Al-Galiby, Qusiy and Lambert, Colin (2016) Quantum theory of sensing and thermoelectricity in molecular nanostructures. PhD thesis, Lancaster University.
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Abstract
This thesis presents a series of studies into the electronic and thermoelectric properties of molecular junction single organic molecules: They include perylene Bisimide (PBIs), naphthalenediimide (NDI), metallo-porphryins and a large set of symmetric and asymmetric molecules. Two main techniques will be included in the theoretical approach, which are Density Functional Theory, which is implemented in the SIESTA code [1], and the Green’s function formalism of elctron transport (Chapter 2), which is implemented in the GOLLUM code [2], it is a next-generation code, born out of the non-equilibrium transport code SMEAGOL code [3]. Both techniques are used to extensively to study a family of perylene bisimide molecules (PBIs) (Chapter 3) to understand the potential of these molecules for label-free sensing of organic molecules by investigating a change in the electronic properties of PBI derivatives. Also, these techniques are used to simulate electrochemical gating of a single molecule naphthalenediimide (NDI) junction (Chapter 4) using a strategy to control the number of electrons on the molecule by modelling different forms of charge double layers comprising positive and negative ions. Chapter 5 will deal with the thermoelectric properties of the single organic molecule. I will demonstrate that varying the transition metal-centre of a porphyrin molecule over the family of metallic atoms allows the molecular energy levels to be tuned relative to the Fermi energy of the electrodes and that leads to the ability to tune the thermoelectric properties of metallo-porphryins. Chapter 6 will present our new approach to materials discovery for electronic and thermoelectric properties of single-molecule junctions. I will deal with a large set of symmetric and asymmetric molecules to demonstrate a general rule for molecular-scale quantum transport, which provides a new route to materials design and discovery. The rule of this approach that “the conductance of an asymmetric molecule is the geometric mean of the conductance of the two symmetric molecules derived from it and the thermopower of the asymmetric molecule is the algebraic mean of their thermopowers”.