Abstract
Pyromellitic dianhydride and oxydianiline polyimide films turn electrically conductive upon irradiation with energetic ions. Raman spectroscopy shows an initial dissociation of the molecular structure at low irradiation doses ranging from 1×1014 to 1×1015 B+/cm2, followed by the appearance, at a high dose of 1×1016 B+/cm2, of structures similar to those observed in amorphous graphite. Comparing the reduced Raman spectra of materials irradiated up to a dose as high as 1×1016 B+/cm2 with the one-phonon density of states of amorphous graphite, one finds that this structural similarity to graphite only exists within a short range. Meanwhile, an ion-beam-induced aggregation of aromatic rings in irradiated polyimide films is indicated by ultraviolet-visible spectroscopy. In view of the structural information from resonant Raman spectroscopy, the existence of structural inhomogeneity is proposed for the high-dose irradiated polyimide. From perspectives of the model of heterogeneous media, the structural similarity to graphite within a short range is attributed to the existence of the second phase composed of broken functionalities of irradiated polyimide and the sp3-bonded carbon atoms.
Published Version
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