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Influence of hydrogen on the electronic structure of grain boundaries in graphene

Perera, Delwin (2017):
Influence of hydrogen on the electronic structure of grain boundaries in graphene.
Darmstadt, TU Darmstadt, [Master Thesis]

Abstract

Graphene is regarded as a promising successor of silicon in many areas of electronics. A particularly interesting application possibility is a graphene-based strain sensor, which could be used for touch screen devices replacing indium-tin-oxide. During the last years, several theoretical studies have proposed that grain boundaries significantly influence the electronic properties of graphene and that strain can modulate this impact. A recent experimental study has shown a piezoresistive effect of nano-crystalline graphene, a system where grain-boundary effects are expected to be significant. Motivated by these works, we study in this thesis the influence of grain boundaries on the atomic and electronic structure of graphene using molecular dynamic simulations and density functional theory calculations. Moreover, we investigate how hydrogen adsorption on the grain boundary affects the electronic structure. In our work we find that annealing of the grain boundary leads to severe corrugation of the graphene sheets. Furthermore, we demonstrate that hydrogen adsorption is thermodynamically favourable and may lead to partial hydrogenation of grain boundaries. Our electronic-structure calculations indicate a semi-metallic or metallic character for all considered grain boundaries. In particular, no band-gap opening has been found for the asymmetric (5,0)|(3,3)grain boundary. While this seems to be in conflict with previous studies, a more recent work appears to substantiate our findings. Furthermore, we find strong indications that hydrogen adsorption does not provide a mean to open up band-gaps, but rather increases the conductivity. Thus, our work suggests that the experimentally observed piezoresistive behaviour of nano-crystalline graphene cannot be assigned to a direct grain boundary effect.

Item Type: Master Thesis
Erschienen: 2017
Creators: Perera, Delwin
Title: Influence of hydrogen on the electronic structure of grain boundaries in graphene
Language: English
Abstract:

Graphene is regarded as a promising successor of silicon in many areas of electronics. A particularly interesting application possibility is a graphene-based strain sensor, which could be used for touch screen devices replacing indium-tin-oxide. During the last years, several theoretical studies have proposed that grain boundaries significantly influence the electronic properties of graphene and that strain can modulate this impact. A recent experimental study has shown a piezoresistive effect of nano-crystalline graphene, a system where grain-boundary effects are expected to be significant. Motivated by these works, we study in this thesis the influence of grain boundaries on the atomic and electronic structure of graphene using molecular dynamic simulations and density functional theory calculations. Moreover, we investigate how hydrogen adsorption on the grain boundary affects the electronic structure. In our work we find that annealing of the grain boundary leads to severe corrugation of the graphene sheets. Furthermore, we demonstrate that hydrogen adsorption is thermodynamically favourable and may lead to partial hydrogenation of grain boundaries. Our electronic-structure calculations indicate a semi-metallic or metallic character for all considered grain boundaries. In particular, no band-gap opening has been found for the asymmetric (5,0)|(3,3)grain boundary. While this seems to be in conflict with previous studies, a more recent work appears to substantiate our findings. Furthermore, we find strong indications that hydrogen adsorption does not provide a mean to open up band-gaps, but rather increases the conductivity. Thus, our work suggests that the experimentally observed piezoresistive behaviour of nano-crystalline graphene cannot be assigned to a direct grain boundary effect.

Place of Publication: Darmstadt
Divisions: 11 Department of Materials and Earth Sciences
11 Department of Materials and Earth Sciences > Material Science
11 Department of Materials and Earth Sciences > Material Science > Materials Modelling
Zentrale Einrichtungen > University IT-Service and Computing Centre (HRZ) > Hochleistungsrechner
Zentrale Einrichtungen > University IT-Service and Computing Centre (HRZ)
Zentrale Einrichtungen
Date Deposited: 19 Sep 2017 11:06
Referees: Albe, Prof. Dr. and Krupke, Prof. Dr.
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