Cobalt hexafluoroacetylacetonate polyether adducts for thin films of cobalt oxides

The novel [Co(C₅F₆HO₂)₂ · 2H₂O · CH₃(OCH₂CH₂)₂OCH₃] and [Co(C₅F₆HO₂)₂ · 2H₂O · CH₃(OCH₂CH₂)₃OCH₃] low-melting adducts have been synthesized and characterized by elemental analysis, IR spectroscopy, mass spectra and TG-DTG thermal measurements. The former adduct is liquid at room temperature, whilst very mild heating of the latter results in a thermal stable liquid compound. Both adducts can easily be evaporated. Deposition experiments, in a low-pressure horizontal hot-wall reactor, on optical transparent SiO₂ substrates, using these precursors, result in CoO or Co₃O₄ films, depending on the deposition conditions. XRD measurements provide evidence that CoO and Co₃O₄ consist of cubic, highly oriented, (2 0 0) and (3 1 1) crystals, respectively. The mean crystallite sizes were evaluated from the XRD line broadening. Both optical spectra and resistivity measurements of Co₃O₄ films show that they are semi-conducting and their band-gap was determined from the optical induced transitions. The film cross section and the surface atomic composition were investigated by SEM and XPS analyses, respectively.