force microscopy (EFM) is a type of dynamic non-contact atomic force microscopy where the
electrostatic force is probed. ("Dynamic" here means that the cantilever is oscillating and does not make
contact with the sample). This force arises due to the attraction or
repulsion of separated charges. It is a long-ranged force and can be detected
100nm from the sample. For example, consider a conductive cantilever tip and sample which are separated a
distance z usually by a vacuum.
A bias voltage between tip and sample is applied by an external battery
forming a capacitor, C, between the two. The capacitance of the system depends on the geometry of the tip and sample.