AU-INDUCED SUPERSTRUCTURE FORMATION ON VICINAL SI(001) STUDIED BY LOW-ENERGY-ELECTRON DIFFRACTION AND REFLECTANCE ANISOTROPY SPECTROSCOPY

We present a low-energy electron diffraction (LEED) and reflectance an isotropy spectroscopy (RAS) study of the ordering of monolayer Au cove rages on clean 1 degrees and 4 degrees offcut Si(001)-(1x2) vicinal su rfaces. On depositing 2.5+/-0.1 ML of Au on the 4 degrees offcut sampl e followed by annealing up to 900 degrees C, a well-ordered single-dom ain Si(001)-(root(26)x3)-Au superstructure is formed, as revealed by L EED, indicating a highly ordered anisotropic surface. Changes in split ting of the LEED spots indicates a larger step separation on the Si(00 1)-Au surface than on the clean surface. RAS is used to follow the for mation of this structure with increased annealing temperature after ro om-temperature deposition of Au. Significant changes in optical anisot ropy are observed. Comparison of the Si(001)-(root(26)x3)-Au superstru cture grown on 1 degrees offcut Si(001) shows a similar RA line shape, although reduced in intensity. Scanning tunneling microscopy (STM) im ages of the double-domain (root(26)x3)-Au superstructure, together wit h the LEED data presented here, indicates that the single-domain super structure will be terminated by long Au row structures aligned paralle l to the surface steps. We fit the RA spectrum for the 4 degrees offcu t (root(26)x3)-Au structure using a Kramers-Heisenberg dielectric func tion expression and identify two surface induced optical anisotropic f eatures at 2.8 and 3.9 eV that are stronger for light polarized perpen dicular to these chains. Similarities with the RA response from the Si (111)-(5x2)-Au superstructure are discussed. [S0163-1829(98)03239-1].