Investigating the Origin of Luminescence in Zinc Oxide Nanostructures With STEM-Cathodoluminescence

Abstract

ZnO nanostructures display luminescence in the UV and across the visible spectrum, and show promise as future nanoscale electronic, optoelectronic, and sensing devices [1]. The visible luminescence arises from surface or bulk states at energies inside the ZnO bandgap, however, a fundamental understanding of the luminescent sources is still lacking. The assignment of particular defects to different visible emission peaks is a highly controversial and active area of current research [1,2]. Here, we perform the first spatially resolved scanning transmission electron microscopy cathodoluminescence (STEM-CL) measurements on ZnO nanostructures, and show the emergence of CL spectral peaks associated with morphological changes in ZnO nanorods. Further studies using parallel techniques in the TEM sensitive to intrinsic and extrinsic defects (e.g. HRTEM, atomic resolution HAADF-STEM, EELS, and EDS) will likely conclusively reveal the origin of emission in ZnO and other technologically relevant, luminescent nanostructures.