Search

Your search keyword '"Cançado, L. G."' showing total 38 results
Start Over Author "Cançado, L. G."
38 results on '"Cançado, L. G."'

1. Structural analysis of polycrystalline graphene systems by Raman spectroscopy

Author

Ribeiro-Soares, J., Oliveros, M. E., Garin, C., David, M. V., Martins, L. G. P., Almeida, C. A., Martins-Ferreira, E. H., Takai, K., Enoki, T., Magalhães-Paniago, R., Malachias, A., Jorio, A., Archanjo, B. S., Achete, C. A., and Cançado, L. G.

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

A theoretical model supported by experimental results explains the dependence of the Raman scattering signal on the evolution of structural parameters along the amorphization trajectory of polycrystalline graphene systems. Four parameters rule the scattering efficiencies, two structural and two related to the scattering dynamics. With the crystallite sizes previously defined from X-ray diffraction and microscopy experiments, the three other parameters (the average grain boundaries width, the phonon coherence length, and the electron coherence length) are extracted from the Raman data with the geometrical model proposed here. The broadly used intensity ratio between the C-C stretching (G band) and the defect-induced (D band) modes can be used to measure crystallite sizes only for samples with sizes larger than the phonon coherence length, which is found equal to 32 nm. The Raman linewidth of the G band is ideal to characterize the crystallite sizes below the phonon coherence length, down to the average grain boundaries width, which is found to be 2.8 nm. "Ready-to-use" equations to determine the crystallite dimensions based on Raman spectroscopy data are given., Comment: 28 pages, 4 figures

Published
2015
Full Text
View/download PDF

2. Group theory for structural analysis and lattice vibrations in phosphorene systems

Author

Ribeiro-Soares, J., Almeida, R. M., Cançado, L. G., Dresselhaus, M. S., and Jorio, A.

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

Group theory analysis for two-dimensional elemental systems related to phosphorene is presented, including (i) graphene, silicene, germanene and stanene, (ii) dependence on the number of layers and (iii) two stacking arrangements. Departing from the most symmetric $D_{6h}^{1}$ graphene space group, the structures are found to have a group-subgroup relation, and analysis of the irreducible representations of their lattice vibrations makes it possible to distinguish between the different allotropes. The analysis can be used to study the effect of strain, to understand structural phase transitions, to characterize the number of layers, crystallographic orientation and nonlinear phenomena., Comment: 24 pages, 3 figures

Published
2014
Full Text
View/download PDF

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
Full Text
View/download PDF

4. Raman-scattering study of the phonon dispersion in twisted bi-layer graphene

Author

Campos-Delgado, J., Cançado, L. G., Achete, C. A., Jorio, A., and Raskin, J. -P.

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

Bi-layer graphene with a twist angle \theta\ between the layers generates a superlattice structure known as Moir\'{e} pattern. This superlattice provides a \theta-dependent q wavevector that activates phonons in the interior of the Brillouin zone. Here we show that this superlattice-induced Raman scattering can be used to probe the phonon dispersion in twisted bi-layer graphene (tBLG). The effect reported here is different from the broadly studied double-resonance in graphene-related materials in many aspects, and despite the absence of stacking order in tBLG, layer breathing vibrations (namely ZO' phonons) are observed., Comment: 18 pages, 4 figures, research article

Published
2013
Full Text
View/download PDF

5. Quantifying defects in graphene via Raman spectroscopy at different excitation energies

Author

Cançado, L. G., Jorio, A., Ferreira, E. H. Martins, Stavale, F., Achete, C. A., Capaz, R. B., Moutinho, M. V. O., Lombardo, A., Kulmala, T., and Ferrari, A. C.

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

We present a Raman study of Ar(+)-bombarded graphene samples with increasing ion doses. This allows us to have a controlled, increasing, amount of defects. We find that the ratio between the D and G peak intensities for a given defect density strongly depends on the laser excitation energy. We quantify this effect and present a simple equation for the determination of the point defect density in graphene via Raman spectroscopy for any visible excitation energy. We note that, for all excitations, the D to G intensity ratio reaches a maximum for an inter-defect distance ~3nm. Thus, a given ratio could correspond to two different defect densities, above or below the maximum. The analysis of the G peak width and its dispersion with excitation energy solves this ambiguity., Comment: Fixed numerical factors in equations (5) and (6)

Published
2011
Full Text
View/download PDF

10. Second Harmonic Generation in WSe 2

Author

Ribeiro-Soares, J, primary, Janisch, C, additional, Liu, Z, additional, Elías, A L, additional, Dresselhaus, M S, additional, Terrones, M, additional, Cançado, L G, additional, and Jorio, A, additional

Published
2015
Full Text
View/download PDF

14. Resonance effects on the Raman spectra of graphene superlattices

Author

Carozo, V., primary, Almeida, C. M., additional, Fragneaud, B., additional, Bedê, P. M., additional, Moutinho, M. V. O., additional, Ribeiro-Soares, J., additional, Andrade, N. F., additional, Souza Filho, A. G., additional, Matos, M. J. S., additional, Wang, B., additional, Terrones, M., additional, Capaz, Rodrigo B., additional, Jorio, A., additional, Achete, C. A., additional, and Cançado, L. G., additional

