Band structure of hydrogenated silicene on Ag(111): Evidence for half-silicane

Abstract

In the case of graphene, hydrogenation removes the conductivity due to the bands forming the Dirac cone by opening up a band gap. This type of chemical functionalization is of utmost importance for electronic applications. As predicted by theoretical studies, a similar change of the band structure is expected for silicene, the closest analogue to graphene. We here report a study of the atomic and electronic structures of hydrogenated silicene, so called silicane. The ($\small 2\sqrt{3} \times 2\sqrt{3}$) phase of silicene on Ag(111) was used in this study since it can be formed homogeneously across the entire surface of the Ag substrate. Low energy electron diffraction and scanning tunneling microscopy data clearly show that hydrogenation changes the structure of silicene on Ag(111) resulting in a (1 $\times$ 1) periodicity with respect to the silicene lattice. The hydrogenated silicene also exhibits a quasi-regular ($\small 2\sqrt{3} \times 2\sqrt{3}$)-like arrangement of vacancies. Angle resolved photoelectron spectroscopy revealed two dispersive bands which can be unambiguously assigned to silicane. The common top of these bands is located at $\small \backsim$ 0.9 eV below the Fermi level. We find that the experimental bands are closely reproduced by the theoretical band structure of free standing silicane with H adsorbed on the upper hexagonal sub-lattice of silicene.