Hart, Martin; (2019) Filling Single-Walled Carbon Nanotubes with Highly Reactive Chemicals. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Since the discovery of single-walled carbon nanotubes (SWCNTs) in 1993, there has been a deep fascination with the 1D (one dimensional) nanometre sized cavity that they possess. Having the ability to confine all manner of materials in such a small space had never been possible before, and the surge of new allotropes and chemicals that have either been grown or encapsulated in this nano-test tube has been staggering. Salts and elements have formed the bulk of the confined materials, but chemistry has also been achieved within the cavity, and the reduction of metal oxides has proven straightforward. Consistency in filling SWCNTs in high yields has been difficult to achieve and finding a routine technique that can ascertain a filling yield have been stumbling blocks for the research area. No standard definition of the filling yield has even been agreed upon. These issues have held the field back from becoming a more popular and viable method for enhancing the properties of SWCNTs. To combat some of these issues, this thesis uses consistent and simple practices to determine the filling yield and aims to make consistently high purity materials which can be used for novel purposes. Elemental phosphorus, arsenic and antimony have all been confined within a range of SWCNTs and have been fully characterised to determine their properties. Tetrahedral phosphorus and arsenic molecules have been stabilised by this method in quantities higher than achieved using other techniques. These can be produced either from melt reactions or vapour phase fillings which confirms that these elements fill the voids of the SWCNT in the form of tetrahedral molecules. The confined phosphorus and arsenic tetrahedra have been shown form two new allotropes namely the zigzag ladders and single zigzag chains. These are expected to form either from thermal excitation or when exposed to an electron beam during high resolution transmission electron microscopy (HRTEM). The structure produced is dependent on the diameter of nanotube and has shown consistent results with what is predicted by DFT calculations. There seems to be some dynamic behaviour at play between the conversion of the allotropes due to the small activation energy calculated for transitioning between the structures. SWCNTs have also been filled with aluminium iodide, a strong Lewis acid, in order to induce charge transfer effects. A reliable method of producing high purity samples was developed and Raman spectroscopy has shown that these materials show chargetransfer in the correct direction. Unfortunately, despite the enhanced properties of the SWCNTs, the samples were found to be no more effectively functionalised than their empty counterparts.

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