Thickness dependent growth of needle-like and flower-like ZnO nanostructures

Abstract

Needle-like nanorods and micron-scale flower-like structures of ZnO were synthesized by thermal evaporation of metallic zinc films with different thicknesses, followed by thermal annealing. Needle-like nanorods of ZnO were found through out the sample surface after annealing of the 1.3 μm thick Zn film. Three-dimensional crystalline nanorod-based flower-like structures of ZnO were also observed after annealing of the relatively thick (3.3 μm) Zn film. Thermal annealing of the Zn films was done at 800 °C in air for different time durations (30, 45, and 90 min). The flower size and number increase with increase in film thickness for the same annealing temperature and time. The X-ray diffraction results show that both the needle-like nanorods and flower-like structures are hexagonal wurtzite structure of ZnO. The room temperature PL spectrum shows a strong defect related violet emission peak centered at 441 nm for both the structures. The possible growth process based on root growth technique is proposed.