[en] Pb-induced superstructures on Si(557) are investigated by low-energy-electron diffraction (LEED) and scanning tunneling microscopy (STM). Using an indirect heating method, we have succeeded in obtaining almost perfect single-domain LEED patterns of one-dimensional wire (chain) structures, so called αx2 and βx2 phases. Careful LEED analysis and STM investigation reveal that these phases are formed on the (223) and (112) facets, respectively. The αx2 phase has regular bundles of triple wires at low annealing temperature but wider bundles through step bunching after a higher temperature annealing. Along the wires of the αx2 phase, which was recently reported to exhibit a transition between one-dimensional (1D) metallic and 2D semiconducting conductance, a clear commensurate x2 modulation is observed at 78-120 K in contrast to the incommensurate and disordered structure reported previously. A tentative atomic structure model of the αx2 phase is proposed based on the dense Pb overlayers on (111) and (223) facets. The details of the STM images of the βx2 phase are discussed

[en] Scanning tunneling microscopy (STM) and angle-resolved photoemission spectroscopy (ARPES) were used to study the atomic and electronic structures of the Si(111)-√21 x √21-(Ag + Cs) surface (√21-Cs in short), which was induced by depositing caesium atoms on the Si(111)-√3 x √3-Ag surface at room temperature (RT). Compared with previously reported STM images of noble-metal induced √21 x √21 phases including the Si(111)-√21 x √21-(Ag+Ag) and Si(111)-√21 x √21-(Ag+Au) surfaces (√21-Ag and √21-Au, respectively), the √21-Cs surface displayed quite different features in STM images. The ARPES data of the √21-Cs surface revealed an intrinsic dispersive surface-state band, together with a non-dispersive one near the Fermi level, which was also different from those of the √21-Ag and √21-Au surfaces. These results strongly suggest different atomic arrangements between Cs- and noble-metal induced √21 x √21 phases. Unlike the √21-Ag and √21-Au phases, the framework of the initial Si(111)-√3 x √3-Ag substrate is totally broken at the √21-Cs phase. (author)