Cathodic electrodeposition

Given the thermodynamic properties of a system, judicious variation of the different plating parameters to assist in manufacturing the desired electrodeposit should be based on an accurate kinetic model. Engelken and Van Doren [6, 7] proposed 

The induced co-deposition concept has been successfully exemplified in the formation of metal selenides and tellurides (sulfur has a different behavior) by a chalcogen ion diffusion-limited process, carried out typically in acidic aqueous solutions of oxochalcogenide species containing quadrivalent selenium or tellurium and metal salts with the metal normally in its highest valence state. This is rather the earliest and most studied method for electrodeposition of compound semiconductors [1]. For MX deposition, a simple (4H-2)e reduction process may be considered to describe the overall reaction at the cathode, as for example in 

When the diffusion rate of selenite or tellurite species toward the cathode becomes equal to the rate of their discharge, deposition of the chalcogen depletes 

A method to circumvent the problem of chalcogen excess in the solid is to employ low oxidation state precursors in solution, so that the above collateral reactions will not be in favor thermodynamically. Complexation strategies have been used for this purpose [1, 2]. The most established procedure utilizes thiosulfate or selenosulfate ions in aqueous alkaline solutions, as sulfur and selenium precursors, respectively (there is no analogue telluro-complex). The mechanism of deposition in such solutions has been demonstrated primarily from the viewpoint of chemical rather than electrochemical processes (see Sect. 3.3.1). Facts about the (electro)chemistry of thiosulfate will be addressed in following sections for sulfide compounds (mainly CdS). Well documented is the specific redox and solution chemistry involved in the formulation of selenosulfate plating baths and related deposition results [11, 12]. It is convenient to consider some elements of this chemistry in the present section. 

In alkaline media, the selenosulfate ions disproportionate to sulfate and highly reactive selenide ions  

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Significant advances in waterborne coatings have been made by PPG Industries utilizing epoxies as co-resins. These coatings are used in cathodic electrodeposited systems, widely accepted for automobile primers. Many patents have been issued for this important technology (50,51). 

Paints are specially formulated for one of two processes. In the first, anodic electrodeposition, the article to be painted is made the anode in a d.c. circuit. Cathodic electrodeposition is the reverse operation. The process takes place under carefully controlled conditions in a tank. Current passes through the paint causing it to deposit uniformly over the article in a uniform film whose thickness can be accurately controlled. The paint film is insoluble in water and exhibits remarkable adhesion after stoving. Electrodeposition is widely used to apply primers, e.g. by car manufacturers, and one coat finishes. 

Cattarin S, Furlanetto E, Musiani MM (1996) Cathodic electrodeposition of Se on H electrodes. J Hectroanal Chem 415 123-132... 

Dennison [43] studied the cathodic electrodeposition of CdS from similar acidic solutions at 90 °C. Although the reactions involved could not be defined exactly, two alternative overall processes were considered ... 

If the electrolysis parameters (precursor concentrations, pH, temperature, cur-rent/potential, substrate) be defined in a precise manner, a self-regulated growth of the compound can be established, and highly (111 )-oriented zinc blende (ZB) deposits up to several p,m thickness are obtained at potentials lying at the anodic limit of the diffusion range (Fig. 3.3) [60]. Currently, the typical method of cathodic electrodeposition has been developed to yield quite compact and coherent, polycrystalline, ZB n-CdSe films of well-defined stoichiometry. The intensity of the preferred ZB(f 11) orientation obtained with as-deposited CdSe/Ni samples has been quite high [61]. 

Alkaline aqueous media containing selenosulfate ions (SeS03 ) and complexes of Cd with EDTA or nitrilotriacetate (NTA) have been successfully utilized to accomplish cathodic electrodeposition of nearly stoichiometric, wurtzite CdSe [62-64]. Similar results have been reported for seleno-cyanate (SeCN ) alkaline baths... 

Darkowski and Cocivera [94] investigated trialkyl- or triarylphosphine tellurides, as low-valent tellurium sources, soluble in organic solvents. They reported the cathodic electrodeposition of thin film CdTe on titanium from a propylene carbonate solution of tri-n-butylphosphine telluride and Cd(II) salt, at about 100 °C. Amorphous, smooth gray films were obtained with thicknesses up to 5.4 p,m. The Te/Cd atomic ratio was seen to depend on applied potential and solution composition with values ranging between 0.63 and 1.1. Polycrystalline, cubic CdTe was obtained upon annealing at 400 C. The as-deposited films could be either p- or n-type, and heat treatment converts p to n (type conversion cf. Sect. 3.3.2). 

Cathodic electrodeposition of microcrystalline cadmium-zinc selenide (Cdi i Zn i Se CZS) films has been reported from selenite and selenosulfate baths [125, 126]. When applied for CZS, the typical electrocrystallization process from acidic solutions involves the underpotential reduction of at least one of the metal ion species (the less noble zinc). However, the direct formation of the alloy in this manner is problematic, basically due to a large difference between the redox potentials of and Cd " couples [127]. In solutions containing both zinc and cadmium ions, Cd will deposit preferentially because of its more positive potential, thus leading to free CdSe phase. This is true even if the cations are complexed since the stability constants of cadmium and zinc with various complexants are similar. Notwithstanding, films electrodeposited from typical solutions have been used to study the molar fraction dependence of the CZS band gap energy in the light of photoelectrochemical measurements, along with considerations within the virtual crystal approximation [128]. 

An instance of cadmium-zinc sulfide (Cd , Zni i S) cathodic electrodeposition can be found in the work of Morris and Vanderveen [130]. These researchers managed to obtain polycrystalline Cd , Zni i S films from stirred aqueous solutions (pH 2,... 

