Variable-temperature STM measurements of step kinetics on Si(001).

Using a variable-temperature scanning tunneling microscope we have measured the time evolution of the atomic-scale morphology of steps on Si(001) at temperatures up to 350 o C. Step-rearrangement events, i.e., local changes in the atomic arrangements, are observed between successive images at temperatures above 225 o C. The observed events always involve single or multiple units of four atoms and occur most frequently at kink sites and at the ends of dimer rows. By measuring the event rate we determine an effective activation-energy barrier of 1.4-1.7 eV. The events cannot be completely characterized as successive random arrangements involving only single units