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We have investigated, using first-principles calculations, the energetic stability and structural properties of antisites, vacancies and substitutional carbon defects in a boron nitride monolayer. We have found that the incorporation of a carbon atom substituting for one boron atom, in an N-rich growth condition, or a nitrogen atom, in a B-rich medium, lowers the formation energy, as compared to antisites and vacancy defects. We also verify that defects, inducing an excess of nitrogen or boron, such as N(B) and B(N), are more stable in its reverse atmosphere, i.e. N(B) is more stable in a B-rich growth medium, while B(N) is more stable in a N-rich condition. In addition we have found that the formation energy of a C(N), in a N-rich medium, and C(B) in a B-rich medium, present formation energies comparable to those of the vacancies, V(N) and V(B), respectively.

We investigate the relative stability and electronic structure of several B x C y N z layered structures using first-principles calculations. The twenty structures we considered are derived from a graphite layer by placing carbon, nitrogen, or boron atoms on each site. Interestingly, a structure with B 3 C 2 N 3 stoichiometry was found to be more stable than the eight BC 2 N structures in our study. The BCN compositions we considered present a wide range of electronic behaviors. In general, we observe that structures with large values of the electronic band gap have a B / N ͑x / z͒ ratio of one.

First-principles calculations have been used to investigate the structural and electronic properties of boron ternary graphite-like monolayers (BCN), using pseudopotential method within density functional theory. Particular emphasis was focused on the effect of composition and atomic arrangement on the structural stability and electronic properties in a 32-atom unit cell. The analysis of the band structures, density of states, total and formation energies reveal that: i) the B3N3C2 graphite-like monolayers have the lowest formation energy among many BC2N monolayers because of the smallest number of the B-C and C-N bonds, and ii) depending on the atomic arrangement, the BCN monolayers behave as a semiconductor or metal, with band gap energy ranging from 0 to 2.45 eV. In addition, our calculations confirm that the stable structure of boron ternary monolayers (BCN) is formed by increasing the number of both C-C and B-N bonds, and independent of the unit cell size.

In this work we have investigated the influence of topology in quantum dynamics in two-dimensional quantum dots in a conic surface. We analyze the quantum dynamics of particles in this dot when submitted to an external magnetic field and Aharonov-Bohm flux in the dot center. We obtain the eigenvalues and eigenfunctions exactly. We investigated the influence of geometry and topology on the magnetization, the Fermi energy, and the persistent currents. It is shown that the curvature of the space changes the oscillation pattern of those physical quantities.

We investigate the stability of boron nitride conical sheets of nanometer size, using first-principles calculations. Our results indicate that cones with an antiphase boundary (a line defect that contains either B-B or N-N bonds) can be more stable than those without one. We also find that doping the antiphase boundaries with carbon can enhance their stability, leading also to the appearance of localized states in the bandgap. Among the structures we considered, the one with the smallest formation energy is a cone with a carbon-modified antiphase boundary that presents a spin splitting of ∼0.5 eV at the Fermi level.

We apply first-principles calculations to study the electronic structure of boron nitride nanocones with disclinations of different angles θ = nπ/3. Nanocones with odd values of n present antiphase boundaries that cause a reduction of the work function of the nanocones, relative to the bulk BN value, by as much as 2 eV. In contrast, nanocones with even values of n do not have such defects and present work functions that are very similar to the BN bulk value. These results should have strong consequences for the field emission properties of boron nitride nanocones and nanotubes.pacs 71.20.Tx, 71.15.Mb, 71.24.+q

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