Graphene-based materials (GBMs) constitute a large family of materials which has attracted great interest for potential applications. In this work, we apply first-principles calculations based on density functional theory (DFT) and fully atomistic reactive molecular dynamics (MD) simulations to study the structural and electronic effects of hydrogenation in Me-graphene, a non-zero bandgap GBM composed of both $sp^2$ and $sp^3$-hybridized carbon. Our DFT results show a substantial tuning of the electronic properties of Me-graphene by hydrogenation, with the bandgap varying from $0.64$ eV to $2.81$ eV in the GGA-PBE approach, passing through metallic ground-states and a narrower bandgap state depending on the hydrogen coverage. The analyses of structural properties and binding energies have shown that hydrogenated Me-graphene presents strong and stable \ce{C-H} bonds, and all of the carbon atoms are in $sp^3$ hybridization resulting in a boat-like favorable conformation for fully-hydrogenated Me-graphene. Our MD simulations have indicated that the hydrogenation of Me-graphene is temperature-dependent, and the covalent adsorption tends to grow by islands. Those simulations also show that the most favorable site, predicted by our DFT calculations, acts as trigger adsorption for the extensive hydrogenation.
We propose a new allotrope of graphane, named as tricycle graphane,with a 4up/2down UUUDUD hydrogenation in each hexagonal carbon ring,which is different from previously proposed allotropes with UUDUUD(boat-1) and UUUUDD (boat-2) types of hydrogenation. Its stability and electronic structures are systematically studied using first-principles method. We find that the tricycle graphane is a stable phase in between the previously proposed chair and stirrup allotropes. Its electronic properties are very similar to those of chair, stirrup, boat-1, boat-2, and twist-boat allotropes. The negative Gib…
The paper presents the first computational experiment on the transformation of a graphene sheet (graphene molecule Cn) into graphane (CH)n of regular chairlike structure. The transformation is considered as stepwise hydrogenation of the pristine molecule governed with a particular algorithm. A spatial distribution of the number of effectively unpaired electrons NDA over the carbon carcass lays the algorithm foundation. The atomically mapped high rank NDA values are taken as pointers of target atoms at each reaction step. A complete hydrogenation followed by the formation of regular chairlike g…
Carbon nanoscrolls (CNSs) are nanomaterials with geometry resembling graphene layers rolled up into a spiral (papyrus-like) form. Effects of hydrogenation and temperature on the self-scrolling process of two nanoribbons interacting with a carbon nanotube (CNT) have been studied by molecular dynamics simulations for three configurations: (1) graphene/graphene/CNT; (2) graphene/graphane/CNT, and (3) graphane/graphane/CNT. Graphane refers to a fully hydrogenated graphene nanoribbon. Nanoscroll formation is observed for configurations (1) and (2) for temperatures 300-1000 K, while nanoribbons wrap…
Graphane is a two-dimensional system consisting of a single planar layer of fully saturated (sp$^3$ hybridization) carbon atoms with H atoms attached to them in an alternating pattern (up and down with relation to the plane defined by the carbon atoms). Stable graphane structures were theoretically predicted to exist some years ago and just experimentally realized through hydrogenation of graphene membranes. In this work we have investigated using \textit{ab initio} and reactive molecular dynamics the role of H frustration (breaking the H atoms up and down alternating pattern) in graphane-like…
While graphene is a semi-metal, a recently synthesized hydrogenated graphene called graphane, is an insulator. We have probed the transformation of graphene upon hydrogenation to graphane within the framework of density functional theory. By analyzing the electronic structure for eighteen different hydrogen concentrations, we bring out some novel features of this transition. Our results show that the hydrogenation favors clustered configurations leading to the formation of compact islands. The analysis of the charge density and electron localization function (ELF) indicates that as hydrogen co…
We performed a first principles investigation on the structural and electronic properties of group-IV (C, SiC, Si, Ge, and Sn) graphene-like sheets in flat and buckled configurations and the respective hydrogenated or fluorinated graphane-like ones. The analysis on the energetics, associated with the formation of those structures, showed that fluorinated graphane-like sheets are very stable, and should be easily synthesized in laboratory. We also studied the changes on the properties of the graphene-like sheets, as result of hydrogenation or fluorination. The interatomic distances in those gra…
We propose, on the basis of our first principles density functional based calculations, a new isomer of graphane, in which the C-H bonds of a hexagon alternate in 3-up, 3-down fashion on either side of the sheet. This 2D puckered structure called 'stirrup' has got a comparable stability with the previously discovered chair and boat conformers of graphane. The physico-chemical properties of this third conformer are found to be similar to the other two conformers of graphane with an insulating direct band gap of 3.1 eV at the Γ point. Any other alternative hydrogenation of the graphene sheet dis…
