The atomic structures which existed during homo-epitaxial growth on a (111) 7x7 surface were investigated by means of reflection high-energy electron diffraction and scanning tunnelling microscopy. Upon analyzing the reflection high-energy electron diffraction intensity rocking curves by using dynamic calculations, it was concluded that the bonds of adatoms on the dimer-adatom stacking-fault structure were broken by 2 adsorbed Si atoms in the initial stages of deposition. The structure then reconstructed into a pyramidal cluster-type structure. At temperatures higher than 400C, the rocking curves during growth were very similar to that for the (111) 7x7 dimer-adatom stacking-fault structure. It was concluded that the surface structures which existed during growth at high temperatures were dimer-adatom stacking-fault structures; including 3x3, 5x5 and 9x9. However, at 280C the rocking curve was very different to the curves which were produced by the dimer-adatom stacking-fault structures. Analysis of the curve by means of reflection high-energy electron diffraction dynamic calculations revealed that the pyramidal cluster-type structure was formed on the surface during growth. On the basis of these results, and the instability of the pyramidal clusters, it was concluded that the formation of the metastable structure promoted epitaxial growth that was accompanied by stacking-fault dissolution at the dimer stacking-fault framework. At substrate temperatures ranging from 400 to 600C, a mixed phase of 5x5 and 7x7 structures was revealed by reflection high-energy electron diffraction intensity oscillations during growth. Stable (long-lifetime) shapes of 5x5 hillocks were observed in scanning tunnelling microscopic images of isolated hillocks that formed on the (111) 7x7 surface. Magic numbers of 5x5 units were found in the hillocks. However, in the case of 7x7 hillocks it was difficult to find stable shapes in scanning tunnelling microscopic images.

A.Ichimiya, H.Nakahara, Y.Tanaka: Journal of Crystal Growth, 1996, 163[1], 39-47