Morphology control of ZnO bilayer structure by low-temperature hydrothermal process

Morphology control of ZnO bilayer structure films has been obtained via low-temperature hydrothermal process without any surfactant-assistance. ZnO bilayer structures including nanoflower layer on nanorod array structure, nanodendrite layer over nanorod array structure, and double nanorods layers structures were successfully fabricated by controlling the ammonia concentration in the initial hydrothermal solution and the immersing ways. The shape evolution of bilayer structure consisting of nanodendrite layer on the top and nanorod array at the bottom was elucidated by growing-renucleating mechanism. The higher ammonia concentration in the initial hydrothermal solution promotes the secondary nucleation and growth on the surface defects of backbones, resulting in the formation of needle-like nanorods in ZnO nanodendrite-nanorod structure. The ZnO film with nanodendrite-nanorod structure has better optical properties and lesser defects compared to that of nanoflower-nanorod structures.