We present the science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems, targeting an evolution in technology, that might lead to impacts and benefits reaching into most areas of society. This roadmap was developed within the framework of the European Graphene Flagship and outlines the main targets and research areas as best understood at the start of this ambitious project. We provide an overview of the key aspects of graphene and related materials (GRMs), ranging from fundamental research challenges to a variety of applications in a large number of sectors, highlighting the steps necessary to take GRMs from a state of raw potential to a point where they might revolutionize multiple industries. We also define an extensive list of acronyms in an effort to standardize the nomenclature in this emerging field.

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Science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems

We predict the stability of an extended two-dimensional hydrocarbon on the basis of first-principles total-energy calculations. The compound that we call graphane is a fully saturated hydrocarbon derived from a single graphene sheet with formula CH. All of the carbon atoms are in $s{p}^{3}$ hybridization forming a hexagonal network and the hydrogen atoms are bonded to carbon on both sides of the plane in an alternating manner. Graphane is predicted to be stable with a binding energy comparable to other hydrocarbons such as benzene, cyclohexane, and polyethylene. We discuss possible routes for synthesizing graphane and potential applications as a hydrogen storage material and in two-dimensional electronics.

Graphane: A two-dimensional hydrocarbon

Note: Times Cited: 875 Reference EPFL-ARTICLE-206025doi:10.1021/cr0501846View record in Web of Science URL: ://WOS:000249839900009 Record created on 2015-03-03, modified on 2017-05-12

Complex Hydrides for Hydrogen Storage

Large-Scale Fabrication of Boron Nitride Nanosheets and Their Utilization in Polymeric Composites with Improved Thermal and Mechanical Properties

Review and analysis of molecular simulations of methane, hydrogen, and acetylene storage in metal-organic frameworks.

Extensive calculations based on density functional theory have been carried out to understand the origin of magnetism in undoped ZnO thin films as found in recent experiments. The observed magnetism is confirmed to be due to Zn, instead of O, vacancy. The main source of the magnetic moment, however, arises from the unpaired 2p electrons at O sites surrounding the Zn vacancy with each nearest-neighbor O atom carrying a magnetic moment ranging from 0.490 to 0.740 B. Moreover, the study of vacancy-vacancy interactions indicates that in the ground state, the magnetic moments induced by Zn vacancies prefer to ferromagnetically couple with the antiferromagnetic state lying 44 meV higher in energy. Since this is larger than the thermal energy at room temperature, the ferromagnetic state can be stable against thermal fluctuations. Calculations and discussions are also extended to ZnO nanowires that have larger surface to volume ratio. Here, the Zn vacancies are found to lead to the ferromagnetic state too. The present theoretical study not only demonstrates that ZnO samples can be magnetic even without transition-metal doping but also suggests that introducing Zn vacancy is a natural and an effective way to fabricate magnetic ZnO nanostructures. In addition, vacancy mediated magnetic ZnO nanostructures may have certain advantages over transition-metal doped systems in biomedical applications.

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Vacancy-induced magnetism in ZnO thin films and nanowires

Based on first principles calculations, we propose a mechanism for the dissociative chemisorption of H2 on carbon nanotubes. The breaking of the H—H bond is concerted with the formation of two C—H bonds on two adjacent carbon nanotubes in solid phase, facilitated by the application of high pressure which shortens the interstitial distance between nanotubes. The process is reversible upon the release of external pressure and could make an important contribution to the observed hydrogen storage capacity of carbon nanotubes. The previously unexplained experimental observations of the direct hydrogenation of fullerenes under high pressure lend further support for such a mechanism.

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Chemisorption of hydrogen molecules on carbon nanotubes under high pressure

Chemisorption of singlet 1 � g O2 on single-walled carbon nanotubes is reexamined by first principles calculations, and the reaction barrier is substantially lower than previously reported when the spin on O2 is correctly treated. The process is initiated by the cycloaddition of a singlet O2 on top of a C-C bond and ended with an epoxy structure with each of the two oxygen atoms occupying a bridge position. The overall process is exothermic, with an activation barrier as low as 0.61 eV for the (8, 0) tube. Our results raise the possibility that carbon nanotubes with small diameters could be degraded after exposure to air and sunlight, similar to the degradation of natural rubber and synthetic plastics.

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Oxidation of carbon nanotubes by singlet O2.

Lattice thermal conductivity is one of the most important thermoelectric parameters in determining the energy conversion efficiency of thermoelectric materials. However, the lattice thermal conductivity evaluation requires time-consuming first-principles (quasi)phonon calculations, which limits seeking high-performance thermoelectric materials through high-throughput computations. Here, we establish a methodology to determine the Debye temperature $\mathrm{\ensuremath{\Theta}}$, Gr\"uneisen parameter $\ensuremath{\gamma}$, and lattice thermal conductivity $\ensuremath{\kappa}$ using computationally feasible elastic properties (the bulk and shear moduli). For 39 compounds with three different prototypes (the cubic isotropic rocksalt and zinc blende, and the noncubic anisotropic wurtzite), the theoretically calculated $\mathrm{\ensuremath{\Theta}},\ensuremath{\gamma}$, and $\ensuremath{\kappa}$ are in reasonable agreement with those determined using (quasi)harmonic phonon calculations or experimental measurements. Our results show that the methodology is an efficient tool to predict the anharmonicity and the lattice thermal conductivity.

Gang Chen

Papers

Vacancy-induced magnetism in ZnO thin films and nanowires

Chemisorption of hydrogen molecules on carbon nanotubes under high pressure

Oxidation of carbon nanotubes by singlet O2.

Lattice thermal conductivity evaluated using elastic properties

CO catalytic oxidation on iron-embedded hexagonal boron nitride sheet