Influence of the Substrate and Tip Shape on the Characterization of Thin Films by Electrostatic Force Microscopy

Electrostatic force microscopy has been shown to be a useful tool to determine the dielectric constant of nanoscaled thin films that play a key role in many electrical, optical, and biological phenomena. Previous approaches have made use of simple analytical models to analyze the experimental data for these materials. Here, we show that the electrostatic force shows a completely different behavior when the shape of the tip and sample are taken into account. We present a complete study of the interaction between the whole tip and the layers below the thin film. We demonstrate that physical magnitudes such as the surface charge density distribution and the size of the materials have a strong influence on the EFM signal. The EFM sensitivity to the substrate below the thin film decreases with the substrate thickness and saturates for thicknesses above two times the length of the tip, when it is close to that of an infinite medium.