4.3.1 Growth of Cactilike ZnO nanostructure from aqueous medium for gas sensor application

Multi-dimensional nanostructure of ZnO was synthesized by facile solution method at 90 o C. The scanning electron microscopy (SEM) images of these films shows vertically aligned ZnO nanoneedles and globe cacti-like morphology. X-ray diffraction (XRD) pattern of these nanoneedles shows highly crystalline ZnO along (002) direction with wurtzite crystal structure. The synthesized ZnO nanostructures are used for NO2 sensing properties at different operating temperatures and gas concentrations. The cacti-like structure exhibits higher gas response at low operating temperature (85% at 275 °C) as compared with nanorods (71% at 325 °C) upon exposure to NO2 gas. The high sensitivity and low operating temperature is attributed to the small size of secondary branches. Additionally, the cacti-like structure is able to respond quickly upon the exposure of NO2 gas. These results show that the cactus-like structure is promising for NO2 gas sensor application at low temperature.