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Your search keyword '"Barros, E. B."' showing total 38 results
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38 results on '"Barros, E. B."'

1. Analytical model of atomic-force-microscopy force curves in viscoelastic materials exhibiting power law relaxation

Author

de Sousa, J. S., Santos, J. A. C., Barros, E. B., Filho, J. Mendes, Alencar, L . M. R., Cruz, W. T., and Ramos, M. V.

Subjects
Condensed Matter - Soft Condensed Matter, Condensed Matter - Materials Science
Abstract

We propose an analytical model for the force-indentation relationship in viscoelastic materials exhibiting a power law relaxation described by an exponent n, where n = 1 represents the standard viscoelastic solid (SLS) model, and n < 1 represents a fractional SLS model. To validate the model, we perform nanoindentation measurements of poylacrylamide gels with atomic force microscopy (AFM) force curves. We found exponents n < 1 that depends on the bysacrylamide concentration. We also demonstrate that the fitting of AFM force curves for varying load speeds can reproduce the dynamic viscoelastic properties of those gels measured with dynamic force modulation methods., Comment: 21 pages, 5 figures

Published
2016
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2. Disorder-induced double resonant Raman process in graphene

Author

Rodriguez-Nieva, J. F., Barros, E. B., Saito, R., and Dresselhaus, M. S.

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

An analytical study is presented of the double resonant Raman scattering process in graphene, responsible for the D and D$^{\prime}$ features in the Raman spectra. This work yields analytical expressions for the D and D$^{\prime}$ integrated Raman intensities that explicitly show the dependencies on laser energy, defect concentration, and electronic lifetime. Good agreement is obtained between the analytical results and experimental measurements on samples with increasing defect concentrations and at various laser excitation energies. The use of Raman spectroscopy to identify the nature of defects is discussed. Comparison between the models for the edge-induced and the disorder-induced D band intensity suggests that edges or grain boundaries can be distinguished from disorder by the different dependence of their Raman intensity on laser excitation energy. Similarly, the type of disorder can potentially be identified not only by the intensity ratio $I_{\mathrm{D}}/I_{\mathrm{D}^{\prime}}$, but also by its laser energy dependence. Also discussed is a quantitative analysis of quantum interference effects of the graphene wavefunctions, which determine the most important phonon wavevectors and scattering processes responsible for the D and D$^{\prime}$ bands., Comment: 10 pages, 4 figures

Published
2014
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3. Group Theory analysis of phonons in two-dimensional Transition Metal Dichalcogenides

Author

Ribeiro-Soares, J., Almeida, R. M., Barros, E. B., Araujo, P. T., Dresselhaus, M. S., Cançado, L. G., and Jorio, A.

Subjects
Condensed Matter - Materials Science, Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

Transition metal dichalcogenides (TMDCs) have emerged as a new two dimensional materials field since the monolayer and few-layer limits show different properties when compared to each other and to their respective bulk materials. For example, in some cases when the bulk material is exfoliated down to a monolayer, an indirect-to-direct band gap in the visible range is observed. The number of layers $N$ ($N$ even or odd) drives changes in space group symmetry that are reflected in the optical properties. The understanding of the space group symmetry as a function of the number of layers is therefore important for the correct interpretation of the experimental data. Here we present a thorough group theory study of the symmetry aspects relevant to optical and spectroscopic analysis, for the most common polytypes of TMDCs, i.e. $2Ha$, $2Hc$ and $1T$, as a function of the number of layers. Real space symmetries, the group of the wave vectors, the relevance of inversion symmetry, irreducible representations of the vibrational modes, optical selection rules and Raman tensors are discussed., Comment: 32 pages, 4 figures

Published
2014
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8. Analytical model of atomic-force-microscopy force curves in viscoelastic materials exhibiting power law relaxation.

Author

de Sousa, J. S., Santos, J. A. C., Barros, E. B., Alencar, L. M. R., Cruz, W. T., Ramos, M. V., and Mendes Filho, J.

Subjects
ATOMIC force microscopy, VISCOELASTIC materials, POWER law (Mathematics), POLYACRYLAMIDE gel electrophoresis, NANOINDENTATION
Abstract

We propose an analytical model for the force-indentation relationship in viscoelastic materials exhibiting a power law relaxation described by an exponent n, where n=1 represents the standard viscoelastic solid (SLS) model and n<1 represents a fractional SLS model. To validate the model, we perform nanoindentation measurements of polyacrylamide gels with atomic force microscopy (AFM) force curves. We found exponents n<1 that depend on the bisacrylamide concentration. We also demonstrate that the fitting of AFM force curves for varying load speeds can reproduce the dynamic viscoelastic properties of those gels measured with dynamic force modulation methods. [ABSTRACT FROM AUTHOR]

Published
2017
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9. Spin polarized vertical transport in stacked TMDCs hetero-junctions.

