Navegando por Autor "Moraes, Elizane Efigenia de"
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Item Charge and spin current rectification through functionalized boron nitride bilayers.(2022) Moraes, Elizane Efigenia de; Pinto, Alysson Alves; Batista, Ronaldo Junio Campos; Oliveira, Alan Barros de; Chacham, HelioRecent experiments have reported the transformation of few-layer hexagonal boron nitride (h-BN) into sp3 -bonded c-BN layers through the application of pressure. A proposed mechanism, based on calculations and experiments, is that the phenomenon is facilitated by BN surface functionalization with OH or H radicals. In the present work, we perform ab initio calculations of ballistic electron transport, between Au electrodes, across such functionalized structures. We find that the stabilization of sp3 binding at zero pressure occurs for partial H coverage (≈58%), whereas large OH coverages (>75%) are necessary. Regarding transport properties, we find that all functionalized BN bilayer films present current rectification, consistent with the experimental findings. Maximum rectification occurs for partial OH and H coverages. The films also show spin-dependent transport, where, for a window of values of applied bias, a single spin component contributes to the total current, characterizing a spin filter behavior. Our results indicate that functionalized BN bilayer films are promising materials for the development of electronic devices where both charge and spin degrees of freedom might be manipulated.Item Graphene/h-BN in-plane heterostructures : stability and electronic and transport properties.(2019) Nascimento, Regiane do; Moraes, Elizane Efigenia de; Matos, Matheus Josué de Souza; Prendergast, David; Manhabosco, Taíse Matte; Oliveira, Alan Barros de; Chacham, Helio; Batista, Ronaldo Junio CamposWe present a first-principles study of structural, electronic, and transport properties of in-plane Gr:BN heterostructures in the form of graphene stripes embedded in a BN matrix. In our calculations, we consider carbon, nitrogen, and boron chemical potentials that are consistent with growth conditions (gas sources and temperatures) at either nitrogen-rich or boron-rich environments. Interestingly, we find that structures with excess of B atoms can be energetically more stable than structures with excess of N atoms even in N-rich growth conditions. The general trend is that N-rich growth conditions favor B/N stoichiometric heterostructures, while B-rich growth conditions favor heterostructures with excess of B atoms at the graphene/BN junctions, such that only B−C bonds occur at both edges of a graphene stripe region embedded in BN. We also investigate the dependence of magnetic properties and the band gap magnitudes of graphene stripe regions embedded in BN with several structural characteristics. We find that graphene stripes with only one bond type (either B−C or N−C) at the graphene/BN edges always present metallic behavior, with zigzag-oriented stripes of this type presenting large magnetic moments. Finally, we obtain the characteristic I−V curves for systems formed by junctions of two graphene stripes embedded in BN, one of them terminated by C−N bonds and the other terminated by C−B bonds. We find that systems of this type should present rectifying behavior.Item Transport properties of hydrogenated cubic boron nitride nanofilms with gold electrodes from density functional theory.(2017) Moraes, Elizane Efigenia de; Coutinho Filho, Maurício Domingues; Batista, Ronaldo Junio CamposThe electrical transport properties of a fourlayered hydrogen-terminated cubic boron nitride sub-nanometer film in contact with gold electrodes are investigated via density functional calculations. The sample exhibits asymmetric metallic surfaces, a fundamental feature that triggers the system to behave like a typical p−n junction diode for voltage bias in the interval −0.2 ≤ V ≤ 0.2, where a rectification ratio up to 62 is verified. Further, in the wider region −0.3 ≤ V ≤ 0.3, negative differential resistance with a peak-to-valley ratio of 10 is observed. The qualitative behavior of the I−V characteristics is described in terms of the hydrogenated cBN film equilibrium electronic structure. Such a film shows metallic surfaces due to surface electronic states at a fraction of eV above and below the Fermi level of the N−H terminated and B−H terminated surfaces, respectively, with a wide bulk-band gap characteristic of BN materials. Such a mechanism is supported by transmission coefficient calculations, with the Landauer−Büttiker formula governing the I−V characteristics.Item Water diffusion in carbon nanotubes for rigid and flexible models.(2023) Mendonça, Bruno Henrique da Silva e; Moraes, Elizane Efigenia de; Batista, Ronaldo Junio Campos; Oliveira, Alan Barros de; Barbosa, Márcia Cristina Bernardes; Chacham, HelioWe compared the diffusion of water confined in armchair and zigzag carbon nanotubes for rigid and flexible water models. Using one rigid model, TIP4P/2005, and two flexible models, SPC/Fw and SPC/FH, we found that the number of the hydrogen bonds that water forms depends on the structure of the nanotube, directly affecting the diffusion of water. The simulation results reveal that, due to the hydrophobic nature of carbon nanotubes and the degrees of freedom imposed by the water force fields, water molecules tend to avoid the surface of the carbon nanotube. This junction of variables plays a central role in the diffusion of water, mainly in narrow and/or deformed nanotubes, governing the mobility of confined water in a nontrivial way, where the greater the degree of freedom of the water force field, the smaller mobility it will have in confinement as we limit the competition between area and volume and it no longer plays the unique role in changing water diffusivity.