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The interaction of H, H2, and MgH2 with graphene is investigated using the density functional theory to explore the possibility of exploiting graphene or functionalized graphene as a hydrogen storage medium. The H atom is positioned at various distances from the graphene surface and the energetics are computed in detail. The extent of interaction of the s electron of H with graphene's pz electrons is well brought out. Similar investigations are carried out for H2, MgH2. In the case of H atom, a HC covalent bond is formed. This process turns out to be a prerequisite for proton transfer through graphene. Interactions of H2 and MgH2 with graphene are different from that of H. It leads to the conclusion that functionalized graphene will better substrate/candidate for applications like hydrogen storage. [ABSTRACT FROM AUTHOR]

The atomistic features of the van der Waals interaction between graphene and 2D h‐BN layer are investigated with and without doping using density functional theory. It is computationally shown, how different types of 2D materials can form heterojunctions with each other without the need for close lattice matching if the atomic species are neighbors in the periodic table. H2, N2, and O2 are introduced as the dopants separately to investigate the van der Waals interaction at the sub‐nanometer scale and its influence on the molecules and interlayer coupling. The geometrical forms and formation energies of differently bonded molecules and atoms immersed in van der Waals forces in the heterostructure are predicted accurately. The spatial dependence of the van der Waals energy between graphene and h‐BN and its effect on the confined molecule/atoms is well brought out in the present investigation. The weak van der Waals forces between graphene and h‐BN do introduce minor changes at the nanoscale but maintain the original band structure which is dominated by graphene. The present graphene and 2D h‐BN van der Waals heterostructure, with enhanced features, offers a unique opportunity to fabricate new materials with different properties. They will become the building blocks in engineering new functional materials. [ABSTRACT FROM AUTHOR]

The electron transport properties with the relativistic intrinsic and Rashba spin-orbit (SO) couplings in a graphene nanoribbon are investigated by using the third-nearest-neighbor tight-binding model and the nonequilibrium Green function method. The numerical results display a perfect quantum spin Hall state (QSH) surrounded by a simple insulator state, presented in Rashba SO coupling vs sublattice potential plane. The QSH state is enhanced by the intrinsic SO coupling, indicating a quantum topological property of graphene nanoribbons. [ABSTRACT FROM AUTHOR]

We discover a method of opening the conductive channels of zigzag graphene nanoribbons (ZGNRs) by using hydrogenation chains to separate the nanoribbon into two strips with a ∼0.7 Å distance, although the overall hydrogenation on graphene transforms the highly conductive semimetal sheet into an insulator. Two edge-like states emerge around each hydrogenation chain. The conductance enhancement, made by the hydrogenation chain, is found in nanoribbons with 5 to 7 chains, e.g. 5ZGNRH, 6ZGNRH, 7ZGNRH, and 7ZGNR2H (7ZGNR with two hydrogenation chains). The ZGNRs with hydrogenation chains illustrate their potential in nanoelectronics and carbon electronics as electronic leads and nonlinear devices. [ABSTRACT FROM AUTHOR]

With nonequilibrium Green’s function approach combined with density functional theory, we perform an ab initio calculation to investigate transport properties of graphene nanoribbon (GNR) junctions self-consistently. Tight-binding approximation is applied to model the zigzag (ZGNR) electrodes, and its validity is confirmed in comparison to the GAUSSIAN03 periodic boundary condition calculation result of the same system. The origin of abnormal jump points usually appearing in the transmission spectrum is explained with the detailed tight-binding ZGNR band structure. Transport property of an edge-defect ZGNR junction is investigated, and the tunable tunneling current can be sensitively controlled by transverse electric fields. [ABSTRACT FROM AUTHOR]

In graphene, band gap opening and tuning are important technological challenges for device applications. Various techniques have been suggested to this technologically complicated problem. Here, we present an ab initio study on the band gap opening in graphene through vacancy, adding impurity atom in the vacancy and substitutional co-doping. In the case of graphene with single vacancy a direct band gap of ~1 eV is obtained. This is a spin polarized state. The graphene system with two monovacancies gives rise to an effective indirect band gap (pseudo gap) of ~1 eV. The graphene substitutionally doped with B and N is co-doped (tri-doped) with S. This tri-doped graphene has turned into a semiconductor (band gap ~1 eV). These graphene semiconductors are better than the other semiconductor because of the presence of massless Dirac fermions in addition to normal electrons. This will have lot of application in device industry compared to a pristine graphene because of the presence of a gap and Dirac fermions. This type of band gap opening, with this type of defects and impurities, we are reporting for the first time. [ABSTRACT FROM AUTHOR]

We report a new method for the design of kagome lattices using zigzag-edged triangular graphene nanoflakes (TGFs) linked with B, C, N or O atoms. Using spin-polarized density functional theory we show that the electronic and magnetic properties of the designed kagome lattices can be modulated by changing their size and the linking atoms. The antiferromagnetic coupling between the two directly linked TGFs becomes ferromagnetic coupling when B, C or N is used as the linking atoms, but not for O atom linking. All the designed structures are semiconductors which can be synthesized from graphene atomic sheets by using electron etching and block copolymer lithography techniques. This study is a good example of how mathematical models can be used to construct magnetic nanostructures involving only s, p elements. [ABSTRACT FROM AUTHOR]

