EXISTENCE OF STRUCTURAL INHOMOGENEITY IN ION-BEAM-MODIFIED POLYIMIDE FILMS

Pyromellitic dianhydride and oxydianiline polyimide films turn electri cally conductive upon irradiation with energetic ions. Raman spectrosc opy shows an initial dissociation of the molecular structure at low ir radiation doses ranging from 1X10(14) to 1X10(15) B+/cm(2), followed b y the appearance, at a high dose of 1X10(16) B+/cm(2), of structures s imilar to those observed in amorphous graphite. Comparing the reduced Raman spectra of materials irradiated up to a dose as high as 1X10(16) B+/cm(2) with the one-phonon density of states of amorphous graphite, one finds that this structural similarity to graphite only exists wit hin a short range. Meanwhile, an ion-beam-induced aggregation of aroma tic rings in irradiated polyimide films is indicated by ultraviolet-vi sible spectroscopy. In view of the structural information from resonan t Raman spectroscopy, the existence of structural inhomogeneity is pro posed for the high-dose irradiated polyimide. From perspectives of the model of heterogeneous media, the structural similarity to graphite w ithin a short range is attributed to the existence of the second phase composed of broken functionalities of irradiated polyimide and the sp (3)-bonded carbon atoms.