High-resolution three-dimensional space-charge and polarization mapping with thermal pulses

Three-dimensional polarization and space-charge mapping with focused thermal pulses was performed on various electret polymers. In polyvinylidene fluoride (PVDF) films with a structured polarization, a lateral resolution of 38 μm and a near-surface depth resolution of better than 0.5 μm was achieved. In piezoelectric sensor cables, this technique may help to optimize the poling conditions. For polytetrafluoroethylene (PTFE) films charged with a 15 keV electron beam through a shadow mask, a complete 3D image of the internal electric field distribution was obtained. The fast data acquisition allowed the recording of up to 2000 beam pointings per sample. For tightly focused laser beams, the lateral diffusion of the heat pulse must be taken into account. In particular, fast thermal diffusion in the metal electrode may become a limiting factor for the in-plane spatial resolution. Finite-element calculations modelling the heat transport highlight the differences between the one- and three-dimensional implementations of the thermal pulse method.