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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.

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

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.

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.

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 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.

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.