Author

Costa, A L M T, Silva, F W N, and Barros, E B

Subjects
BAND gaps, TRANSITION metals, SEMICONDUCTORS, FERMI energy, BALLISTIC conduction
Abstract

Electronic and transport properties of stacked metal/semiconductor and metal/metal heterojunctions of transition metal dichalcogenides (TMDCs) are studied in this paper. MoS2, MoSe2, WS2, and WSe2 are considered for the semiconducting material, while NbS2, NbSe2, CoS2, and CoSe2 are considered for the metallic contact. Our density functional theory-based calculations reveal a strongly spin-polarized conductance for the studied systems. Furthermore, our results predict that the band gap of the semiconducting TMDC shifts above the Fermi energy of the connected system, leading to a diode-like semiconductor/metal contact. Moreover, the quantum conductance calculations for these junctions, carried out within the Landauer–Büttiker formalism for ballistic transport, shows that even the metal/metal heterojunctions have a diode-like character near the Fermi level. This interesting behaviour is discussed in terms of the misalignment between electronic states on each of the materials comprising the junction. [ABSTRACT FROM AUTHOR]

Published
2020
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26. Synthesis and Characterization of Selenium−Carbon Nanocables

Author

Rodrigues, O. E. D., primary, Saraiva, G. D., additional, Nascimento, R. O., additional, Barros, E. B., additional, Mendes Filho, J., additional, Kim, Y. A., additional, Muramatsu, H., additional, Endo, M., additional, Terrones, M., additional, Dresselhaus, M. S., additional, and Souza Filho, A. G., additional

Published
2008
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31. Phonon-assisted exciton relaxation dynamics for a (6,5)-enriched DNA-wrapped single-walled carbon nanotube sample

Author

Chou, S. G., primary, DeCamp, M. F., additional, Jiang, J., additional, Samsonidze, Ge. G., additional, Barros, E. B., additional, Plentz, F., additional, Jorio, A., additional, Zheng, M., additional, Onoa, G. B., additional, Semke, E. D., additional, Tokmakoff, A., additional, Saito, R., additional, Dresselhaus, G., additional, and Dresselhaus, M. S., additional

Published
2005
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32. Raman spectroscopy of graphitic foams

Author

Barros, E. B., primary, Demir, N. S., additional, Souza Filho, A. G., additional, Mendes Filho, J., additional, Jorio, A., additional, Dresselhaus, G., additional, and Dresselhaus, M. S., additional

Published
2005
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35. Intense conductivity suppression by edge defects in zigzag MoS2 and WSe2 nanoribbons: a density functional based tight-binding study.

Author

Silva FW, Costa AL, Liu L, and Barros EB

Abstract

The effects of edge vacancies on the electron transport properties of zigzag MoS2/WSe2 nanoribbons are studied using a density functional theory (DFT)-based tight-binding model with a sp(3)d(5) basis set for the electronic structure calculation and applying the Landauer-Büttiker approach for the electronic transport. Our results show that the presence of a single edge vacancy, with a missing MoS2/WSe2 triplet, is enough to suppress the conductance of the system by almost one half for most energies around the Fermi level. Furthermore, the presence of other single defects along the same edge has little effect on the overall conductance, indicating that the conductance of that particular edge has been strongly suppressed by the first defect. The presence of another defect on the opposite edge further suppresses the quantum conductance, independently of the relative position between the two defects in opposite edges. The introduction of other defects cause the suppression to be energy dependent, leading to conductance peaks which depend on the geometry of the edges. The strong conductance dependence on the presence of edge defects is corroborated by DFT calculations using SIESTA, which show that the electronic bands near the Fermi energy are strongly localized at the edge.

Published
2016
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36. Synthesis and characterization of selenium-carbon nanocables.

Author

Rodrigues OE, Saraiva GD, Nascimento RO, Barros EB, Mendes Filho J, Kim YA, Muramatsu H, Endo M, Terrones M, Dresselhaus MS, and Souza Filho AG

Abstract

In this letter, we report the synthesis and characterization of a novel Se-C hybrid nanostructure. X-ray diffraction data indicates a high degree of crystallinity for the nanostructured Se shell. High resolution transmission electron microscopy images show that the Se-C nanostructures consist of coaxial nanocables made of single wall carbon nanotubes, as the core, surrounded by a trigonal Selenium shell. Resonance Raman spectroscopy was used to access the properties of both the carbon nanotubes and selenium. The behavior of the radial breathing mode and the G-band indicates that the Se shell primarily covers semiconducting nanotubes. X-ray photoelectron spectroscopy show that the nanocables have a thin coverage of selenium oxide. We envisage that this system could be used in the fabrication of photonic devices as an interface between electronic and photonic materials.

Published
2008
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37. Cost-effectiveness of risk-reduction measures from a national viewpoint: a case study of the Angra nuclear plant in Brazil.

Author

de Oliveira LF, Barros EB, Fleming PV, and Rosa LP

Subjects
Bayes Theorem, Brazil, Cost-Benefit Analysis, Accident Prevention, Nuclear Reactors, Risk, Safety
Abstract

In this paper a systemic or national approach to cost-effectiveness analysis of risk-reduction measures is reviewed, and its advantages and limitations are discussed. The method is applied to the problem of the cost-effectiveness of increasing the Angra 3 NPP containment wall thickness from the present 60 cm to 180 cm thick in order to prevent damage to the reactor core in case of a direct commercial aircraft crash on it. It is concluded that this measure is not cost-effective if the referred approach is considered.

Published
1987
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