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On her 100th anniversary, we honour Rosalind Franklin with this Letter. Her legacy is a career packed with important scientific breakthroughs before she died of cancer at age 37. She has become one of the most iconic X-ray diffraction scientists, applying this technique to carbons, DNA and viruses. Here, we discuss her meticulous and careful work on carbon materials.

Interatomic potentials underpin many atomistic simulations and great effort is devoted to develop and benchmark potentials. In 2016 [Carbon 109, 681–693], we tested six common carbon potentials and compared their ability to describe disordered carbon structures. Here, we expand this study with eight additional potentials: AIREBO, REBO2-S, Erhart/Albe, ABOP, GAP, Tersoff-S, Tersoff/Nordlund and Tersoff with modified cutoff. Using molecular dynamics we produce and anneal amorphous carbon structures of different densities. Characterization using coordination analysis, ring statistics, radial distribution functions and diffraction intensity show that no two potentials give the same result. To address this lack of transferability, we have developed a web application tool, www.carbonpotentials.org which collates all carbon potentials and enables real-time and equivalent comparison. Unlike a traditional publication that is frozen in time, the tool is expandable and can accommodate new potentials and data.

A one-dimensional (1D) graphene fiber with a novel structure has been prepared by a heat treatment of rice husk, a natural by-product that contains high amounts of silica. A step-by-step heat treatment of rice husk revealed that (i) carbonization yields porous carbon and silica, (ii) 1D β-SiC nanowires are formed by the carbothermic reduction of silica, (iii) finally 1D graphene fibers are created by silicon sublimation from 1D β-SiC nanowires. Raman spectroscopy and electron microscopy studies revealed that the graphene fiber is composed of a turbostratic multilayer structure. The SiC-derived material exhibits a large crystalline size and turbostratic stacking making each layer as quasi-free-standing graphene, which is confirmed by the 3.9 times higher Raman G′-band intensity over the G-band intensity. Molecular dynamics simulations revealed a high diffusion rate of Si atoms and a volume reduction of the SiC structure at the sublimation temperature. Since the silicon sublimation occurred from multiple points of the SiC nanowire, this led to radially-collapsed fibers and faceted structures with thick-graphitic-layer that are inter-connected (deflated-balloons and inter-connected balloon-like fibers). This facile synthesis route opens up a new avenue to the cost-effective and etching-free production of self-standing graphene for its bulk usage.

Two-dimensional graphene has remarkable properties that are revolutionary in many applications. Scrolling monolayer graphene with precise tunability would create further potential for niche applications but this has proved challenging. We have now established the ability to fabricate monolayer graphene scrolls in high yield directly from graphite flakes under non-equilibrium conditions at room temperature in dynamic thin films of liquid. Using conductive atomic force microscopy we demonstrate that the graphene scrolls form highly conducting electrical contacts to highly oriented pyrolytic graphite (HOPG). These highly conducting graphite–graphene contacts are attractive for the fabrication of interconnects in microcircuits and align with the increasing interest in building all sp2-carbon circuits. Above a temperature of 450 °C the scrolls unravel into buckled graphene sheets, and this process is understood on a theoretical basis. These findings augur well for new applications, in particular for incorporating the scrolls into miniaturized electronic devices.

The diffraction behaviour of stacked layers of graphene and hexagonal boron nitride (h-BN) are studied computationally by direct calculation of the diffraction pattern using the Debye scattering equation. Analysis of the position and prole of the diffraction peaks show that while single-layer graphene is unambiguously a 2D material, ordered stacks of three or more layers diffract as bulk material. Following the Scherrer equation, we correlate the known crystallite size with the diffraction peak parameters and observe strong affine relationships which exist separately for single-layer, bi- layer and three or more layer (bulk) structures. We determine a series of expressions to calculate the crystallite size which do not suffer the well-known size-dependence or rely on assumptions about the shape. We present a detailed workflow showing how these expressions can be applied to experimental data.

