexible kapton substrate and the pH sensitive iridium oxide layer was electrodeposited on a planar platinum electrode. Antimony-based pH electrodes have also been used for the measurement of myocardial pH in addition to their application in esophageal acid reflux detection. 

S.A. Marzouk, Improved electrodeposited iridium oxide pH sensor fabricated on etched titanium substrates. Anal. Chem. 75, 1258—1266 (2003). 

A. Bezbaruah and T. Zhang, Fabrication of anodically electrodeposited iridium oxide film pH microelectrodes for microenvironmental studies. Anal. Chem. 74, 5726-5733 (2002). 

A second application of current interest in which widely separated length scales come into play is fabrication of modulated foils or wires with layer thickness of a few nanometers or less [156]. In this application, the aspect ratio of layer thickness, which may be of nearly atomic dimensions, to workpiece size, is enormous, and the current distribution must be uniform on the entire range of scales between the two. Optimal conditions for these structures require control by local mechanisms to suppress instability and produce layer by layer growth. Epitaxially deposited single crystals with modulated composition on these scales can be described as superlattices. Moffat, in a report on Cu-Ni superlattices, briefly reviews the constraints operating on their fabrication by electrodeposition [157]. 

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