The atomic structures which existed during homo-epitaxial growth on a (111) 7 x 7 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) 7 x 7 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 3 x 3, 5 x 5 and 9 x 9. 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 5 x 5 and 7 x 7 structures was revealed by reflection high-energy electron diffraction intensity oscillations during growth. Stable (long-lifetime) shapes of 5 x 5 hillocks were observed in scanning tunnelling microscopic images of isolated hillocks that formed on the (111) 7 x 7 surface. Magic numbers of 5 x 5 units were found in the hillocks. However, in the case of 7 x 7 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