Declerck, Xavier
[UCL]
(eng)
Graphene has been at the center of a tremendous research effort since its clear identification in 2004 by Andre Geim and Konstantin Novoselov. As a proof of the outstanding interest in graphene, Geim and Novoselov were awarded with the Nobel Prize in Physics in 2010, six years only after their seminal work. This interest is driven by the innovative character of graphene and its extraordinary combination of properties, unmatched by any other material known so far. Graphene is a two-dimensional one-atom thick layer of carbon. In-plane, it posseses one of the largest bond-strength (stronger than diamond), while keeping a high out-of-plane flexibility. Along with its mechanical properties, graphene exhibits exceptional chemical and optical properties. However, the most fascinating properties are undoubtedly its electronic properties. Electrons in graphene behave like massless particles, leading to new behaviors in condensed matter physics. In addition, graphene is a zero band gap semiconductor, meaning the conduction and valence band meet at exactly one single point. Finally, graphene exhibits very high electron mobilities, which are of particular interest for future electronic devices. As in conventional electronics, different ways to tailor the properties of graphene are currently under investigation (i.e. by altering locally its atomic structure or by incorporating foreign atoms in the carbon network) in order to create new specific devices for a large set of various
applications.
The discovery of graphene initiated the research in other two-dimensional materials, among which the single sheet of boron nitride (BN). The latter shares with graphene analogous geometry but its electronic properties are drastically different. Indeed, a single layer of BN is an insulating material. More recently, interest has grown in combining graphene together with BN, using either boron nitride as a passive material (substrate, encapsulation), or as an active system to create a new range of properties, differing from the ones of the pristine components.
The present thesis investigates the properties of graphene and boron nitride nanostructures within the framework of density functional theory. Firstly, point defects as well as lines of defects are introduced in graphene. Their influence on the transport properties of graphene are estimated and transport fingerprints are predicted for each specific defect. Secondly, the doping of graphene by incorporation of boron and nitrogen atoms is examined. More specifically, scanning tunneling microscopy images are simulated in order to identify specific defects in experiments. Then, the electronic transport properties of BN-graphene composites are investigated and amazing spin filtering properties are evidenced. Finally, the electronic properties of graphene misorientedly stacked on a BN substrate are presented, evidencing, as observed experimentally, little alteration of the electronic properties of suspended
graphene. These calculations suggest the BN single layer to be the ideal substrate for future graphene-based electronics.
Bibliographic reference |
Declerck, Xavier. Electronic and transport properties of boron nitride and graphene-based nanostructures. Prom. : Charlier, Jean-Christophe |
Permanent URL |
http://hdl.handle.net/2078.1/125510 |