Synthesis of nanostructured ZnO and ZnO-NiO composite thin films via spray pyrolysis for advanced gas sensors

Abstract This study aims to synthesize pure ZnO and ZnO–NiO composite thin films by using the spray pyrolysis technique, with the varying compositions of ZnO and NiO. Pure ZnO thin films, compositions of ZnO 90 wt.% + NiO 10 wt.%. ZnO 80 wt.% + NiO 20 wt.%, and ZnO 70 wt.% + NiO 30 wt.% were deposited on pre-cleaned glass slides at a substrate temperature of 380 °C. These films are deposited by dissolving nickel acetate tetrahydrate and zinc acetate dihydrate primary salts in 40 milliliters of deionized water at a concentration of 0.1 M. Structural, elemental, and morphological properties of the films were examined by using X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), and field emission scanning electron microscopy (FESEM). XRD studies showed a decrease in crystallite size from 20.5 nm for pure ZnO to 13.01 nm for ZnO 70 wt.% + NiO 30 wt.% . Raman spectroscopy is used to study the vibrational modes of the deposited samples. Additionally, optical properties are determined by ultraviolet absorbance spectroscopy and photoluminescence spectroscopy. Photoluminescence (PL) spectra were recorded at an excitation wavelength of 325 nm, showing enhanced near-band-edge emissions. The optical bandgap is determined using the Tauc plot, and it is increased from 3.13 eV (pure ZnO) to 3.41 eV (ZnO 70 wt.% + NiO 30 wt.% . Pure ZnO and ZnO-NiO composite materials were investigated for gas sensing studies, particularly in the detection of ammonia. The ZnO 80 wt.% + NiO 20 wt.%,) film exhibited superior gas sensing performance, with a fast response time (19 s) and recovery time (18 s) towards 50 ppm of ammonia at room temperature. This research opens new avenues for using ZnO-NiO composites in ammonia gas sensors.