FI-STM INVESTIGATION OF THE SI(111)2X1 CLEAVED SURFACE

The (111) surfaces of Si obtained by cleaving in ultrahigh vacuum were investigated by a scanning tunneling microscope attached to a field ion microscope for in situ tip preparation. The (111) surfaces were invariably reconstructed to (2 x 1) with the [110BAR] row direction in most cases normal to [112BAR], the employed direction of cleavage. Other remarkable features were cleavage facets close to {779} besides the ordinary {111}, very different morphology of terrace edges dependent on the orientation with respect to the reconstruction row, and anti-phase boundaries of the [110] reconstructed rows exhibiting high chemical activity. Dislocations in Si were for the first time successfully imaged in STM as topological defects from which monatomic steps originate. The implications of the experimental findings were discussed in terms of atomistic models for the Si(111)2 x 1 superstructure and a dislocation mechanism for formation of anti-phase boundaries.