Enhancement of hydrogen gas sensing of nanocrystalline nickel oxide by pulsed-laser irradiation.

This paper reports the effect of post-laser irradiation on the gas-sensing behavior of nickel oxide (NiO) thin films. Nanocrystalline NiO semiconductor thin films were fabricated by a sol-gel method on a nonalkaline glass substrate. The NiO samples were irradiated with a pulsed 532-nm wavelength, using a Nd:YVO(4) laser beam. The effect of laser irradiation on the microstructure, electrical conductivity, and gas-sensing properties was investigated as a function of laser power levels. It was found that the crystallinity and surface morphology were modified by the pulsed-laser irradiation. Hydrogen gas sensors were fabricated using both as-deposited and laser-irradiated NiO films. It was observed that the performance of gas-sensing characteristics could be changed by the change of laser power levels. By optimizing the magnitude of the laser power, the gas-sensing property of NiO thin film was improved, compared to that of as-deposited NiO films. At the optimal laser irradiation conditions, a high response of NiO sensors to hydrogen molecule exposure of as little as 2.5% of the lower explosion threshold of hydrogen gas (40,000 ppm) was observed at 175 °C.