Isotopes of heavier gases including carbon (13C/14C), nitrogen (13N), and oxygen (18O) are highly important because they can be substituted for naturally occurring atoms without significantly perturbing the biochemical properties of the radiolabelled parent molecules. These labelled molecules are employed in clinical radiopharmaceuticals, in studies of brain disease and as imaging probes for advanced medical imaging techniques such as positron-emission tomography (PET). Established distillation-based isotope gas separation methods have a separation factor (S) below 1.05 and incur very high operating costs due to high energy consumption and long processing times, highlighting the need for new separation technologies. Here, we show a rapid and highly selective adsorption-based separation of 18O2 from 16O2 with S above 60 using nanoporous adsorbents operating near the boiling point of methane (112 K), which is accessible through cryogenic liquefied-natural-gas technology. A collective-nuclear-quantum effect difference between the ordered 18O2 and 16O2 molecular assemblies confined in subnanometer pores can explain the observed equilibrium separation and is applicable to other isotopic gases., Separation of isotopes of heavier gases than hydrogen or helium is essential for biomedical applications, but current methods are very energy and time consuming. Here the authors report cryogenic separation of oxygen and methane isotopes through adsorption in nanoporous materials, based on a collective nuclear quantum effect.

11 pags., 8 figs., 1 tab., The relatively weak London dispersion forces are the only interactions that could cause aggregation between simple aromatic molecules. The use of molecular dynamics and high-levelab initiocomputer simulations has been used to describe the aggregation and interactions between molecular systems containing benzene, naphthalene and anthracene. Mixtures containing one type of molecule (homogenous) and more than one type of molecule (heterogenous) were considered. Our results indicate that as molecular weight increases so does the temperature at which aggregation will occur. In all simulations, the mechanism of aggregation is through small clusters coalescing into larger clusters. The structural analysis of the molecules within the clusters reveals that benzene will orient itself in T-shaped and parallel displaced configurations. Molecules of anthracene prefer to orient themselves in a similar manner to a bulk crystal with no T-shaped configuration observed. The aggregation of these aromatic molecules is discussed in the context of astrochemistry with particular reference to the dust formation region around stars., NAMD was developed by the Theoretical and Computational Biophysics Group in the Beckman Institute for Advanced Science and Technology at the University of Illinois at UrbanaChampaign. This work was in part supported by resources provided by the Pawsey Supercomputing Centre with funding from the Australian Government and the Government of Western Australia, with the assistance of computational resources from the Pople high-performance computing cluster of the Faculty of Science at the University of Western Australia and with the assistance of resources from the National Computational Infrastructure (NCI), which is supported by the Australian Government. AK gratefully acknowledges an Australian Research Council (ARC) Future Fellowship (Project No. FT170100373). I. S. M. fellowship is funded by Australian Research Council (No. FT140100191). I. C. acknowledges funding from the European Research Council under the European Union’s Seventh Framework Programme (FP/2007– 2013)/ERC2013-SyG, Grant Agreement No. 610256 NANOCOSMOS. DT acknowledges MEAE and MESRI for the financial support.

Amorphous carbons are disordered carbons with densities of circa 1.9–3.1 g/cc and a mixture of sp2 and sp3 hybridization. Using molecular dynamics simulations, we simulate diffusion in amorphous carbons at different densities and temperatures to investigate the transition between amorphous carbon and the liquid state. Arrhenius plots of the self-diffusion coefficient clearly demonstrate that there is a glass transition rather than a melting point. We consider five common carbon potentials (Tersoff, REBO-II, AIREBO, ReaxFF and EDIP) and all exhibit a glass transition. Although the glass-transition temperature (Tg) is not significantly affected by density, the choice of potential can vary Tg by up to 40%. Our results suggest that amorphous carbon should be interpreted as a glass rather than a solid.

