Fig. 3

Force dependence for the piezogenerated charge mapping. a DPFM-Si and b DPFM-So of the proposed PPLN test sample, obtained at different applied forces, scale bar 5 μm. In order to demonstrate the origin of the recorded current, different forces where applied during the scan-see red line dot. The current recorded increases with the applied force, as expected from a piezoelectric charge generation. c charge vs force spectroscopy sweep obtained from the profiles of Fig. 3a. The current profiles where integrated with a time constant of 390 ms in order to obtain the charge generated at a specific pixel. The linear relation displayed between force and collected charge confirms the piezoelectric nature of the generated charge. d current profiles extracted from Fig. 3a for different applied forces. Applying 9 μN is not enough to read the current generated as it lies below the current threshold of the amplifier. As the force is increased, the amplifier responds to the generated charge