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Theoretical modelling of epitaxial graphene growth on the Ir(111)surface

Student thesis: Doctoral ThesisDoctor of Philosophy

The main problem aecting the widespread use of graphene based products is
the ability to produce high quality graphene in large quantities. One possible
method of achieving this is to grow it epitaxially. In this thesis a selection of
the important processes involved in epitaxial graphene growth are studied in
detail using density functional theory based calculations. It begins with an
investigation into the initial stages of the growth process, specically determining
the kinetics of the decomposition of ethylene on the Ir(111) surface, in
order to nd the decomposition mechanism and the resulting carbon feedstock
species that will go on to form graphene. To achieve this the energy barriers
of the relevant reactions are determined using the nudged elastic band (NEB)
method, and then the reaction kinetics are modelled using both rate equations
and a specically developed kinetic Monte Carlo code. The decomposition is
determined for a variety of dierent experimental conditions, including temperature
programmed growth and chemical vapour deposition. Broadly the
results show that the decomposition mechanism involves the breaking of the
C-C bond, resulting in the production of C monomers.
Following from this the nucleation of carbon clusters on the Ir(111) surface
from C monomers prior to graphene formation is investigated. The full, temperature
dependent work of formation is devised and calculated for a variety of
dierent cluster types. From this value it is possible to determine the critical
cluster size, where the addition and removal of C monomers is equally likely.
Based on this, small arch-shaped clusters containing four to six C atoms are
predicted to be long-lived on the surface, suggesting that they may be key in
graphene formation.
Finally the healing of single vacancy defects in graphene on the Ir(111) surface
is examined. These defects are undesirable and negatively aect the useful
properties of graphene. The attempted healing of the defects by ethylene
molecules is simulated with molecular dynamics and used to predict partially
healed structures. The energy barriers to the healing are determined using
NEB calculations. The results suggest that the vacancy defects can be healed
directly by dosing with ethylene molecules during graphene growth.
Original languageEnglish
Awarding Institution
Award date2017


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