Doctor of Philosophy
Michael G. Cottam
A fundamental study of the electronic and magnetic properties of graphene modified by defects is presented. This work includes both theoretical and experimental investigations of graphene, graphene-metal composites and related structures, together with edge effects. The theoretical model employed for the description of p-electrons in graphene is based on the tight-binding Hamiltonian. On the experimental side we place special emphasis on the electron spin resonance technique (ESR).
After describing the theoretical and experimental methods, we first investigate the origin of paramagnetism in graphene nanoribbons (GNRs) using a combination of ESR and other characterisation techniques, corroborated by a theoretical model. We find two paramagnetic species in our GNRs related to structural defects. Subsequently, interactions between magnetic species, introduced in GNRs as impurities are investigated. These are RKKY-type indirect exchange interactions involving the p-electrons in graphene. The influence of zigzag edges on the RKKY interaction is looked at in detail by using a Green's function method for the bulk and edge modes of GNRs. We also study the influence of metal nanoparticles on the electronic properties of graphene thin films. Specifically, we focus on copper nanoparticles (Cu-NPs), which are expected to form weak bonds with graphene preserving its electronic properties. We introduce a doping mechanism for this system related to the electron-hole symmetry breaking of the electronic band in graphene when its surface is decorated with Cu-NPs. Additional discussion on the paramagnetic nature of other materials, including Au25+ molecular nanoclusters and defects in silicon epilayers are provided. These investigations focus on the ESR techniques and relevant theoretical models for interpreting the data.
Akbari-Sharbaf, Arash, "Defect-Related Magnetic and Electronic Properties of Graphene" (2014). Electronic Thesis and Dissertation Repository. 2441.