Self-assembly epitaxial growth of nanorods on nanowalls in hierarchical ZnO hexagonal nanocastle

Three-dimensional (3D) hierarchical porous nanostructure materials with controlled morphology have attracted much attention for their unique properties and wide applications. In the present work, a novel 3D hierarchical ZnO nanostructure was prepared through chemical vapor deposition, which is self-assembled by an array of vertical 1D nanorods on top of 2D nanowalls network in 3D hexagonal nanocastle. As revealed by transmission electron microscopy, the hierarchical nanostructures are composed of single crystal ZnO along the [0001] direction, and the preferred surfaces of nanowalls are . Based on those experimental results, a growth mechanism which involves a Zn-self-catalytic vapor-liquid-solid and vapor-solid mode is proposed to explain the formation of nanorods on nanowalls in 3D nanocastle. Raman and photoluminescence spectrum demonstrated that these 3D hierarchical ZnO nanostructures are nearly free of strain and exhibit an intense ultraviolet emission at 377.6 nm with negligible defect-related green bands.