Effect of pH values on the structural, morphological and sensing properties of ZnO nanostructure

In the present investigation ZnO thin films have been prepared by sol-gel spin coating technique with different pH values. The effect of pH values of precursor solution on the crystal structural, morphological and humidity sensing properties of ZnO nanostructures have been investigated using different characterization technique. The crystal structure and phase analysis has been examined by powder X-ray diffraction (PXRD) technique. The PXRD pattern clearly revealed the ZnO thin films have hexagonal wurtzite crystal structure. The average crystallite size of ZnO thin films have been calculated using Scherer formula and found to be ~24 nm to ~30 nm. The microstrain (ɛa) and (ɛc) of ZnO thin films for different pH values 8 and 11, have been calculated and found to be 7.59, 0.1017; 7.57, 0.1094 respectively. The scanning electron microscopy (SEM) image depicts the formation of spherical nanostructurewith diameter range 80 to 95 nm distributed throughout the surface. The atomic force microscopy (AFM) image also shows the spherical nanostructureconsistently distributed throughout the surface with diameter range 75 to 80 nm.It was also found that increasing the pH values from 8 to 11 modified the grains and grains boundary. The humidity sensing properties of ZnO thin films prepared from pH values of 8 to 11 and found to be lower hysteresis loss, less aging effect and good sensitivity in the range of 8.37 MΩ/%RH to 12.25 MΩ/%RH respectively