One-dimensional collective excitations in Ag atomic wires grown on Si(557)

The interaction between adsorbate layers of transition metal atoms and strongly anisotropic surfaces can lead to various quasi-one-dimensional (1D) signatures, as demonstrated here for Ag adsorbed on Si(557). Using low energy electron diffraction in combination with scanning tunneling microscopy and electron energy loss spectroscopy, we correlated the structure with the properties of low dimensional collective excitations. Semiconducting structures with double periodicity along the chains are formed at Ag coverages below 0.3 ML. At higher coverages, the formation of wires with (√3 × √3) order sets in. Only these wires are metallic, as is evident from the appearance of plasmonic losses, which show 1D dispersion only along the wires. This 1D property even persists up to one monolayer, where a densely packed array of metallic (√3 × √3) stripes is formed. The triple steps between the wires are obviously insulating. Only plasmonic subband transitions are visible, which are characteristic for quasi-1D metallic stripes of finite width.