Environmentally Benign Structural, Topographic, and Sensing Properties of Pure and Al-Doped ZnO Thin Films

In the present research work, Zn_1- Al O thin films with varying proportions of Al (x = 0.00, 0.01, 0.02, and 0.03) are prepared by a chemical sol-gel spin-coating technique. The crystal structural, morphological, and humidity-sensing properties of the synthesized Zn_1- Al O thin films, with varying concentrations of Al (x = 0.00, 0.01, 0.02, and 0.03), were characterized by X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM); a special humidity-controlled chamber was designed for the humidity-sensing studies. In structural and phase analyses, XRD patterns of Zn_1- Al O thin films show a hexagonal wurtzite crystal structure. The average crystallite sizes of Zn_1- Al O thin films were calculated and found to be ∼18.00, 22.50, 26.30, and 29.70 nm using the X-ray diffraction (XRD) pattern. The surface morphology of Zn_1- Al O Al (x = 0.00, 0.01, 0.02, and 0.03) thin films obtained from AFM micrographs analysis indicates the modification of the spherical grains into nanorods, which were distributed throughout the surface of the films. The SEM image of 3 wt % Al-doped ZnO nanomaterials also shows that spherical nanoparticles changed to nanorod-like structures with a high packing density. Furthermore, increasing the Al-doping concentration from 0 to 3 wt % in ZnO NPs shows lower hysteresis loss, less aging effect, and good sensitivity in the range of 9.8-16.5 MΩ/%RH. The sensitivity of the sensing materials increased with increasing Al-doping concentration, which is very useful for humidity sensors.