Electrodeposition Model

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... 

Generally, the experimental results on electrodeposition of CdS in acidic solutions of thiosulfate have implied that CdS growth does not involve underpotential deposition of the less noble element (Cd), as would be required by the theoretical treatments of compound semiconductor electrodeposition. Hence, a fundamental difference exists between CdS and the other two cadmium chalcogenides, CdSe and CdTe, for which the UPD model has been fairly successful. Besides, in the present case, colloidal sulfur is generated in the bulk of solution, giving rise to homogeneous precipitation of CdS in the vessel, so that it is quite difficult to obtain a film with an ordered structure. The same is true for the common chemical bath CdS deposition methods. 

By electrodeposition of CuInSe2 thin films on glassy carbon disk substrates in acidic (pH 2) baths of cupric ions and sodium citrate, under potentiostatic conditions [176], it was established that the formation of tetragonal chalcopyrite CIS is entirely prevalent in the deposition potential interval -0.7 to -0.9 V vs. SCE. Through analysis of potentiostatic current transients, it was concluded that electrocrystallization of the compound proceeds according to a 3D progressive nucleation-growth model with diffusion control. 

I. Development of a simple, Butler-Volmer equation-based kinetic model for MiXi (CdTe) electrodeposition. J Electrochem Soc 132 2904-2909... 

Verbrugge MW, Tobias CW (1985) A mathematical model for the periodic electrodeposition of multicomponent alloys. J Electrochem Soc 132 1298-1307... 

More than 20 years ago, Matsushita et al. observed macroscopic patterns of electrodeposit at a liquid/air interface [46,47]. Since the morphology of the deposit was quite similar to those generated by a computer model known as diffusion-limited aggregation (D LA) [48], this finding has attracted a lot of attention from the point of view of morphogenesis in Laplacian fields. Normally, thin cells with quasi 2D geometries are used in experiments, instead of the use of liquid/air or liquid/liquid interfaces, in order to reduce the effect of convection. 

Johans et al. derived a model for diffusion-controlled electrodeposition at liquid-liquid interface taking into account the development of diffusion fields in both phases [91]. The current transients exhibited rising portions followed by planar diffusion-controlled decay. These features are very similar to those commonly observed in three-dimensional nucleation of metals onto solid electrodes [173-175]. The authors reduced aqueous ammonium tetrachloropalladate by butylferrocene in DCE. The experimental transients were in good agreement with the theoretical ones. The nucleation rate was considered to depend exponentially on the applied potential and a one-electron step was found to be rate determining. The results were taken to confirm the absence of preferential nucleation sites at the liquid-liquid interface. Other nucleation work at the liquid-liquid interface has described the formation of two-dimensional metallic films with rather interesting fractal shapes [176]. 

With regard to eqn. (2), which represents the metal deposition half reaction in electroless deposition, in a simplistic sense we see that it is analogous to an electrodeposition process. With respect to the reducing agent reaction, organic [20, 21] and relatively complex inorganic oxidation reactions [22] have similarly been widely studied electrochemically. It is therefore reasonable to think that electroless deposition could be described, or modeled, using an electrochemical approach. 

The incorporation of a third element, e.g. Cu, in electroless Ni-P coatings has been shown to improve thermal stability and other properties of these coatings [99]. Chassaing et al. [100] carried out an electrochemical study of electroless deposition of Ni-Cu-P alloys (55-65 wt% Ni, 25-35 wt% Cu, 7-10 wt% P). As mentioned earlier, pure Cu surfaces do not catalyze the oxidation of hypophosphite. They observed interactions between the anodic and cathodic processes both reactions exhibited faster kinetics in the full electroless solutions than their respective half cell environments (mixed potential theory model is apparently inapplicable). The mechanism responsible for this enhancement has not been established, however. It is possible that an adsorbed species related to hypophosphite mediates electron transfer between the surface and Ni2+ and Cu2+, rather in the manner that halide ions facilitate electron transfer in other systems, e.g., as has been recently demonstrated in the case of In electrodeposition from solutions containing Cl [101]. 

Modeling the Mn-Al system is particularly difficult because the kinetics of the Mn and A1 deposition reactions can not be measured directly. Although it is possible to estimate the current-potential relationships for both Mn and A1 from electrodeposit composition, no examination along these lines appears in the literature. A close ex-... 

An overview of a scientific subject must include at least two parts retrospect (history) and the present status. The present status (in a condensed form) is presented in Chapters 2 to 21. In this section of the overview we outline (sketch) from our subjective point of view the history of electrochemical deposition science. In Section 1.2 we show the relationship of electrochemical deposition to other sciences. In this section we show how the development of electrodeposition science was dependent on the development of physical sciences, especially physics and chemistry in general. It is interesting to note that the electron was discovered in 1897 by J. J. Thomson, and the Rutherford-Bohr model of the atom was formulated in 1911. 

When the charge-transfer step in an electrodeposition reaction is fast, the rate of growth of nuclei (crystallites) is determined by either of two steps (I) the lattice incorporation step or (2) the diffusion of electrodepositing ions into the nucleus (diffusion in the solution). We start with the first case. Four simple models of nuclei are usually considered (a) a two-dimensional (2D) cylinder, (b) a three-dimensional (3D) hemisphere, (c) a right-circular cone, and (d) a truncated four-sided pyramid (Fig. 7.2). 

Here we examine models that try to explain how textures develop during deposition on oriented (single-crystal), textured, polycrystalline, and amorphous substrates. We select electrodeposition of nickel as a model system. 

Theories of leveling by additives are based on (1) the correlation between an increase in polarization produced by the leveling agents (29) and (2) preferential adsorption of a leveling agent on high points (peaks or flat surfaces) (30). Theories and modeling of superconformal electrodeposition are discussed in Section 19.4. 

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