Noncontact AFM imaging on a Si(111)2×1-Sb surface with occupied lone-pair orbitals

Force interaction between an orbital of a dangling bond out of a Si tip apex and an occupied lone-pair orbital on a Si(111)2×1-Sb surface is experimentally investigated to clarify the imaging mechanism of noncontact AFM. Sb adatoms with occupied lone-pair orbitals are clearly observed on the 2×1 zigzag chain structure surface. The discontinuity in the frequency-shift curve is not observed at the Sb sites. Possible contrast mechanisms are discussed and the most understandable in terms of the chemical bonding interaction weaken by the existence of the anti-bonding orbital with one electron.