A discussion on the likely mechanisms for dielectric charging in AFM

Charge distribution estimation at the surface and in the bulk of dielectrics is of great interest, both theoretically and experimentally, not only because it brings information on the storage and transport properties of the medium, but also because of various possible applications of thin dielectric layers e.g. in the field of miniaturized components. Scaling down the dimensions of these components to nanoscale level creates difficulties with the application of the commonly used diagnostic methods. With a resolution in the nanometer range, the atomic force microscopy (AFM) can be used to this field. By applying a voltage between the microscope tip and a sample, both conducting and insulating surfaces can be imaged. The AFM can be applied for charging of samples in contact mode or when a tip-to-sample spacing is introduced. The purpose of this work is to discuss about appropriate mechanisms for dielectric charging in AFM that are still controversial in the literature.