Electrostatic force gradient signal:: resolution enhancement in electrostatic force microscopy and improved Kelvin probe microscopy

In the present work the electrostatic interaction of a real scanning force microscopy (SFM) probe with a sample is studied theoretically as well as experimentally. To model the probe, a complex system composed of a macroscopic cantilever, a mesoscopic tip cone and a nanometric tip apex is proposed. The corresponding interaction is calculated analytically by means of an appropriate approximation. In most experimental situations we find that the total interaction is dominated by the cantilever and/or the tip cone and not by the tip apex. Experimental determination of tip-sample interaction supports this model. In addition, we find that a real SFM probe may lead to misinterpretation of experimental data in the so-called Kelvin probe microscopy (KPM). Again, experimental data confirm that the effects described by the model we propose may induce severe errors in KPM. As shown in this work, the resolution in KPM and electrostatic force microscopy is dramatically enhanced and data interpretation simplified if the force gradient rather than the force is used as signal source for the electrostatic interaction.