High-purity graphite is a sought-after material for lithium-ion batteries and graphene production. Most organic materials do not graphitise upon heating unless a metal catalyst is present. The catalyst becomes embedded in the graphite and is difficult to remove. Here, we present a catalysis-free technique capable of producing highly crystalline graphite from materials generally considered incapable of this transformation. Using the furnace inside an Atomic Absorption Spectrometer, we perform repeated high-temperature pulsing of polyvinylidene chloride followed by analysis with Raman, X-ray diffraction and transmission electron microscopy. Unexpectedly, ~90% of the sample transforms into highly ordered graphite with very few defects. A combustion route is proposed in which oxygen attacks the structural units that inhibit graphitisation. We apply the same approach to cellulose and obtain ten times more ordered material than conventional furnaces, confirming that polyvinylidene chloride is not an isolated case. Potentially, this method could be used to synthesise graphite from any organic material, including waste sources such as biomass. Non-graphitising carbon materials typically cannot be converted to graphite without the use of metal catalysts. Here, catalyst-free, high-temperature pulsing is shown to convert polyvinylidene chloride and cellulose into highly ordered graphite.

An atomic absorption spectrometer unit fitted with a graphite furnace module is used to perform high temperature treatment on three carbonized polymers: polyvinyl chloride (PVC), polyvinylidene chloride (PVDC) and polyacrylonitrile (PAN). Using short pulses up to 45 s, we heat small samples to a maximum of 3000 °C. High-resolution transmission electron microscopy and X-ray diffractometry are used to track the growth of crystallites in the materials as a function of the heating temperature. We observe the well-known behaviour of large crystalline graphite growth in PVC-derived samples and the formation of curved graphitic layers in PVDC- and PAN-derived samples. This graphite furnace atomic absorption spectrometer approach is an attractive alternative to conventional laboratory-scale graphite furnaces in research of high temperature treatment of carbon and other refractory materials.

Producción Científica, Carbide-derived carbons (CDCs) are nanoporous carbons with a tunable pore size, making them desirable for their adsorption properties. Despite their applicability, reliable structural models are difficult to construct due to the interplay between strong short-range order and long-range disorder. Here, a mimetic methodology is developed to generate atomistic models of CDCs using Molecular Dynamics and the Environment Dependent Interaction Potential. This approach reproduces the main characteristics of experimentally-prepared CDCs, including microstructure, porosity at the nanometre scale, and graphitization with increasing temperature. An Arrhenius-based approach is used to bridge the timescale gap between Molecular Dynamics and experiment and build a connection between the simulation and synthesis temperatures. The method is robust, easy to implement, and enables a fast exploration of the adsorption properties of CDCs., Ministerio de Economía, Industria y Competitividad (project MAT2014-54378-R), Junta de Castilla y León (programa de apoyo a proyectos de investigación - Ref. VA050U14

In simulations of carbon materials it is common practice to view the coefficients of the cutoff function as free parameters which can be optimised according to the system of interest. This work exa...

Diamond is known to possess a range of extraordinary properties that include exceptional mechanical stability. In this work, it is demonstrated that nanoscale diamond pillars can undergo not only elastic deformation (and brittle fracture), but also a new form of plastic deformation that depends critically on the nanopillar dimensions and crystallographic orientation of the diamond. The plastic deformation can be explained by the emergence of an ordered allotrope of carbon that is termed O8-carbon. The new phase is predicted by simulations of the deformation dynamics, which show how the sp3 bonds of (001)-oriented diamond restructure into O8-carbon in localized regions of deforming diamond nanopillars. The results demonstrate unprecedented mechanical behavior of diamond, and provide important insights into deformation dynamics of nanostructured materials.

Disordered carbons comprise graphene fragments assembled into three-dimensional networks. It has long been debated whether these networks contain positive curvature, as seen in fullerenes, negative curvature, as proposed for the schwarzite structures, or zero curvature, as in ribbons. We present a mesh-based approach to analyze the topology of a set of nanoporous and glassy carbon models that accurately reproduce experimental properties. Although all three topological elements are present, negatively curved structures dominate. At the atomic level, analysis of local environments shows that sp- and sp3-bonded atoms are associated with line defects and screw dislocations that resolve topological complexities such as termination of free edges and stacking of low curvature regions into ribbons. These results provide insight into the synthesis of porous carbon materials, glassy carbon and the graphitizability of carbon materials. NRF (Natl Research Foundation, S’pore) Published version

