Investigations of spray-deposited NiO thin films for ultrasensitive formaldehyde detection

Formaldehyde detection in the environment is the most important due to its carcinogenic effects on human health. In this study, we present the synthesis of nickel oxide (NiO) films at various substrate temperatures with a cost-effective spray pyrolysis technique. Deposited thin films are investigated for micro-structural, topographical, optical and formaldehyde sensing characteristics. According to XRD analysis, the coated films exhibit polycrystalline behavior with cubic structure. Structural specifications such as lattice parameters, crystallite size, strain, dislocation density, and crystallinity of the films are investigated. SEM is used to examine the surface characteristics of the prepared films. The optical bandgap of the sprayed films is calculated from transmittance data utilizing the Tauc plot. Structural distinctions of the NiO films are investigated with Raman spectroscopy. Several harmful gases, including ammonia, ethanol, methanol, acetone, xylene and formaldehyde sensing characteristics have been studied. The material coated at 400 °C has revealed better selectivity and sensitivity of 598 towards 25 ppm of formaldehyde at ambient temperature with a quick response of 16.5 s and recovery of 29.8 s. •NiO thin films are deposited at different substrate temperatures using the spray pyrolysis technique.•A significant impact of deposition temperature on structural, morphological, optical and gas-sensing properties has been reported.•The film deposited at a substrate temperature of 400 °C shows better structural morphological and optical properties.•Formaldehyde sensing properties have been studied, and an ultrasensitive response is observed against the sample synthesised at 400 °C.•As this sensor element has shown a massive response towards formaldehyde, it can be transferred to fabricate formaldehyde sensors which can be operated at field conditions.