Strong surface effect on cathodoluminescence of an individual tapered ZnO nanorod

Spatial-resolved cathodoluminescence spectra are collected at spots with different diameters on individual single-crystalline tapered ZnO nanorods to study the size-dependent surface effect. A significant increase in the intensity ratio of the deep level to the near band edge emission is observed with ever-increasing nanorod surface-aspect ratio. This ratio shows notable superlinear behavior especially on the larger surface-aspect-ratio side, which can be well understood with consideration of both surface effect and self-absorption. Further discussion reveals that surface recombination dominates the deep-level emission. Our results indicate that the surface effect is crucial to modulation of the physical properties of nanostructures even before their sizes close to quantum size regime and the self-absorption effect must be taken into account for quasi-quantitative analysis at the nanoscale level, which may find its practical applications in the design of functional nanodevices.