A study of polybromide chain formation using carbon nanomaterials via density functional theory approach

\ua9 2016 The Author(s). This open access article is distributed under a Creative Commons Attribution (CC-BY) 4.0 license. We use a density functional theory approach under the local density approximation (DFT/LDA) to describe the formation of polybromide chain structures, their stretching frequency modes and charge transfer induced by the interaction of these molecules with a graphene sheet. In many cases, we find polybromides to be more thermodynamically stable than the equivalent Br2 molecular structures adsorbed on graphene sheet. This results in lower frequency stretch modes at around 170–190 cm−1. We propose that these are rarely observed experimentally due to the bromination techniques used, which introduces molecular Br2 into the carbon host material. Charge transfer with their host material means that these molecules and their associated hole charge in the neighbouring carbon materials, are then coulombically repelled from other bromine molecules which acts as a barrier to combination into polybromides. Our calculated barrier for polybromide formation (2Br2→Br4) on a graphene sheet was 0.35 eV which is an exothermic process with an enthalpy value of −0.28 eV. Therefore, thermodynamically, chain polybromide formation seems to be favourable but kinetically, is unlikely, since there is an activation barrier that needs to be overcome to give stable bromine chain structures

High Methanol Oxidation Activity of Well-Dispersed Pt Nanoparticles on Carbon Nanotubes Using Nitrogen Doping

Pt nanoparticles (NPs) with the average size of 3.14 nm well dispersed on N-doped carbon nanotubes (CNTs) without any pretreatment have been demonstrated. Structural properties show the characteristic N bonding within CNTs, which provide the good support for uniform distribution of Pt NPs. In electrochemical characteristics, N-doped CNTs covered with Pt NPs show superior current density due to the fact that the so-called N incorporation could give rise to the formation of preferential sites within CNTs accompanied by the low interfacial energy for immobilizing Pt NPs. Therefore, the substantially enhanced methanol oxidation activity performed by N-incorporation technique is highly promising in energy-generation applications

Adatoms and nanoengineering of carbon

We present a new and general mechanism for inter-conversion of carbon structures via a catalytic exchange process, which operates under conditions of Frenkel pair generation. The mechanism typically lowers reaction barriers by a factor of four compared to equivilent uncatalysed reactions. We examine the relevance of this mechanism for fullerene growth, carbon onions and nanotubes, and dislocations in irradiated graphite

First-principles calculations on the structure of hydrogen aggregates in silicon and diamond

We report the results of first-principles calculations on the early stages of hydrogen aggregation in silicon and diamond. We demonstrate that the hydrogenated glide dislocation dipole is the preferred structure for small numbers of H atoms in silicon and that it expands by dislocation glide, with hydrogen condensing in the shuffle plane between the dislocations. This structure is a good candidate for the initial stage in the development of hydrogen-induced platelets. We investigate the effect of shear and dilation on the energies of hydrogenated structures and compare the relative stabilities of these structures in silicon and diamond. We describe the method of determination of the Burgers vectors of dilation and shear for the dislocation dipoles by varying the lattice vectors of their supercells

Simulation of the delamination of thin films

We simulate thin film delamination using a lattice springs model. We use this model to construct a phase diagram of different delamination behaviours, produced by varying the compression of the film and also the radius to which local relaxation is allowed to take place about failing bonds. From this we see a progression from laminar and linear behaviours to radial and rounded features as compressive stress is increased. Sinusoidal telephone cord behaviour occurs only at a small range of fairly low stresses, and thin films. © EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2005

Kinetic Monte Carlo study of dislocation motion in silicon: Soliton model and hydrogen enhanced glide

The problems with dislocations in semiconductors are becoming tractable with modern computing by hybrid techniques. These apply static first principles calculations of energetics for important processes (e.g. kink formation and migration energies) and kinetic Monte Carlo techniques to follow the dynamic interaction of these processes over length and time scales inaccessible to, for example, molecular dynamic simulation. The simplest model system for covalent and ceramic solids is silicon, but there is debate over the structure and properties of dislocations there. The movement of the dislocation by the simple bond switching mechanism was studied from first principles, finding activation energies close to experiment, but lately the alternative mechanism invoking free radicals or solitons was found to give similar energies. We report results from an n-fold way kinetic Monte Carlo approach, applied to a simple system to verify the standard model for kink pair nucleation limited dislocation glide (the Hirth-Lothe model). We then apply an improved technique to the kinetics of the soliton model and to hydrogen enhanced dislocation glide. © 2001 Elsevier Science B.V. All rights reserved

Linewise kinetic Monte Carlo study of silicon dislocation dynamics

We present a number of n-fold way kinetic Monte Carlo simulations of the glide motion of 90° partial dislocations in silicon. We undertake a survey of ratios of kink formation energy Fk to kink migration barrier Wm, over a range of temperatures and applied stresses. These simulations are compared with Hirth-Lothe theory and an extension to the Hirth-Lothe theory of Kawata and Ishiota. The latter is found to give the best description of the system. Using literature first principle values for the kink and soliton formation and migration energies, a model combining both strained bond and soliton mediated motion shows a negligible contribution to dislocation motion from the solitons. The high soliton pair creation barrier was limiting and a soliton mediated mechanism for dislocation motion would have to achieve thermal equilibrium concentration via impurity or point defect interaction to be effective. We also show that if this can be overcome solitons greatly increase the mobility of the dislocation, even without a binding energy between solitons and kinks. The simulation coded here is easily expandable to incorporate further dislocation line effects such as impurities at the line

Kinetic Monte Carlo study of dislocation motion in silicon: Soliton model and hydrogen enhanced glide

The problems with dislocations in semiconductors are becoming tractable with modern computing by hybrid techniques. These apply static first principles calculations of energetics for important processes (e.g. kink formation and migration energies) and kinetic Monte Carlo techniques to follow the dynamic interaction of these processes over length and time scales inaccessible to, for example, molecular dynamic simulation. The simplest model system for covalent and ceramic solids is silicon, but there is debate over the structure and properties of dislocations there. The movement of the dislocation by the simple bond switching mechanism was studied from first principles, finding activation energies close to experiment, but lately the alternative mechanism invoking free radicals or solitons was found to give similar energies. We report results from an n-fold way kinetic Monte Carlo approach, applied to a simple system to verify the standard model for kink pair nucleation limited dislocation glide (the Hirth-Lothe model). We then apply an improved technique to the kinetics of the soliton model and to hydrogen enhanced dislocation glide. © 2001 Elsevier Science B.V. All rights reserved

Linewise kinetic Monte Carlo study of silicon dislocation dynamics

We present a number of n-fold way kinetic Monte Carlo simulations of the glide motion of 90° partial dislocations in silicon. We undertake a survey of ratios of kink formation energy Fk to kink migration barrier Wm, over a range of temperatures and applied stresses. These simulations are compared with Hirth-Lothe theory and an extension to the Hirth-Lothe theory of Kawata and Ishiota. The latter is found to give the best description of the system. Using literature first principle values for the kink and soliton formation and migration energies, a model combining both strained bond and soliton mediated motion shows a negligible contribution to dislocation motion from the solitons. The high soliton pair creation barrier was limiting and a soliton mediated mechanism for dislocation motion would have to achieve thermal equilibrium concentration via impurity or point defect interaction to be effective. We also show that if this can be overcome solitons greatly increase the mobility of the dislocation, even without a binding energy between solitons and kinks. The simulation coded here is easily expandable to incorporate further dislocation line effects such as impurities at the line