Sensitivity of Nanostructured Mn-Doped Cobalt Oxide Films for Gas Sensor Application

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 ℃.