Exploring the role of film thickness and oxygen vacancies on the H₂S gas-sensing performance of RF magnetron-sputtered NiO thin films

This work explores the thickness effect of RF magnetron-sputtered nickel oxide (NiO) thin films for evaluating their H₂S gas-sensing characteristics. NiO thin films were prepared on alumina substrates by varying the deposition time, and the resulting film thicknesses were 25 nm, 52 nm, and 76 nm. X-ray diffraction results demonstrate the polycrystalline nature and cubic structure of NiO thin films. Photoluminescence spectroscopy measurements revealed increased defect content (Ni interstitials and O vacancies) in the 52-nm-thick NiO thin film. Furthermore, X-ray photoelectron spectroscopy results confirmed the thickness effect on NiO thin film stoichiometry. Conductivity measurements at working temperatures ranging from 200 to 450 °C were also used to investigate the gas-sensing tests. The NiO thin film with a thickness of 52 nm proved to be an excellent H₂S gas sensor, with a remarkable sensor response of 260% and a response/recovery time of ~ 52 s/23 s for 50 ppm H₂S at a relatively low operating temperature of 275 °C. Additionally, the film displays a low H₂S detection limit of ~ 0.2 ppm. This study investigates the relationship between the thickness, structural, optical, and electrical properties of NiO thin film-based H₂S gas sensors and their gas-sensing capabilities.