Electret films with extremely high charge stability prepared by thermal evaporation of Teflon AF

Abstract

Abstract We report on the preparation of Teflon AF based electret films by thermal evaporation and corona discharge. Due to a special construction of the evaporator, smooth films without micropores could be deposited even at rates above 10 nm/s. The influence of film thickness, substrate temperature, charge density and type of charge carrier on the charge stability was investigated together with the mechanism of charge decay. Negatively charged films of 9.5 μm evaporated Teflon AF 1600 turned out to exhibit a much higher charge stability compared to commercial 25 μm Teflon FEP electret foils at almost 1/3 thickness and proved to be also superior to spin-coated Teflon AF 1600 films. This is discussed in terms of absence of discharge via the surface. Charge decay was shown to take place by internal drift and diffusion through the bulk of the film and not along the surface or via external discharge mechanisms as reported for Teflon FEP.