Large‐Scale Synthesis of Vertically Aligned ZnO Hexagonal Nanotube‐Rod Hybrids Using a Two‐Step Growth Method

Zn ‐polar (0001) surfaces are more chemically reactive than other surfaces of ZnO crystals and drive preferential anisotropic and asymmetric growth along the [0001] direction, which facilitates growth of c ‐axis oriented, one‐dimensional ZnO nanostructures. Accordingly, capping the top (0001) surface of ZnO crystals can impede c ‐axis growth and thus serve to modulate growth habits. In this study, we generated vertically aligned ZnO hexagonal nanotube‐rod (h‐ NTR ) hybrids by modulating growth habits during a second‐stage process. Electron microscopy studies revealed the formation of very thin (10–20 nm) single‐crystalline nanotube walls along the edges of underlying hexagonal rod tops capped with Si. In addition, spatially resolved investigation of ZnO h‐ NTR indicated an abrupt increase in the measured bandgap across rod‐tube junctions, which was ascribed to a quantum confinement effect and Burstein–Moss effect of carriers within the very thin nanotube walls.