Valence control of cobalt oxide thin films by annealing atmosphere

The cobalt oxide (CoO and Co3O4) thin films were successfully prepared using a spin-coating technique by a chemical solution method with CH3OCH2CH2OH and Co(NO3)2·6H2O as starting materials. The grayish cobalt oxide films had uniform crystalline grains with less than 50 nm in diameter. The phase structure is able to tailor by controlling the annealing atmosphere and temperature, in which Co3O4 thin film was obtained by annealing in air at 300–600, and N2 at 300, and transferred to CoO thin film by raising annealing temperature in N2. The fitted X-ray photoelectron spectroscopy (XPS) spectra of the Co2p electrons are distinguishable from different valence states of cobalt oxide especially for their satellite structure. The valence control of cobalt oxide thin films by annealing atmosphere contributes to the tailored optical absorption property.