Observation of silicon surfaces using ultrahigh-vacuum noncontact, atomic force microscopy

Noncontact imaging has been developed for atomic force microscopy in ultrahigh vacuum in order to avoid the damage to the sample surface caused by the intense interaction between the clean surfaces of the sample and probe tip, which is a problem commonly observed in contact imaging. Initially it was thought that the noncontact (NC) mode might fail to achieve atomic level resolution due to the long distance between the tip and sample. Recently, it has been proved that this is not so. We used an FM detection system utilizing an oscillating cantilever with a constant-amplitude voltage supplied to the piezotransducer; and successfully obtained NC-mode stable atomic-resolution AFM images of the 2 x 1 structure of the Si(100) surface as well as the 7 x 7 structure of the Si(111) surface. We also compared AFM and STM images of the 7 x 7 structure in the same area of view.