ASYMMETRICAL DIMERS ON THE GE(001)-2X1-SB SURFACE OBSERVED USING X-RAY-DIFFRACTION

The atomic structure of the 2 X 1 reconstruction induced by the adsorption of Sb on Ge(001) has been determined by X-ray diffraction. Sb can be grown on Ge(001) in large ordered domains at elevated temperatures. Sb-Sb dimers replace the Ge dimers of the clean Ge(001) surface and pick up all dangling bonds. The dimers have a bond length of 2.90 angstrom and are midpoint-shifted by 0.16 angstrom with respect to the substrate bulk unit cell. Such an asymmetric dimer is reported for the first time for a group IV/V system. Relaxations of the four topmost substrate layers are measured as well, and these compare favourably to elastic strain calculations.