Quantum transport in molecular junctions and graphene based nanostructures

(eng) Till recently, graphene was nothing but a theoretical concept. Nevertheless, a couple of years ago, researchers managed to actually prepare graphene samples. Owing to its unusual electronic properties and great promises for applications in nanoelectronics, this two-dimensional material has stirred a huge excitement in the scientific community. However, graphene is a zero-gap semiconductor preventing its use in most of field controlled applications such as field-effect transistors (FETs). Many efforts are therefore devoted to the patterning and characterization of graphene quantum dots and nanoribbons in which energy gaps may open due to the electronic confinement imposed by the edges. In this dissertation, the electronic and transport properties of graphene and graphene nanoribbons are explored by means of ab initio techniques. Special attention is devoted to the impact of topological imperfections, such as point-defects and edge reconstructions. In particular, we provide theoretical clues about the most stable defect topologies and we unveil the mechanisms that rule their electronic structure, chemical reactivity and scattering properties. Our forecasts are expected to be observed experimentally.