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Molecular Doping of Graphene Based Materials.

Samuels, Alexander James. (2013) Molecular Doping of Graphene Based Materials. Doctoral thesis, University of Surrey (United Kingdom)..

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Abstract

Carbon is one of the most versatile materials available to man, for hundreds of years the 3D forms of carbon (diamond and graphite) have been exploited for their electrical and physical properties, however only in recent decades have the OD (fullerenes), 1D (nanotubes) and 2D (graphene) forms of carbon been available to study and use for new technologies. The experimental realisation of single layer (SLG) and few layer (FLG) graphene has led to an explosion of interest in the properties and capabilities of this material. Although single layer graphene had been considered theoretically a number of years earlier, it had long been the consensus that a single atom thick material would not be stable in the free state. The work presented here focuses on the electronic properties of single and bilayer graphene and the possibility to tune these properties using the adsorption of various molecules on the surface of a graphene layer. With the use of ab initio density functional theory calculations this thesis describes the interaction of a number of small inorganic molecules, metallocene molecules and organic molecules with single and bilayer graphene. We find that small inorganic molecules generally bind to graphene with low binding energies of 0.1 - 0.2 eV, inducing moderate electron charge transfers of up to 0.07 e/molecule with minimal changes to the band structure of graphene in most cases. Meanwhile organic and metallo-organic molecules are found to exhibit higher binding energies of 0.4 - 1.7 eV due to strong π-π stacking interactions, resulting in permanent doping and high charge transfers of up to 0.52 e/molecule. Organic molecules are also found to alter the band structure of graphene through band hybridisation between graphene’s π electron bands and the impurity bands associated with the frontier orbitals of the molecules in the vicinity of the Dirac point. In the case of bilayer graphene (BLG), the asymmetrical distribution of electron charge between the top and bottom layers as a result of molecular doping is found to be of particular importance with regard to tuning the band gap of BLG and hence the allowed optical transitions. 3,6-difluoro-2,5,7,7,8,8-hexacyano-quinodimethane (F2-HCNQ, p-type) and decamethyl-cobaltocene (DMC, n-type) are found to be the best molecules at inducing band gaps of up to 0.15 eV, while the dopant modified band structure allows optical transitions in the important atmospheric range of 2.7 - 4.8 pm. Finally, dual sided doping with DMC and F2-HCNQ is found to result in a large band gap of up to 0.25 eV.

Item Type: Thesis (Doctoral)
Divisions : Theses
Authors : Samuels, Alexander James.
Date : 2013
Additional Information : Thesis (Ph.D.)--University of Surrey (United Kingdom), 2013.
Depositing User : EPrints Services
Date Deposited : 14 May 2020 14:03
Last Modified : 14 May 2020 14:06
URI: http://epubs.surrey.ac.uk/id/eprint/856409

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