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EVALUATION OF THIN FILM CAPACITORS FABRICATED FROM HETEROGENEOUS POLYPYRROLE BASED LANGMUIR-BLODGETT FILMS R. B. Rosner and M. F. Rubner* Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA

ABSTRACT The electrical properties of Langmuir-Blodgett films of conducting polypyrrole were investigated in an effort to illucidate the molecular architecture of these multilayer films and determine the mechanism of conduction. Values of the dielectric constant and transverse conductivity recorded as a function of frequency were determined from electrical measurements performed on devices made with the conductive polymer. The highly anisotropic nature of the conductivity as well as the frequency dependence demonstrated by both the conductivity and dielectric constant provide evidence for a highly ordered molecular structure in which the conductive and insulative components of the multilayer film form an organized, layered structure. Even greater control of the electrical and structural properties has been achieved through the fabrication of a thin film superlattice in which the conducting polymer and an insulating derivative were deposited as alternating bilayers. The properties of the superlattice were close to those predicted for an inhomogeneous, mixed media.

INTRODUCTION The desire to control the order and molecular and supermolecular organization of thin films of conducting polymers has recently stimulated interest in utilizing the Langmuir-Blodgett (LB) technique to process these novel materials. Towards this goal, our group has developed a number of different approaches that can be used to manipulate electrically conductive polyheterocycles, such as poly(3-alkylthiophenes) and polypyrroles, into LB films [1,2]. In the case of the polypyrroles, electrically conductive monolayers are created by polymerizing pyrrole monomer in the presence of a surface active pyrrole at the air-water interface of the LB trough. The resultant mixed monolayers are then transferred into multilayer thin films using the standard LB vertical transfer technique. When 3-octadecanoyl pyrrole (3-ODOP) is used as the surface active molecule, the multilayers are comprised of well ordered domains of insulating 3-ODOP and partially ordered domains of electrically conductive polypyrrole. In this paper, we discuss the electrical properties of these heterogeneous multilayers in the form of thin film capacitors.

EXPERIMENTAL The synthesis of the surface active pyrrole molecules, 3-octadecyl pyrrole (3-ODP) and 3octadecanoyl pyrrole (3-ODOP), used in this study as well as information on monolayer formation and manipulation have been described in detail in previous publications [1]. Transverse conductivities and dielectric measurements were made on films deposited onto platinum coated glass slides. Two methods were employed in making the electrical contacts to the top of the film; one involving an array of aluminum electrodes; the second a mercury drop. In the former case, a series of a