J.E.B. would like to acknowledge the Australian Research Council (ARC) for financial support through a Future Fellowship (Grant No. FT130101355). J.E.B. and D.G.M. acknowledge funding under the ARC Discovery Project scheme (Grant No. DP140102331). B.H. acknowledges funding through the ORNL Neutron Scattering Facilities, DOE Office of Science User Facilities operated by the Oak Ridge National Laboratory. N.A.M. acknowledges financial support through a fellowship, Grant No. FT120100924. I.S.-M. acknowledges financial support through a fellowship, Grant No. FT140100191. Work by R.B. was supported by the Energy Frontier Research in Extreme Environments (EFree) Center, an Energy Frontier Research Center funded by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES) under Award No. DE-SC0001057. Computational resources are provided by the Pawsey Supercomputing Centre with funding from the Australian Government and the Government of Western Australia. The XRD measurements presented here were performed at HP CAT (Sector 16), Advanced Photon Source (APS), Argonne National Laboratory. HPCAT operations are supported by DOE-NNSA under Award No. DE-NA0001974, with partial instrumentation funding by NSF. The Advanced Photon Source is a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DEAC02-06CH11357. This work has been partially supported by the U.S. Department of Energy. ORNL is managed by UT-Battelle, LLC, under Contract No. DE-AC05-00OR22725 for the U.S. Department of Energy

We perform a comparative study of six common carbon interatomic potentials: Tersoff, REBO-II, ReaxFF, EDIP, LCBOP-I and COMB3. To ensure fair comparison, all the potentials are used as implemented in the molecular dynamics package LAMMPS. Using the liquid quenching method we generate amorphous carbons at different densities, and subsequently anneal at high temperature. The amorphous carbon system provides a critical test of the transferability of the potential, while the annealing simulations illustrate the graphitization process and test bond-making and -breaking. A wide spread of behavior is seen across the six potentials, with quantities such as sp2 fraction, radial distribution function, morphology, ring statistics, and 002 reflection intensity differing considerably. While none of the potentials is perfect, some perform particularly poorly. The lack of transferability can be traced to the details of the functional form, suggesting future directions in the development of carbon potentials.

Junctions between carbon nanotubes and flat or curved graphene structures are fascinating for a number of reasons. It has been suggested that such junctions could be used in nanoelectronic devices, or as the basis of three-dimensional carbon materials, with many potential applications. However, there have been few detailed experimental analyses of nanotube-graphene connections. Here we describe junctions between nanotubes and graphene shells in a material produced by passing a current through graphite. Transmission electron micrographs show that the junction angles are not random but fall close to multiples of 30°. We show that connections with these angles are the only ones which are consistent with the symmetry of the hexagonal lattice, and molecular models show that a continuous lattice requires the presence of large carbon rings at the junction. Some of the configurations we propose have not been previously considered, and could be used to construct new kinds of three-dimensional carbon architecture. We also discuss the possible formation mechanism of the junctions.

Glassy carbon (GC) is usually considered the prototypical super-elastic material, which can almost fully recover its shape after compression of several gigapascals (GPa). In this work, nanoindentation is used to study the mechanical response of GC, which was subjected to a range of high pressures using a diamond anvil cell (DAC). We show that GC starts to lose its elasticity after compression to 6 GPa and becomes clearly mechanically anisotropic after being compressed beyond ∼30 GPa. Molecular dynamics (MD) simulations are used to calculate Young's modulus before and after compression. Through our experimental results and MD simulations, we show that the elasticity of GC is at a minimum around 30 GPa but recovers after compression to higher pressures along the DAC compression axis.

Glassy carbon is a technologically important material with isotropic properties that is nongraphitizing up to $\ensuremath{\sim}3000\text{ }\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ and displays complete or ``superelastic'' recovery from large compression. The pressure limit of these properties is not yet known. Here we use experiments and modeling to show permanent densification, and preferred orientation occurs in glassy carbon loaded to 45 GPa and above, where 45 GPa represents the limit to the superelastic and nongraphitizing properties of the material. The changes are explained by a transformation from its $s{p}^{2}$ rich starting structure to a $s{p}^{3}$ rich phase that reverts to fully $s{p}^{2}$ bonded oriented graphite during pressure release.

