Room temperature RF magnetron sputtered nanocrystalline NiO thin films for highly responsive and selective H2S gas sensing at low ppm concentrations

Abstract

We report on the H2S gas sensing performance of nanocrystalline NiO thin films sputtered on alumina substrate via RF magnetron sputtering using NiO target at room temperature. Nanocrystalline nature with granular morphology of the films was observed along with the hydrophobic nature (θw ∼ 123.5°), as investigated by GIXRD, FESEM, and wettability measurements. PL spectrum indicates the presence of oxygen or nickel vacancies/defects, which was further confirmed by the XPS measurements. The H2S gas sensing characteristics of NiO thin films have been studied at different operating temperatures (200–425 °C) and gas concentrations (1–200 ppm). It shows the highest sensor response (Rg/Ra) of ∼ 28.8 for 200 ppm H2S gas at 400 °C (with a fast response/recovery time of ∼ 108 s/47 s). Further, NiO thin films confirm the high sensitivity, selectivity, and stability towards H2S gas with detection limit of 135 ppb. The H2S gas sensing mechanism with NiO is also explained.