Preparation of Nanostructured Co3O4 Thin Films Using Spray Technique for Gas Sensing Applications

Abstract

Nanostructured thin films of cobalt oxide (Co₃O₄) were deposited on glass substrates using chemical spray pyrolysis at a substrate temperature of 673K. The deposited films were annealed at 773K for 60, 90, and 120 minutes to investigate their physical and gas sensing properties. X-ray diffraction results showed that the as-deposited films were amorphous, while the annealed films exhibited a polycrystalline cubic structure. The crystallite size increased from 51.74 to 55.33 nm with increasing annealing time. Microstrain and dislocation density were also evaluated. Atomic force microscopy analysis was used to examine the surface topography of the films. Optical properties were studied using UV-visible spectroscopy, revealing two direct band gaps: Eg₁ ranging from 1.98 to 2.09 eV and Eg₂ from 2.5 to 3.4 eV. Gas sensors fabricated from annealed and unannealed films showed improved sensitivity with operation temperature at 200°C for NO₂ and at 100°C for H₂S gases.