The electron beam induced functionalization of graphene through the formation of covalent bonds between free radicals of polyaromatic molecules and CC bonds of pristine graphene surface has been explored using first principles calculations and high-resolution transmission electron microscopy. We show that the energetically strongest attachment of the radicals occurs along the armchair direction in graphene to carbon atoms residing in different graphene sub-lattices. The radicals tend to assume vertical position on graphene substrate irrespective of direction of the bonding and the initial configuration. The “standing up” molecules, covalently anchored to graphene, exhibit two types of oscillatory motion – bending and twisting – caused by the presence of acoustic phonons in graphene and dispersion attraction to the substrate. The theoretically derived mechanisms are confirmed by near atomic resolution imaging of individual perchlorocoronene (C24Cl12) molecules on graphene. Our results facilitate the understanding of controlled functionalization of graphene employing electron irradiation as well as mechanisms of attachment of impurities via the processing of graphene nanoelectronic devices by electron beam lithography.

The formation and healing processes of the fundamental topological defect in graphitic materials, the Stone-Wales (SW) defect, are brought into a chemical context by considering the rotation of a carbon–carbon bond as chemical reaction. We investigate the rates and mechanisms of these SW transformations in graphene at the atomic scale using transmission electron microscopy. We develop a statistical atomic kinetics formalism, using direct observations obtained under different conditions to determine key kinetic parameters of the reactions. Based on the obtained statistics we quantify thermally and irradiation induced routes, identifying a thermal process of healing with an activation energy consistent with predicted adatom catalysed mechanisms. We discover exceptionally high rates for irradiation induced SW healing, incompatible with the previously assumed mechanism of direct knock-on damage and indicating the presence of an efficient nonadiabatic coupling healing mechanism involving beam induced electronic excitations of the SW defect.

In this perspective we examine recent theoretical developments in methods for calculating the electrostatic properties of charged particles of dielectric materials. Particular attention is paid to the phenomenon of like-charge attraction and we investigate the specific conditions under which particles carrying the same sign of charge can experience an attractive interaction. Given favourable circumstances, it is shown that even weakly polarisable materials, such as oil droplets and polymer particles, can experience like-charge attraction. Emphasis is also placed on the numerical accuracy of the multipole approach adopted in many electrostatic solutions and on the importance of establishing strict convergence criteria when addressing problems involving particulate materials with high dielectric constants.

Highlights•An out-of-plane spiro structure is reported for a transition state of monovacancy.•The activation energy for this vacancy migration pathway is lower than for the in-plane ‘straight swap’ mechanism.•The estimated rate of vacancy migration is in a good agreement with experimental observations.A comprehensive investigation of monovacancy diffusion in graphene has been carried out with the use of density functional theory and the climbing image nudged elastic band method. An out-of-plane spiro structure is found for the first-order saddle point, which defines the transition state in the vacancy diffusion pathway. The obtained activation energy for diffusion is significantly lower than the reported values for the in-plane saddle point structures. The time between consecutive vacancy jumps in graphene is estimated to be in the range of 100–200 s at room temperature in a good agreement with experimental observations.Graphical abstract

Density functional theory is employed to explore the binding of carbon dioxide and methane in a series of isoreticular metal–organic frameworks, with particular emphasis on understanding the impact of directly incorporated nitrogen and oxygen heteroatoms on the affinity of the ligand for CO2 and CH4. While the strongest binding sites for both CO2 and CH4 were found to be directly above the aromatic rings of the core of the ligand, the introduction of heteroatoms to the core systems was shown to significantly alter both the binding strength and preferred binding locations of CH4 and CO2. The presence of pyrazine rings within the ligand was observed to create new binding sites for both CO2 and CH4 and, in the case of CO2, severely reduce the binding strength or entirely eliminate binding sites that were prominent in the analogous carbocyclic ligands. These results suggest that while the presence of framework nitrogen and oxygen heteroatoms provides a route to ligands with enhanced affinity for methane, a similar increase in affinity for CO2 is not guaranteed.

