From Silicene to Half-Silicane by Hydrogenation

Graphane is graphene fully hydrogenated from both sides, forming a 1x1 structure, where all C atoms are in sp(3) configuration. In silicene, the Si atoms are in a mixed sp(2)/sp(3) configuration; it is therefore natural to imagine a silicane structure analogous to graphane. However, a monatomic silicene sheet grown on substrates generally reconstructs into different phases, and only partially hydrogenated silicene with reconstructions had been reported before. In this work, we produce half-silicane, where one Si sublattice is fully H-saturated and the other sublattice is intact, forming a perfect 1 x 1 structure. By hydrogenating various silicene phases on a Ag(111) substrate, we found that only the (2 root 3x2 root 3)R30 degrees phase can produce half-silicane. Interestingly, this phase was previously considered to be a highly defective or incomplete silicene structure. Our results indicate that the structure of the (2 root 3x2 root 3)R30 degrees phase involves a complete silicene-1x1 lattice instead of defective fragments, and the formation mechanism of half-silicane was discussed with the help of first-principles calculations.