Effect of precursor solutions stirring on deep level defects concentration and spatial distribution in low temperature aqueous chemical synthesis of zinc oxide nanorods

Abstract

Hexagonal c-axis oriented zinc oxide (ZnO) nanorods (NRs) with 120-300 nm diameters are synthesized via the low temperature aqueous chemical route at 80 degrees C on silver-coated glass substrates. The influence of varying the precursor solutions stirring durations on the concentration and spatial distributions of deep level defects in ZnO NRs is investigated. Room temperature micro-photoluminesnce (mu-PL) spectra were collected for all samples. Cathodoluminescence (CL) spectra of the as-synthesized NRs reveal a significant change in the intensity ratio of the near band edge emission (NBE) to the deep-level emission (DLE) peaks with increasing stirring durations. This is attributed to the variation in the concentration of the oxygen-deficiency with increasing stirring durations as suggested from the X-ray photoelectron spectroscopy analysis. Spatially resolved CL spectra taken along individual NRs revealed that stirring the precursor solutions for relatively short duration (1-3 h), which likely induced high super saturation under thermodynamic equilibrium during the synthesis process, is observed to favor the formation of point defects moving towards the tip of the NRs. In contrary, stirring for longer duration (5-15 h) will induce low super saturation favoring the formation of point defects located at the bottom of the NRs. These findings demonstrate that it is possible to control the concentration and spatial distribution of deep level defects in ZnO NRs by varying the stirring durations of the precursor solutions.<p>Funding Agencies|Avdanced Functional Materials (AFM) SFO project at Linkoping Univeristy, Sweden</p

Toward the Optimization of Low-temperature Solution-based Synthesis of ZnO Nanostructures for Device Applications

“…Based on the importance of the stirring on the synthesis of ZnO NRs we have been motivated to investigate the effect of stirring durations of the synthesis solution as a possible way to tune the radiative point defects in the ZnO NRs. [56] The main observations in this study is found that stirring durations have a significant influence on the morphology and point defects concentrations and their spatial distribution along the synthesized ZnO NRs. We observed that the diameters of the synthesized ZnO NRs were increased from 120, 180 and to 300 nm as the stirring durations were increased from 1, 3 to 5 h, respectively, as shown in …”

“…Below are a description and discussion of these results that were published in the six appended papers. [34,52,[56][57][58][59] …”

“…[56][57][58] Moreover, high crystal quality well-oriented Co-doped ZnO NRs were also synthesized by manipulating the way of mixing the synthesizer solution. [34,52,59] All these parameters were precisely selected considering that the final properties of the ZnO NRs are susceptible to the synthesis conditions.…”

“…The synthesis solutions used were 0.05 M concentration for the zinc nitrate and 0.075 M concentration for the HMTA with a molar ratio of 1:2. [56][57][58] Then we investigated the effect of stirring durations of the synthesis solutions on the optical properties of the ZnO NRs. [56] Four synthesis precursor's (solution) consisting of zinc nitrate and HMTA were dissolved separately in 100 ml DI-water each and were then carefully mixed and stirred at room-temperature for 1, 3, 5 and 15 h, respectively, with a stirring speed of 600 rpm.…”

“…[56][57][58] Then we investigated the effect of stirring durations of the synthesis solutions on the optical properties of the ZnO NRs. [56] Four synthesis precursor's (solution) consisting of zinc nitrate and HMTA were dissolved separately in 100 ml DI-water each and were then carefully mixed and stirred at room-temperature for 1, 3, 5 and 15 h, respectively, with a stirring speed of 600 rpm. The ZnO NRs were then synthesized by immersing a seeded glass substrate coated with Ag inside the synthesis solution while keeping them in a preheated oven at 80 C for 6 h.…”