Abstract
Copper oxide (CuO) thin films have been deposited on glass substrates by a facile sol–gel dip-coating technique with varying withdrawal speeds from 0.73 to 4.17 mm/s. The variation in the film thickness manifested by dip-coating withdrawal speeds was investigated in detail to investigate its effect on the structural, morphological, opto-electrical, and wettability properties of CuO thin films for carbon dioxide (CO2) gas-sensing applications. The crystallinity, as well as phase purity of dip-coated CuO, was confirmed by both x-ray diffraction (XRD) and Raman spectral analyses. The surface morphology of the films characterized by scanning electron microscopy revealed that pore density decreases with increasing withdrawal speeds and the grain size is found to increase with the increasing film thickness corroborating the XRD results. The optical bandgap of dip-coated CuO films was estimated in the range of 1.47–1.52 eV from the UV–vis–NIR transmission data, and it is found to decrease with the increase in Urbach tail states accompanied by the increase in the film thickness. The ratio of the electrical and optical conductivity of CuO films was found to decrease with increasing withdrawal speeds due to the variation in the carrier concentration. Among all the studied films, the sample deposited at a 0.73 mm/s withdrawal speed exhibited the highest crystallinity, porous morphology, highest pore density, opto-electrical conductivity, as well as water contact angle and, therefore, the maximum gas sensing response of CO2 vapor in the air recorded at room temperature.
Highlights
We investigated the effect of withdrawal speeds on the physical properties of cupric oxide (CuO) thin films prepared by the sol–gel dip-coating technique and structural, optical, and morphological properties were analyzed in detail for investigating the suitability of dip-coated CuO films for CO2 gas sensing applications at room temperature
The impact of the film thickness manifested by dip-coating withdrawal speeds on the structural, morphological, opto-electrical, and wettability nature of the dip-coated CuO thin films was investigated in detail
The structural properties characterized by x-ray diffraction (XRD) revealed that the thin films are polycrystalline in nature and have a monoclinic CuO crystal structure with preferential orientations along the (111) and (111) planes and they are free from impurity phases further confirmed by Raman spectroscopic analysis
Summary
Scitation.org/journal/adv bulky and suffer from short-life time, expensive maintenance, as well as their vulnerability to interference gases.. The change in resistance of materials originates from the surface reaction with ambient gaseous species in addition to the material compositions To this end, the porous structure of the CuO film may be beneficial for the surface reaction along with gas diffusion, leading to a faster sensing response.. There are some reports on the influence of various preparation techniques and deposition of CuO thin films, but the effects of the film thickness to tailor the physical properties for CO2 gas sensing applications of CuO deposited by the dip-coating technique are rarely explored. We investigated the effect of withdrawal speeds on the physical properties of CuO thin films prepared by the sol–gel dip-coating technique and structural, optical, and morphological properties were analyzed in detail for investigating the suitability of dip-coated CuO films for CO2 gas sensing applications at room temperature. We made an attempt to correlate experimental results with the light of possible mechanisms underlying the phenomena
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