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Electrochemistry of FeSO4-Na2S2O3 and CuSO4-Na2S2O3 Systems for Template-Assisted Nanowire Synthesis


Two related series of investigations are presented in this dissertation. First, two candidate systems for electrochemical deposition of metal sulfides for photovoltaic applications have been characterized. Secondly, a general electrochemical synthesis method allowing countable numbers of wires embedded in porous anodic alumina arrays to be measured using macroscopic contacts was developed.

Electrochemical studies of the FeSO4-Na2S2O3 system and the CuSO4-Na2S2O3 system were undertaken to evaluate their suitability as electrodeposition baths for FeS2 and CuxS, respectively. Each solution system was studied extensively using cyclic voltammetry to characterize electrochemical processes at various concentrations. The iron sulfide / thiosulfate system was found to be unsuitable for the synthesis of FeS2 due to the preferential formation of FeS. The copper sulfide / thiosulfate system was found to be suitable for the synthesis of Cu2S, with thiosulfate concentration being the most important parameter due to the high complexation of Cu(I) by thiosulfate.

Investigations into the electrochemical synthesis of metal wires in porous anodic alumina templates revealed an interesting synthesis mechanism wherein sparse, isolated wires are created in a very small fraction of the available pores. These wires are nucleated through the reduction of metal from the deposition bath by aluminum at the base of the alumina pores. This reduction causes a localized increase in acidity, accelerating the dissolution of the alumina barrier layer and allowing more typical wire deposition to occur. The sparse nucleation is exaggerated by the increasing rate of wire deposition as the wires lengthen and the swift rate of overgrowth formation at the surface of the template, resulting in domes of overgrowth attached to countable numbers of nanowires. This geometry has been exploited to obtain in situ measurements of known numbers of nanowires.

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