Synthesis and Characterization of Al-Doped SnO₂ Semiconducting Thin Films on Glass Substrate by Sol–Gel Technique for Gas Sensors in Aerospace Applications

This paper outlines the synthesis and characterization of semiconducting films composed of 0–2.0% Al-doped SnO₂, tailored for gas sensor applications in aerospace contexts. The films were fabricated via the sol–gel method on glass substrates. Transparent solutions were prepared from Al and Sn salt precursors, methanol, and glacial acetic acid. Solution characteristics, such as pH and rheological properties, were evaluated prior to the coating process. Gel coatings were dried at 300 °C for 10 min and annealed at 600 °C for 1 h in air. Structural, microstructural, and optical properties were analyzed using Fourier transform infrared spectrophotometer, X-ray diffraction, scanning electron microscopy, refractometer, and UV/VIS spectrophotometer. The study revealed that solution properties influenced film structure and microstructure, with acidic conditions affecting hydrolysis, condensation, and gelation, and higher viscosities resulting in thicker films. SnO₂ formation occurred between 410 and 500 °C, with a preferential (110) texture observed after annealing. Incorporating Al altered film morphology and microstructure, reducing microcrack formation and introducing nano-sized particles, thereby enhancing film quality and structural integrity. Refractive index, film thickness, and energy range of the Al–SnO2 films met requirements for gas sensor production. Gas sensitivity tests showed approximately 53% sensitivity to CO₂ at room temperature. The findings suggest that Al-doped SnO₂ films exhibit promising characteristics for aerospace gas sensing applications.