AFM AND STM STUDIES OF THE CARBONIZATION AND GRAPHITIZATION OF POLYIMIDE FILMS

Kapton polyimide and high-modulus polyimide (PPT) films were carbonize d and graphitized at various temperatures from 600 to 3000-degrees-C. Their surface was studied by atomic-force microscopy and/or by scannin g tunneling microscopy in order to follow the modification of the larg e-scale morphology and the atomic structure as a function of the heat- treatment temperature (HTT). On the pristine Kapton films, the local o rder of the molecules is brought to the fore. With increasing HTT (600 to 1000-degrees-C) the structure becomes more disordered while at lar ger scale a bumpy morphology appears. During graphitization, the bumpy morphology gradually disappears and is replaced by graphitized terrac es whose size increases with HTT. At atomic scale, it is shown that th e graphene layers progressively grow for HTT higher than 1800-degrees- C. On the films treated between 1800 and 2400-degrees-C, graphene laye rs containing point defects are imaged and (square-root 3 X square-roo t 3)R 30-degrees superstructures are observed near large defects. On t he samples treated at 2400 and 2600-degrees-C, moire patterns are obse rved and are attributed to stacking faults (turbostratic structure).