Quantum control of the electronic and thermal properties of Fullerenes and
      Exohedral Fullerenes
Creators: name: Almutlaq, Nasser
Publisher: name: Lancaster University
Year: 2018

description: 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.