Deposition of cobalt oxide thin films by plasma-enhanced chemical vapour deposition (PECVD) for catalytic applications

Abstract Plasma-enhanced chemical vapour deposition (PECVD) was used to prepare thin films of cobalt oxide. Cobalt oxide-based (CoO and Co 3 O 4 ) catalysts were chosen due to their efficiency in mineralisation of organic pollutants achieved by catalytic ozonation. In this work, two types of PECVD processes were used for the production of cobalt oxide thin films. In the first one, a solution of nitrate salt of cobalt was sprayed into a RF low pressure plasma discharge (40 MHz, 600 Pa, 200 W) to obtain Co x O y layers. In the second MOPECVD (metal organic plasma-enhanced chemical vapour deposition) process, cobalt oxide thin films were deposited using a capacitive coupled external electrodes RF plasma reactor (13.56 MHz, 100 Pa, 200 W) with cobalt carbonyl Co 2 (CO) 8 dissolved in hexene as precursor sprayed in a gas carrier (argon and oxygen). In the case of coatings produced from a solution of cobalt nitrate salt, a layer of 1 μm of Co 3 O 4 in crystalline form was obtained after annealing. Considering the thin films obtained from cobalt carbonyl precursor, analyses confirmed the presence of cobalt oxide in a polymeric layer on the surface of the substrate. XRD investigation showed the presence of a crystalline phase of Co 3 O 4 (crystallite size of about 40 nm).