Reconstructions of Ag on high-index silicon surfaces

Si(5 5 12), a recently discovered, stable high-index surface of silicon, may offer a superior template for the growth of one-dimensional metallic structures. We are using reflection high-energy electron diffraction, scanning tunneling microscopy (STM), and synchroton radiation photoemission to determine the morphology and electronic structure of Ag on this surface. Si( 5 5 12) exhibits a sharp (2x1) reconstruction after flashing to equivalent-to-1250-degrees-C. Despite the many different atomic substructures present in this reconstruction, several distinct surface sore levels in the Si 2p core, and surface states in the valence band, are observed. The nature of these states is very similar to those on the clean Si(100)-(2x1) surface, which suggest that they are derived from the dimer/tetramer subunits. The growth of Ag is split into two distinct regimes. For growth at low coverages (theta-is-less-than-0.25 ML) and then the 1x spots sharpen slightly, as theta and T approach 0.25 ML and 450-degrees-C, respectively. A very weak 3X periodicity is observed along the row direction on these surfaces. STM results show that in this low theta/T regime, Ag forms very long monoatomic chains on top of the tetramer rows on these surfaces. For higher coverages (theta-is-less-than-0.4 ML) and temperatures (450-degree-C-is-less-than-T-is-less-than-600 degrees-C)< the 3x diffraction spots increase greatly in intensity, indicating a stronger 3x periodicity forming along the row direction. Preliminary STM data indicate a variety of 3x-like structures coexisting on these high theta/T surfaces, with some indications of nanofaceting.