Surface π bonding in the (2 × 1) reconstruction of Si (111)

Abstract

The role of a bonding in the (2 × 1) reconstruction of Si (111) is examined. The difference in total energy (ΔE) between the planar and twisted SiSi π systems in a single π bond (Si2H4), a pair of π bonds (Si4H6) and an Si6 chain with three π bonds embedded in an Si12 cluster show a definite trend: ΔE decreases as the number of π bonds increases. For the largest system studied, an Si12 cluster model of the Si (111) surface, ΔE is negligibly small. The corresponding ΔE values for C2H4 and for models of the (2 × 1) reconstruction of the diamond (111) surface are larger than the values for silicon. Such differences between silicon and carbon can be understood in terms of smaller energy needed for atomic rehybridization (s2p2 → sp3 transition) for silicon. The results suggest that the partial breaking of SiSi π bonds does not energetically inhibit surface reconstruction. © 1988.