Highly porous NiO microstructure for NO2 detection

Nickel oxide (NiO) thin films were deposited on to the glass substrates via chemical bath deposition (CBD) method at various deposition times of 5, 6, 7 and 8 h. The X-ray diffraction (XRD) study showed the cubic crystal structure of NiO. The field emission scanning electron microscopy (FE-SEM) images exhibit the porous structured morphology composed of randomly oriented nanosheets. The atomic force microscopy (AFM) analysis reveals the maximum surface roughness of 107.9 nm for NiO film deposited at 7 h. The X-ray photoelectron spectroscopy (XPS) study reveals the presence of Ni2+ and Ni3+ chemical states. The transmission electron microscopy (TEM) images reveal an average size of 5 nm for NiO nanocrystalline particles. The nitrogen dioxide (NO2) gas sensing performance was tested at various working temperatures and gas concentrations. The sensing tests showed 45.6 % response to 100 ppm NO2 at 200 °C with Tresponse = 13 s and Trecovery = 146 s.