Conduction mechanism in plasma-polymerized tetrafluoroethylene films

Abstract

The ac conductivity and capacitance of plasma-polymerized tetrafluorethylene were measured over the frequency range 10-3- 105 Hz. Experimental evidence is given that the measured conductivity is a bulk phenomenon over the entire frequency range. These measurements show that there are three different conduction processes, each of them dominating in certain frequency and temperature regions. At intermediate frequencies and temperature, a dipole orientation process dominates which gives rise to a large dispersion of the ac conductivity and charge storage in the films. Both ir observations and ESR data as well as the electrical measurements confirmed that -C - O groups formed by oxidation of the films after preparation are responsible for this effect. Concentrations of the order of N×1020 cm -3 were determined from electrical as well as from ir data. Hopping conductivity dominates at high frequencies and low temperatures, whereas at very low frequencies and high temperatures, a frequency-independent dc conductivity is found and ascribed to a Poole-Frenkel emission process.