Graphane is a two-dimensional system consisting of a single layer of fully saturated (sp$^3$ hybridization) carbon atoms. In an ideal graphane structure C-H bonds exhibit an alternating pattern (up and down with relation to the plane defined by the carbon atoms). In this work we have investigated using \textit{ab initio} and reactive molecular dynamics simulations the role of H frustration (breaking the H atoms up and down alternating pattern) in graphane-like structures. Our results show that significant percentage of uncorrelated H frustrated domains are formed in the early stages of the hyd…
Hydrogenated graphene, graphane, is studied on oxygen-terminated silicon dioxide substrate using ab initio calculations. A structure with hydrogenation only on one side of the graphene layer is found stable and its hydrogen configurations are presented. Additionally, we form zigzag graphene nanoribbons by selectively removing hydrogens from the epitaxial graphane layer. In these ribbons, the spin degeneracy of the freestanding antiferromagnetic zigzag ribbons is broken, and band gaps of different magnitude emerge for the opposite spin species. This degeneracy breaking is due to a charge imbala…
Graphane is obtained by perfectly hydrogenating graphene. There exists an intermediate material, partially hydrogenated graphene (which we call \textit{hydrographene}), interpolating from pure graphene to pure graphane. It has various intriguing electronic and magnetic properties. We investigate a metal-insulator transition, employing a quantum-site percolation model together with a graph theoretical approach. Hydrographene is an exceptional case in which electronic properties cannot be determined solely by the density of states at the Fermi energy. Though there are plenty of zero energy state…
Hydrogenation has proven to be an effective tool to open the bandgap of graphene. In the present density functional study we demonstrate that single-side-hydrogenated graphene is a semiconductor with an indirect bandgap of 1.89 eV, in between the gapless graphene and wide bandgap graphane. We show that its electronic structure and lattice characteristics are substantially different from those of graphene, graphone, or graphane. The lattice parameter and C-C bond length are found to be lengthened by 15% of those of graphene. Our binding energy analysis confirms that such a single sided hydrogen…
Graphane is graphene fully hydrogenated from both sides, forming a 1x1 structure, where all C atoms are in sp3 configuration. In silicene, the Si atoms are in a mix-sp2/sp3 configuration, it is therefore natural to imagine silicane in analogue to graphane. However, monoatomic silicene sheet grown on substrates generally reconstructs into different phases, and only partially hydrogenated silicene with reconstructions had been reported before. In this report we produce half-silicane, where one Si sublattice is fully H-saturated and the other sublattice is intact, forming a perfect 1x1 structure.…
Since the advent of graphene ushered the era of two-dimensional materials, many forms of hydrogenated graphene have been reported, exhibiting diverse properties ranging from a tunable band gap to ferromagnetic ordering. Patterned hydrogenated graphene with micron-scale patterns has been fabricated by lithographic means. Here we report successful millimeter-scale synthesis of an intrinsically honeycomb patterned form of hydrogenated graphene on Ru(0001) by epitaxial growth followed by hydrogenation. Combining scanning tunneling microscopy observations with density-functional-theory (DFT) calcul…
Recent studies on graphene hydrogenation processes showed that hydrogenation occurs via island growing domains, however how the substrate can affect the hydrogenation dynamics and/or pattern formation has not been yet properly investigated. In this work we have addressed these issues through fully atomistic reactive molecular dynamics simulations. We investigated the structural and dynamical aspects of the hydrogenation of graphene membranes (one-side hydrogenation, the so called graphone structure) on different substrates (graphene, few-layers graphene, graphite and platinum). Our results als…
The quantum-mechanochemical-reaction-coordinate simulations have been performed to investigate the mechanical properties of hydrogen functionalized graphene. The simulations disclosed atomically matched peculiarities that accompany the deformation-failure-rupture process occurred in the body. A comparative study of the deformation peculiarities related to equi-carbon-core (5,5) nanographene and nanographane sheets exhibited a high stiffness of both bodies that is provided by the related hexagon units, namely benzenoid and cyclohexanoid, respectively. The two units are characterized by anisotro…
