Highly selective NO2 sensor based on p-type nanocrystalline NiO thin films prepared by sol gel dip coating

Nanocrystalline NiO thin films were synthesized on ITO substrates by a solgel dip coating method using the mixture of NiC4H6O4 center dot 4H(2)O, NH3 center dot H2O and C3H8O as the precursor. Structure of NiO thin films was characterized by means of X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and ultraviolet-visible spectroscopy, and the results showed that the films were composed of cubic NiO nanocrystalline particles having diameters in the range of 2030 nm, which provides a large specific surface area. NiO thin films showed p-type semiconductor behavior due to the non-stoichiometry. A band gap of 3.75 eV was obtained by UVvis measurement. The sensor based on NiO thin films demonstrated a good reversibility and repeatability to NO2 at evaluated operating temperatures. The films also showed an excellent NO2 selectivity compared to formaldehyde, ethanol, methanol, xylene, hydrogen, ammonia and methane at 150 degrees C, demonstrating a potential application in low-energy consumption gas sensor devices.