Tunable Band Gap in Hydrogenated Quasi-Free-Standing Graphene

Abstract

We show by angle-resolved photoemission spectroscopy that a tunable gap in quasi-free-standing monolayer graphene on Au can be induced by hydrogenation. The size of the gap can be controlled via hydrogen loading and reaches approximately 1.0 eV for a hydrogen coverage of 8%. The local rehybridization from sp(2) to sp(3) in the chemical bonding is observed by X-ray photoelectron spectroscopy and X-ray absorption and allows for a determination of the amount of chemisorbed hydrogen. The hydrogen induced gap formation is completely reversible by annealing without damaging the graphene. Calculations of the hydrogen loading dependent core level binding energies and the spectral function of graphene are in excellent agreement with photoemission experiments. Hydrogenation of graphene gives access to tunable electronic and optical properties and thereby provides a model system to study hydrogen storage in carbon materials.

Direct observation of a dispersionless impurity band in hydrogenated graphene

“…Hereafter one monolayer (ML) of Au was deposited on graphene and intercalated into the graphene/Ni interface by annealing 7,18,19 . This procedure liberates graphene from the strong interaction to the Ni substrate, rendering it quasi-free-standing.…”

“…It has been shown that hydrogen readily forms a covalent bond with graphene 6 . The bonding environment of C-H is usually well defined and H/C ratios equal to ∼25% have been realized 7,8 . It is therefore tempting to ask whether impurity band formation happens in hydrogenated graphene (Hgraphene), in close analogy to B doped diamond.…”

“…For electron-doped (n-doped) graphene on SiC, small H amounts yield a shrinkage of the Fermi surface and a metal to insulator transition (MIT) has been observed with a combined transport and ARPES study 14 . For pristine quasi-freestanding graphene, the opening of a bandgap has been reported upon hydrogenation 7,15 . However, the formation of a hydrogen impurity band has not yet been observed experimentally and therefore the question of its existence and electronic properties remains an open topic.…”

Cooperative Interplay of van der Waals Forces and Quantum Nuclear Effects on Adsorption: H at Graphene and at Coronene

“…Hydrogen adsorption on carbon based materials such as graphite and graphene is relevant to hydrogen storage, 9 band gap engineering, [10][11][12][13] and potentially as the first step in H 2 formation in the interstellar medium. [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] Although there is enormous interest in H adsorption on carbonaceous surfaces, with graphene, graphite and polycyclic aromatic hydrocarbons (PAHs) being the most widely studied model systems, we still don't fully understand the seemingly simple process of how a single H atom adsorbs on the surface.…”

Ab-<i>initio</i> studies of adsorbate-surface interactions

“…Investigating this problem is important because, even though we know that the Hydrogen atom colliding against a metallic surface has a huge technological applications and importance for many fields of science [45][46][47] , we still do not have a deep knowledge of how this phenomenon happens. 48 This investigation is also instructive, as yet, no practical application of the newly developed formalism has been presented, although the method of exact factorization has been used to compute the time-dependence potential energy surfaces for problems that can be solved, either analytically or numerically, by alternative procedures.…”