Effect of Spin Speed on the Physical Characteristics of CuO Films Synthesized by Sol–Gel Spin Coating for H₂S Gas Sensing

In this paper, we study the effects of spinning speed on the electrical, optical, structural, morphological, and gas sensing properties of thin films deposited on glass substrates by sol–gel spin coating, using copper acetate dihydrate as the precursor. The deposition of the films was carried out at varying spinning speeds from 1500 rpm to 2500 rpm to achieve different thicknesses ranging from 157 nm to 470 nm, respectively. The results revealed that the resistivity of the films decreased from 75.5 Ω·m to 42.5 Ω·m with the decrease in spinning speed. X-ray diffraction (XRD) studies demonstrated that the crystallite size varied in the range of 18.14–27.48 nm. The band gap of the samples was found to vary from 2 eV to 1.69 eV, revealing that these samples were suitable for gas sensing applications. Field-emission scanning microscopy (FESEM) studies showed that the prepared samples were porous in nature and were suitable for H₂S gas detection. The films were examined at different operating temperatures with different concentrations of H₂S gas. The results showed that the response toward hydrogen sulfide gas varied with varying thickness of the samples. The CuO thin films showed the highest response toward hydrogen sulfide gas at a temperature of 25°C.