Electronic Properties of Vanadium Atoms Adsorption on Clean and Graphene-Covered Cu(111) Surface.

The electronic properties of vanadium atoms adsorbed on clean and graphene-covered Cu(111) surface have been systematically studied using ab initio theoretical method. Two coverages (1/9 ML and 1 ML) of vanadium adsorption are considered in this work. Our calculations indicate that V staying underneath the Cu surface is found to be the most stable adsorption site at the aforementioned two coverages for V/Cu(111). However, such adsorption may lead to undesired properties. Therefore, we introduce graphene as a buffer layer to effectively alleviate the direct interaction between V and Cu surface. The calculations show that electronic properties of the original graphene layer are significantly affected by the interactions of C atoms with the V adatoms; the Dirac point of graphene is "destroyed" as a consequence at both coverages. In the V/Gra/Cu(111) system, the interaction between graphene layer and the substrate Cu atoms remains weak as in the Gra/Cu(111) system. Moreover, a relatively low coverage of 1/9 ML gives rise to a spin-polarized system while a non-spin-polarized system is observed at the coverage of 1 ML. This finding offers a new way for the application of vanadium-based materials in reality.

Quantum Spin Hall States in Stanene/Ge(111).

For topological insulators to be implemented in practical applications, it is a prerequisite to select suitable substrates that are required to leave insulators' nontrivial properties and sizable opened band gaps (due to spin-orbital couplings) unaltered. Using ab initio calculations, we predict that Ge(111) surface qualified as a candidate to support stanene sheets, because the band structure of √3 × âˆš3 stanene/Ge(111) (2 × 2) surface displays a typical Dirac cone at Γ point in the vicinity of the Fermi level. Aided with the result of Z2 invariant calculations, a √3 × âˆš3 stanene/Ge(111) (2 × 2) system has been proved to sustain the nontrivial topological phase, with the prove being confirmed by the edge state calculations of stanene ribbons. This finding can serve as guidance for epitaxial growth of stanene on substrate and render stanene feasible for practical use as a topological insulator.