Effect of pH on the structural, optical and nanomechanical properties of CdS thin films grown by chemical bath deposition

CdS nano-structured thin films were prepared on glass substrates with chemical bath deposition technique for different pH values. The effects of pH and annealing on the structural, optical and nanomechanical properties of CdS films were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-vis spectrophotometer and nanoindentation techniques. The results of XRD analysis and SEM investigation reveal that both different pH values of the bath solution and annealing affect the crystal structure and the surface morphology of the films markedly. Also, the results of the optical absorption show that the Eg values of the films decrease with increasing pH values. In this kind of study the mechanical properties of the CdS thin films determined using nanoindentation tests are being reported here for the first time. Nanoindentation experimental results show that nanohardness and elastic modulus values exhibit a peak load dependence. Our results reveal that, the annealing of CdS films at 300 °C results in slow and normal grain coarsening. The slow grain growth also influences the lattice strain (microstrain) which effects nanohardness and elastic modulus. The results also indicate that there is a direct dependence of the physical and optical properties of the CdS films on pH and annealing process.