Probing Defects by Positron Annihilation Lifetime Spectroscopy in Electrochemically Synthesized ZNO Nanocomposites: A Comparative Study

The present article gives a detailed comparative description of the dopant and particle size dependant changes in the structural arrangement of intrinsic defects present in electrochemically synthesized ZnO:M or ZnO:MO nanocomposites. X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) have been carried out to find the shapes and sizes of the nanocrystalline ZnO composites. Presence of defects in detail is carried out using positron annihilation spectroscopy, which reveals the presence of zinc vacancy. The studies reveal that small particles which are spherical in nature around a critical size (~23 nm) are in receipt of better positive surface charge due to the higher occupancy of the doubly charged oxygen vacancy as compared to the larger nanostructures whereas singly charged oxygen vacancy predominates. This change in electronic structure has been acting as an initiator yet another interesting phenomenon, described as positron confinement inside nanocrystals. To conclude, based on all the above mentioned techniques, a model of the structural arrangement of the intrinsic defects in the present samples has been reconciled.