The thickness dependence of dielectric properties in the plasma polymer thin films

Abstract

In this study, the results of dielectric spectroscopy of plasma polymerized poly(ethylene oxide) thin films are presented. The films were deposited by plasma-assisted physical vapour deposition at radio-frequency plasma discharge power of 5W, and film thicknesses of 20, 100, and 250 nm. Dielectric measurements of the films were performed in the frequency range of 10(-1)-10(7) Hz and temperature was scanned between 173 and 353 K. The dielectric constant (epsilon') and dielectric loss (epsilon '') of plasma polymerized poly(ethylene oxide) thin films were calculated by measuring capacitance (C) and dielectric loss factor (tan delta). It was observed that there were two relaxation mechanisms in the investigated frequency range. These were called alpha and beta relaxations. These relaxations shift toward higher frequencies with increasing temperature. Moreover, alpha-relaxation starts to appear at different temperatures. This shows the difference between the polarizability abilities of samples at the same temperature and same frequencies. The reason for this behavior can be expressed by the dead layer concept, which is a result of good adhesion of the bottom layer of plasma polymer to the substrate. In light of these interpretations, with thinner samples it is possible to have structurally similar thin films like thin films deposited at high plasma power. A thinner film may support more transparency and these thinner films may be effective as coverage of optical devices, such as lenses, visors, etc.