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 (n ano- and micrometric) techniques. On a vitreous carbon substrate, the analy sis of the electrochemical results reveals that the tin electrodeposition p rocess occurs through an instantaneous nucleation and three-dimensional gro wth limited by diffusion. Well defined tetragonal microcrystallites of simi lar size have been observed when the deposit was obtained at low rates. The formation of tetragonal microcrystallites has also been observed on orient ed graphite also favoured by the slow growth of the tin deposit. The AFM im ages indicate that the crystallites have as predecessors three-dimensional poorly-structured overlapped aggregates formed as a result of surface diffu sion of the aggregates formed previously. Some of them evolve to incipient flat crystallites that later grow preferentially in the z-direction under d iffusion control of the Sn(II) species in solution. The easier deposition o f 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 explai n the well defined tetragonal shape of the microcrystallites. (C) 1999 Else vier Science S.A. All rights reserved.