Vertically aligned growth of ZnO nanonails by nanoparticle-assisted pulsed-laser ablation deposition

Vertically aligned ZnO nanonails have been successfully grown on annealed sapphire substrates at comparatively high gas pressure using catalyst-free nanoparticle-assisted pulsed-laser ablation deposition (NAPLD). The growth behavior of the ZnO nanonails has been investigated by variation of the ablation time, which we name 'isolated particle initiated growth' and a three-step growth mechanism for ZnO nanonails is proposed. SEM analysis reveals that each of the uniquely shaped ZnO nanonails consists of a so-called hexagonal rod-shaped 'root' and a slightly tapered 'stem'. The well-aligned ZnO nanonails exhibit a strong ultraviolet (UV) emission at around 390 nm under room temperature and only negligible visible emission, which indicates that there is a very low concentration of oxygen vacancies in the highly oriented ZnO nanonails. The as-synthesized nanonail arrays on sapphire substrate could offer novel opportunities for both fundamental research and technological applications.