Scanning tunneling microscopy of Bi- induced Ag(111) surface structures

Submonolayer Bi-induced structures at the surfaces of 20-monolayer (ML)-thick Ag(111) films on Si(111)7 x 7 substrates were investigated using scanning tunneling microscopy. Bi atoms initially adsorbed randomly in the region of Bi coverage (theta(Bi) ) below 1/3 ML. However, local root 3 x root 3 ordering was extended with increasing theta(Bi) and root 3 x root 3 reconstruction was completed at theta(Bi) = 1/3 ML. At larger theta(Bi), the surface was covered with a striped structure. Bi atoms were arranged with centered rectangular unit cells, although the contrast of the cell changed periodically along the {01 (1) over bar} direction. As a result, bright and dark stripes along the {(2) over bar 11} direction appeared alternatively at the surfaces. A close-packed Bi-induced (3 0 12) structure is proposed as a model for the striped surface structure.