| Research Abstract |
The electrostatic force microscope (EFM) offered new opportunity to measure a variety of electrostatic properties on the surface on a sub-micron scale. For example, potentiometry, imaging of contact-electrified charge and its dissipation process on insulating surface and so on have been demonstrated. However, so far, the lateral resolution of the EFM has been insufficient. This is due to the following two main reasons : (i) It is much difficult to measure weak distance dependence of the electrostatic force with a good signal-to-noise (S/N) ratio. (ii) It is much difficult to separate the electrostatic force from the van der Waals force. Thus, the technical improvements have been required to increase the lateral resolution of the EFM.
In this project, we demonstrated a novel method to detect the van der Waals and the electroatatic force interactions simultaneously on atomic scale, which is based on frequency modulation (FM) detection method. In the noncontact AFM images measured on the GaAs (110) surface, the rectangular lattice and the atomicscale point defects can be clearly and reproducibly resolved. On the other hand, in the EFM images, point defect appeared as bright respect to the background at positive bias voltage, while it appeared dark contrast at negative bias voltage.Thus, the contrast of the EFM images depends on the sample bias voltage V.This means that the EFM images really resulted from the charge at the point defect on the GaAs (110) surface. Thus, for the first time, the atomic resolution imaging has been achieved for the electrostatic force measurement.
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