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

Using scanning tunneling microscopy (STM) observations, it has been found that deposition of 0.8–1.3 monolayer of Ag onto the mixed Si(111)α−√3×√3/β−√3×√3-Bi surfaces followed by annealing at 150–250°C induces formation of new ordered and quasi-ordered (Bi,Ag)/Si(111) metastable structures, √19×√19, 4×4, 2√3×2√3, and ‘3√3×3√3’. Scanning tunneling spectroscopy has demonstrated that the 2√3×2√3 structure is semiconducting, while the √19×√19 and 4×4 structures are metallic. Structural models of the √19×√19 and 4×4 have been proposed based on placing a single Ag(111)1×1 layer with selected Ag atoms being substituted for Bi atoms onto the bulk-like Si(111)1×1 surface. The models have been proved with DFT calculations and comparison of simulated and experimental STM images. Calculated band structure of the Si(111)4×4 structure displays a spin–split metallic surface-state band with splitting of ∆k≈0.002Å−1 and ∆E≈10meV in the vicinity of the Fermi level.