AN STM STUDY OF CURRENT-INDUCED STEP BUNCHING ON SI(111)

We report quantitative measurement of terrace size as a function of an nealing time for step bunching induced by direct current heating in th e step-down direction for the temperatures 945 degrees C and 1245 degr ees C. This result is shown to be inconsistent with simple models of s tep bunching in which there is a temperature-independent electromigrat ion force on diffusing surface atoms. Deposition of Si atoms onto the surface held at 945 degrees C with current running in the step-down di rection slows the step bunching. By estimating the parameters governin g step Row from experimental observations, this result is shown to be inconsistent with simple models of step bunching incorporating an elec tromigration force as the source of diffusional anisotropy. The evolut ion of step bunching was monitored by measuring the growth of the terr ace sizes revealing a functional form of t(proportional to), with alph a similar to 0.5.