Preparation and characterization of thin films nanostructures based on ZnO and other oxides

Abstract

In this work, we studied the effect of the withdrawal speed on the properties of nickel oxide thin films, the effect of silver doping on the properties of zinc oxide and the elaboration of p-NiO/n-ZnO heterostructure thin films. All thin films were deposited onto glass substrates using the sol-gel dip-coating method. The structural, optical and morphological properties of the films were investigated using X-ray diffraction, spectrophotometer and atomic force microscopy (AFM), respectively. It was found that the increase in withdrawal speed leads to the deterioration of the crystallinity of NiO thin films and to the decrease in the optical transmittance. However, the surface roughness was found to be increased when the withdrawal speed increased. With regard to the effect of Ag-doped ZnO thin films, the XRD results revealed that the crystalline quality decreased when the Ag concentration increased with a shift of the diffraction peak (101) toward higher angles. This shift suggests the substitution incorporation of Ag species into the ZnO lattice. For the morphological study, films with high Ag-doping concentration showed low surface roughness, the RMS values were decreased from 8.60 to 4.62 nm for pure and 5Wt % Ag-doped concentration, respectively. The optical analysis showed that the Ag-doping increase the optical transmittance of ZnO thin films. Hence, these results revealed that the Ag-doped ZnO thin films can be used in different applications especially optoelectronics. Finally, n-ZnO/p-NiO heterostructure thin films with different coating number of n-ZnO layer (2, 6, 9 and 12) were prepared. The XRD results confirmed the formation of the n-ZnO/p-NiO heterostructure through the existence of two sets of diffraction belonging to NiO and ZnO. The photocatalytic properties of the p-NiO/n-ZnO heterostructure were investigated by measuring the degradation of Methylene Blue dye under solar light irradiation. It was found that the thickness of the n-type layer plays a critical role in the heterostructure performance. The thickness obtained for 6 coating layers shows the best photocatalytic activity with degradation rate in the order of 98.67% for 4.5h of irradiation exposure.