Elaboration and characterization of nanostructuring NiO thin films for gas sensing applications

Abstract

This work has been based on the chemical spray pyrolysis technique, it is a very attractive method, that for its ease and low cost on the one hand and the quality of the films prepared by it on the other hand, it is used to produce thin films for different applications including the most important (MOS)-based gas sensors, Such as (NiO)-based gas sensors. At first, a comprehensive study is presented on the effect of deposition parameters on the structural, optical and electrical properties of undoped and Co and Cu-doped (NiO) thin films; the finest samples obtained are then used in the sensor to study their sensing performance for some Volatile organic gases such as ethanol, acetone and methanol. In the following we summarize the most important results obtained:  The XRD patterns showed that the structure of the undoped and doped NiO films is polycrystalline structure with the preferred direction (111) also showed that there was no significant shift in the direction of diffraction peaks after doping with cobalt or copper. The crystalline size (D) is increased by thermal annealing and decreases by increasing the doping in the (NiO) samples. From the transmittance spectra, for all samples it was observed that the optical transparency values were moderate to relatively weak, it decrease by thermal annealing, by increasing the molar concentration of the precursor solution, or by increasing the percentage of doping with cobalt or copper. Cobalt or copper doping was also found to be decreasing the band gap energy for the above mentioned reasons, and its values ranged from 3.86 to 3.64 eV for undoped NiO films. For doped films, it ranged between 3.61 and 3.48 eV to cobalt doped films and between 3.60 and 3.43 eV to copper doped films. It was observed that the electrical conductivity of all samples is good and it is the P-type and it has been shown to increase by thermal annealing or by increasing the proportion of doping with cobalt or copper in general, and its value exceeded (0.29 Ω-1.cm-1) when doped By 12 at.% of Copper.  Five samples were selected from the prepared samples to study their sensing performance towards ethanol, acetone and methanol vapors, where all films had high ohmic resistance. Optimum operating temperatures, sensitivity, selectivity and detection limits were determined to the gas-based sensor.