On account of the fact that the electrode potential of molybdenum is more negative than the discharge potential of hydrogen, principle difficulties arise to cathodically electrodeposit molybdenum chalcogenide films from aqueous solutions. Theoretically, the deposition of pure molybdenum by electrolytic reduction of molybdates in acidic aqueous solutions is possible according to the reaction... 

Aqueous electrolytes proposed in the literature for cathodic electrodeposition of lead selenide are generally composed of dissolved selenous anhydride and a lead salt, such as nitrate or acetate. Polycrystalline PbSe films have been prepared by conventional electrosynthesis from ordinary acidic solutions of this kind on polycrystalline Pt, Au, Ti, and Sn02/glass electrodes. The main problem with these applications was the PbSe dendritic growth. Better controlled deposition has been achieved by using EDTA in order to prevent PbSeOs precipitation, and also acetic acid to prevent lead salt hydrolysis. 

Being isomorphous, PbSe and PbTe form solid solutions in the whole range of compositions. Cathodic electrodeposition of the PbSe Tei-x ternary (0 < x < 1)... 

Takahashi et al. [220] first reported the formation of Bi-Te alloy films with varying chemical composition by means of cathodic electrodeposition from aqueous nitric acid solutions (pH 1.0-0.7) containing Bi(N03)3 and Te02. The electrodeposition took place on Ti sheets at room temperature under diffusion-limited conditions for both components. In a subsequent work [221], it was noted that the use of the Bi-EDTA complex in the electrolyte would improve the results, since Bi " is easily converted into the hydrolysis product, Bi(OH)3, a hydrous polymer, thus impairing the reproducibility of electrodeposition. The as-produced films were found to consist of mixtures of Te and several Bi-Te alloy compounds, such as Bi2Tc3, Bi2+xTe3 x, Bi Tee, and BiTe. Preparation of both n- and p-type Bi2Te3 was reported in this and related works [222]. 

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... 

Dennison S (1993) Studies of the cathodic electrodeposition of CdS from aqueous solution. Electrochim Acta 38 2395-2403... 

Baranski AS, Fawcett WR, McDonald AC, Nobriga RM, McDonald JR (1981) The structural characterization of cadmium sulfide films grown by cathodic electrodeposition. J Electrochem Soc 129 963-968... 

Lyons LE, Morris GC, Horton DH, Keyes JG (1984) Cathodically electrodeposited films of cadmium telluride. J Electroanal Chem 168 101-116... 

Saraby-Reintjes A, Peter LM, Ozsan ME, Dennison S, Webster S (1993) On the mechanism of the cathodic electrodeposition of cadmium telluride. J Electrochem Soc 140 2880-2888... 

Basol BB (1988) Electrodeposited CdTe and HgCdTe solar Cells. Sol Cells 23 69-88 Bhattacharya RN, Rajeshwar K, Noufi RN (1985) In situ preparation of p-Type CdTe thin films by cathodic electrodeposition. J Electrochem Soc 132 732-734 Llabres J (1984) In situ preparation of undoped p-Type CdTe by cathodic electrochemical deposition. J Electrochem Soc 131 464 65... 

Sugfmoto Y, Peter LM (1995) Photoeffects during cathodic electrodeposition of CdTe. J Electroanal Chem 386 183-188... 

Guillen C, Galiano E, Herrero J (1991) Cathodic electrodeposition of CuInSe2 Thin Films. Thin Solid Films 195 137-146... 

Lead sulfide, PbS, nanoparticulate thin films having pancake-like geometry and exhibiting ID quantum confinement, as controlled by the lowest dimension of the particles, have been synthesized by cathodic electrodeposition on TTO/glass and titanium electrodes from a pH 0.62 solution containing Pb(N03)2 and Na2S203 [162]. 

Recendy, ID quantum dots of gallium selenide with average diameter 8-10 nm, connected in the form of chains of average length 50-60 nm, were synthesized on rro substrates by cathodic electrodeposition from acidic aqueous solutions of gallium(III) nitrate and selenious acid [186], The structural analysis from XRD patterns revealed the formation of Ga2Se3/GaSe composition. The films were found to be photoactive in aqueous sodium thiosulfate solution and showed p-type conductivity. 

Folonari, C. V. and Garlasco, R., Ion-paired HPLC characterization of cathodic electrodeposition paint polymers, /. Chromatogr. Sci., 19, 639, 1981. 

Cathodic electrodeposition coatings, 10 410 Cathodic inhibitors, 7 815 Cathodic protection, 7 804-806 Cathodic stripping voltammetry, 9 569 Cathodoluminescence microscopy, 16 484 Catholyte systems, 9 675-676... 

Karappuchamy etal. [164] have described cathodic electrodeposition of porous ZnO thin film modified with the dye in an aqueous solution of zinc nitrate and riboflavin 5 -phosphate. 

Recently, the mechanism of cathodic electrodeposition of ZnO thin films from aqueous Zn(N03)2 baths has been studied using a rotating disc electrode [165]. Non-electrochemical methods of preparation of ZnO were also described, but they are not covered in this review. 

The ZnO/eosinY hybrid films were prepared by cathodic electrodeposition from a hydrogen peroxide oxygen precursor in chloride medium [484,] and the role of reduced eosin bound to ZnO in the electrocatalysis was discussed. 

The structure, morphology, and photoelectrochemical properties of CdSe and CdSe Tei-x semiconductor thin Alms prepared by cathodic electrodeposition on Ni and Ti electrodes from acidic solution containing CdS04, Se02, and Ti02 were investigated [192]. 

Cathodic electrodeposition of CdTe in acidic solutions with higher tellurium... 

Camarero et al. [41] have prepared graded cadmium-mercury-telluride thin films (CdxFlgi cTe) applying cathodic electrodeposition at variable deposition voltage. Atomic proportions of mercury in the range 0.05-0.15 were considered. 

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