Fleischmann and Thirsk

Fig. 10). With the completion of the structure transition, the current should drop to zero, which is indeed the case except for peak B, where a slight leak current is seen (ascribed to the side reaction Cu++ I c > Cu+). According to the theory by Bewick, Fleischmann and Thirsk (BFT) the transients can be used to distinguish between instantaneous and progressive nucleation [45], A corresponding analysis revealed that the falling part of the transients agrees well with the model for instantaneous nucleation, while the rising part shows a systematic deviation. This was explained by the existence of surface defects on a real electrode in contrast to the ideal case of a defect-free surface assumed in the theoretical model. By including an adsorption term in the BFT theory to account for Cu deposition at defects, the experimentally obtained transients could indeed be reproduced very well [44], We shall return to the important role of surface defects in metal deposition later (sec. 3.2).

In the results obtained from an analysis of surface diffusion between steps (Fleischmann and Thirsk, 1960 Damjanovic and Bockris, 1963), the model is a simple one. The properties of steps (e.g., their movement and eventual formation of spirals) will be discussed in Section 7.15. Of course, they are not really simple straight edges. Scanning tunneling microscopy has made it possible to obtain images of the steps. A real monatomic step is shown in Fig. 7.139 and is seen to be quite frazzled. 

The first theoretical treatment of the metal deposition mechanism via surface diffusion was given by Lorenz [2.24], who adapted the theory of Burton, Cabrera and Frank [2.1] to the case of electrolytic metal deposition. Later the problem was treated by Vermilyea [2.29], Despic and Bockris [2.25], Fleischmann and Thirsk [2.28], and Damjanovic and Bockris [2.26], who brought the theory of surface diffusion to its present state. 

The metal deposition mechanism via direct transfer was suggested for the first time by Volmer [2.33], and was discussed later by Lorenz [2.24], Fleischmann and Thirsk [2.28], Mott and Watts-Tobin [2.34], and others. A comprehensive treatise on this problem is given by Vetter [2.27]. 

Both equations have been derived for the case of electrocrystallization by Fleischmann and Thirsk [5.36]. 

In some cases of 2D growth where active centers play a role, nucleus formation can proceed instantaneously in the beginning of the pulse. In this case, the current density is given according to Fleischmann and Thirsk by... 

The technique of studying the early stages of the rising transients was pioneered by Fleischmann and Thirsk [1], and first applied to the study of the electrocrystallization of Pb02 [2]. The early rising portion of a current-time transient is considered to be slow or fast , if, respectively, (/ or(/ -is proportional totimef[2,28]. Figure3.12... 

Concluding we should point out that Burton, Cabrera and Frank [4.35, 4.53] (see also Lorenz [4.54, 4.55]) have solved also the problem of stationary surface diffusion towards steps with circular symmetry. The theory of the more complex case of combined surface diffusion and bulk diffusion limitations can be found in the works of Fleischmann and Thirsk [4.48], Damjanovich and Bockris [4.50] and Gilmer et al. [4.56]. Note, however, that all these theoretical considerations do not accoimt for difficulties coimected with the so-called Ehrlich-Schwoebel barrier [4.57-4.62]. Elastic [4.63, 4.64] and entropic [4.65] interactions between growing steps are also neglected. 

A detailed theory of the spiral growth of crystals has been developed by Burton, Cabrera, Frank, Mott and Levine [4.33-4.41] who have considered the case of spiral growth from a supersaturated vapor phase. Later the theory was adapted to electrocrystahization by Vermilyea [4.44] and Fleischmann and Thirsk [4.48] and developed further and verified experimentally by Budevski, Bostanov, Staikov, Nanev et al. [4.28, 4.69-4.75] (see also the pioneering work of Kaischew, Budevski and MaUnovski [4.76]). 

Fleischmann M, Thirsk HR (1963) in Delahay P (ed) Advances in electrochemistry and electrochemical engineering, Wiley-Interscience, New York, vol 3 p 123... 

M. Fleischmann and H. R. Thirsk, Advances in electrochemistry and electrochemical engineering, P. Delahay and C. W. Tobias, Eds., Interscience Publishers, John Wiley and Sons, Inc., New York, 1963. 

M. Fleischmann and R. Thirsk, Electrochim. Acta 2 22 (1960). Potentiostatic transient and crystal growth. 

M. Fleischmann, H. Thirsk in Advances in Electrochemistry and Eledrochemical Engineering (Ed. P. Delahay), John WUey Sons, New York, 1993, pp. 123-210. 

---