First-principles investigation of functionalization of graphene
Author
Korkmaz, Yaprak
Advisor
Gülseren, Oğuz
Date
2013Publisher
Bilkent University
Language
English
Type
ThesisItem Usage Stats
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Abstract
The graphene sheet is a single-atom thick novel material and attracts great
interest due to its unique features. However, it is a metallic material with no
bandgap, which makes it difficult to integrate in electronic applications. Adatom
adsorption is one of the promising ways to make this structure functional. To
this end, electronic and structural properties of graphene have been investigated
by using density functional theory formalism in order to understand atomic level
interaction between halogen adatoms and graphene layer. The most common
adatom, hydrogen, has also been studied. In this study, plane-wave, pseudopotential
density functional theory calculations were carried out using generalized
gradient approximations for the exchange correlation potential with the Quantum
Espresso package. In order to obtain fully relaxed structures, geometry optimization
has been performed in all of the calculations. The adatom-graphene system
is modelled with a 4 × 4 graphene supercell. Adsorption energies of halogen
adatoms and dimers adsorbed on highly symmetric positions on graphene layer
are calculated. Different configurations of adatoms have been tested. Specific
properties such as band structure and density of states of these system have been
investigated. The results show that a fully covered graphene layer is stable and
optimized structures exhibit a band gap of a few eV. The most stable structure
among halogen adatoms is the fluorine adsorbed on graphene. It has the highest
electronegativity, which is the reason for high electron transfer from the graphene
layer. This is the reason of the formation of covalent bonds. Furthermore, the
most stable configuration is found to be chair configuration with the halogen
atoms alternating in both sides of the layer.