New insight into growth mechanism of ZnO nanowires electrodeposited from nitrate-based solutions

The electrodeposition of ZnO nanowire arrays from nitrate-based solutions was systematically studied as a function of electrodeposition parameters such as the concentration of zinc and nitrate ion precursors, applied current and charge. A model based on the local concentrations of Zn2+ and OH-, generated from the electrochemical reduction of NO3-, is proposed to explain the growth mechanism of ZnO nanowires. The ratio between OH- production and Zn2+ diffusion rates is identified as a crucial parameter, determining the nanowire growth regime and therefore the nanowire dimensions. As a result of the model and using NaNO3 as an additional source of NO3-, the versatility of ZnO deposition was enhanced in comparison with the deposition from sole Zn(NO3)(2) solutions. Arrays of large aspect ratio (similar to 450) ZnO nanowires were successfully obtained at growth rates compatibles with large-scale production. The obtained ZnO nanowire arrays were characterized and analyzed by field emission scanning and transmission electron microscopies, X-ray diffraction, X-ray photoemission and optical spectroscopies. (C) 2012 Elsevier Ltd. All rights reserved.