Difference between the forces measured by an optical lever deflection and by an optical interferometer in an atomic force microscope

Using a simple model, we investigated the difference between the forces measured by an atomic force microscope (AFM) with an optical lever deflection method and that with an optical interferometer method. Then, using a mica with an atomically flat surface as a test sample, we confirmed experimentally the above difference, which says that the optical lever deflection method detects not only the surface corrugation but also the frictional force, while the optical interferometer method detects only the surface corrugation. Based on the above results, we proposed a method to measure the three-dimensional force vector by using both the optical lever AFM/LFM and the optical interferometer AFM simultaneously. Furthermore, we mention that the measurement of three-dimensional spatial distribution of the force vector will implement the computed tomography technique into AFM measurements, which yields a three-dimensional spatial distribution of the force origin.