A first-principles investigation on substitutions in the carbon allotropes glitter and graphene

Baldissin, G

Abstract

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.

Citation

Baldissin, G. A first-principles investigation on substitutions in the carbon allotropes glitter and graphene. (Thesis). University of Salford

• Thesis Type: Thesis
• Deposit Date: Jun 28, 2014
• Publicly Available Date: Jun 29, 2016
• Additional Information: Funders : Engineering and Physical Sciences Research Council (EPSRC);GTA scheme