Dielectric properties of thin insulating layers measured by Electrostatic Force Microscopy

In order to measure the dielectric permittivity of thin insulting layers, we developed a method based on electrostatic force microscopy (EFM) experiments coupled with numerical simulations. This method allows to characterize the dielectric properties of materials without any restrictions of film thickness, tip radius and tip-sample distance. The EFM experiments consist in the detection of the electric force gradient by means of a double pass method. The numerical simulations, based on the equivalent charge method (ECM), model the electric force gradient between an EFM tip and a sample, and thus, determine from the EFM experiments the relative dielectric permittivity by an inverse approach. This method was validated on a thin SiO2 sample and was used to characterize the dielectric permittivity of ultrathin poly(vinyl acetate) and polystyrene films at two temperatures.