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Title: Design a novel methodology for the goal-directed control of epitaxial graphene fabrication
Authors: Issakov, Nikolai
Advisors: Makatsoris, C
Keywords: Carbide dervied carbon;Epitaxial growth
Issue Date: 2013
Publisher: Brunel University School of Engineering and Design PhD Theses
Abstract: The elusive 2D carbon poly-type was argued more than 70 years ago. Meanwhile, the recent discovery of graphene has proved that such materials can indeed be obtained and are thermodynamically stable. Graphene has demonstrated the unique properties that lead to many innovations in laboratory conditions. However, the current approaches available for the industrial fabrication yield the low graphene quality against the theoretical predictions. Furthermore, any graphene combination with the supporting units causes a newly-induced quality for adaptation to the other condensed matters. Therefore, the unusual ability for sensitive alteration in the external world has turned into a regulation for intended graphene engineering. The submitted investigation has been undertaken to elaborate a novel methodology for the goal-directed control of epitaxial graphene fabrication by using interaction design. This is the most perspective pathway to scale-up production of intended quality subjected to the manufacturing of novel carbide derived carbon (CDC) patterns via interaction with specific substrates under hydrogen halides impact. The graphene layers and structural arrangement of the composite systems, as well as their electronic properties depend on the particular substrate, coherent commensuration of the adjacent units, interaction between them and the physical environment of fabrication. It is crucial to understand the interaction processes leading to stable construction. Density Functional Theory (DFT) implemented in the CASTEP system has been employed in this research in order to develop this knowledge and also to determine how to tune and engineer the band gaps of such composite assemblies. The substrate alternating reconstructions, polarity of surface terminations, commensuration and number of layers, their stacking order and distances between constituting units are taken into consideration for intended simulation. The (3x3) and (√3x√3) reconstructions of 4H-SiC poly-type are the starting points for epitaxial growth (EG) on the Si-face and C-face unit cells. The results of the substrate induced interaction are interpreted via the versatility of band states gradually traced from the dehydrogenated SiC framework to CDC bi-layer. The distinctive feature resulted from the substrate influence is kept as the transitional band for different arrangements and locations in vicinity of the Fermi level. The first buffering C-plane reinforces substrate distinctions between the initial configurations and polarities. The n-type of gap state is the characteristic of the Si-face termination, whereas, the p-type is found for the C-face case. Both structures are devoid of the freestanding graphene signs. The appropriate indications of dominant graphene identity are found for the (0001) - (√3x√3) substrate only, at a close distance between two upper C-planes acceptable for covalent bonds. As for graphene EG the chemical conversion by using fluorination is employed to avoid the possible damage inspired by initial substrate roughness. The few layered CDC assemblage on the (0001) - (√3x√3) support is trailed via gradual Si – F interaction and SiFx groups penetrating through the bulk. Regular control over potential energy surfaces, minimal energy pathways, transition states and activation barriers enable the indicative indexes for reaction credibility and progress. By means of the Arrhenius equation using the activation energy values the average temperature of 1500 - 2000 C are predicted for the real conversion events. Under these conditions the wet surface etching for the topmost Si-atoms and release of oxidised CDC are accompanied with a complementary promotion mechanism which resulted in a highly ordered graphene structure.
Description: This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.
Appears in Collections:Electronic and Computer Engineering
Dept of Electronic and Computer Engineering Theses

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