International audience; Using a combination of transmission electron microscopy and density functional modeling we examine covalent bridging between carbon nanoforms, focusing on fullerene attachment to carbon nanocones (nanohorns). We show that oxygen mediates covalent cross-linking between carbon nanoforms, analogously to oxygen-mediated fullerene dimerisation (C120O). We confirm this theoretically and experimentally for fullerenes bonded to nanocone tips. Oxygen bridging only occurs in systems with relatively localized double bond character, i.e., in the case of nanocones, bridging only occurs between fullerenes and high angle nanocone tips.

International audience; The response of pristine, nitrogen and boron doped carbon nanotube (CNT) sensors to NO2, CO, C2H4 and H2O at ppm concentrations was investigated at both room temperature and 150 degrees C. N-doped CNTs show the best sensitivity to nitrogen dioxide and carbon monoxide, while B-doped CNTs show the best sensitivity to ethylene. All tubes (including undoped) show strong humidity response. Sensing mechanisms are determined via comparison with density functional calculations of gas molecule absorption onto representative defect structures in N and B-doped graphene. N-CNTs show decreased sensitivity with temperature, and detection appears to occur via gas physisorption. B-CNTs appear to react chemically with many of the absorbed species as shown by their poor baseline recovery and increasing sensitivity with temperature. This limits their cyclability. Overall gas sensitivity is as good or better than post-growth functionalised nanotubes, and used in combination, CNTs, N-CNTs and B-CNTs appear highly promising candidates for cheap, low power, room temperature gas sensing applications. (C) 2013 Elsevier Ltd. All rights reserved.

Carbon nanohorns (sometimes also known as nanocones) are conical carbon nanostructures constructed from an sp(2) carbon sheet. Nanohorns require no metal catalyst in their synthesis, and can be produced in industrial quantities. They provide a realistic and useful alternative to carbon nanotubes, and possibly graphene, in a wide range of applications. They also have their own unique behavior due to their specific conical morphology. However, their research and development has been slowed by several factors, notably during synthesis, they aggregate into spherical clusters ∼100 nm in diameter, blocking functionalization and treatment of individual nanocones. This limitation has recently been overcome with a new approach to separating these "dahlia-like" clusters into individual nanocones. In this review, we describe the structure, synthesis, and topology of carbon nanohorns, and provide a detailed review of nanohorn chemistry.

This work is licensed under a Creative Commons Attribution 4.0 International License. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder to reproduce the material. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/, Lateral slicing of micron length carbon nanotubes (CNTs) is effective on laser irradiation of the materials suspended within dynamic liquid thin films in a microfluidic vortex fluidic device (VFD). The method produces sliced CNTs with minimal defects in the absence of any chemical stabilizers, having broad length distributions centred at ca 190, 160 nm and 171 nm for single, double and multi walled CNTs respectively, as established using atomic force microscopy and supported by small angle neutron scattering solution data. Molecular dynamics simulations on a bent single walled carbon nanotube (SWCNT) with a radius of curvature of order 10 nm results in tearing across the tube upon heating, highlighting the role of shear forces which bend the tube forming strained bonds which are ruptured by the laser irradiation. CNT slicing occurs with the VFD operating in both the confined mode for a finite volume of liquid and continuous flow for scalability purposes.

The transformation of amorphous carbon nanorods into multi-wall nanotubes is studied using molecular dynamics. The effect of the density, width and shape of the initial nanorod is investigated. High-temperature annealing simulations show that the transformation is a robust process which occurs at all densities, regardless of the nanorod shape. The least-defective nanotubes arise from tetrahedral amorphous carbon precursors with an initial density of 3 g/cc. By excising selected regions of the nanorod, we show that the perimeter in cross-section determines the tube diameter, with the number of walls being primarily controlled by the density of the rod. This transformation suggests an alternative approach for generating carbon nanotube networks in the laboratory using ion-beam deposition in combination with lithography.

