BISMUTH ON GASB(110) - STRUCTURAL DETERMINATION OF THE 1X1 AND 1X2 PHASES BY SURFACE X-RAY-DIFFRACTION

The surface geometry of the 1 x 1 and 1 x 2 phases of bismuth on GaSb( 110) has been determined using surface X-ray diffraction with synchrot ron radiation. The bismuth atoms form zigzag chains along the [1(1) ov er bar 0] direction of the substrate. For the 1 x 1 phase four differe nt registries of the bismuth chains with respect to the GaSb(110) subs trate are possible. It was found that only the epitaxial continued lay er structure was in good agreement with the experimental data. In the 1 x 2 reconstruction every second zigzag chain in the uppermost substr ate layer is missing. The reconstructed surface is terminated with a f ull monolayer of Ri atoms which also form zigzag chains. The Ri atoms in the chains bond alternately to the first and second layer substrate atoms and the Bi chains are inclined at 34 degrees to the surface. Th is new structural model explains the higher thermal stability of the 1 x 2 phase compared to that of the 1 x 1 phase.