Interaction between particles with inhomogeneous surface charge distributions: Revisiting the Coulomb fission of dication molecular clusters.

An analytical solution describing the electrostatic interaction between particles with inhomogeneous surface charge distributions has been developed. For particles, each carrying a single charge, the solution equates to the presence of a point charge residing on the surface, which makes it particularly suitable for investigating the Coulomb fission of doubly charged clusters close to the Rayleigh instability limit. For a series of six separate molecular dication clusters, center-of-mass kinetic energy releases have been extracted from experimental measurements of their kinetic energy spectra following Coulomb fission. These data have been compared with Coulomb energy barriers calculated from the electrostatic interaction energies given by this new solution. For systems with high dielectric permittivity, results from the point charge model provide a viable alternative to kinetic energy releases calculated on the assumption of a uniform distribution of surface charge. The equivalent physical picture for the clusters would be that of a trapped proton. For interacting particles with low dielectric permittivity, a uniform distribution of charge provides better agreement with the experimental results.

The influence hydrogen atom addition has on charge switching during motion of the metal atom in endohedral Ca@C60H4 isomers.

Density functional theory has been applied in a study of charge transfer between an endohedral calcium atom and the fullerene cage in Ca@C60H4 and [Ca@C60H4](+) isomers. Previous calculations on Ca@C60 have shown that the motion of calcium within a fullerene is accompanied by large changes in electron density on the carbon cage. Based on this observation, it has been proposed that a tethered endohedral fullerene might form the bases of a nanoswitch. Through the addition of hydrogen atoms to one hemisphere of the cage it is shown that, when compared with Ca@C60, asymmetric and significantly reduced energy barriers can be generated with respect to motion of the calcium atom. It is proposed that hydrogen atom addition to a fullerene might offer a route for creating a bi-stable nanoswitch that can be fine-tuned through the selection of an appropriate isomer and number of atoms attached to the cage of an endohedral fullerene.This article is part of the themed issue 'Fullerenes: past, present and future, celebrating the 30th anniversary of Buckminster Fullerene'.

Growth of single-layer boron nitride dome-shaped nanostructures catalysed by iron clusters.

We report on the growth and formation of single-layer boron nitride dome-shaped nanostructures mediated by small iron clusters located on flakes of hexagonal boron nitride. The nanostructures were synthesized in situ at high temperature inside a transmission electron microscope while the e-beam was blanked. The formation process, typically originating at defective step-edges on the boron nitride support, was investigated using a combination of transmission electron microscopy, electron energy loss spectroscopy and computational modelling. Computational modelling showed that the domes exhibit a nanotube-like structure with flat circular caps and that their stability was comparable to that of a single boron nitride layer.