Step permeability and the relaxation of biperiodic gratings on Si(001)

We have used low energy electron microscopy to study the time dependence of atomic height islands and holes at the extrema of a fabricated biperiodic grating on Si(001), From the pairwise disappearance of these islands and holes as the grating thermally smooths we conclude that steps on Si(001) are remarkably permeable, i.e., adatoms can cross steps without becoming incorporated into them. Comparison of the time dependence of the island areas with model calculations shows that the adatom incorporation probability is actually much smaller than the crossing probability.