Effect of preparation technique on the selected characteristics of Zn1−xCoxO nanocrystalline thin films deposited by sol–gel and magnetron sputtering

Abstract

We have investigated structural, optical and magnetic properties of Zn1−xCoxO (0⩽x⩽0.2) nanocrystalline thin films deposited on glass substrates by sol–gel dip coating and reactive radio-frequency magnetron sputtering technique. The effects of the preparation technique and Co doping concentration on the ZnO thin films have been examined. The results reveal that the sol–gel prepared thin films are less c-axis oriented than those of magnetron sputtered thin films. None of the prepared thin films contained secondary phases. With the increase of Co doping concentrations, the crystallite size and orientation degree of the films change in both of the film deposition techniques. The film surfaces with both deposition techniques are homogeneous and dense; the grains on the surface is randomly scattered. Grain size decreases with increasing Co content. With both film deposition techniques, the band gap energy of the films decreases with increasing Co doping ratio and film thickness except for the 9.1at.% Co doped ZnO magnetron sputtering films. It is found that Co has the valance state of 2+in ZnO lattice. Considering the magnetic properties, it has been observed that there is a paramagnetic behavior and no ferromagnetic signals over temperature range of 5–300K for the samples prepared by both of the sol–gel dip coating and magnetron sputtering techniques.