Preservation of a 7×7 periodicity at a buried amorphous Si/Si(111) interface

The interface between a silicon (111) surface and an amorphous silicon layer deposited at room temperature is shown to retain the (7×7) periodicity of the substrate surface. Transmission electron microscopy shows the reconstructed, buried interface both by diffraction and by imaging at high resolution in plan-view and cross-section geometries. The interface reconstruction appears to differ from the surface Si reconstruction mainly by the absence of an ordered array of adatoms. If the amorphous-crystalline interface is moved nominally 15 A? by solid-phase regrowth, the 7×7 periodicity is removed. The resultant amorphous-crystal interface is exceptionally flat and shows a 1×1 diffraction pattern. The (100) 2×1 reconstruction is not preserved after amorphous Si deposition.