The weak hydrogen bond is an important type of noncovalent interaction, which has been shown to contribute to stability and conformation of proteins and large biochemical membranes, stereoselectivity, crystal packing, and effective gas storage in porous materials. In this work, we systematically explore the interaction of methane with a series of functionalized organic molecules specifically selected to exhibit a weak hydrogen bond with methane molecules. To enhance the strength of hydrogen bond interactions, the functional groups include electron-enriched sites to allow sufficient polarization of the C–H bond of methane. The binding between nine functionalized benzene molecules and methane has been studied using the second order Møller–Plesset perturbation theory to reveal that benzenesulfonic acid (C6H5–SO3H) and phenylphosphonic acid (C6H5–PO3H2) have the greatest potential for efficient methane capture through hydrogen bonding interactions. Both acids exhibit efficient binding potential with up to three methane molecules. For additional insight, the atomic charge distribution associated with each binding site is presented.

The effect of electron irradiation on the dynamic behavior of Fe atoms, embedded into monovacancy (Fe@MV) and divacancy (Fe@DV) defects in graphene, has been investigated using ab initio molecular dynamics. This study reveals the detailed mechanisms of transformation and migration of Fe@MV and Fe@DV defects in graphene recently observed in aberration-corrected high-resolution transmission electron microscopy (AC-HRTEM) experiments [Nano Lett. 2013, 13, 1468]. An important atomic-scale insight into the dynamics of atomic Fe on graphene, unavailable to AC-HRTEM observations, has been provided. It was found that structural changes of the studied defects are induced by electron impacts on carbon atoms bonded to Fe. The threshold energies for ejection of these carbon atoms are significantly lower compared to that in pristine graphene. For electron impacts with the subthreshold transferred energies, migration of the defects and flipping of Fe atoms between different sides of the graphene plane can occur. The stability of a Fe@MV defect under electron irradiation strongly depends on the substrate side position of the Fe atom with respect to the direction of the electron beam. The Fe@DV → Fe@MV transformations take place spontaneously in the presence of carbon adatoms, which are available in abundance on graphene in AC-HRTEM. The present study facilitates a greater general understanding of the dynamic behavior of substitutional metal atoms in graphene.

•Certain types of charged particles can undergo a counterintuitive electrostatic interaction.•Aerosol growth in Titan’s atmosphere can unfold through a charge scavenging process.•The results have a wider application in the electrostatic description of charged particles.The formation of aerosols in the atmosphere of Titan is based extensively on ion-neutral chemistry and physical condensation processes. Herein it is shown that the formation of aerosols may also occur through an alternative pathway that involves the physical aggregation of negatively charged particles, which are known to be abundant in the satellite’s atmosphere. It is shown that, given the right circumstances, like-charged particles with a dielectric constant characteristic of nitrated hydrocarbons have sufficient kinetic energy to overcome any repulsive electrostatic barrier that separates them and can subsequently experience an attractive interaction at very short separation. Aerosol growth can then unfold through a charge scavenging process, whereby nitrated aggregates preferentially grow by assimilating smaller like-charged particles. Since hydrocarbon aerosols have much lower dielectric constants, it is shown that a similar mechanism involving hydrocarbon particles will not be as efficient. As a consequence of this proposed growth mechanism, it is suggested that the lower atmosphere of Titan will be enriched in nitrogen-containing aerosols.

In this perspective we examine recent theoretical developments in methods for calculating the electrostatic properties of charged particles of dielectric materials. Particular attention is paid to the phenomenon of like-charge attraction and we investigate the specific conditions under which particles carrying the same sign of charge can experience an attractive interaction. Given favourable circumstances, it is shown that even weakly polarisable materials, such as oil droplets and polymer particles, can experience like-charge attraction. Emphasis is also placed on the numerical accuracy of the multipole approach adopted in many electrostatic solutions and on the importance of establishing strict convergence criteria when addressing problems involving particulate materials with high dielectric constants.