The effect of manganese doped cobalt oxide (Co₃O₄:Mn) was investigated by two different ratios (1% and 3%), which were precipitated by spray pyrolysis technique (SPT), and was adopted using a laboratory designed glass atomizer. Glass substrates were used to deposit films on them, heated at a temperature of 420 ℃. The structural properties were studied through X-ray diffraction. The results showed that all deposit nanostructured films were polycrystalline and there was a decrease in the preferred reflection intensity along (311) plane resulting in a decrease in the crystallite size. Surface properties were analyzed through atomic force microscopy (AFM), which showed a decrease in the roughness and the particle size growth was a vertical columnar rod. The optical characterization displayed that the transmittance of pure Co₃O₄ nanostructured films was 48% and decreased to 35% for 1% of the Mn concentration, and continued to decrease to 33% with the increase of manganese concentration up to 3%. Optical energy bandgap of pure Co₃O₄ nanostructured films was 1.435 eV and decreased to 1.419 eV for 1% of Mn concentration, and continued to decrease to 1.367 eV with the increase of Mn concentration up to 3%. The highest percentage sensitivity was for the sample doped with 3% Mn, which was about 65%, for NO₂ gas concentration of 600 ppm, at an operating temperature of 200 ℃.

Tin oxide was prepared by chemical methods and then doped with different weight ratios of vanadium 2wt% and 4wt%. The structural, morphological, and optical properties were studied. It was found that all the recorded films had a polycrystalline diffraction pattern and that the predominant reflection was (111) plane. The doping processes resulted in the improvement of crystalline structure and the disappearance of a number of secondary reflections and the direction of the film in a single crystalline pattern, thus reducing the values of energy gap and percentage transmittance. The morphological properties were studied by converting the three-dimensional images into graphic drawings to enable us to easily calculate surface parameters.