VARIABLE-TEMPERATURE STM MEASUREMENTS OF STEP KINETICS ON SI(001)

Using a variable-temperature scanning tunneling microscope we have mea sured the time evolution of the atomic-scale morphology of steps on Si (001) at temperatures up to 350-degrees-C. Step-rearrangement events, i.e., local changes in the atomic arrangements, are observed between s uccessive images at temperatures above 225-degrees-C. The observed eve nts always involve single or multiple units of four atoms and occur mo st frequently at kink sites and at the ends of dimer rows. By measurin g the event rate we determine an effective activation-energy barrier o f 1.4-1.7 eV. The events cannot be completely characterized as success ive random arrangements involving only single units. Rather, correlati ons are observed between neighboring dimer columns, and the event rate depends on the local atomic-step configuration.