The default theory of radiation damage in graphite invokes Frenkel pair formation as the principal cause of physical property changes. We set out its inadequacies and present two new mechanisms that contribute to a better account for changes in dimension and stored energy. Damage depends on the substrate temperature, undergoing a change at approximately 250oC. Below this temperature particle radiation imparts a permanent, nano-buckling to the layers. Above it, layers fold, forming what we describe as a ruck and tuck defect. We present first principles and molecular mechanics calculations of energies and structures to support these claims. Necessarily we extend the dislocation theory of layered materials. We cite good experimental evidence for these features from the literature on radiation damage in graphite.

The transformation of carbon peapods (encapsulated fullerenes in nanotubes) into double-walled nanotubes was studied using molecular dynamics simulation. The simulations reproduce the two main trends known experimentally: the production of low-defect nanotubes and the templating effect of the outer tube. The process involves a low-temperature polymerization of the fullerenes followed by higher temperature self-assembly into a tube. Modelling of this second stage is made possible by the use of the Environment-Dependent Interaction Potential, a large number of atoms and long-time annealing. Analysis shows that the outer tube acts as a container for the self-assembly process, analogous to previous simulations and experiments in which free surfaces, either external or internal, template the formation of highly ordered sp2 phases.

The mechanical properties of carbide-derived carbons (CDCs) are computed using molecular dynamics simulations, spanning the experimental density range and synthesis temperatures. The structures consist of nanoporous networks with continuous graphene walls enclosing the pores. Calculation of elastic constants and simulation of tensile strain reveal a direct relationship between the microstructure and elasticity, with the density and temperature inducing significant changes in the pore topology and medium-range order. CDCs have a high elastic moduli and high ultimate tensile strengths while showing resistance to brittle fracture. This suggests that CDCs are a promising route to achieve dense 3D graphene networks with tunable mechanical properties.The mechanical properties of carbide-derived carbons (CDCs) are computed using molecular dynamics simulations, spanning the experimental density range and synthesis temperatures. The structures consist of nanoporous networks with continuous graphene walls enclosing the pores. Calculation of elastic constants and simulation of tensile strain reveal a direct relationship between the microstructure and elasticity, with the density and temperature inducing significant changes in the pore topology and medium-range order. CDCs have a high elastic moduli and high ultimate tensile strengths while showing resistance to brittle fracture. This suggests that CDCs are a promising route to achieve dense 3D graphene networks with tunable mechanical properties.

Under forward bias SiC p-i-n diodes exhibit an anomaly enhancement of the partial dislocation mobility. Through first-principle calculations, we have shown that Peierls barriers and electrical activities are strongly dependent on the dislocation core structures. Further we have found that solitons or antiphase defects along the dislocation line cannot explain alone the enhancement of the dislocation velocity. We have proposed a new theoretical model that can explain the enhancement of the dislocation mobility under forward bias. This model can be applied to any semiconductor materials in order to predict the behaviour under electron-hole plasma injections

We present a novel interpretation of defected tubes based on a dislocation model. A scroll (a sheet rolled without closure) is considered as an axial edge dislocation in a multiwall nanotube (MWNT). Screw dislocation type defects separate scroll from nested-tubes within the same nanotube. The glide of the screw dislocation causes the transformation between these two forms. In some cases, the mechanism of formation of an MWNT could, therefore, start with the formation of a scroll which, by gliding of a screw dislocation, is transformed into the more stable MWNT We compare the structure and energetics of prismatic screw and edge dislocations in graphite and carbon nanotubes. We present calculations for the Peierls barrier of the first kind for graphite and we discuss this result for glide motion of screw dislocations in nanotubes. There is no evidence for stable sp3 atoms in any of the studied nanostructures.

We report calculations in support of the application of LDA within DFT to graphite and go on to report the inner core structure and energetics of prismatic dislocations with Burgers vector c/2: two types of edge and one of screw type. We find the screw dislocations preserve sp2 hybridisation and graphite bonding, whereas one edge type (zigzag) gives rise to interlayer single bonds and sp3 hybridisation, while the other type (armchair) does not, preferring instead to rehybridise towards sp and form bonds with itself approaching triple character. For computational and physical reasons these calculations were based on AA graphite, rather than Bernal (AB) graphite. © 2007 WILEY-VCH Verlag GmbH & Co. KGaA.

