Strong correlation between optical properties and mechanism in deficiency of normalized self-assembly ZnO nanorods

Abstract

Although, post annealing is an efficient way to annihilate/restructure deficiencies in self-assembly (SA) ZnO nanorods (ZNRs), the detailed investigation about the surface properties of annealed SA-ZNRs is a long standing issue and the major discrepancy is mainly due to single step annealing. We demonstrate the strategic two step annealing process to create reliable structural configuration in SA-ZNRs during the first round of annealing at 800 °C in vacuum (VA process), and create intrinsic defects in the second step of annealing in oxygen rich atmosphere (OA process) to correlate the formation of the defects related to green/orange-red emission. SA-ZNRs annealed in VA-OA processes reveal positive correlations between the oxygen flow rate and formation of oxygen interstitials (O_i) and zinc vacancies (V_Zn). The OA-VA processes exhibit the relation of residual O_i and additional V_o. According to VA-OA and OA-VA processes, we propose that the green emission in ZnO annealed in oxygen poor/rich condition is mainly due to the formation of V_o/V_Zn and annealing at oxygen rich condition creates O_i that lead to strong orange-red emission. Rather than O1s, we propose a reliable method by considering the peak shift of Zn2p in XPS to inspect the ZnO matrix, which has good interdependence with the characteristics of PL.