Contact electrification of high-K oxides studied by electrostatic force microscopy

In order to clarify the mechanisms of charge transfer on insulating surfaces by contact electrification, we performed charge-transfer experiments on high-K oxides using the tip of an electrostatic force microscope. In particular, we investigated the influence of the applied voltage between the tip and the surface and the contact duration on the amount of transferred charges on Al2O3. The electronic motion in the insulating material is analyzed in terms of hopping processes assisted by the electric field created by the tip inside the oxide. We show that this electric field must be described by a three-dimensional model. In this frame, the transfer mechanism is analyzed as an instantaneous wetting of the surface by the charges—the surface being a region of large trap concentration—followed by a progression of the charges inside the oxide.