Carbon nanotubes present interesting potential applications especially in nanoelectronics. Their electrical properties are known to be a function of their chirality. It happens that 1/3 of CNs are metallic and 2/3 are semiconductors. Narrow nanotubes are expected to be wide-band gap semiconductors. Several experimental results have shown that the thickness of a multi-wall nanotube along the axis can change, while the interlayer spacing remains fairly constant. These observations suggest the coexistence in the same tube of a scroll structure and a multi-wall nested tube. We explain this defect as a screw dislocation which by gliding transforms between these two forms. In this paper, we present a density functional theory study of the structure and energetics of screw dislocations in AA and ABC graphite, and we discuss their role in the scroll-to-nanotube transformation in multi-wall nanotubes.

Pristine and oxygen plasma functionalised carbon nanotubes (CNTs) were studied after the evaporation of Pt and Pd atoms. High resolution transmission electron microscopy shows the formation of metal nanoparticles at the CNT surface. Oxygen functional groups grafted by the plasma functionalization act as nucleation sites for metal nanoparticles. Analysis of the C1s core level spectra reveals that there is no covalent bonding between the Pt or Pd atoms and the CNT surface. Unlike other transition metals such as titanium and copper, neither Pd nor Pt show strong oxygen interaction or surface oxygen scavenging behaviour. (C) 2013 Elsevier B.V. All rights reserved.

A practical numerical method for the rapid construction of nanotube caps is proposed. Founded upon the notion of lattice duality, the algorithm considers the face dual representation of a given nanotube which is used to solve an energy minimization problem analogous to The Thomson Problem. Not only does this produce caps for nanotubes of arbitrary chirality, but the caps generated will be physically sensible and in most cases the lowest energy structure. To demonstrate the applicability of the technique, caps of the (5,5) and the (10,0) nanotubes are investigated by means of density-functional tight binding (DFTB). The calculation of cap energies highlights the ability of the algorithm to produce lowest energy caps. Due to the preferential construction of spherical caps, the technique is particularly well suited for the construction of capped multiwall nanotubes (MWNTs). To validate this proposal and the overall robustness of the algorithm, a MWNT is constructed containing the chiralities (9,2)@(15,6)@(16,16). The algorithm presented paves the way for future computational investigations into the physics and chemistry of capped nanotubes.

Conventional three-dimensional crystal lattices are terminated by surfaces, which can demonstrate complex rebonding and rehybridisation, localised strain and dislocation formation. Two-dimensional crystal lattices, of which graphene is the archetype, are terminated by lines. The additional available dimension at such interfaces opens up a range of new topological interface possibilities. We show that graphene sheet edges can adopt a range of topological distortions depending on their nature. Rehybridisation, local bond reordering, chemical functionalisation with bulky, charged, or multi-functional groups can lead to edge buckling to relieve strain, folding, rolling and even tube formation. We discuss the topological possibilities at a two-dimensional graphene edge, and under what circumstances we expect different edge topologies to occur. Density functional calculations are used to explore in more depth different graphene edge types.

The breakdown of the diamond lattice is explored by ion implantation and molecular dynamics simulations. We show that lattice breakdown is strain-driven, rather than damage-driven, and that the lattice persists until 16% of the atoms have been removed from their lattice sites. The figure shows the transition between amorphous carbon and diamond, with the interfaces highlighted with dashed lines.

International audience; We present a study of purification of single-walled carbon nanotubes (SWCNTs) using different oxidation temperatures and chemical treatments. We have developed a simple two annealing-steps procedure resulting in high nanotube purity with minimal sample loss. The process involves annealing the SWCNTs at 300 °C for 2 h with subsequent reflux in 6 M HCl at 130 °C, followed by further annealing at 350 °C for 1 h with reflux in 6 M HCl at 130 °C. The process results in effective removal of carbon impurities and metal particles which are associated with SWCNTs production. The process is less time consuming (complete in 4.5 h) than conventional acid purification methods which require over 5 h, and less destructive than conventional methods with a yield of 26%. SWCNT purity was assessed using Raman spectroscopy, thermogravimetry and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy.

