Phase detection method with positive-feedback control using a quartz resonator based atomic force microscope in a liquid environment

An atomic force microscope (AFM) using a quartz resonator sensor has great potential as a highly sensitive force detection device. An AFM can detect the solvation force in a liquid environment. We used the phase detection method with positive feedback to improve AFM sensitivity. Phase shift curves as a function of distance show oscillations with periods that correspond to the diameter of a molecule placed between the AFM tip and the surface of a sample substrate. These oscillations are due to the solvation forces when the surface of the substrate is compressed with the AFM tip.