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A new family of planar nanostructures having graphene-like electronic band structure is theoretically investigated by density functional theory (DFT). Based on general perturbation theory and a tight-binding model, it was shown that graphene-like planar structures, consisting of identical nanoparticles with relatively weak contacts between them, should have an electronic band structure with Dirac cones. Two such structures, consisting of 71- or 114-silicon atom nanoparticles, were investigated by DFT using VASP software package. The band-structure calculations show the presence of Dirac cones with electron group velocity equal to 1.05 × 105 and 0.53 × 105 m/s, respectively. By generalizing the theory, a new family of 3D structures having intersecting areas with linear dispersion in the band structures was derived. As an example, the band structure of identical 25-atom silicon nanoclusters arranged in a simple cubic lattice was calculated. It was shown that the band structure has features similar to the Dirac cones. [ABSTRACT FROM AUTHOR]

It is now well established that many of the technologically important properties of two-dimensional (2D) materials, such as the extremely high carrier mobility in graphene and the large direct band gaps in MoS2 monolayers, arise from quantum confinement. However, the influence of reduced dimensions on electron-phonon (e-ph) coupling and its attendant dephasing effects in such systems has remained unclear. Although phonon confinement is expected to produce a suppression of e-ph interactions in 2D systems with rigid boundary conditions, experimental verification of this has remained elusive. Here, we show that the e-ph interaction is, indeed, modified by a phonon dimensionality crossover in layered Nb3SiTe6 atomic crystals. When the thickness of the Nb3SiTe6 crystals is reduced below a few unit cells, we observe an unexpected enhancement of the weak-antilocalization signature in magnetotransport. This finding strongly supports the theoretically predicted suppression of e-ph interactions caused by quantum confinement of phonons. [ABSTRACT FROM AUTHOR]

Influence of ordered monovacancies on elastic properties of graphene is theoretically investigated by density functional theory (DFT) calculations. Inverse linear dependence of the graphene Young's modulus on the concentration of vacancies has been revealed and migration rate of the vacancies has been calculated as a function of applied strain. It is shown that the migration rate can be controlled by applying various strains or temperatures. The influence of ordered monovacancies on magnetic properties of graphene as well as graphene-like hexagonal carbon silicide (2D-SiC) and the boron nitride (h-BN) structures is investigated. It is established that the presence of vacancies in all systems yields the appearance of local magnetic moment. However, in 2D-SiC structure the magnetic moment occurs only in the case of a Si vacancy. Influence of the distance between vacancies on the ferromagnetic or anti-ferromagnetic ordering for all structures is established. [ABSTRACT FROM AUTHOR]

The effect of isolated vacancies on the elastic properties of a graphene sheet has been investigated by the ab initio density functional method. An almost inverse linear dependence of the Young's modulus on the concentration of vacancies has been revealed. The height of potential barriers for the motion of vacancies in various directions has been calculated as a function of various independent applied strains. The velocity of vacancies at various temperatures has been calculated as a function of applied strains using the transition state theory. [ABSTRACT FROM AUTHOR]

It is now well established that many of the technologically important properties of two-dimensional (2D) materials, such as the extremely high carrier mobility in graphene and the large direct band gaps in MoS2 monolayers, arise from quantum confinement. However, the influence of reduced dimensions on electron-phonon (e-ph) coupling and its attendant dephasing effects in such systems has remained unclear. Although phonon confinement is expected to produce a suppression of e-ph interactions in 2D systems with rigid boundary conditions, experimental verification of this has remained elusive. Here, we show that the e-ph interaction is, indeed, modified by a phonon dimensionality crossover in layered Nb3SiTe6 atomic crystals. When the thickness of the Nb3SiTe6 crystals is reduced below a few unit cells, we observe an unexpected enhancement of the weak-antilocalization signature in magnetotransport. This finding strongly supports the theoretically predicted suppression of e-ph interactions caused by quantum confinement of phonons. [ABSTRACT FROM AUTHOR]