Efeitos da desordem e segregação nas propriedades eletrônicas de camadas de carbonitreto de boro

Abstract

Materials with sp2 covalent bonds can present distinct electronic structures. For instance, a graphite sheet (graphene) is a conductor while an analogous boron nitride sheet, h - BN, is a wide gap insulator. The complete substituition of carbon atoms by boron and nitrogen atoms in a graphite sheet leads to the formation of hexagonal boron nitride. Experimentaly, it is possible to make partial substitutions of carbon atoms by boron and nitrogen leading to the formation of BxCyNz layeredcompouds of distinct stoichiometries. These structures present intermediate electronic properties between those of graphite and h - BN, which could be very useful for technological applications. The stability and structural properties of BxCyNz sheets with several configurations and stoichiometries can be studied by means of first-principles calculations. Alternatively, its possible to study these structures by means of a first-neighbor valence-bond model, based on the parametrization ofbinding energies obtained from first-principles calculations. This model generates similar results to the first-principles ones, with a much lower computational cost. We apply this model to obtain the total energies and the lower energy conformations of BxCyNz sheets, by means of a simulated annealing program. In addition, we studied the electronic properties of selected theoretical "samples" by means of first-principle calculation.