Effects of Cu doping on the structural and nanomechanical properties of ZnO thin films

The effects of Cu doping on the microstructures, surface morphological and nanomechanical properties of Cu-doped ZnO (CZO) thin films deposited on glass substrates by radio frequency magnetron sputtering method are investigated. The microstructural properties and surface morphological features of CZO thin films are characterized using X-ray diffraction (XRD) and atomic force microscopy (AFM), respectively. The XRD results indicated that CZO thin films exhibited (002)-preferred orientation. From AFM observations, an increase in surface roughness of CZO thin films was observed when the Cu-doping concentration was increased from 2 at% up to 6 at%. Moreover, the nanoindentation tests performed with the continuous contact stiffness measurements (CSM) mode revealed that both the hardness and Young’s modulus of CZO thin films are increased with increasing the Cu-doping concentration, with the maximum value being obtained at 6 at%. Further increasing the Cu concentration up to 8 at% appeared to result in reduced microstructure texturing and nanomechanical performances, indicating that grain boundary effect might have played an important role.