Synthesis of zinc oxide nanowires on seeded and unseeded gold substrates: Role of seed nucleation and precursor concentration

• Vertically aligned ZnO nanowires were synthesized on gold-coated glass substrates.
• Pre-seeding substrates with ZnO nanoparticles results in denser and smaller wires.
• Nanowire coverage ratio is proportional to concentration for unseeded substrates.
• A quantitative model is proposed to describe the nucleation process.

ZnO nanowires were synthesized on gold-coated glass substrates using the hydrothermal method. The effects of precursor concentration, substrate annealing and seeding on the morphology, dimension, and distribution of resultant nanowires were investigated. We found that the density of nanowires on substrates pre-seeded with ZnO nanoparticles is about two orders of magnitude greater than unseeded ones, while the dimension of ZnO nanowires for pre-seeded samples is much smaller than unseeded samples. In addition, we found that the fraction of substrate area covered by nanowires for unseeded samples is proportional to the precursor concentration, and proposed a simple nucleation model to explain this behavior. For pre-seeded substrates, ZnO nanowire density first increases with concentration and decreases as concentration exceeds 20 mM. We attribute this behavior to the competition for ions among the dense wires of varying length as well as the fusion of neighboring wires into larger ones.