Estudo teórico das propriedades eletrônicas e estruturais de nanotubos mistos de carbono e h-BN.

Abstract

The study of nanomaterials, both theoretically and experimentally, has been increasingly recurrent in the literature, mainly due to the wide range of applications and advances in techniques for analyzing and synthesizing these materials. In this work, we investigate, by means of firstprinciples calculations, the electronic and structural properties of mixed double-walled carbon and hexagonal boron nitride (h-BN) nanotubes, of the zigzag and armchair type, with the addition of carbon, boron and nitrogen impurities. Furthermore, we evaluated how the application of different values of electric field, perpendicular and parallel to the symmetry axis of the nanotubes, modified the electronic structure of the material. Such analysis was performed using the SIESTA Code, a computational tool, which uses the Density Functional Theory (DFT) as a parameter for its execution. Initially, four mixed double-walled nanotubes were configured, with different coaxial carbon and h-BN arrangements, which we defined as base nanotubes. From these nanotubes, another sixteen were made, however, impurities were added to these. In this way, we obtained eight nanostructures with P-type and eight N-type impurities. From the calculations performed in SIESTA, it was possible to systematize the results referring to the formation energy per atom, the electronic structure of bands, the density of states and the spin polarization of each nanotube. In these nanomaterials, we observed that the energy of formation per atom points to a similar stability pattern in all nanotubes, however, mixed nanostructures with external carbon tubes showed greater stability than when arranged with h-BN nanotubes outside. As for spin polarization, we noticed that the base nanotubes showed no difference between the up and down charges, whereas the nanotubes with impurities exhibited non-zero spin polarization, mainly in P-type impurities, causing magnetization in these materials. We also observed that the different values of electric field applied perpendicularly to the symmetry axis of the tubes contributed to the control of the gap, since fields applied in parallel did not modify the electronic structure of the nanotubes bands. We also evaluated that the addition of foreign atoms to the intrinsic lattice caused the emergence of electronic states in the Fermi level region, both in the valence band and in the conduction band, depending on the impurity introduced into the lattice and that these, when associated with the application of the external electric field, potentiated the emergence of states close to the Fermi level. In short, our data show agreement with the literature and show the unusual properties of these nanomaterials.