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 (∼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.