Site-Specific Displacement of Si Adatoms on Si(111)-(7x7)

Tunneling and field-emitted electrons from the tip of a scanning tunneling microscope were used to reversibly displace Si adatoms on Si(111)-(7x7) at 30 to 175K. Displacement rates were determined as a function of current, sample bias voltage, and lateral distance from the tip. The displacement is found to be site specific, with strong preference for center Si adatoms in the faulted half of the unit cell. Si adatoms return to the normal site by the same method or by annealing above 155K with an activation energy of 0.49±0.03 eV and preexponential of 1012.2±0.9 s-1 . copyright 1997 The American Physical Society