Photoinduced force microscopy imaging using heterodyne-FM technique

In photoinduced force microscopy (PiFM), amplitude modulation techniques, such as direct mode, and heterodyne amplitude modulation techniques have been used to detect the photoinduced force. These amplitude modulation techniques are affected by other forces because the resonance frequency of a cantilever shifts and non-conservative force damp the cantilever motion. Here, we investigate and propose the heterodyne frequency modulation technique (heterodyne-FM) for reduction of the influence of the other forces and photothermal force. Heterodyne-FM PiFM enabled the acquisition of PiFM images and force spectra without those artifacts. Using the heterodyne-FM technique, we succeed to visualize and evaluate photoinduced force between a tip and a quantum dot on gold surface.