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(11
1)7 X 7 reconstructed surface were observed. The force gradient acting
on the tip was detected by frequency modulation method. Rectangle lat
tice 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 w
as observed on the InP(110) surface at room temperature, but not on th
e Si(111)7 X 7 surface. These results clearly show that the noncontact
UHV AFM has true atomic-scale lateral resolution and is quite effecti
ve for atomic surface structure analysis in real space.