Does semihydrogenated graphene on lattice matched transition metal substrates has a uniform hydrogen adsorption pattern?

Abstract

Graphone, uniformly semihydrogenated graphene, though an interesting material, is known to be highly unstable due to large chemical imbalance between the sublattices of the bipartite graphene lattice. The freestanding semihydrogenated graphene (GrH) sheet can be stabilized by changing the hydrogen adsorption pattern in such a way that the chemical imbalance is removed. However, when placed on lattice-matched transition metal surfaces we find that the highly unstable uniformly semihydrogenated graphene is stabilised and on Ni(111) surface it shows equal stability with at least three other structures. The other three structures are rectangular graphone, zigzag graphone and armchair graphone. On Co(111) and Cu(111) surfaces rectangular graphone shows more stability than other structures. Nonetheless the corelevel shifts of these four semihydrogenated graphene on the (111) surfaces of Ni, Co and Cu shows differences which are less than 0.2 eV. It is thus highly unlikely that X-ray Photoelectron spectroscopy measurements will be able to discern different H adsorption patterns. Therefore our study contradicts the notion that upon hydrogenation of graphene sheet supported on a lattice matched transition metal substrates a uniform H adsorption pattern will be formed. Furthermore we find that the electronic and magnetic properties at the interface of semihydrogenated graphene and metal surface show variation with H adsorption patterns. This makes the study of hydrogenated graphene on transition metal surfaces more intriguing and important from the point of view of using the interface as a device. Of all structures studied in this paper we find that only uniform graphone on Cu(111) surface shows higher possibility for spin polarized conduction at the interface.