Growth kinetics, composition, and morphology of Co₃O₄ thin films prepared by pulsed liquid-injection MOCVD

Cobalt oxide films were grown by pulsed liquid injection MOCVD using Co(thd)2 dissolved in monoglyme as the precursor. The structure, morphology, and growth rate of the layers deposited on silicon substrates were studied as a function of solution concentration, deposition temperature, and oxygen partial pressure. X-ray diffraction (XRD) of films deposited from 350°C to 540°C showed a pure Co₃O₄ spinel structure and no CoO was detected, even at the lowest oxygen pressure. X-ray photoelectron spectroscopy (XPS) was used to study the surface composition and oxidation states. Surprisingly, XPS spectra recorded for most of the films seemed to correspond to CoO. This unexpected oxidation state on the surface was assigned to the effect of the high density of edges and corners present in the surface morphology.