Scanning pyroelectric detection of changes in the spontaneous polarization of P(VDF-TrFE) thin films

This is the first demonstration of a novel surface scanning method for the quantitative determination of the local pyroelectric coefficient in ferroelectric thin films. It is called pyroelectric force microscopy (PFM) and allows generating a map of the pyroelectric response with very high spatial resolution. The method is based on the surface potential mode of a standard atomic force microscope (AFM), which additionally has to be equipped with a temperature modulation unit. By applying a sufficiently high electric potential to the conductive tip locally a preferential macroscopic orientation of the polarization in the ferroelectric crystallites could be achieved. This so-called poling step was done in-situ in contact mode AFM and was also used to create nano-domains of differently oriented spontaneous polarizations. In the as-poled samples small heat fluctuations were achieved by laser diode excitation from the bottom side thus inducing changes in the surface potential due to the pyroelectric effect. These surface potential variations were detected simultaneously from above and used to extract a map of the pyroelectric coefficient. The potential of the method is demonstrated on the basis of ferroelectric semi-crystalline poly(vinylidene fluoride/trifluoroethylene) copolymer thin films.