Ion-induced conductivity in poly (phenylene sulfide)
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I. INTRODUCTION
II. SUMMARY OF PPS DATA
Although polymeric materials are normally dielectrics, it has been found recently that the electrical properties of polymers can be altered substantially both chemically and by ion irradiation. Electrically conductive polymers offer a number of advantages for uses in microelectronic devices. Among these advantages are that polymers are easy to prepare in large quantities, they are inexpensive, and they have properties that can be made variable over a wide range. The observation of enhanced conductivity in organic polymers resulting from energetic ion irradiation has been reported and discussed by many workers1"12 and reviewed by Venkatesan et al.u In particular, Bartko et aV have reported greatly enhanced conductivity in poly (phenylene sulfide), PPS, films irradiated with very high-energy heavy ions. The aim of their work was to determine how polymer conductivity is affected by the electronic energy deposition rates, {dE/dx)e of the ions used. Conductivities up to 0.5 S/cm were reported at ion doses up to 1016 ions cm" 2 , and the conductivity was found to be a rapidly increasing function of ion dose for those cases where enhanced conductivity was observed. We report here additional experimental measurements that have been done on ion-implanted PPS. The results of ion-induced conductivity measurements on PPS reported to date are summarized, and a semiempirical model that correlates observed conductivity with parameters associated with the energy loss of the heavy ions is presented.
The results of 0.323 MeV Li, 5.6 MeV F, and 50 MeV I ion-irradiation of PPS have been reported previously,9 and the experimental details of the irradiations and conductivity measurements have been described. These conductivity measurements have been supplemented by additional PPS irradiations with 28 MeV Si, 40 MeV Ca, and I at 37.5 and 25 MeV. All irradiations were carried out on the tandem Van de Graaff accelerator at the University of Pittsburgh. A summary of all of the Westinghouse Research and Development (R&D) Center PPS conductivity measurements is contained in Fig. 1. Shown for comparison are the results of conductivity measurements made by the Masachusetts Institute of Technology (MIT) group 4 on PPS irradiated with 0.20 MeV Br and 0.10 MeV As ions. The data in pig- 1 show the abrupt onset and rapid increase of PPS conductivity with increasing ion dose. In the case of the MIT data, saturation occurs at high ion doses, whereas the Westinghouse R&D data show no evidence of saturation at the doses studied. The causes of conductivity resulting from ion irradiations have been a subject for speculation, and several proposed mechanisms have been presented.4'7'9 In the present work we attempt to correlate the observed conductivity with parameters related to the transfer of energy from the ion to the polymer.
J. Mater. Res. 3 (6), Nov/Dec 1988
http://journals.cambridge.org
III. THEORY The available data on PPS conductivity produced by high-energy ion irradiations have been examined in
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