Growth and characterization of ZnO nanoflakes by hydrothermal method: Effect of hexamine concentration

Flake-like ZnO nanostructures, which have potential applications in fields of photo catalysts, biosensors, solar cells, et al., were fabricated on indium doped tin oxide substrates through hydrothermal method at 90 °C. Zinc chloride hydrate and hexamine (HMT) were used as zinc source and the alkali source, respectively, no other surfactants were involved. The morphology evolution of ZnO from nanoflakes to the occurrence of nanorods can be attributed to the competition between the absorption effect of chloride ions and HMT. With the adsorption of chloride ions onto the polar faces instead of growth units, ZnO nanoflakes were formed by restraining the crystal growth along <0001> direction. Controllable growth of different ZnO nanostructures was achieved by tuning the corresponding stoichiometric ratios of reactants. ZnO nanoflakes were formed with equivalent concentrations of zinc chloride hydrate and HMT. Increase in the concentration of HMT resulted in the fabrication of the rod-on-flake structure, or even multilevel ZnO nanoflakes. Scanning electron microscopy results revealed that all these ZnO nanoflakes are with typical wurtzite hexagonal phase. The crystal and optical properties of the as-synthesized samples were characterized by X-ray diffraction spectrum and room temperature photoluminescence spectrometer, which showed close relationship with structure variations.