RF sputtered SnO₂: NiO thin films as sub-ppm H₂S sensor operable at room temperature

A room temperature sub-ppm H₂S sensor based on RF sputtered SnO₂: NiO thin film has been demonstrated. For this, SnO₂ thin films have been modified with ultrathin layers (30 nm) of NiO. These films were characterized using Scanning electron Microsopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Gas sensing properties of these films were systematically investigated and compared with those of pure SnO₂ and NiO films. Sensing studies revealed that these films are highly sensitive to H₂S at room temperature. The sensor response exhibited by NiO modified SnO₂ film, is 9 and 415 times greater than that exhibited by pure SnO₂ and NiO films, respectively. The sensor response in case of SnO₂:NiO is due to contribution from two different mechanisms- (i) oxidation reaction between adsorbed oxygen and H₂S and (ii) destruction of p-n junctions due to conversion of Nickel Oxide to metallic Nickel Sulphide (product of chemical reaction between NiO and H₂S). Presence of XPS sulphide peaks at binding energies of ∼163 eV corresponding to S-2p_3/2 and S-2p_1/2, on H₂S exposure confirms the formation of Nickel Sulphide. Present experiments proved the ability of these films to detect low concentrations of H₂S i.e. parts per billion reproducibly. These films were also found to be stable for extended period of time, hinting at commercial viability of the sensor.