Quantum control of the electronic and thermal properties of Fullerenes and Exohedral Fullerenes

Almutlaq, Nasser and Lambert, Colin (2018) Quantum control of the electronic and thermal properties of Fullerenes and Exohedral Fullerenes. PhD thesis, Lancaster University.

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In recent years, driven by the need to downsize to the molecular level, advances in technology has made the manufacture of nanoscale devices possible. In this thesis I will investigate the theoretical electronic and thermal properties of a carbon based class of nanoscale materials by examining the possibility of using fullerenes and decachlorofullerenes as building blocks towards viable molecular scale devices. In particular I have looked at ways to enhance the electronic communication between fullerenes through introducing exohedral varients, which I found to have a positive effect on the electronic and thermoelectric properties. The methods used in this work are based on density functional theory, combined with quantum transport calculations using Greens functions. Fullerenes are promising building blocks for nano-scale electronics, as they have relatively large spherical surface area and are geometrically symmetric. If fullerenebased thermoelectricity is to become a viable technology, then fullerenes exhibiting both positive and negative Seebeck coefficients will be needed and therefore I also calculate the thermoelectric properties of the naturally occurring fullerene C60 known as the buckyball together with an exohedral example namely C50Cl10. C60 is known to have a negative Seebeck coefficient of S which varies in the range of - 18 to -23 µV/K and therefore in this thesis I address the challenge of identifying a fullerene with a positive-Seebeck-coefficient. I investigated the thermoelectric properties of single-molecule junctions of the exohedral fullerene C50Cl10 connected to gold electrodes and found that it has a positive Seebeck coefficient. Furthermore, in common with C60, the Seebeck coefficient can be increased by placing more than one C50Cl10 in series. For a single C50Cl10, I find S=+8 µV/K and for two C50Cl10’s in series I find S=+30 µV/K. I also find that the C50Cl10 monomer and dimer have power factors of 0.5×10-5 W/m.K2 and 6.0×10-5 W/m.K2 respectively. These results demonstrate that exohedral fullerenes could provide a new class of thermoelectric materials with desirable properties, which complement those of all-carbon fullerenes, thereby enabling the boosting of the thermovoltage in all-fullerene tandem structures. I calculate the structural and electronic and thermoelectrics properties of carbon nanotube peapods. In contrast with carbon-only peapods, the magnitude of this effect is sensitive to the orientation and spacing of the fullerenes and exohedral fullerenes as a consequence, a rotation or translation of the C50Cl10 can cause the zero-bias electrical conductance to switch, as a result of that the new possibilities of engineering the transport properties of carbon nanotube peapods.

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Thesis (PhD)
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06 Jun 2018 10:38
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16 Jul 2024 05:42