Radiation-Induced Transient Currents in Films of Poly(arylene ether ketone) Including Phthalide Moiety.

The electrical properties of thin films of poly(arylene ether ketone) copolymers (co-PAEKs) with a fraction of phthalide-containing units of 3, 5, and 50 mol% in the main chain were investigated by using radiation-induced conductivity (RIC) measurements. Transient current signals and current-voltage (I-V) characteristics were obtained by exposing 20 ÷ 25 µm thick films of the co-PAEKs to monoenergetic electron pulses with energy ranging from 3 to 50 keV in an electric field ranging from 5 to 40 V/µm. The Rose-Fowler-Vaisberg semi-empirical model based on a multiple trapping formalism was used for an analysis of the RIC data, and the parameters of the highly dispersive charge carrier transport were evaluated. The analysis revealed that charge carriers moved in isolation from each other, and the applied electric fields were below the threshold field triggering the switching effect (a reversible high-to-low resistivity transition) in the co-PAEK films. It was also found that the co-PAEK films, due to the super-linear I-V characteristics, are highly resistant to electrostatic discharges arising from the effects of ionizing radiation. This property is important for the development of protective coatings for electronic devices.

Analysis of the time-of-flight transients in molecularly doped polymers using the Gaussian disorder model.

Using published data for four molecularly doped polymers, which exhibit flat plateaus on the time-of-flight transients, we compared theoretical curves with experimental ones. The numerical calculations as well as parameter values were based on the Gaussian disorder model. In no case were flat plateaus predicted to appear. According to theory carrier transit should proceed in the non-equilibrium regime. We saw close agreement for the transit times in weakly polar polymers even at high fields but only at elevated temperatures, while in highly polar polymers similar agreement occurred only at low fields. In addition, the Gaussian disorder model does not account for the current shape universality (regarding field variation) frequently observed experimentally in polar molecularly doped polymers.

Verification of the dispersive charge transport in a hydrazone:polycarbonate molecularly doped polymer.

We report results of specially planned experiments intended to verify the dispersive character of the charge carrier transport in polycarbonate molecularly doped with hydrazone at 30 wt% loading, using for this purpose samples specifically featuring a well-defined plateau on a linear-linear plot. For this purpose we propose a new variant of the time-of-flight technique which allows easy changing of the generation zone width from about 0.5 µm (surface excitation) through intermediate values to full sample thickness (bulk excitation). To achieve this, we use electron pulses of 3-50 keV energy rather than traditional light pulses provided by lasers. Experimental results corroborated by numerical calculations uniquely prove that carrier transport in this molecularly doped polymer is dispersive, with the dispersion parameter equal to 0.75. Nevertheless, the mobility field dependence follows the famous Poole-Frenkel law.