Surface charge on ferroelectric thin film by high electric field induced at scanning probe microscope tip

We report the surface charge on ferroelectric thin film by the high electric field induced at a scanning probe microscope tip and its influence on the signal obtained in the measurement of surface potential. To calculate the electric field induced at a SPM tip when a domain of the ferroelectric thin film is switched by a given bias, two schematic models of a spherical SPM tip and a cone-shaped SPM tip are considered. For the cone-shaped SPM tip, the electric field was larger than that of the spherical SPM tip, which is probably due to its relatively high capacitance. Based on the consideration of Schottky emission, the Schottky currents of the two models showed values large enough to induce a charge on the surface of the ferroelectric thin film. From the Schottky currents, the induced charge densities of the two models were obtained and these induced charge densities exceed the charge density of saturated polarization in ferroelectric PbZr_0.53Ti_0.47O₃ thin film above 1.1 V for the cone-shaped SPM tip or 2.0 V for the spherical SPM tip.