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 were measured by the x-ray standing-wave (XSW) technique, rue XSW results are consistent with symmetric Sb dimers, whose formation has recently been predicted by four competing models. The (004) and (022) XSW analysis 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)reconstruction was measured by Rutherford backscattering to be 0.48 monolayers. This coverage agrees with the two proposed structural models that have two Sb dimers per (2X4) unit cell and disagrees with the models that propose one or three Sb dimers. Finally, a(lll) XSW measurement, which tested for lateral displacement of the Sb dimers in the [110] direction, was used to discriminate between the remaining two models.