Epitaxial growth of silicene on ultra-thin Ag(111) films

Epitaxial growth of silicene on atomically flat ultra-thin Ag(111) films was investigated using scanning tunneling microscopy. The Ag films were prepared by low-temperature deposition of Ag on Si substrates, followed by soft annealing at room temperature. Patchy 4 x 4, root 13 x root 13, root 7 x root 7, and 2 root 3 x 2 root 3 silicene domains were nucleated on regions that were one monolayer lower than the pristine Ag surface after the initial morphological change had been completed. On the first-layer silicene containing the above domains, two types of root 3 x root 3 silicene domains (root 3 x root 3-alpha and beta) were formed in the second layer. A bias voltage-independent Moire pattern was observed for the root 3 x root 3-alpha silicene, and a bias voltage-dependent standing wave pattern for the root 3 x root 3-beta silicene. The root 3 x root 3-beta silicene had a dispersion relation that could be fitted using a linear function, although the resulting Fermi velocity was twice as large as the expected value.