Electronic properties of graphene from tight-binding simulations

Andreas Uppstu

Research output: ThesisDoctoral ThesisCollection of Articles

Abstract

Graphene is an effectively two-dimensional semimetallic material consisting of a sheet of carbon atoms arranged in a hexagonal lattice. Due to its high electron mobility and special electronic properties, it is considered to be a promising candidate for various future electronic applications. Freestanding graphene was discovered as late as in 2004, but since then it has become the focus of numerous studies, sparking not only scientific but also significant commercial interest. Realizing the potential of the material requires both theoretical, numerical, and experimental studies. An important computational model for studying the electronic properties of graphene is the so-called tight-binding (TB) model. In the TB model, the charge carriers of a material are described using effective parameters, which can be either derived from more complex models or fitted to experimental or computational results. In this Thesis, the TB model was used to study both the local density of states (LDOS) of graphene as well as electronic transport in graphene. Simulating the LDOS of graphene is important, since it may be more or less directly measured using scanning tunneling microscopy (STM), and is thus extremely helpful for characterizing the properties of nanometer-sized graphene samples. The results presented in this Thesis, which show good agreement between simulations and STM measurements, help to determine the electronic structure of graphene quantum dots on various substrates. Simulations of electronic transport aid in making graphene useful for semiconductor applications. Graphene may be turned semiconducting by various means, such as by cutting it into ribbons or by adding disorder. In this Thesis, it was showed how scaling theory can be utilized to obtain the conductance of a mesoscopically sized disordered graphene device using first-principles-based results and how the localization length of the charge carriers can be obtained effectively using the so-called Kubo-Greenwood method. The results aid in interpreting experimental conductance measurements and in estimating how strong disorder is required to turn graphene into an effective semiconductor.
Original languageEnglish
QualificationDoctor's degree
Awarding Institution
  • Aalto University
Supervisors/Advisors
  • Nieminen, Risto, Supervisor
  • Harju, Ari, Advisor
Publisher
Print ISBNs978-952-60-5814-6
Electronic ISBNs978-952-60-5815-3
Publication statusPublished - 2014
MoE publication typeG5 Doctoral dissertation (article)

Keywords

  • graphene
  • tight-binding
  • electronic transport
  • scanning tunneling microscopy

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