Oxygen partial pressure effects on the RF sputtered p-type NiO hydrogen gas sensors

摘要

Highlights•NiO thin films were grown by RF sputtering system under different oxygen partial pressures.•Surface morphology modification of the thin films depending on the oxygen partial pressures was obtained.•NiO thin film hydrogen gas sensor devices were produced successfully.•At least 10% of the response was obtained to the 10 ppm H2gas sensor.•Hydrogen sensing mechanism of the gas sensor devices was disscused.AbstractNiO thin films were grown by Radio Frequency (RF) Magnetron Sputtering method under different oxygen partial pressures, which are 0.6 mTorr, 1.3 mTorr and 2.0 mTorr. The effects of oxygen partial pressures on the thin films were analyzed through Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS) and Hall measurements. The change in the surface morphology of the thin films has been observed with the SEM and AFM measurements. While nano-pyramids have been obtained on the thin film grown at the lowest oxygen partial pressure, the spherical granules lower than 60 nm in size has been observed for the samples grown at higher oxygen partial pressures. The shift in the dominant XRD peak is realized to the lower two theta angle with increasing the oxygen partial pressures. XPS measurements showed that the Ni2p peak involves satellite peaks and two oxidation states of Ni, Ni2+and Ni3+, have been existed together with the corresponding splitting in O1s spectrum. P-type conductivity of the grown NiO thin films are confirmed by the Hall measurements with concentrations on the order of 1013holes/cm−3. Gas sensor measurements revealed minimum of 10% response to the 10 ppm H2level. Enhanced responsivity of the gas sensor devices of NiO thin films is shown as the oxygen partial pressure increases.