Effect of Discharge Frequency on the Plasma Polymerization of Ethane

Abstract

The effect of discharge frequency on the kinetics of plasma polymerization of ethane was studied over the frequency range from 50 Hz to 13.56 MHz, in a tubular reactor at a pressure of 0.5 torr, a flow rate of 20 cm3STP/min and a discharge power level of 10 watts. The discharge voltage and current were also measured at the same time. On the basis of these data, the following polymerization mechanisms are proposed, i. e., ion bombardment in the frequency range from 50 Hz to 50 KHz, electron bombardment from 50 KHz to 6 MHz and free radical and/or ion-electron pair diffusion from 6 MHz to 13.56 MHz. In the region that ion or electron bombardment is the predominant mechanism, most films were cracked, but in the region that the free radical and/or ion-electron pair diffusion are predominant, transparent or colored films were obtained in the relatively wide discharge parameter range. The infrared spectra and dielectric properties of the films formed in the three frequency regions were also measured. The infrared spectrum showed a broad absorption in the wave length region over 8 μm. This absorption depends on the polymerization condition, suggesting the existence of OH and CO as well as unsaturated groups. The dielectric properties are also affected by the condition of polymerization, treatment after film formation, film thickness and so on. In our experimental condition, an appearent loss peak can be observed at a temperature of -30 °C for a measuring frequency of 1 KHz. The activation energy of this loss peak was about 0.68 eV for each sample formed at the different discharge conditions. It is proposed that this loss peak is attributable to γp assigned to the carbonyl group.