Gas sensing properties of AACVD-derived ZnO/Co3O4 bilayer thin film nanocomposites

ZnO/Co3O4 nanocomposites with different Co3O4 concentrations and layer thicknesses were obtained by two-stage aerosol vapor deposition (AACVD). In pure oxide films ZnO particles have a mean size of 64 ± 11 nm, and Co3O4 particles 55 ± 10 nm. It was shown based on EDX data that cobalt oxide content in the films with its deposition time being 10, 20 and 30 min is 4.7, 7.2 and 12.4 mol.% respectively. Coating thickness was estimated using AFM as 144 ± 59, 173 ± 36 and 207 ± 71 nm for these samples. The film thickness of ZnO and Co3O4 was 115 ± 34, 149 ± 26 respectively. Gas-sensitive properties to a wide range of analyte gases: CO, NH3, H2, CH4, C6H6, ethanol, acetone and NO2 at 125–300 °C were measured. It was found that the individual ZnO film showed a high and selective response to 0.3–100 ppm NO2, and the Co3O4 and sample with Co3O4 deposition time of 10 min (ZCo10) had response to 4–100 ppm acetone and ethanol at moderate temperatures. ZnO and ZCo10 films were shown to exhibit minimal drop in response at elevated humidity.