Ring charging of a single silicon dangling bond imaged by noncontact atomic force microscopy

The electrostatic properties of defects of the Si(111)-(root 3 x root 3)R degrees 30 surface are studied using noncontact atomic force microscopy and Kelvin probe force microscopy with subnanometer resolution and subelementary charge sensitivity. We identify nonparabolicities in the frequency-voltage spectroscopy of single dangling bonds (DBs), which reveal the transition from empty to single electronically occupied DBs. Kelvin probe imaging reveals that the DB charging, however, occurs with a ring shape with radius similar to 500 pm located along the circumference of the DB wave function. The ring charging is explained by a tip-induced modulation of the hole recombination rate at the DB-substrate interface.