Electron Energy Loss and Auger Spectroscopies of Conducting Polyimide Produced by Ion Beam Irradiation

Abstract

The appearance of electronic conductivity in polyimide irradiated with ion beams has been attributed to the formation of extended systems of π orbitals. We have studied by reflection energy loss (REELS) and Auger (AES) spectroscopies the electronic properties of PMDA-ODA polyimide films irradiated by N⁺ ions. This confirmed the graphite-like electronic structure of the conducting phase. In particular the REELS spectrum shows the plasmon at 7 eV attributed by Taft and Philipp¹ to the collective excitation of π electrons in graphite together with the 25 eV plasmon which results from a [sgrave] + π excitation. These results are in agreement with the evolution discussed by Marletta in BTDA-ODA polyimide², but are interpreted by the formation of a graphite-like phase which is known to determine the electronic properties of disordered carbon layers³. The insulator-metal transition may be interpreted by a percolation mechanism between conducting blobs which result from radical clustering as shown by the development of a strong ESR signal.