SITE-SPECIFIC DISPLACEMENT OF SI ADATOMS ON SI(111)-(7X7)

Tunneling and field-emitted electrons from the tip of a scanning tunne ling microscope were used to reversibly displace Si adatoms on Si(111) -(7 x 7) at 30 to 175 K. Displacement rates were determined as a funct ion of current, sample bias voltage, and lateral distance from the tip . The displacement is found to be site specific, with strong preferenc e for center Si adatoms in the faulted half of the unit cell. Si adato ms return to the normal site by the same method or by annealing above 155 K with an activation energy of 0.49 +/- 0.03 eV and preexponential of 10(12.2+/-0.9) s(-1).