Morphology and atomic structure of the SiC(0001̄)3 × 3 surface reconstruction

The atomic structure of SiC(0001̄)C surface of the 6H polytype has been studied in UHV by scanning tunnelling microscopy, low energy electron diffraction and Auger electron spectroscopy. A number of different reconstructions could be reproducibly prepared in UHV by a combination of annealing a sample with and without silicon flux at temperatures in the range 450–1400°C. One of them has been identified as SiC(0001̄)3 × 3 structure. A geometrical model of this reconstruction has been proposed. In accordance with that, the unit cell consists of ten atoms bonding to produce six dimers and three adatoms. The six- and nine-atom rings surround unoccupied sites of the outermost carbon atoms of the SiC substrate. Each unit cell contains five dangling bonds, three of which are associated with adatoms and are responsible for protrusions in filled-state scanning tunnelling microscopy images. The other two are associated with carbon atoms of the substrate. Furthermore, islands with an unreconstructed SiC(0001̄)1 × 1 surface prepared in UHV have been observed with atomic resolution for the first time by means of STM.