International audience; We examine the behavior of hydrogen ions, atoms, and molecules in α-boron using density functional calculations. Hydrogen behaves as a negative-U center, with positive H ions preferring to sit off-center on interlayer bonds and negative H ions sitting preferably at in-plane sites between three B12 icosahedra. Hydrogen atoms inside B12 icosahedral cages are unstable, drifting off-center and leaving the cage with only a 0.09 eV barrier. While H0 is extremely mobile (diffusion barrier 0.25 eV), H+ and H- have higher diffusion barriers of 0.9 eV. Once mobile, these defects will combine, forming H2 in the interstitial void space, which will remain trapped in the lattice until high temperatures. Based on these results we discuss potential differences for hydrogen behavior in β-boron and compare with experimental muon-implantation data.

We present a density-functional theory study of low-density bromination of graphene and graphite, finding significantly different behavior in these two materials. In graphene, we find a new ${\mathrm{Br}}_{2}$ form where the molecule sits perpendicular to the graphene sheet with an extremely strong molecular dipole. The resultant ${\mathrm{Br}}^{+}$--${\mathrm{Br}}^{\ensuremath{-}}$ has an empty ${p}_{z}$ orbital located in the graphene electronic $\ensuremath{\pi}$ cloud. Bromination opens a small (86-meV) band gap and strongly dopes the graphene. In contrast, in graphite, we find ${\mathrm{Br}}_{2}$ is most stable parallel to the carbon layers with a slightly weaker associated charge transfer and no molecular dipole. We identify a minimum stable ${\mathrm{Br}}_{2}$ concentration in graphite, finding low-density bromination to be endothermic. Graphene may be a useful substrate for stabilizing normally unstable transient molecular states.

International audience; Vertically aligned multiwalled carbon nanotubes (v-MWCNTs) are functionalized using atomic oxygen generated in a microwave plasma. X-ray photoelectron spectroscopy depth profile analysis shows that the plasma treatment effectively grafts oxygen exclusively at the v-MWCNT tips. Electron microscopy shows that neither the vertical alignment nor the structure of v-MWCNTs were affected by the plasma treatment. Density functional calculations suggest assignment of XPS C 1s peaks at 286.6 and 287.5 eV, to epoxy and carbonyl functional groups, respectively.

Iwata and Watanabe's model for the observed low-temperature specific heat of neutron-irradiated graphite [T. Iwata and M. Watanabe, Phys. Rev. B 81, 014105 (2010)] assumes that self-interstitial atoms exist as clusters of nearly free C2 molecules. We suggest that their hypothesis is not supported by other experiments and theory, including our own calculations. Not only is it inconsistent with the long-known kinetics of interstitial prismatic dislocation loop formation, density-functional theory shows that the di-interstitial is covalently bonded to the host crystal. In such calculations no prior assumptions are made about the nature of the bonding, covalent or otherwise.

International audience; We present a combined theoretical and experimental comparative study of the deposition of five different metals on perfect and defective graphene and multi-walled carbon nanotubes (MWNTs): Ti, Ni, Pd, Pt and Au. Atomistic modelling successfully provides a comprehensive picture of surface binding, diffusion and aggregation properties for these metals, highlighting some fundamental differences in their surface chemical and electronic behaviour. We correlate these theoretical results with experimental TEM images of metal deposited MWCNTs.

International audience; The interaction between evaporated gold and pristine or oxygen plasma treated multi-walled carbon nanotubes (MWCNTs) is investigated. Experimental and theoretical results indicate that gold nucleation occurs at defect sites, whether initially present or introduced by oxygen plasma treatment. Uniform gold cluster dispersion is observed on plasma treated carbon nanotubes (CNTs) and associated with the presence of uniformly dispersed oxidized vacancy centres on the CNT surface.