Pure nanocrystalline SnO2 films were grown on a clean glass substrate by using sol–gel dip coating and chemical bath deposition (CBD) techniques for gas sensor applications. The films were annealed in air at 300[Formula: see text]C, 400[Formula: see text]C, and 500[Formula: see text]C for 60[Formula: see text]min. The deposited films with a thickness of approximately 300 [Formula: see text] 20 nm were analyzed through X-ray diffraction, scanning electron microscopy (SEM), atomic force microscopy (AFM), and optical absorption spectroscopy. Results revealed that the films produced by dip coating exhibited a tetragonal rutile structure and those produced by CBD showed a tetragonal rutile and orthorhombic structure. The crystalline sizes of the films produced by dip coating annealed at 300[Formula: see text]C, 400[Formula: see text]C, and 500[Formula: see text]C were 8, 14, and 22.34 nm and those for CBD films at these temperatures were 10, 15, and 22 nm, respectively. AFM and SEM results indicated that the average grain size increased as annealing temperature increased. The transmittance and absorbance spectra were then recorded at wavelengths ranging from 300[Formula: see text]nm to 1000[Formula: see text]nm. The films produced by both the methods yielded high transmission at visible regions. The optical band gap energy of dip-coated films also increased as annealing temperature increased. In particular, their optical band gap energies were 3.5, 3.75, and 3.87[Formula: see text]eV at 300[Formula: see text]C, 400[Formula: see text]C, and 500[Formula: see text]C, respectively. By comparison, the energy band gap of CBD-prepared films decreased as annealing temperature increased, and their corresponding band gaps were 3.95, 3.85, and 3.8[Formula: see text]eV at the specified annealing temperatures. The films were further investigated in terms of their sensing abilities for carbon monoxide (CO) gas at 50 ppm by measuring their sensitivity to this gas at different times and temperatures. Our results demonstrated that dip-coated and CBD-prepared films were highly sensitive to CO at 200[Formula: see text]C and 250[Formula: see text]C, respectively.

Nanocrystalline SnO2 and SnO2:Cu thin films derived from SnCl[Formula: see text]H2O precursors have been prepared on glass substrates using sol–gel dip-coating technique. The deposited film was [Formula: see text][Formula: see text]nm thick and the films were annealed in air at 500[Formula: see text]C for 1[Formula: see text]h. Structural, optical and sensing properties of the films were studied under different preparation conditions, such as Cu-doping concentration of 2%, 4% and 6[Formula: see text]wt.%. X-ray diffraction studies show the polycrystalline nature with tetragonal rutile structure of SnO2 and Cu:SnO2 thin films. The films have highly preferred orientation along (110). The crystallite size of the prepared samples reduced with increasing Cu-doping concentrations and the addition of Cu as dopants changed the structural properties of the thin films. Surface morphology was determined through scanning electron microscopy and atomic force microscopy. Results show that the particle size decreased as doping concentration increased. The films have moderate optical transmission (up to 82.4% at 800[Formula: see text]nm), and the transmittance, absorption coefficient and energy gap at different Cu-doping concentration were measured and calculated. Results show that Cu-doping decreased the transmittance and energy gap whereas it increased the absorption coefficient. Two peaks were noted with Cu-doping concentration of 0–6[Formula: see text]wt.%; the first peak was positioned exactly at 320[Formula: see text]nm ultraviolet emission and the second was positioned at 430–480[Formula: see text]nm. Moreover, emission bands were noticed in the photoluminescence spectra of Cu:SnO2. The electrical properties of SnO2 films include DC electrical conductivity, showing that the films have two activation energies, namely, [Formula: see text] and [Formula: see text], which increase as Cu-doping concentration increases. Cudoped nanocrystalline SnO2 gas-sensing material has better sensitivity to CO gas compared with pure SnO2.