Formation and electronic properties of hydrogenated few layer graphene

Abstract

Motivated by the controversial experimental conclusions on the affinity of few layer graphenes (FLGs) towards hydrogen plasma, we systematically investigate the hydrogenation of FLGs within the framework of density functional theory. The approaching hydrogen atoms from both sides of an FLG induce a structural transition from a layered structure into a hydrogen passivated thin diamond film (HP-TDF). The very low transition barrier of FLG hydrogenation indicates the feasibility of FLG hydrogenation through the proposed mechanism. The increasing formation energy with the thickness of FLGs implies that hydrogenation of single layer graphene is easier than that of FLG, which is in agreement with most experimental observations. Moreover, the electronic properties of HP-TDFs and the hydrogenated bilayer graphene ribbons are also studied.

Opening and tuning of band gap by the formation of diamond superlattices in twisted bilayer graphene

“…When interlayer C-C bonds are created between adjacent graphene planes within AB-and AA-aligned pairs of atoms, two-dimensional (2D) nanostructures are formed resembling the atomic structures of bulk cubic and hexagonal diamond, respectively. [23][24][25][26][27]29 In TBG, where the two graphene layers are rotated with respect to each other by twist angles θ between 0° and 60°, the honeycomb lattices of each layer generate a superlattice of domains that are characterized by a specific type of local alignment; these superlattices have the same symmetry with but a larger periodicity than the original honeycomb lattice and are called Moiré patterns. [43][44][45][46] For twist angles over the range from 0° to ~16° (or, equivalently, from ~44° to 60°), these local domains consist of AAand AB-stacked atoms.…”

“…[20][21][22] In multilayer graphene, another way of introducing sp 3 bonding and altering the electronic band structure is the formation of interlayer bonds, namely, covalent C-C bonds between atoms of adjacent graphene layers. 16 Several theoretical studies have demonstrated that hydrogenation and formation of such interlayer bonds usually opens a band gap in the electronic band structure; [23][24][25][26][27] again, however, depending on the spatial arrangement of these interlayer bonds, certain features of the electronic band structure of the pristine, non-bonded configuration are preserved. 16 In a recent study, 16 we showed that creation of interlayer C-C bonds in TBG with the individual graphene planes rotated with respect to each other by angles around 30° leads to the formation of superlattices of caged structures (fullerenes) that have the same periodicity with that of the Moiré pattern characteristic of the TBG; depending on the size of these local fullerene structures, the Dirac cones are either preserved or lost opening a narrow gap in the band structure.…”

“…Previous studies reported structures formed by interlayer bonding in AA-and ABstacked graphene bilayers, [23][24][25][26][27] as well as in MWCNTs of mixed chirality. 29 In those studies, hydrogen atoms at a surface coverage of 50% were used to passivate dangling bonds at the outer surfaces, being distributed on the surface in a checkerboard pattern; it was shown that the presence of these chemisorbed H atoms stabilized the interlayerbonded structures.…”

“…29 In those studies, hydrogen atoms at a surface coverage of 50% were used to passivate dangling bonds at the outer surfaces, being distributed on the surface in a checkerboard pattern; it was shown that the presence of these chemisorbed H atoms stabilized the interlayerbonded structures. The resulting configurations are characterized by a local crystalline structure that resembles that of diamond; some authors have called them "diamane" or "diamond-like C 2 H nanolayer", 24,27 while others have used the terms "hydrogenated bilayer graphene", 25 "hydrogenated few layer graphene", 26 or bilayer graphane. 23 In the study of Ref.…”

“…23 In the study of Ref. 26, it was demonstrated that the energy barriers for the formation of such configurations starting from atomic H and pristine few-layer graphene (FLG) are very low, implying that such structures can be experimentally feasible. 6 The purpose of this article is to investigate the possible nanostructures that can be formed as a result of covalent interlayer C-C bonding between planes of twisted bilayer graphene based on density functional theory (DFT) calculations.…”