True atomic resolution imaging with noncontact atomic force microscopy

With an atomic force microscope (AFM) operating in the noncontact mode in an ultrahigh vacuum (UHV), the InP(110)1 X 1 surface and the Si(111)7 X 7 reconstructed surface were observed. The force gradient acting on the tip was detected by frequency modulation method. Rectangle lattice on the InP(110)1 X 1 surface, the adatoms and the corner holes on the Si(111)7 X 7 surface have been clearly and reproducibly resolved, including the atomic-scale point defects. The motion of the defects was observed on the InP(110) surface at room temperature, but not on the Si(111)7 X 7 surface. These results clearly show that the noncontact UHV AFM has true atomic-scale lateral resolution and is quite effective for atomic surface structure analysis in real space.