The evolution of 3×3, 6×6, √3×√3R30° and 6√3×6√3R30° superstructures on 6H–SiC (0 0 0 1) surfaces studied by reflection high energy electron diffraction

The technique of reflection high energy electron diffraction (RHEED) has been applied to study the evolution of various superstructures on 6H–SiC (0 0 0 1) as a function of annealing temperature. Between the evolution of the stable 3×3 and √3×√3R30° phases on a silicon-enriched 6H–SiC (0 0 0 1), a mixed phase 3×3/2×2 reconstruction followed by a well-defined 6×6 reconstruction was observed by RHEED for the first time. The 6×6 reconstruction is distinct from the pseudo-periodic 6×6 structure suggested previously for graphite moire pattern on 6H–SiC (0 0 0 1) [Surf. Sci. 48 (1975) 463; Surf. Sci. 256 (1991) 354]. chanisms for the formation of these superstructures in the sequence of 3×3,6×6,√3×√3R30° and 6√3×6√3R30° between 800°C to 1200°C were discussed. The 6×6 structure is proposed to evolve directly from the 3×3 following the missing of consecutive Si clusters in the twisted silicon adlayer model. Annealing the 6×6 reconstructed surface to 1000°C gives rise to a √3×√3R30° reconstruction. From here, the segregation of carbon domains occurs readily and these form an incommensurate 6√3×6√3R30 epilayer at 1200°C. At the early stages of the annealing, the 6√3×6√3R30 RHEED pattern consists of a series of cluster satellite streaks superimposed on 1×1 SiC. Further annealing results in the appearance of graphite streaks with its basis vectors rotated 30° to SiC. Prolonged annealing of the graphitized surface results in the growth of single crystalline graphite multilayers on the 6H–SiC substrate.