Published
2013
Full Text
View/download PDF

16. In Situ Atomic Force Microscopy Tip-Induced Deformations and Raman Spectroscopy Characterization of Single-Wall Carbon Nanotubes

Author

Araujo, P. T., primary, Barbosa Neto, N. M., additional, Chacham, H., additional, Carara, S. S., additional, Soares, J. S., additional, Souza, A. D., additional, Cançado, L. G., additional, de Oliveira, A. B., additional, Batista, R. J. C., additional, Joselevich, E., additional, Dresselhaus, M. S., additional, and Jorio, A., additional

Published
2012
Full Text
View/download PDF

19. Nanowires and Nanoribbons Formed by Methylphosphonic Acid

Author

Archanjo, B. S., primary, Carvalho, L. A. S., additional, Rassa, M., additional, Miquita, D. R., additional, de Oliveira, F. A. C., additional, Cançado, L. G., additional, Agero, U., additional, Plentz, F., additional, Cury, L. A., additional, Gonzalez, J. C., additional, Moreira, R. L., additional, Paniago, R., additional, Magalhães-Paniago, R., additional, and Neves, B. R. A., additional

Published
2007
Full Text
View/download PDF

25. Anisotropy of the Raman Spectra of Nanographite Ribbons

Author

Cançado, L. G., primary, Pimenta, M. A., additional, Neves, B. R. A., additional, Medeiros-Ribeiro, G., additional, Enoki, Toshiaki, additional, Kobayashi, Yousuke, additional, Takai, Kazuyuki, additional, Fukui, Ken-ichi, additional, Dresselhaus, M. S., additional, Saito, R., additional, and Jorio, A., additional

Published
2004
Full Text
View/download PDF

29. Spectroscopy of small diameter single-wall carbon nanotubes.

Author

Jorio, A., Fantini, C., Cançado, L. G., Ribeiro, H. B., Santos, A. P., Furtado, C. A., Dresselhaus, M. S., Dresselhaus, G., Samsonidze, Ge. G., Chou, S. G., Grueneis, A., Jiang, J., Kobayashi, N., Saito, R., and Pimenta, M. A.

Subjects
NANOTUBES, CARBON, RAMAN spectroscopy, CHIRALITY, MANY-body problem, RESONANCE
Abstract

Resonance Raman spectroscopy of small diameter (below 1.2 nm) single-wall carbon nanotubes (SWCNT) is presented. The diameter and chirality dependent many-body corrections to the tight binding based Kataura plot are discussed. The radial breathing modes also show small chirality dependence, giving evidence for the deviations of the small nanotube diameters from the ideal folded graphene structure. The use of spectroscopy for the characterization of small environmental effects and the (n,m) population on HiPco and CoMoCAT SWNT samples is pointed out. The richness of the intermediate frequency modes is highlighted. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

Published
2005
Full Text
View/download PDF

30. Double resonance Raman spectroscopy and optical properties of single wall carbon nanotubes.

Author

Saito, R., Grüneis, A., Jiang, J., Jorio, A., Cançado, L. G., Fantini, C., Pimenta, M. A., Samsonidze, Ge. G., Dresselhaus, G., Dresselhaus, M. S., and Filho, A. G. Souza

Subjects
NANOTUBES, CARBON, RESONANCE Raman effect, RAMAN spectroscopy, PHONONS, GRAPHITE
Abstract

Recent progress on double resonance Raman spectroscopy and related optical properties of single wall carbon nanotubes (SWNTs) is presented. The electron-photon and electron-phonon interactions for graphite and SWNTs are calculated within the tight-binding scheme. Optical absorption matrix element and phonon relaxation time calculations are consistent with experimental observations. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

Published
2004
Full Text
View/download PDF

31. Electron-Phonon Interaction and Raman Intensities in Graphite.

Author

Grüneis, A., Saito, R., Jiang, J., Cançado, L. G., Pimenta, M. A., Jorio, A., Fantini, C., Samsonidze, Ge. G., Dresselhaus, G., Dresselhaus, M. S., and Filho, A. G. Souza

Subjects
ELECTRON-phonon interactions, ELECTROMAGNETIC interactions, RAMAN spectroscopy, GRAPHITE, DEFORMATION potential
Abstract

We calculate the second order Raman spectra in graphite and compare it to recent measurements on highly oriented pyrolytic graphite (HOPG). Electron-phonon interaction is calculated as the inner product of the amplitude of vibration with the deformation potential vector. The deformation potential vector is calculated by atomic basis functions and the potential fitted by Gaussians. When we include the electron-phonon matrix element, the peak positions and the shapes agree well with the experimental results. The characteristic double peak structure of the G′ band in HOPG is reproduced well. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

Published
2004
Full Text
View/download PDF

32. Resonance Raman Scattering in Carbon Nanotubes and Nanographites.

Author

Pimenta, M. A., Jorio, A., Dantas, M. S. S., Fantini, C., de Souza, M., Cançado, L. G., Samsonidze, Ge. G., Dresselhaus, G., Dresselhaus, M. S., Grüneis, A., Saito, R., Filho, A. G. Souza, Kobayashi, Y., Takai, K., Fukui, K., and Enoki, T.

