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Abstract:
We have used low-energy electron microscopy to
measure step motion on Si(111) and Si(001) near
dislocations during growth and sublimation. Steps on
Si(111) exhibit the classic rotating spiral motion
predicted by Burton, Cabrera and Frank [1]. Steps on
Si(001), however, move in a strikingly different
manner that appears to violate the Gibbs-Thomson
relation. The step profiles exhibit both positive
and negative curvature and move with an almost
discontinuous, ratchet-like motion. The anomalous
behavior can be understood in detail by considering
how the local step velocity is affected by the
non-uniform strain field arising from the
dislocation. The strain from the dislocation locally
favors one of the two surface domains, leading to a
thermodynamic force on the steps. By computing the
surface strain field for various dislocation
geometries, and simulating the step motion during
sublimation, we are able to determine the specific
slip system observed in experiment [2].
[1] W. K. Burton, N. Cabrera, and F. C. Frank,
Proc. Roy. Soc., A243 (1950) 229.
[2] J. B. Hannon, V. B. Shenoy, and K. W. Schwarz,
Science 313 (2006) 1266. |
