Junsuke Yamanishi

Heterodyne technique in photoinduced force microscopy with photothermal effect

The heterodyne technique is used to detect short-range forces. Using the heterodyne technique, we demonstrate photoinduced force microscopy (PiFM) imaging and z-spectroscopy without the artifact of photothermal vibration. The rejection ratio was at least 99.975% under a high-scattering condition. In addition, the heterodyne technique employs the optimal amplitude at the first resonance frequency of the cantilever to detect the photoinduced force sensitively. According to our calculation, the optimal ratio of the amplitude to the distance between the dipole of the tip and that of the sample is 0.4448. The heterodyne technique can be employed to perform PiFM without the artifact by using the optimal amplitude.

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.

Distance dependence of atomic-resolution near-field imaging on α-Al2O3 (0001) surface with respect to surface photovoltage of silicon probe tip

Recently, we achieved atomic-resolution optical imaging with near-field scanning optical microscopy using photon-induced force detection. In this technique, the surface photovoltage of the silicon-tip apex induced by the optical near field on the surface is measured as the electrostatic force. We demonstrated atomicresolution imaging of the near field on the α-Al2O3 (0001) surface of a prism. We investigated the spatial distribution of the near field by scanning at different tip-sample distances and found that the atomic corrugation of the near-field signal was observed at greater distances than that of the atomic force microscopy signal. As the tip-sample distance increased, the normalized signal-to-noise ratio of the near field is in a gradual decline almost twice that of the frequency shift (Δf).