Quantification of Probe-Sample Electrostatic Forces with Dynamic Atomic Force Microscopy

TL;DR

This paper introduces a resonance-based atomic force microscopy method to quantify electrostatic forces at the probe-sample interface, revealing the electric field strength limits and implications for material processes.

Contribution

The study presents a novel AFM technique to measure electrostatic forces and electric field strength at the probe tip, enhancing understanding of electro-mechanical interactions in AFM.

Findings

Electrostatic forces can dominate cantilever response in AFM measurements.

Electric field strength at the probe apex is limited to about 0.5 V/nm.

The method provides insights into local electrostatic effects influencing material behavior.

Abstract

Atomic Force Microscopy (AFM) methods utilizing resonant mechanical vibrations of cantilevers in contact with a sample surface have shown sensitivities as high as few picometers for detecting surface displacements. Such a high sensitivity is harnessed in several AFM imaging modes. Here, we demonstrate a cantilever-resonance-based method to quantify electrostatic forces on a probe arising in the presence of a surface potential or when a bias voltage is applied to the AFM probe. We find that the electrostatic forces acting on the probe tip apex can strongly dominate cantilever response in electromechanical measurements and produce signals equivalent to few pm of surface displacement. In combination with modeling, the measurements of the force were used to determine the strength of the electrical field at the probe tip apex in contact with a sample. We find an evidence that the electric field strength in the junctions is limited by about 0.5 V/nm. This field can be sufficiently strong to significantly influence material states and kinetic processes through charge injection, Maxwell stress, shifts of phase equilibria, and reduction of energy barriers for activated processes. Besides, the results provide a baseline for accounting for the effects of local electrostatic forces in electromechanical AFM measurements as well as offer additional means to probe ionic mobility and field-induced phenomena in solids.