Tin electrodeposition on carbon electrodes.: From nuclei to microcrystallites

Tin electrodeposition from sulfuric acid solutions has been studied on two carbon substrates combining the use of electrochemical and morphological (nano- and micrometric) techniques. On a vitreous carbon substrate, the analysis of the electrochemical results reveals that the tin electrodeposition process occurs through an instantaneous nucleation and three-dimensional growth limited by diffusion. Well defined tetragonal microcrystallites of similar size have been observed when the deposit was obtained at low rates. The formation of tetragonal microcrystallites has also been observed on oriented graphite also favoured by the slow growth of the tin deposit. The AFM images indicate that the crystallites have as predecessors three-dimensional poorly-structured overlapped aggregates formed as a result of surface diffusion of the aggregates formed previously. Some of them evolve to incipient flat crystallites that later grow preferentially in the z-direction under diffusion control of the Sn(II) species in solution. The easier deposition of tin on tin as opposed to a carbon substrate and the low-energetic barrier for the reorganization of tin atoms on the crystalline lattice will explain the well defined tetragonal shape of the microcrystallites. (C) 1999 Elsevier Science S.A. All rights reserved.