Graphene is of interest in the development of next-generation electronics due to its high electron mobility, flexibility and stability. However, graphene transistors have poor on/off current ratios because of the absence of a bandgap. One approach to introduce an energy gap is to use hydrogenation reaction, which changes graphene into insulating graphane with sp3 bonding. Here we show that an electric field can be used to control conductor-to-insulator transitions in microscale graphene via a reversible electrochemical hydrogenation in an organic liquid electrolyte containing dissociative hydr…
Chemisorption of hydrogen on graphene is studied using atomistic simulations with the second generation of reactive empirical bond order Brenner inter-atomic potential. The lowest energy adsorption sites and the most important metastable sites are determined. The H concentration is varied from a single H atom, to clusters of H atoms up to full coverage. We found that when two or more H atoms are present, the most stable configurations of H chemisorption on a single graphene layer are ortho hydrogen pairs adsorbed on one side or on both sides of the graphene sheet. The latter has the highest hy…
A great efficacy of molecular quantum chemistry applied to basic graphene problems has been recently demonstrated by the authors when studying the formation of peculiar composites between carbon nanotubes and graphene as well as considering tensile deformation and fracture of a graphene sheet in due course of a mechanochemical reaction. The optimistic results obtained in the studies make it possible to shift attention from the solid state problems and consider the graphane formation as multistep hydrogenation of the pristine molecule. To proceed we have to answer the following questions: 1) wh…
Hydrogenation of graphene on the α-quartz (0001) SiO_2 substrate is studied, considering different surface terminations in order to take into account the amorphic nature of the material. Our ab initio calculations show that the formation of graphane by hydrogen adsorption on graphene is energetically favored on hydroxyl and oxygen terminated surfaces, whereas silicon termination and reconstruction of the oxygen termination hinder adsorption. Our results indicate that in order to fabricate graphane on SiO_2, it is beneficial to oxygenize the surface and saturate it with hydrogen. For the pristi…
The paper presents evidence of a rather strong correlation of odd electrons in the singlet state of graphene. Due to the correlation, the chemical modification of graphene can be considered following a certain algorithmic computational procedure. Originated due to the correlation and distributed over the carbon atoms of graphene membrane with fraction numbers NDA, effectively unpaired electrons lay the algorithm foundation. The highest NDA value points to the target atom that enters a chemical reaction at the considered step. Following the pointers, a stepwise design of polyderivatives can be …
DFT calculations of the electronic structure of graphane and stoichiometrically halogenated graphene derivatives (fluorographene and other analogous graphene halides) show (i) localized orbital basis sets can be successfully and effectively used for such 2D materials; (ii) several functionals predict that the band gap of graphane is greater than that of fluorographene, whereas HSE06 gives the opposite trend; (iii) HSE06 functional predicts quite good values of band gaps w.r.t benchmark theoretical and experimental data; (iv) the zero band gap of graphene is opened by hydrogenation and halogena…
Graphene - a monolayer of carbon atoms densely packed into a hexagonal lattice - has one of the strongest possible atomic bonds and can be viewed as a robust atomic-scale scaffold, to which other chemical species can be attached without destroying it. This notion of graphene as a giant flat molecule that can be altered chemically is supported by the observation of so-called graphene oxide, that is graphene densely covered with hydroxyl and other groups. Unfortunately, graphene oxide is strongly disordered, poorly conductive and difficult to reduce to the original state. Nevertheless, one can i…
TiFe intermetallic compound has been extensively studied, owing to its low cost, good volumetric hydrogen density, and easy tailoring of hydrogenation thermodynamics by elemental substitution. All these positive aspects make this material promising for large-scale applications of solid-state hydrogen storage. On the other hand, activation and kinetic issues should be amended and the role of elemental substitution should be further understood. This work investigates the thermodynamic changes induced by the variation of Ti content along the homogeneity range of the TiFe phase (Ti:Fe ratio from 1…
A density functional theory study of the structural and electronic properties and relative stability of fluorinated sp3 silicon nanotubes and their corresponding silicon nanowires built along various crystallographic orientations is presented. The structural stability is found to increase linearly with the fluorine surface coverage and for coverages exceeding 25% the tubular structures are predicted to be more stable than their wire-like counterparts. The bandgaps of the fully fluorinated systems are lower than those of their fully hydrogenated counterparts by up to 0.79 eV for systems having …
