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Halstead, M. J. (2023) Computational Study on Polarisation Behaviour of Functionalised Endohedral Metallofullerenes. PhD thesis, University of Nottingham.

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Abstract

This work focused on investigating the potential for selected functionalised endohedral metallofullerene isomers to be viable candidates for a molecular polarisation switch, with a particular focus on the Ca@C60 system. This work combines classical electrostatic analysis and Density Functional Theory (DFT) to investigate the correlation between the encapsulated calcium metal ion position and distribution of surface charge that results in polarisation on the fullerene cage. In addition, the modification of internal potential energy barriers through functionalisation of the fullerene cage was investigated as a route to developing a bistable polarisation switch.

A classical electrostatic analysis of a point charge within a dielectric sphere was undertaken to produce an analytical solution describing how the surface charge polarisation responds to the precise position of an encapsulated point charge. The analytical solution shows that for a positive point charge, the surface charge is attracted to the positive calcium ion as it is displaced across the fullerene cage, “following” the point charge across the cage. This was verified through DFT calculations on the Ca@C60 system. This analytical solution was then extended to present an analytical solution for the case of a dipole inside an endohedral fullerene, verified through DFT calculations on HF@C60.

Hydrogenated and fluorinated functionalised C60 candidates were selected for testing on the basis that these molecules could be experimentally produced with a reasonable degree of isomer specificity and selection. DFT computational parameters were rigorously tested against experimental evidence to ensure the calculations were “fit-for-purpose” using these parameters. DFT calculations provided insight into how functionalisation affects the internal potential energy barriers experienced by the encapsulated calcium. In particular, how an energy gap is created between minima in the Mexican-hat potential and how increasing degrees of functionalisation impact the position of the energy barriers within the fullerene cage. Partial charge analysis clearly demonstrated that the motion of the encapsulated calcium, confined within the selected functionalised fullerene cages, was strongly correlated to the distribution of charge density on the cage surface, with measurements of changes in surface charge polarisation.

Comparing and contrasting the candidate hydrogenated and fluorinated endohedral fullerenes against specific switching criteria enabled the selection of 1,2-Ca@C60H2 as the most promising candidate to develop a polarisation switch – a high yield functionalised endohedral fullerene with a sufficient and minimally shifted energy barrier and energy gap between minima that leads to a clearly defined change in surface charge polarisation. A potential route to scalability is discussed, through the creation of stable binary endohedral fullerene lattices that could lead to novel large-scale molecular switching arrays and nanomaterials with novel optical and electronic properties.

Item Type:	Thesis (University of Nottingham only) (PhD)
Supervisors:	Besley, E. Stace, A.
Keywords:	metallofullerenes, molecular electronics
Subjects:	Q Science > QC Physics > QC501 Electricity and magnetism Q Science > QD Chemistry > QD450 Physical and theoretical chemistry T Technology > TK Electrical engineering. Electronics Nuclear engineering > TK7800 Electronics
Faculties/Schools:	UK Campuses > Faculty of Science > School of Chemistry
Item ID:	74167
Depositing User:	Halstead, Matthew
Date Deposited:	06 Jun 2024 10:39
Last Modified:	06 Jun 2024 10:39
URI:	https://eprints.nottingham.ac.uk/id/eprint/74167

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