XPS investigation of CoOx-based MRISiC structures for hydrocarbon gas sensing

Sensors based on metal-reactive insulator-silicon carbide (MRISiC) devices are widely employed for monitoring industrial processes because of their resistance to harsh and high-temperature environments. MRISiC structures composed of the films of Pt and cobalt oxide (CoOx) were fabricated and investigated. The films of Pt and CoOx were deposited on SiC substrates by using r.f. magnetron sputtering. The depth profiles of their chemical composition were studied by XPS combined with cyclic Ar+ sputtering. The surface morphology was investigated by AFM. XPS analysis of the Co 2p peaks and shake-up satellites revealed the presence of the mixed-valency oxide Co3O4 on the sample surface, while deeper in the film only stoichiometric CoO was present. The platinum film deposited on the top of cobalt oxide was found to be metallic and uniform enough to inhibit further oxidation of Co2+. The hydrocarbon (propene) gas sensing performance of the Pt/CoOx/SiC devices was studied.