Reconstructions of 6H-SiC(0001) surfaces studied by scanning tunneling microscopy and reflection high-energy electron diffraction

Surface reconstructions and surface decomposition of 6H-SiC(0001) covered with Si were observed using scanning tunneling microscopy (STM) and reflection high-energy electron diffraction (RHEED). The 3 x 3 structure terminated with Si atoms was obtained by annealing at 1050 degreesC; this changed to a mixture of the graphite 1 x 1 and SiC 6 x 6 by annealing at 1300 degreesC. The graphite 1 x 1 consisted of two types of graphite lattices, rotated 30 degrees with respect to the SiC lattice and along the SiC lattice.. The SiC 6 x 6 was terminated with C atoms. The RHEED spots due to the double diffraction between the SiC (02) spot and the graphite spot rotated by 30 degrees with respect to the SiC lattice were observed. The thickness of the graphite layer and the area of the graphite region increased by successive annealing. String-shaped structures were formed along the steps at 1450 degreesC. Further annealing up to 1800 degreesC resulted in the formation of a thick graphite layer and amorphous carbon.