THE STRUCTURE OF AN ULTRATHIN AU FILM ON SI(001)

The symmetric dimer structure of a reconstructed Si(001)-2x1 surface a nd the structure of an ultrathin Au film were studied by Coaxial Impac t Collision Ion Scattering Spectroscopy(CAICISS). In our study, using the capability of CAICISS for the determination of the three-dimension al 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 a toms in the dimer-forming direction was about 0.835 Angstrom. For a su bmonolayer 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 Angst rom, 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.