Characterization of ZnO Nanostructures: A Challenge to Positron Annihilation Spectroscopy and other Methods

ZnO is of considerable interest for optoelectronic device applications due to its wide band gap and high exciton binding energy. In spite of decades of study and recent progress in research on ZnO properties, there remained unresolved controversies which are mainly related to native defects formed during crystal growth. Positron annihilation spectroscopy (PAS) is among the methods to tackle this structural issue [1, 2].
ZnO nanostructures, like e.g. nanorods [3] and tetrapods [4], are of special interest for device applications [5, 6]. However, their characterization remains an ongoing challenge.
This talk intends to review our recent efforts and latest achievements in this direction. Results obtained will comprise PAS in the form of Slow Positron Implantation Spectroscopy (SPIS) and Pulsed Low Energy Positron Lifetime Spectroscopy (PLEPS), Nuclear Reaction Analysis (NRA), Atomic Force Microscopy (AFM), conductive AFM (C-AFM), Nuclear Magnetic Resonance (NMR), Electron Spin Resonance (ESR), Photoluminescence (PL) spectroscopy, and latest theoretical investigations of structure-related and positron properties of selected defects.
The fundamental importance of a relationship between fabrication conditions, native defect formation, and resulting optical and electronic properties is demonstrated by getting either inferior (nanorods) or significantly improved (tetrapods) optical properties compared to single crystal samples, depending on the nanostructure fabrication method.