Miller, Abigail
(2022)
Computational design of electrostatically stable endohedral fullerene superlattices.
PhD thesis, University of Nottingham.
Abstract
Fullerenes and their clusters exhibit a diverse range of interesting electronic, magnetic, structural and chemical properties. This work looks at using an analytical model to give a sound physiochemical description of multiply charged fullerene clusters. Using the model introduced by Lindgren et al. in 2018, based upon the solution proposed by Bichoutskaia et al. in 2010, with added considerations of the dispersion effects, we can better understand the mechanisms of fullerene aggregate behaviour in a less computationally expensive manner. We provide an insight into the aggregation and fragmentation processes occurring in experiment and reproduce the results for minimum stable cluster sizes that have been seen experimentally. Finally, we draw predictions on clusters with charges not yet modelled computationally.
Alongside fullerene clusters, the assembly of nanoparticles of two different materials into Binary Nanoparticle Superlattices (BNSL) has been proven to be a cheap and effective route to producing a wide variety of materials with properties desirable for use in novel applications. Experiments have shown that the presence of charge is integral to the formation of ordered arrays. However, analysis of the forces responsible have been limited to pairwise interactions. To control the structure and morphology of novel BNSL structures, an in depth understanding of the forces responsible for long-range order are required. Here, our many-body electrostatic solution has been applied to seven frequently observed superlattice structures and has shown that multipolar interactions contribute significantly to lattice energy and thus stability. Additionally, a combination of AB and AB2 BNSL structures, which have not been observed experimentally, are modelled in order to investigate whether many-body electrostatic interactions are sufficient to stabilise such structures. Coulombic and multipolar contributions to the interaction energy are investigated as a function of component ratio, allowing a comparison between the value of the minimum electrostatic energy to that found at the maximum packing fraction in hard-sphere theory.
Ultimately, nanoparticle lattices and endohedral fullerenes have both been identified as potential building blocks for future electronic, magnetic and optical devices. Here it is proposed that it could be possible to combine those concepts and design stable nanoparticle lattices composed of binary collections of endohedral fullerenes. The inclusion of an atom, for example Ca or F, within a fullerene cage is known to be accompanied by a redistribution of surface charge, whereby the cage can acquire either a negative (Ca) or positive (F) charge. It is predicted that certain binary combinations could result in the formation of stable nanoparticle lattices with the familiar AB and AB2 stoichiometries. Much of the stability is due to Coulomb interactions, however, charge-induced and van der Waals interactions, which always enhance stability, are found to extend the range of charge on a cage over which lattices are stable. An extension of the calculations to the fabrication of structures involving endohedral C84 is also discussed.
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