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Title: A first-principles investigation on substitutions in the carbon allotropes glitter and graphene
Author: Baldissin, G.
Awarding Body: University of Salford
Current Institution: University of Salford
Date of Award: 2013
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In the literature, a number of syntheses of carbon materials under extreme condition exhibit the presence of a carbon phase, called n-diamond, whose crystal structure remains unclear. Several crystallographic arrangements have been proposed, which are critically assessed in this work with regards to dynamical stability. It is shown that tetragonal carbon (glitter) is the only structure that satisfies this criterion. Glitter is a metallic 3-, 4-connected allotrope containing 1,4-cyclohexadieneoid units, giving a high energy meta- stable phase. Applying a fully first principles approach, which couples den- sity functional theory (DFT) calculations and Ising-like parameterisation, the possibility of stabilising the structure with nitrogen, boron and silicon substitutions has been investigated, finding that there are arrangements with negative formation energy. These novel arrangements have been tested for vibrational stability, whereby it has been proven that they are dynamically stable. Moreover a bandgap opens, leading to semiconductor bulk materials based on Si, C, B and N. Graphene, a carbon allotrope having the so-called chicken-net structure, is a zero-bandgap semiconductor, which make it promising for nano-electronic applications. However tuning and modifying the bandgap would expand the range of possible applications, in particular for post-silicon transistors. The effect of B substitutions in the graphene lattice has been studied, in terms of stability and electronic structure. The doping at low B concentration has been studied with a direct DFT approach while the effect at higher concentration has been studied with the above-mentioned coupled approach. Novel arrangements, that have semiconductor behaviour, have been proven to be dynamically stable at 0 K. The effect of a second B-C layer has also been investigated, finding that is effective on bandgap tuning.
Supervisor: Not available Sponsor: Engineering and Physical Sciences Research Council (EPSRC) ; GTA scheme
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Energy