Valence-band structure of PMDA-ODA polyimide studied by x-ray photoelectron spectroscopy and theoretical calculations*

Abstract

The valence-band structure of pyromellitic dianhydride-4,4′-oxydianiline (PMDA-ODA) film was investigated experimentally and theoretically. High-resolution valence band spectra were obtained with an x-ray photoelectron spectroscopy (XPS) instrument equipped with a monochromatic high-power Al Kα x-ray source. Several new valence-band structures were observed. Electron energy loss spectra showed the presence of an inelastic peak at about 6.5 eV loss energy. A photoelectron background was synthesized from the electron energy loss spectrum by a convolution procedure. This background gave a good understanding of the valence band spectrum. Valence effective Hamiltonian and extended Hückel calculations were performed to study the XPS intensities of the valence-band structures. The intensities were approximated by utilizing the XPS intensity model with net atomic populations. The total intensities were partitioned into intensity contributions from various functional groups of the polyimide. Three energetically separated regions with dominating contributions from the imide nitrogens, the ODA carbons, and the imide oxygens, respectively, were found.