Adsorbate induced refacetting: Pb chains on Si(557)

The structure on the atomic and mesoscopic scale of Pb adsorbed on Si(557) has been investigated by high-resolution low energy electron diffraction (SPA-LEED). Depending on Pb coverage in the range between 1.2 and 1.6 monolayers (ML), formation of various facets [(112), (335), (223), and a meta-stable (557) orientation] is induced by the Pb layers. The facet orientation in general does not coincide with the macroscopic orientation of the (557) surface. After an initial annealing step to 600 K, starting with 1.2ML of Pb, this new vicinality can be tuned gradually and reversibly even at temperatures below 180 K by further adsorption, but also by desorption of Pb. Superstructures of the Pb layers on the terraces were identified on the most stable (223) facets. Here parts of the devil's staircase and the stripe-incommensurate (SIC) phases known from Si(111) surfaces (Yakes et al 2004 Phys. Rev. B 69 224103) develop. A new mechanism for facet formation with different orientations, based on avoidance of step decoration by adsorbed Pb, is proposed.