Computational study of interfaces and edges of 2D materials

Abstract

The discovery of graphene and its intriguing properties has given birth to the field of two-dimensional (2D) materials. These materials are characterized by a strong covalent bonding between the atoms within a plane, but weak, van derWaals, bonding between the planes. Such materials can be isolated as single or few atomic layers, or controllably grown by van der Waals epitaxy. Graphene has no band gap, but other 2D materials are natural semiconductors, such as the (group VI) transition metal dichalcogenides (TMDs) MX2, M = Mo;W, X = S; Se;Te. As the band gap of single layers of these TMDs is direct, they attract a large interest because of their potential applications in opto-electronics. This thesis concerns interfaces and edges of TMDs. It can be divided into two major parts. The first part, chapters 2,3, and 4, deals with the interfaces between these materials and metal contacts, which play a crucial role in the successful operation of electronic devices. In part two, chapters 5 and 6, we focus on the edges of 2D TMDs. Whereas the interior is semiconducting, many TMD edges are metallic and show a rich structure of electronic states with energies in the band gap. The metallicity is localized at the first few atomic rows along the edges, and it has one-dimensional character.