Interfacing a nanostructured nickel oxide layer displaying fractal-like features with graphene: chemiresistive...

An interface between graphene and a nanostructured nickel oxide (NiO) layer with fractal-like features was prepared by spark ablation coupled with impaction printing at 0.2 mbar. The chemiresistive behavior of the interface was investigated by exposing the surface to ammonia (NH₃) and nitrogen dioxide (NO₂). Results showed that the NiO layer made the overall system more selective towards NH₃, indicating that the p-type character of the graphene layer was strengthened by the oxide deposition, which was consistent with the results of microRaman spectroscopy. With respect to the pristine graphene layer, the response to NO₂ decreased by a factor of approximately 2 over the NO₂ concentration range from 2 to 6 ppm, while we observed a 3-fold increase in the response to NH₃ over a concentration range of 10 to 40 ppm. The graphene layer covered with NiO, showing the highest response to NH₃, was selected to fabricate a graphene-based field effect transistor to be operated as a gas sensor and to eventually investigate the effect of NH₃ on carrier mobility. The NH₃ sensing based on tracing the Dirac point shift was demonstrated. Compared with the resistivity variation measured in the chemiresistive configuration, when the change in the Dirac point was traced, the calibration curves showed a three-fold increase in the sensitivity towards NH₃. These findings further show the enhancement of the sensing properties of graphene due to the incorporation of nanostructured, fractal-like NiO layer.