Trimming of aqueous chemically grown ZnO nanorods into ZnO nanotubes and their comparative optical properties

Highly oriented ZnO nanotubes were fabricated on a silicon substrate by aqueous chemical growth at low temperature $\left(<100°\text{C}\right)$ by trimming of ZnO nanorods. The yield of nanotubes in the sample was 100%. Photoluminescence spectroscopy of the nanotubes reveals an enhanced and broadened ultraviolet (UV) emission peak, compared with the initial nanorods. This effect is attributed to whispering gallery mode resonance. In addition, a redshift of the UV emission peak is also observed. Enhancement in the deep defect band emission in the nanotubes compared to nanorods was also manifested as a result of the increased surface area.