First-principles electronic structure calculations based on spin-polarized density functional theory were carried out to study the adsorption of oxygen-containing functional groups -OH, -CHO, and -COOH on a two-dimensional (2D) infinite graphene sheet without edge states and defects. We find that the energy gain of adsorption can be significantly improved when the graphene sheet is supported via a point contact, a prototype for graphene sheet supported by catalysts, nanoparticles or nanopillars, or a surface with steps, edges, adatoms, or defects. This was modeled by placing a single atom of Fe, Co, and Ni under the graphene surface. Thus supported graphene not only becomes magnetic, but the carbon atoms in contact with the metal atoms become chemically more active as well. The use of point contact support to improve adsorption has advantages over that of introducing defects: (I) It does not destroy the intrinsic 2D geometry of the graphene sheet. (2) Patterned structures can be created by tailoring the position of the metal atoms supporting the graphene sheet. (3) The geometry distortion created by point contact can be made more uniform and lead to better adsorption energies. (4) Reduction of the work function of supported graphene makes the manipulation of electrons more flexible and controllable in tuning their electronic structure and magnetic properties. [ABSTRACT FROM AUTHOR]

Based on detailed first-principles investigations of the hexagonal antidot patterned graphene nanomeshes, we have studied the mechanisms of the conducting property modification of graphene. The band-folding analysis shows that the (3 n ,3 m ) ( n and m are integers) superlattice would have fourfold degeneracy at Г point. An effective method by removing this fourfold degeneracy, such as regularly arranging antidots to make the (3 n ,3 m ) nanomesh, is proposed to open a sizable bandgap no matter whether the sublattice equivalence keeps or not. In the nanomeshes patterned with the magnetic antidots, the antiferromagnetic coupling adds a quantum parameter to break the sublattice equivalence, resulting in the bandgap opening at the twofold degenerate K (K′) point. Our studies also show that the gap width could be tuned by controlling the antidot density. These results could facilitate the fascinating applications of graphene in the next-generation nanoelectronics. [ABSTRACT FROM AUTHOR]

Abstract: From the first principles study, it is shown that chemically inert monolayer graphene becomes active by strain engineering. The sheets are stretched biaxially to introduce strain of 1.43%, 5%, 8.5% and 10% in the C–C bond lengths. The introduction of strain enhances the chemical reactivity of graphene surface and hence they become chemically more active than the pristine one. The interaction of borane and molecular hydrogen increases with increase in strain in the substrate (strained graphene) and these molecules bind with considerable binding energy. Since graphene sheets can be freely suspended without any substrate, we can stretch the sheets by tuning distance between the clamped edges of the holding frame. In this way, stacks of stretched graphene sheets can be manufactured and a good hydrogen storage medium can be obtained. Likewise, one can tailor graphene in such a way to exhibit its multi-faceted applicability by strain engineering. [Copyright &y& Elsevier]

Abstract: The hydrogen storage of Ca-decorated graphene is studied by using a recently developed van der Waals density functional [vdW-DF, M. Dion, et al., Phys. Rev. Lett. 92 (2004) 246401]. Our vdW-DF calculations show that Ca-decorated graphene with a coverage of 33.4% can only store 2.6wt.% of hydrogen. vdW-DF significantly improves the underestimation (overestimation) of binding strength of Ca with graphene as well as the adsorption energies of H2 molecules on Ca-decorated graphene with respect to the conventional local and semilocal approximations. [Copyright &y& Elsevier]

Abstract: We present the results of our theoretical investigation on ripples and elastic properties of single layer graphene sheets in both membrane and ribbon conformations. The formation of ripples in both the systems is simulated and analyzed using two-dimensional vibrating membrane model. We have chosen both square graphene membrane, armchair and zigzag graphene nanoribbons with different sizes. The amplitude of vibrational modes of each system is determined using this model. We observed that the vertical displacement (amplitude of the ripples) reaches a maximum height of about 0.99nm from the mean plane in both conformations whose lengths are integral multiple of the basic armchair/zigzag units. We have studied the dynamical elastic properties through the calculation of parameters like normalized stiffness, speed parameter, Cauchy number and critical velocity with reference to a new aspect ratio of graphene sheets. We have made correlations between the calculated parameters with the formation of ripples and found that the out-of-plane deformations are spontaneous and significant in square conformation of graphene than the graphene nanoribbons. The vibrational modes obtained for GNRs and membranes are acoustic modes. The results of our study will be very much useful in selecting graphene sheets with suitable conformation and chirality for designing nanoscale devices. [Copyright &y& Elsevier]

• A new basic and intriguing theoretical study based on experimental stabilization of 18 atom carbon ring. • 18 and 12-member carbon rings are computationally stabilized on graphene sheet. • Bond lengths are equal in both carbon rings and bonds are made of double bonds. • Bonds are covalent and there is no sp-hybridization. • Carbon acquires an electronic configuration 1 s2 2 s4, resonating with 1 s2 2 s2 2p2. Multi-member rings composed of 18 and 12 carbon atoms are designed and stabilised on graphene, the one atom thick carbon substrate, computationally using density functional theory. The resultant structures are intriguing. Bond lengths are found to be equal in both the carbon rings and the atoms are connected through double bonds. The 18-member carbon ring is not circular in shape, whereas the 12-member ring has the circular configuration. The system of 18-member carbon ring on graphene is metallic. Our studies have shown that a weak but definite bonding between the ring structures and the graphene substrate decides the shape of the new carbon allotrope. [ABSTRACT FROM AUTHOR]