Effect of Ni doping on structural, optical and gas sensing properties of ZnO films for the development of acetone sensor devices

The development of sensor materials for environmental air surveillance is very challenging. In order to meet the demand, the present study corelates the effect of nickel doping on structural, optical, morphological and gas sensing ability of zinc oxide thin films. The films were deposited on the glass substrates using spray pyrolysis technique. The crystalline character and morphological analysis of the films were characterized by X-ray diffraction (XRD) and Field emission scanning electron microscopy (FESEM). The hexagonal wurtzite structure of polycrystalline nature is observed from the XRD patterns. The preferred orientation is (101), however doping has significantly triggered (002) orientation. Systematic decrement in the lattice parameters and bond length have been observed which led to structural distortions as result of mismatch in ionic radii of dopant and host materials. FESEM analysis reveals that thin film samples exhibit nanoflake morphology. A well-defined morphology is observed with Ni doping. The compositional analysis (Energy dispersive X-ray spectroscopy) shows that the Ni content was increased with doping which confirm the successful Ni doping. Optical analysis of the samples was performed using UV-Vis spectroscopical analysis. Transmission spectra indicated the highest transmission value in the case of undoped ZnO samples (More than 80%). Gradually decreasing band gap values of ZnO films were observed with Ni doping. The sensor response was investigated for undoped and Ni doped ZnO samples at room temperature in the absence and presence of acetone with 50 ppm concentration. Optimum response (similar to 78%) is obtained for Ni doped ZnO (2% Ni) samples with response time of 33s. Spray synthesized 2% Ni doped ZnO thin film samples show promising approach to achieve high response at ambient temperature.