Nonequilibrium electron charging in carbon-nanotube-based molecular bridges

We evidence the importance of electron charging under nonequilibrium conditions for carbon-nanotube-based molecular bridges, using a self-consistent Green's function method with an extended Huckel Hamiltonian and a three-dimensional Poisson solver. Our analysis demonstrates that such feature is highly dependent on the chirality of the carbon nanotube as well as on the type of the contact metal, conditioning in a nongeneralized way the system's conduction mechanism. Based on its impact on transport, we argue that self-consistency is essential for the current-voltage calculations of semiconducting nanotubes, whereas less significant in the case of metallic ones.Comment: 4 pages, 4 figure

Atomistic quantum transport modeling of metal-graphene nanoribbon heterojunctions

We calculate quantum transport for metal-graphene nanoribbon heterojunctions within the atomistic self-consistent Schr\"odinger/Poisson scheme. Attention is paid on both the chemical aspects of the interface bonding as well the one-dimensional electrostatics along the ribbon length. Band-bending and doping effects strongly influence the transport properties, giving rise to conductance asymmetries and a selective suppression of the subband formation. Junction electrostatics and p-type characteristics drive the conduction mechanism in the case of high work function Au, Pd and Pt electrodes, while contact resistance becomes dominant in the case of Al.Comment: 4 pages, 5 figure

Theoretical study of the role of metallic contacts in probing transport features of pure and defected graphene nanoribbons

Understanding the roles of disorder and metal/graphene interface on the electronic and transport properties of graphene-based systems is crucial for a consistent analysis of the data deriving from experimental measurements. The present work is devoted to the detailed study of graphene nanoribbon systems by means of self-consistent quantum transport calculations. The computational formalism is based on a coupled Schrödinger/Poisson approach that respects both chemistry and electrostatics, applied to pure/defected graphene nanoribbons (ideally or end-contacted by various fcc metals). We theoretically characterize the formation of metal-graphene junctions as well as the effects of backscattering due to the presence of vacancies and impurities. Our results evidence that disorder can infer significant alterations on the conduction process, giving rise to mobility gaps in the conductance distribution. Moreover, we show the importance of metal-graphene coupling that gives rise to doping-related phenomena and a degradation of conductance quantization characteristics

Bending-active plates : strategies for the induction of curvature through the means of elastic bending of plate-based structures

Commonly referred to as bending-active, the term has come to describe a wide variety of systems that employ the large defor-mation of their constituent components as a primary shape-forming strategy. It is generally impossible to separate the struc-ture from its geometry, and this is even more true for bending-active systems. Placed at the intersection between geometry, de-sign and engineering, the principle objective of this thesis is to develop an understanding of the structural and architectural po-tential of bending-active systems beyond the established typolo-gies which have been investigated so far. The main focus is set on systems that make use of surface-like elements as principle build-ing blocks, as opposed to previous and existing projects that pre-dominantly employed linear components such as rods and laths. This property places the analysed test cases and developed proto-types within a specific category of bending-active systems known as bending-active plate structures. The first chapters serve as a general introduction to the topic. An overview of relevant recent projects is presented in the introduction, followed by a discussion on the scope of research on bending-active structures. The following chapters lay the theoretical basis in terms of geometry of surfaces and mechanical behaviour of plates. This dual and complementary description serves as the necessary background to understand the limits and potential associated to the deformability of plate elements. The following chapter delves into the first of the two strategies developed as part of this research. Termed form conversion, this approach establishes a one-to-one relationship between the initial base surface and its bending-active discrete counterpart. The chapter proceeds with the presentation of a series of full-scale prototypes that were realised to test the validity of the form con-version approach. Geometrical and mechanical features are dis-cussed in the conclusion of the chapter. The second developed method, named integral approach, is pre-sented in the next section. This approach takes advantage of the inherent deformation properties of explicitly designed material patterns. The description of the method is followed by the presen-tation and discussion of the prototypes chosen to test the integral approach. Finally, the thesis concludes with a critical discussion of the presented approaches and a discussion on potential developments for future research

Electron backscattering from stacking faults in SiC by means of \textit{ab initio} quantum transport calculations

We study coherent backscattering phenomena from single and multiple stacking faults (SFs) in 3C- and 4H-SiC within density functional theory quantum transport calculations. We show that SFs give rise to highly dispersive bands within both the valance and conduction bands that can be distinguished for their enhanced density of states at particular wave number subspaces. The consequent localized perturbation potential significantly scatters the propagating electron waves and strongly increases the resistance for $n$-doped systems. We argue that resonant scattering from SFs should be one of the principal degrading mechanisms for device operation in silicon carbide.Comment: 5 pages, 4 figure

Announcement of a special virtual issue on the EuroGRAPHENE program

The Carbon journal is pleased to announce the publication of a virtual special issue on research funded by the EuroGRAPHENE program of the European Science Foundation. In order to ensure rapid publication, the contributed primary research articles have already appeared in regular Carbon volumes over the course of 2014, and are now compiled together as a virtual special issue on the journal website.1 The present article by our team of guest editors serves as an introduction to this special issue, and also a commentary on the graphene field and the important role played by the EuroGRAPHENE program