Polarization profiling of the surface region of PVDF and P(VDF-TrFE)

Inhomogeneous polarization profiles are a typical property of ferroelectric polymers. Particularly in the surface region, the occurrence of a nonpolar layer is often observed. Different mechanisms can cause the decrease of the polarization near the surface. The first is the injection of charge from the metal contacts into the polymer during the poling when high electric fields are applied to the sample. The second is a structural variation of the sample near the surface e. g., a lower degree of crystallinity than in the bulk. The LIMM method i.e., a scan of the polarization profile with thermal waves, is particularly appropriate for an investigation of the surface near region of a sample. The resolution of LIMM has been improved to be better than 100 nm by an increase of the modulation frequencies into the MHz region. With this increased resolution, the surface near polarization in samples of polyvinylidenefluoride and its copolymers with trifluorethylene has been investigated