Effects of withdrawal speed on the structural, morphological, electrical, and optical properties of CuO thin films synthesized by dip-coating for CO2 gas sensing

Abstract

Copper oxide (CuO) thin films have been deposited on glass substrates by a facile sol-gel dipcoating technique with varying withdrawal speeds from 0.73 to 4.17 mm/s. The variation of 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 CO2 gas-sensing applications. The crystallinity, as well as phase purity of dip-coated CuO, were confirmed by both X-ray diffraction (XRD) and Raman spectral analyses. The surface morphology of the films characterized by the scanning electron microscopy (SEM) revealed that pore density decreases with the increase of withdrawal speeds and grain size is found to increase with the increase of film thickness corroborating the XRD results. The optical bandgap of dipcoated 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 increment of Urbach tail states accompanied by the increase of film thickness. The ratio of the electrical and optical conductivity of CuO films is found to decrease with increasing withdrawal speeds due to the variation of carrier concentration. Among all the studied films, the sample deposited to 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 maximum gas sensing response of carbon dioxide (CO2) vapor in the air recorded at room temperature.

On the structural evolution of nanoporous optically transparent CuO photocathodes upon calcination for photoelectrochemical applications

“…The direct transfer of the freshly dip-coated samples into a pre-heated furnace (125 °C) was critical to the stabilization of the CuO framework, due to desorption of hydroxyl and water molecules from the samples' surfaces followed by a 24 h stabilization step at 250 °C for 24 hours to allow for sufficient condensation of the hydrolyzed precursors. 58,63,64 Even though fabrication of porous CuO thin lms by dip-coating has been studied, [65][66][67][68][69] preparation of uniform and continuously connected nanoporous and optically transparent CuO thin lms by so-templating (using a copolymer as structure-directing agent) via the EISA method has, to the best of our knowledge, not been reported yet. Advantageously, the EISA process allows for precise control for adjusting the porosity, 52,70 and thus the mass transport properties, 71 when the nanoporous network is in contact with an electrolyte.…”

Highly Sensitive and Selective Hydrogen Gas Sensor with Humidity Tolerance Using Pd-Capped SnO2 Thin Films of Various Thicknesses

“…The crystallite size of the thin films was calculated using the Scherrer formula, indicating an increase in crystallite size with increasing film thickness up to 357.4 nm [26,27]. Additionally, the micro-strain decreased with increased film thickness, indicating an improvement in the film's crystallinity [28]. The XRD pattern in Figure 2a did not reveal the Pd peak [29], indicating a very low crystallinity content.…”

“…At temperatures below 250 • C, gas molecules lack the thermal and kinetic energy required to overcome the surface barrier, leading to low-adsorption capacity of gas molecules [41]. However, when the temperature of the Pd-caped SnO 2 thin film exceeds 250 • C, the gas molecules adsorb on the sensing material and desorb before the electron transfer due to their high activation energy, resulting in a decrease in the sensor response of the sensing material [28]. Additionally, the difference in the magnitude of the sensor response among different sensors may be due to the variation in the thickness of the deposited materials.…”

Tailor-made Tenorite (CuO) Interface Films for Enhanced Photocatalysis: An Improved Dip-Coating Approach with Enhanced Surface Topography and Hydrophobicity

“…Because of the monoclinic phase of CuO, it is more thermostable than Cu2O, which has a cubic phase (Hamad et al 2022). On the other hand, CuO is a prevalent semiconducting metal oxide based on its conductivity and the presence of p-type semiconductors owing to copper gaps in the crystalline lattice (Musa et al 2021), which has a sensitive under visible light with strong photocatalytic oxidation activity in eliminating organic contaminants under both artificial and solar light (Uma et al 2021;Zhang et al 2021;Yahia et al 2022). Tenorite has appealing properties, including strong electrical conductivity, excellent stability, and high catalytic activity.…”