Oxygen effects on the electronic transport in stanene.

In this work, we study theoretically the structural, electronic and transport properties of oxidized stanene using a combination of density functional theory (DFT), quantum molecular dynamics and the Landauer-Büttiker theory for the ballistic transport. Our results clearly show that oxygen adsorb onto stanene surface in both molecular or atomic forms, thus causing considerable modifications to its electronic structure and transport properties. Nevertheless, our quantum conductance calculations reveal that, in spite of oxidation, stanene still remains a good conductor that might be applied as field effect transistors, gas sensors and other devices.

BNC nanoshells: a novel structure for atomic storage.

Quantum molecular dynamics (QMD) and density functional theory are employed in this work in order to study the structural and electronic properties of carbon, boron nitride or hybrid BNC nanoshells. The studied nanoshells can be formed by stacking two zigzag graphene nanoribbons, two zigzag boron nitride nanoribbons or one zigzag graphene nanoribbon on a boron nitride nanoribbon. In all cases only one of the edges of the ribbon is passivated, while the other one is left unpassivated. Our QMD results show that these nanoribbons collapse just a few femtoseconds after the beginning of the simulation, forming a coalesced structure in the shape of a shell. Our band structure calculations revealed that this structures may be metallic or semiconductor, depending on its stoichiometry. Furthermore, a spin splitting for energies near the Fermi level is predicted for both the pure carbon and the hybrid BNC-nanoshell systems. We further show that when a transverse electric field is applied to these systems, the nanoshell structure tends to open up. This effect can lead to the application of these nanoshells for molecular storage. As a proof of concept, We investigate this storage effect for the H2 molecule.

Intense conductivity suppression by edge defects in zigzag MoS2 and WSe2 nanoribbons: a density functional based tight-binding study.

The effects of edge vacancies on the electron transport properties of zigzag MoS2/WSe2 nanoribbons are studied using a density functional theory (DFT)-based tight-binding model with a sp(3)d(5) basis set for the electronic structure calculation and applying the Landauer-Büttiker approach for the electronic transport. Our results show that the presence of a single edge vacancy, with a missing MoS2/WSe2 triplet, is enough to suppress the conductance of the system by almost one half for most energies around the Fermi level. Furthermore, the presence of other single defects along the same edge has little effect on the overall conductance, indicating that the conductance of that particular edge has been strongly suppressed by the first defect. The presence of another defect on the opposite edge further suppresses the quantum conductance, independently of the relative position between the two defects in opposite edges. The introduction of other defects cause the suppression to be energy dependent, leading to conductance peaks which depend on the geometry of the edges. The strong conductance dependence on the presence of edge defects is corroborated by DFT calculations using SIESTA, which show that the electronic bands near the Fermi energy are strongly localized at the edge.

Transport properties through hexagonal boron nitride clusters embedded in graphene nanoribbons.

First-principles calculations are employed in the study of the electronic and quantum transport properties of hexagonally shaped boron nitride (h-BN) clusters embedded in either zigzag or armchair graphene nanoribbons. Chemical doping of the h-BN cluster was taken into consideration by using carbon atoms to replace either the boron (B27N24C3) or the nitrogen (B27N24C3) sites in the central ring. While the quantum conductance of the system with zigzag edges is found to be spin-dependent, it was observed that the system with an armchair edge requires an electron imbalance in order to show a spin-dependent conductance. Furthermore, the possibility of molecular adsorption onto these doped systems is studied. The effects of the attached molecules to the quantum conductance shows the potential of these hybrid systems for molecular sensing applications.

Synthesis and characterization of selenium-carbon nanocables.

In this letter, we report the synthesis and characterization of a novel Se-C hybrid nanostructure. X-ray diffraction data indicates a high degree of crystallinity for the nanostructured Se shell. High resolution transmission electron microscopy images show that the Se-C nanostructures consist of coaxial nanocables made of single wall carbon nanotubes, as the core, surrounded by a trigonal Selenium shell. Resonance Raman spectroscopy was used to access the properties of both the carbon nanotubes and selenium. The behavior of the radial breathing mode and the G-band indicates that the Se shell primarily covers semiconducting nanotubes. X-ray photoelectron spectroscopy show that the nanocables have a thin coverage of selenium oxide. We envisage that this system could be used in the fabrication of photonic devices as an interface between electronic and photonic materials.

Cost-effectiveness of risk-reduction measures from a national viewpoint: a case study of the Angra nuclear plant in Brazil.

In this paper a systemic or national approach to cost-effectiveness analysis of risk-reduction measures is reviewed, and its advantages and limitations are discussed. The method is applied to the problem of the cost-effectiveness of increasing the Angra 3 NPP containment wall thickness from the present 60 cm to 180 cm thick in order to prevent damage to the reactor core in case of a direct commercial aircraft crash on it. It is concluded that this measure is not cost-effective if the referred approach is considered.