Structuring of Conducting Polymers by Ion Implantation
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ABSTRACT Conducting polypyrrole polymer films have been modified by ion implantation. The resulting cross linking leads to changes in resistivity and electrochemical behaviour. By ion implantation through masks or with a focused ion beam lateral structures can be produced which can be imaged by scanning electron microscopy and optical absorption. The implanted polypyrrole layers can be removed by electrochemical treatment while not implanted regions can be electroplated. Therefore in combination with electrochemical treatment three dimensional structures have been generated and were investigated by atomic force microscopy. In order to study structures in the submicrometer range implantation experiments with a focused ion beam were performed and the minimal line widths were investigated by scanning electron microscopy. INTRODUCTION The synthesis of conducting polymers in the late 70's was an attempt to combine the properties of polymers with those of metals. Although highly conductive polymers could be synthesized [1] there are still problems with the required chemical stability for the industrial application.
Conducting polymers consist of an extended 7r-system and in this state they are semiconducting or insulating. By oxidation or reduction ("doping") charge carriers are introduced accompanied by the incorporation of counter ions. This process leads to an increase in conductivity by several orders of magnitude. The doping procedure can be performed chemically, electrochemically or by ion implantation [2, 3]. However, compared to chemical or electrochemical doping ion implantation leads to lower conductivities. This is not surprising because the charge transfer and deposition of counter anions by ion implantation is accompanied by changes in the polymer structure. Besides the application of ion implantation as doping method some work has been reported about the modification of the properties of intrinsically conducting polymers: in [4] changes of the morphology after ion implantation were correlated with changes in conductivity ; variations of conductivity and electrochemical behaviour by ion implantation were presented in [5, 6]; Lin et al. could show electrical pn-junction behaviour after implantation of potassium in conducting polymers [7]. In our earlier work we demonstrated the change of resistivity depending on the implantation parameters [6]. This change of resistivity leads to very low current density in cyclovoltammetric experiments during the first few cycles. With increasing numbers of cycles the current density approaches the original value of the untreated polymer, indicating 317 Mat. Res. Soc. Symp. Proc. Vol. 396 @1996 Materials Research Society
a removal of the implanted region, which was confirmed by XPS measurements [8]. Lateral structured conducting polymers have been developed into three dimensional structures by electroplating and electrochemical etching. One purpose of this paper is to show the topography of these structures and its dependence on the electrochemical method. The structures
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