Annealing Temperature Effects on the Optical Properties of MnO 2 : Cu Nanostructured Thin Films

In this work, the effect of annealing temperature on the microstructure, morphology, and optical properties of Cu-doped nanostructured MnO2 thin films were studied. The thin films were prepared by sol-gel spin-coating technique on glass substrates and annealed in the air ambient at 300, 350, 400 and 450 °C temperatures. The structural, morphological and optical properties of the annealed MnO2: Cu films have been studied by X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), UV-Vis spectroscopy and Fourier Transform Infrared (FTIR) Spectroscopy. The XRD patterns showed that the crystallinity of the films was decreased with increasing annealing temperature. FE-SEM images of films showed that an increase in annealing temperature affected the densification of the films and increased the porosity of the films. For the first time, the thickness, optical constants and complex dielectric function of MnO2: Cu thin films were determined by simulating transmission spectra using Forouhi-Bloomer model in the optimization process. The optical band gap of MnO2: Cu thin films were enhanced with increasing annealing temperature from 1.86 eV to 1.98 eV. The presence of Mn-O and other bonds in the films were confirmed by FTIR spectroscopy.