The structure of an ultrathin Au film on Si(001)

The symmetric dimer structure of a reconstructed Si(001)-2x1 surface and the structure of an ultrathin Au film were studied by Coaxial Impact Collision Ion Scattering Spectroscopy(CAICISS). In our study, using the capability of CAICISS for the determination of the three-dimensional structure of the surface, the dimer bond length of Si(001)-2x1 was found to be 2.17 Angstrom; i.e., the displacement of the first layer atoms in the dimer-forming direction was about 0.835 Angstrom. For a submonolayer coverage, it was found that Au atoms tended to form dimers on Si(001) and that the atomic distance of the Au dimer was 2.88 Angstrom, like that of bulk Au. On this two-dimensional Au layer, Au atoms with a height of nearly 1.45 Angstrom were found in a direction of 21 degrees with respect to the [110] azimuth.