Cathodoluminescence inhomogeneity in ZnO nanorods

Abstract

Luminescence properties of vertically aligned, crystalline ZnO nanorods are studied by cathodoluminescence (CL) spectroscopy and microscopy. Results show that luminescence characteristics vary dramatically with location on the nanorod as well as CL excitation depth. CL inhomogeneity is observed between the nanorod tip and sidewalls, accompanied by a variation in the chemical environment of surface oxygen ions as probed by photoemission spectroscopy. Our findings demonstrate that CL can provide useful information on the local optical properties of nanostructured materials, which is simply beyond the capability of other methods.

Observation of whispering gallery modes from hexagonal ZnO microdisks using cathodoluminescence spectroscopy

“…The size dependence of the structured green CL spacing confirms that the enhanced edge emission in the ZnO microdisks is clearly unrelated to increased surface emission widely reported in ZnO nanowires due to surface band bending effects or an increased concentration of surface defects. 26,27 The energy spacing between the emission peaks from the 5 lm and 9 lm microdisks is in the range of 23-24 meV and 34-40 meV, respectively. These spacing values are significantly smaller than the longitudinal optical (LO) phonon energy of 72 meV, indicating they are not related to the vibronic states as reported previously by Reynolds et al For optical resonators, it is important to analyse the observed resonance to understand the nature of the light confinement.…”

Zinc Oxide Nanophotonics

“…In addition, it has been studied that with decreasing diameter, these maxima peaks continuously shift to higher energies. The size dependence of the mode spacing shows that the increased emission from ZnO WGMs is not related to increased surface emission described in ZnO nanowires due to surface band-bending effects or an increased concentration of surface defects [88,89]. For previously studied WGMs, the mode spacing values are significantly smaller than the longitudinal optical phonon energy of 72 meV, thus the emissions are not attributed to the vibronic states as previously reported [90].…”

Defect Control of ZnO Nano-particles Fabricated by Pulsed Nd:YAG Laser Ablation

“…[26] It has also been reported that the defects can act as trapping centres to compete with the near band edge emission and quench the excitonic luminescence of ZnO nano-particles. [8] The CL results indicate that intrinsic defects in the inner regions of the ZnO nano-particles are negligible, meaning that the inner region has a crystalline structure. Moreover, the enhanced intensity of the UV peak due to the increase of oxygen pressure indicates a better crystalline structure of ZnO nano-particles.…”

“…[2,3,6,7] However, the surface defects of nano-size ZnO particles have been found to quench the luminescence of exciton and hinder the charge transfer between ZnO and adsorbed molecules at the interface. [8][9][10] Controlling the defect distribution during the growth process is of crucial importance if we want to improve the luminescence property of ZnO nano-particles. Therefore, synthesizing pure defect free ZnO nanostructures with a controlled morphology and diameter is one of the major focuses in nano-science research.…”