The fascinating physics of carbon surfaces: first-principles study of hydrogen on C(0 0 1), C(1 1 1) and graphene

Abstract

Abstract.With the aid of ab-initio, parameter free calculations based on densityfunctional and many-body perturbation theory, we investigate the electronic band structure and electron affinity of diamond surfaces. We focus on clean, ideal (001) and (111) surfaces, and on the effect of hydrogen adsorption. Also single sheets of graphane, that is graphene functionalized upon hydrogen, are investigated. At full H-coverage nearly-free electron states appear near the conduction band minimum in all the systems under study. At the same time, the electron affinity is strongly reduced becoming negative for the hydrogenated diamond surfaces, and almost zero in graphane. The effects of quasi-particle corrections on the electron affinity and on the nearly free electron states are discussed.Confidential: not for distribution.

Partially Hydrogenated Graphene: Semiconductor Material with a Tunable Gap and Its Non-Destructive Optical Characterization

“…The calculated band structure for graphene and graphane were found to be in very good agreement with other independent theoretical works: graphene showed no band gap, and graphane DFT LDA band gap was 3.1 eV. However, it is worth noting that DFT underestimates the gap [9,10]; taking this into consideration, a ~5 eV bandgap for graphane was obtained by using scissors operator. As mentioned above, hydrogen coverage was defined not only in terms of hydrogen percentage, but also in terms of the geometrical bonding scheme, referred here as H super-structures.…”

Defect induced modification of the surface gap and optical properties of C(111)2 × 1 surface

“…Finally, the optical properties of completely hydrogenated C(111) are well defined both experimentally and theoretically (see Ref. 2 for details).…”

“…Chemical inertness and biocompatibility make them promising for applications, for instance, as a coating for biomedical implants, and many others. Since hydrogen always passivates diamond surfaces or boundaries, it is important to understand the microscopic behaviour of hydrogen at various carbon surfaces 1, 2. In addition, hydrogen has been used to successfully modify another allotrope of carbon, graphene, its 100% H saturation creates a new material graphane 3, 4, and the partial hydrogenation allows tailoring graphene's electronic properties 5, 6.…”

“…The microscopic details of the C(111)2 × 1 reconstruction, however, were controversial regarding π ‐chain buckling and/or dimerization (see details in Refs. 2, 14). As generally accepted now, the clean surface reconstruction consists of undimerized and non‐buckled π ‐chains, we will call this ‘ideal C(111)2 × 1’ surface 9.…”

“…The problem originates from the metallic band structure of the reconstructed surface: it contains overlapping filled and empty surfaces states with no surface gap. It is believed now that the undimerized non‐buckled C(111)2 × 1 does produce zero band gap 2. Strangely enough, spurious and easily reproducible theoretically (simply with not sufficient surface Brillouin zone; SBZ sampling) dimerization of the π ‐chains in Ref.…”