HIGH-RESOLUTION STRUCTURAL-ANALYSIS OF THE SB-TERMINATED GAAS(001)-(2X4) SURFACE

The precise locations of Sb atoms for the GaAs(001):Sb-(2X4) surface w ere measured by the x-ray standing-wave (XSW) technique, rue XSW resul ts are consistent with symmetric Sb dimers, whose formation has recent ly been predicted by four competing models. The (004) and (022) XSW an alysis determined the Sb dimer height and bond length to be 1.72 and 2 .84 Angstrom, respectively. The Sb coverage of the(2 x 4)reconstructio n was measured by Rutherford backscattering to be 0.48 monolayers. Thi s coverage agrees with the two proposed structural models that have tw o Sb dimers per (2X4) unit cell and disagrees with the models that pro pose one or three Sb dimers. Finally, a(lll) XSW measurement, which te sted for lateral displacement of the Sb dimers in the [110] direction, was used to discriminate between the remaining two models.