The polyimide (PMDA-ODA) titanium interface. Part 3. A theoretical study

Abstract

Ab initio SCF calculations are used to determine the possible interaction sites in model structures of the polyimide pyromellitic dianhydride-oxydianiline (PMDA-ODA) interacting with Ti atoms. The results are compared with the observed XPS spectra. Several sites of interaction for one or two atoms of Ti with model molecules have been investigated. It is shown that for one interacting Ti a favorable structure corresponds to the formation of a π-complex between Ti and the aromatic ring of the PMDA unit. Other possible sites are, the center of one heterocycle of PMDA, one >C=O group of PMDA and one aromatic ring of ODA. When two Ti atoms interact with PMDA-ODA with the first atom located over the aromatic ring of PMDA, then the possible sites of interaction for the second atom are, one aromatic ring of ODA, one >C=O group of PMDA and one heterocycle of PMDA. Calculated Koopmans' ionization energies, for two Ti atoms located at their most stable positions, reproduce the main features of the XPS spectra of the Ti/polyimide system except for the low energy C1s peak observed at about 282 eV. Our calculations confirm that this peak can be assigned to a carbide bond between one carbon and a Ti atom.