Cobalt oxide-based films: sol-gel synthesis and characterization

Recently, much attention has been focused on cobalt oxide-based materials. In this study, Co3O4, CoO and CoO-SiO2 coatings were synthesized via sol-gel using cobalt acetate [Co(CH3COO)(2)-4H(2)O] and tetraethoxysilane [Si(OC2H5)(4)] (TEOS) as starting compounds. The precursor choice was made taking into account that acetate decomposes under thermal treatment without leaving residual contaminants inside the coatings. The films were prepared by a dip-coating procedure from alcoholic solutions of the proper precursors and subsequently annealed under different conditions. Co3O4 coatings were obtained after heating in air or nitrogen at 300 degreesC. Treatments in reducing atmosphere (H-2/Ar) yielded CoO layers up to 500 degreesC, and films of metallic cobalt for firing at higher temperatures. CoO-SiO2 coatings were heated in air between 300 and 900 degreesC. CoO cluster formation in the silica glass layer is not yet well clarified. The chemical composition and the microstructural evolution of the coatings were studied by X-ray photoelectron spectroscopy (XPS), secondary-ion mass spectrometry (SIMS), UV-Vis spectroscopy and X-ray diffraction (XRD). (C) 2001 Elsevier Science B.V. All rights reserved.