Annealing Temperature Dependence of Various Properties of ZnO Nanoparticles Investigated with Soft XAS.

In this paper, structural, optical and electronic properties of ZnO nanoparticles were investigated with the variation in the annealing temperature. X-ray diffraction, High-Resolution Transmission Electron Spectroscopy, Absorption spectroscopy, Raman Spectroscopy and Soft X-ray spectroscopy techniques were invoked to investigate and gauge the effect of annealing temperature on these properties. Intact Hexagonal Wurtzite phase of the nanoparticles with increasing crystallinity and spherical shape with particle size between 20 nm and 23 nm [using both X-ray Diffractometer (XRD) and High-resolution Transmission of electron microscopy (HRTEM)], blue shift of absorption peak from 372 nm to 366 nm and Optical Band Gap from 3.24 eV to 3.17 eV (UV-Vis-NIR), narrowing of E 2 H mode in Raman Spectra; all indicated enhanced crystallinity with increased annealing temperature. Effects produced by the sole variable such as annealing temperature on the indicative parameters in a definite order catapult the annealing conditions as a significant candidate for customized properties. To have a deeper insight at the electronic levels, Synchrotron-based X-ray absorption spectroscopic studies of ZnO nanoparticles were undertaken. The analysis of Soft XAS spectra showed the change in number of O 2 p and Zn 4 p unoccupied states with increasing particle size and crystallinity of ZnO nanoparticles for varying annealing temperature. Dependence of the crystallite size (D) and micro-strain (ε) on annealing temperature (Ta) calculated using XRD patterns (top left side figure), band gap energy Eg and Urbach energy Eu on annealing temperatures, measured using absorption spectra (top right side figure) and Raman spectra for the ZnO nanoparticles annealed at different temperatures (300, 400 and 500∘C) (bottom figure), showing the structural, optical properties dependence on the annealing temperature, supporting enhanced crystalline nature and increased grain sizes for the ZnO nanoparticles. [ABSTRACT FROM AUTHOR]