Subjects
RESONANCE, NANOTUBES, PHOTONS, CONDUCTION bands
Abstract

In this work, we discuss the resonant Raman process in nanographites and carbon nanotubes, relating the most important Raman features to a first-order (single resonance) or a second-order (double resonance) process. We also show that, in the case of 1D systems, the term “resonance” has a more strict meaning and occurs when the energy of the photon does not simply coincide with the energy of a possible electron-hole pair, but rather matches the separation between van Hove singularities in the valence and conduction bands. © 2003 American Institute of Physics [ABSTRACT FROM AUTHOR]

Published
2003
Full Text
View/download PDF

33. The use of Raman spectroscopy to characterize the carbon materials found in Amazonian anthrosoils.

Author

Ribeiro‐Soares, J., Cançado, L. G., Falcão, N. P. S., Martins Ferreira, E. H., Achete, C. A., and Jorio, A.

Abstract

This manuscript presents the Raman characterization of the stable carbon materials found in a special type of soil, named Terra Preta de Índio (Indian Dark Earths). The Terras Pretas de Índios have been studied as a potential model for sustainable agriculture in the humid tropics. The stability of organic matter and the long-term high-level of ion exchange capacity in these soils are due to unusually high amount of black carbon. Here, we show how Raman spectroscopy can be used to characterize the stable carbon content in the Terras Pretas de Índios (TPI-carbons). The tangential stretching mode (G band) and the disorder-induced mode (D band) are analyzed in comparison to laboratory-produced amorphous carbons at different degree of disorder used here as reference materials. Statistical analysis show predominance of sp2 phase and crystallite sizes within the limit range between nanographite and amorphous carbons, while Raman mapping of a TPI-carbon grain shows that the surface is more disordered than the grain core. The analysis used here can also differentiate the TPI-carbon structures from different types of charcoal. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Published
2013
Full Text
View/download PDF

34. Optical absorption of graphite and single-wall carbon nanotubes.

Author

Saito, R., Grüneis, A., Samsonidze, G. G., Dresselhaus, G., Dresselhaus, M. S., Jorio, A., Cançado, L. G., Pimenta, M. A., and Souza Filho, A. G.

Subjects
DIPOLE moments, GRAPHITE, CARBON, NANOTUBES, ELECTRONIC structure, BRILLOUIN zones, LUMINESCENCE, RAMAN spectroscopy
Abstract

A review of the electronic dipole transitions in graphite and single-wall carbon nanotubes is presented. Because of its singular electronic structure, the optical absorption matrix element as a function of wave vector has a node in the two-dimensional Brillouin zone of graphite, which depends linearly on the optical polarization direction. In the case of the single-wall carbon nanotubes, the dipole selection rule and the van Hove singularity in the joint density of states will give a characteristic behavior, which is observed by luminescence and resonance Raman spectroscopy. [ABSTRACT FROM AUTHOR]

Published
2004
Full Text
View/download PDF

35. General equation for the determination of the crystallite size La of nanographite by Raman spectroscopy.

Author

Cançado, L. G., Takai, K., Enoki, T., Endo, M., Kim, Y. A., Mizusaki, H., Jorio, A., Coelho, L. N., Magalhães-Paniago, R., and Pimenta, M. A.

Subjects
*GRAPHITE, *EQUATIONS, *NANOSTRUCTURES, *RAMAN spectroscopy, *PHYSICS
Abstract

This work presents a systematic study of the ratio between the integrated intensities of the disorder-induced D and G Raman bands (ID/IG) in nanographite samples with different crystallite sizes (La) and using different excitation laser energies. The crystallite size La of the nanographite samples was obtained both by x-ray diffraction using synchrotron radiation and directly from scanning tunneling microscopy images. A general equation for the determination of La using any laser energy in the visible range is obtained. Moreover, it is shown that ID/IG is inversely proportional to the fourth power of the laser energy used in the experiment. [ABSTRACT FROM AUTHOR]

Published
2006
Full Text
View/download PDF

38. Mechanism of near-field Raman enhancement in one-dimensional systems.

Author

Cançado LG, Jorio A, Ismach A, Joselevich E, Hartschuh A, and Novotny L

Abstract

We develop a theory of near-field Raman enhancement in one-dimensional systems, and report supporting experimental results for carbon nanotubes. The enhancement is established by a laser-irradiated nanoplasmonic structure acting as an optical antenna. The near-field Raman intensity is inversely proportional to the 10th power of the separation between the enhancing structure and the one-dimensional system. Experimental data obtained from single-wall carbon nanotubes indicate that the Raman enhancement process is not significantly influenced by the specific phonon eigenvector, and is mainly defined by the properties of the nanoplasmonic structure.

Published
2009
Full Text
View/download PDF

Catalog

Books, media, physical & digital resources
See catalog results