Electrocrystallisation and the potential step method

Abstract

A result pertaining to potential step technique and the surface-diffusion model is presented. The interesting aspect of result lies in its invariant nature with respect to distribution of growth sites on surface. This generalises result of Schnittler. Following Burton et al. 1 there have been several attempts to find role that surface diffusion of adatoms plays in determining rates of electrocrystallisation. Recognising a mass transport step on surface implies non-homogeneity of surface (in both microscopic and macroscopic sense) and any attempt to obtain quantitative effects of surface diffusion requires a knowledge of geometry of surface. In almost all cases considered mathematically thus far, this demand has been met by an assumption of a parallel-step structure for surface. Hence results also, at least one suspects so, lean heavily on this assumption. Although certain types of averageing and randomness can be introduced in such models, conclusions that can be asserted (even if somewhat apologetically) as being independent of (or invariant with) details of surface configuration are always welcome. One such attempt was made by Schnittler 2 concerning results for potential-on and -off experiments in electrocrystallisation. He pointed out invariance (to detailed distribution of growth sites Sx, $2 . . . . ) of transient when potential is switched off after having been maintained at level q~ until a steady state is reached. By a simple mathematical argument, we shall show (Appendix) in this paper how a corresponding result exists for more general case of changing t/I to q~ instead of equilibrium. This, apart from generalising Schnittler's result, provides an extra parameter viz. thi at input stage.