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-2p3/2 and S-2p1/2, 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.