Dielectric properties of the surface layer in ultra-thin films of a VDF/TrFE copolymer

We measured the temperature and frequency dispersion of the permittivity of vinylidene fluoride and trifluoroethylene (VDF/TrFE) thin films spin-coated on glass substrates with evaporated aluminium electrodes. Assuming the existence of two surface layers with different dielectric properties from the bulk material, a thickness of 2 nm was deduced for each surface layer. The temperature dependence of the frequency dispersion of the permittivity of the surface layers was obtained. Each surface layer has a dielectric relaxation which is essentially the same as the segment mode of the amorphous region of the bulk. It shows no anomaly at the temperature of the paraelectric-ferroelectric phase transition for thick samples. The surface layers appear to be amorphous.