SiC(0001)3x3-Si surface reconstruction - A new insight with a STM

The atomic structure of silicon rich SiC(0001) surfaces of the 6H polytype has been studied for the first time by scanning tunnelling microscopy in the UHV. The surface exhibited a hexagonal arrangement with one adatom per unit cell which was identified as a SiC(0001)3 X 3-Si reconstruction. The reconstruction could be reproducibly prepared in the UHV by annealing a sample under silicon flux al temperatures in the range 850-1100 degrees C. Surplus silicon does not affect the surface structure and epitaxially aggregates into large islands which have the same orientation as the substrate. Occasionally a Si(111)7 X 7 reconstruction can been observed on top, A novel model of the SiC(0001)3 X 3-Si structure is proposed. The unit cell is suggested to consist of 11 Si atoms which are situated in two layers. Their bonding produces three dimers and three rest atoms in the first layer, and one adatom in the second layer. In the first layer, bonding of dimers and rest atoms builds nine- and six-atom rings, which surround unoccupied sites of the outermost silicon atoms of the SiC substrate. A unit cell contains three dangling bonds, one of which is associated with an adatom and is responsible for 3 X 3 protrusions, and the other two are associated with silicon atoms of the substrate.