MATERIALS TRANSACTIONS
Online ISSN : 1347-5320
Print ISSN : 1345-9678
ISSN-L : 1345-9678
Electrical Conductivity Enhancement of PTFE (Teflon) Induced by Homogeneous Low Voltage Electron Beam Irradiation (HLEBI)
Yoshitake NishiShota IizukaMichael C. FaudreeRyuichiro Oyama
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2012 Volume 53 Issue 5 Pages 940-945

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Abstract

Electrical conductivity (σ) enhancement, control, aging stability, and linear relation between σ and reciprocal temperature (1/T) in PTFE (Teflon) had been examined by homogeneous low potential electron beam irradiation (HLEBI). Irradiations up to 0.432 MGy were found to raise the σ of PTFE more than two orders of magnitude. In addition, control of electron movement or Fermi level by HLEBI on polymers seems possible since at low HLEBI levels up to 0.216 MGy, a strong dependence on σ was observed. Aging stability investigation showed the saturated conductivities at 106 s (σs) (2.5 × 10−16 and 3.6 × 10−15 S m−1) obtained at EB doses of 0.0432 and 0.432 MGy, respectively were approximately 4.9 and 70.6 times higher than σ of untreated PTFE (5.1 × 10−17 S m−1). Although the aging initially reduced the σ of irradiated samples, σs were remarkably higher than the untreated. For example, the lower dose 0.0432 MGy samples decayed significantly, but its σs value (2.5 × 10−16 S m−1) was still about 490% above untreated condition at 5.1 × 10−17 S m−1. ESR (electron spin resonance) measurements showed aging for 106 s only slightly reduced the peak intensity of irradiated PTFE. This indicated the charge carriers generated did not easily decay. Results agree with the literature where PTFE was irradiated with VUV and radicals such as CF3+ did not substantially decay with aging. Since the slopes of linear relationships between logarithmic electrical conductivity (ln σ) and reciprocal temperature (1/T) of all PTFE samples irradiated were approximately equal to that before treatment from 303 to 375 K, HLEBI didn’t convert the σ system. The small irradiation dose of 0.0432 MGy raised the electrical conductivity at room temperature. At higher temperatures above ∼375 K, the 0.0432 and 0.432 MGy-HLEBI generated drops in conductivity σ. When unstable dangling bonds with isolated radicals at terminated sites are assumed to be formed in irradiated PTFE, the σ recovery by heating to 424 K as well as high σ of irradiated PTFE could be explained. HLEBI probably generated dangling bonds in the form of radicals acting as acceptors to carry charge. Since a chemical dopant was not needed to act as a charge carrier, HLEBI could probably be an attractive method to attain homogeneous doping of organic films.

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© 2012 The Japan Institute of Metals and Materials
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