Preparation and Characterization of CuO/ZnO Nanostructures Thin Films using Thermal Evaporation for Advanced Gas Sensing Applications

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Abstract
In the current study, thin films of copper oxide (CuO-based) and zinc oxide (ZnO-doped) were fabricated using the thermal evaporation technique. The evaporation process occurs at 1×10–7 bar pressure and 0.5 nm s–1deposition rate. At room temperature (RT), the film thickness is (50 ± 0.2) nm and is deposited on glass substrates. After deposition, films are annealed at 573 K for 2 h. XRD analysis proved that CuO is monoclinic wurtzite-type with the presence of ZnO in the prepared films. This process yielded films with a homogeneous surface, as confirmed by AFM. As ZnO doping increased, roughness increased by 25 %, the root mean square value increased by 23.55 %, and the average grain diameter increased by 65.94 %. The FE-SEM analysis showed equally scattered (CuO/ZnO) nanoparticles (NPs). The optical characteristics of (CuO/ZnO) show that the absorbance and absorption coefficient increase with ZnO content. Transmittance and energy band gaps reduced from 0.889 to 0.742 at λ = 360 nm and 3.608 to 3.504 eV, respectively, as ZnO concentrations increased. The greatest reported sensitivity to NO2 at a concentration of 0.20 wt.% was 47.06 % at operating temperature of 100 °C. This sensitivity was achieved within a reaction time of 36 s and a recovery time of 19.8 s. The sensitivity of the sample (0.20 wt.%) normally decreases with increasing temperature. This suggests that the gas sensor can interact with NO2 gas without needing any activation energy and that the interaction is based on physical adsorption and polarity. Nevertheless, the sensitivity of the (Pure, 0.08, and 0.14) wt.% samples exhibited a positive correlation with temperature within a specific range. The findings regarding the structural and conductive properties of (CuO/ZnO) thin films have potential applications in diverse optoelectronics devices and gas sensors. HIGHLIGHTS Fabrication of (CuO/ZnO) nanostructures using thermal evaporation method. Study and analysis of the structural and morphological properties of the nanocomposites. Description of the optical properties of (CuO/ZnO) thin films. Fabrication of (CuO/ZnO) a gas sensor for the detection of NO2. Obtaining the best sensitivity, response time and recovery time for nitrogen oxide gas for (CuO/ZnO) thin films. GRAPHICAL ABSTRACT

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