Two-dimensional bismuth-silver structures on Si(111)

Using scanning tunneling microscopy (STM) observations, it has been found that deposition of 0.8-13 monolayer of Ag onto the mixed Si(111)alpha root 3 x root 3 / beta - root 3 x root 3-Bi surfaces followed by annealing at 150-250 degrees C induces formation of new ordered and quasi-ordered (Bi,Ag)/Si(111) metastable structures, root 19 x root 19, 4 x 4, 2 root 3 x 2 root 3, and '3 root 3 x 3 root 3'. Scanning tunneling spectroscopy has demonstrated that the 2 root 3 x 2 root 3 structure is semiconducting, while the root 19 x root 19 and 4 x 4 structures are metallic. Structural models of the root 19 x root 19 and 4 x 4 have been proposed based on placing a single Ag(111)1 x 1 layer with selected Ag atoms being substituted for Bi atoms onto the bulk-like Si(111)1 x 1 surface. The models have been proved with DFT calculations and comparison of simulated and experimental STM images. Calculated band structure of the Si(111)4 x 4 structure displays a spin-split metallic surface-state band with splitting of Delta k approximate to 0.002 angstrom(-1) and Delta E approximate to 10 meV in the vicinity of the Fermi level. (C) 2014 Elsevier B.V. All rights reserved.