Synthesis of Mg doped ZnO cauli-flower nanostructures using chemical spray and its investigation for ammonia gas sensing at room temperature.

In this study, we report the synthesis, optical characterization and ultra-sensitive ammonia gas sensing properties of Mg-doped ZnO cauliflower like nanostructures obtained via chemical spray pyrolysis technique. The morphological and structural properties of the prepared films were investigated by Field Emission Scanning electron microscope (FESEM) and X-ray diffraction (XRD). Gas sensing and optical characterizations were carried out using Keithley electrometer and Uv-Vis. Spectrophotometer. Cauliflower-like nanostructures were obtained with diameter 33.16 nm of 5 % Mg-doped ZnO films. Significant changes in the pivot-like morphology of 1 % Mg-doped ZnO sample to cauliflower like morphology indicates that higher Mg doping concentration affects the morphology. Surface to volume ratio increased as the particle size reduced from 38 nm to 33 nm with increasing Mg doping. This emphasizes that the morphology and the surface area play an important role in the surface phenomenon of materials. The XRD results reveal that obtained films have hexagonal (wurtzite) crystal structure of ZnO. The gas sensing properties of Mg-doped ZnO nanostructures were tested based on resistance variation upon the exposure of ammonia vapor at room temperature. The ability 5 % Mg-doped ZnO nanostructures to sense 5 ppm ammonia gas was enhanced with least response (24 s) and recovery time (27 s). It may be due to Mg-doping tuned the required surface morphology of ZnO. Moreover, the ammonia gas sensing mechanism of Mg-doped ZnO nanostructures is demonstrated. Optical energy bandgap is decreased due to the increased defects formation with higher Mg doping. Based on the gas sensing and optical properties, Mg-doped ZnO materials are the promising candidate for ammonia gas sensor and opto-electronic device applications.