The Experts below are selected from a list of 240 Experts worldwide ranked by ideXlab platform
C. N. R. Rao - One of the best experts on this subject based on the ideXlab platform.
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Electrochemical tuning of band structure of single-walled carbon nanotubes probed by in situ resonance Raman scattering
Journal of Applied Physics, 2002Co-Authors: Shankar Ghosh, A. K. Sood, C. N. R. RaoAbstract:In situ resonance Raman scattering of single-walled carbon nanotubes investigated under electrochemical biasing demonstrates that the intensity of the radial breathing Mode varies significantly in a nonmonotonic manner as a function of the cathodic bias voltage, but does not change appreciably under anodic bias. The Tangential Mode is, however, not affected. These results can be quantitatively understood in terms of the changes in the energy gaps between the one-dimensional van Hove singularities in the electron density of states arising possibly due to the alterations in the overlap integral of π bonds between the p orbitals of the adjacent carbon atoms.
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Pressure-induced reversible transformation in single-wall carbon nanotube bundles studied by Raman spectroscopy
Chemical Physics Letters, 2000Co-Authors: Pallavi V Teredesai, A. K. Sood, D.v.s Muthu, R Sen, A Govindaraj, C. N. R. RaoAbstract:We report our high-pressure Raman studies on single-wall carbon nanotube bundles carried out up to 25.9 GPa. The intensity of the radial Modes decreases more drastically as compared to that of the Tangential Modes. The former could be followed up in pressure runs to 3 GPa. The most intriguing observation is the anomalous pressure behaviour of the 1594 cm y1 Tangential Mode between 10 and 16 GPa. This feature, as well as the pressure dependence of intensity, peak position and linewidth, are reversible on decompression. The anomalous pressure dependence is argued to be associated with faceting of the tubes in the bundle, showing their remarkable resilience. q 2000 Elsevier Science B.V. All rights reserved.
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Pressure-induced reversible transformation in single-wall carbon nanotube bundles studied by Raman spectroscopy
Chemical Physics Letters, 2000Co-Authors: Pallavi V Teredesai, A. K. Sood, D.v.s Muthu, R Sen, A Govindaraj, C. N. R. RaoAbstract:We report our high-pressure Raman studies on single-wall carbon nanotube bundles carried out up to 25.9 GPa. The intensity of the radial Modes decreases more drastically as compared to that of the Tangential Modes. The former could be followed up in pressure runs to 3 GPa. The most intriguing observation is the anomalous pressure behaviour of the 1594 cm−1 Tangential Mode between 10 and 16 GPa. This feature, as well as the pressure dependence of intensity, peak position and linewidth, are reversible on decompression. The anomalous pressure dependence is argued to be associated with faceting of the tubes in the bundle, showing their remarkable resilience
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Pressure Behaviour of Single Wall Carbon Nanotube Bundles and Fullerenes: A Raman Study
physica status solidi (b), 1999Co-Authors: A. K. Sood, D.v.s Muthu, R Sen, A Govindaraj, Pallavi V. Teresdesai, C. N. R. RaoAbstract:We shall discuss our recent high pressure Raman studies on single wall carbon nanotube (SWNT) bundles and compare them with pressure induced amorphous and polymeric phases of crystalline $C_{60}$ and $C_{70}$. Our high pressure Raman studies on SWNT bundles carried out upto 25.9 GPa show that the intensities of both the radial Modes $(\omega \approx 170 cm^{-1})$ as well as Tangential Modes $(around 1590 cm^{-1})$ decrease significantly with pressure, so much that the radial Modes cannot be observed beyond 2.6 GPa. Most interestingly, the frequency of the dominant Tangential Mode increases upto 11 GPa, then decreases till 16 GPa and again increases. Raman spectra were resolved into four Modes upto 10 GPa beyond which only one or two Modes could be fitted to the recorded spectra. The pressure-softening of the Mode between 11 and 16 GPa as well as other features of the Raman spectra are reversible in the decreasing pressure cycle. These results, though not understood at present, can be associated with the distortion of the circular cross section of the tubes in the bundle, eventually leading to a possible transition of the SWNT bundle to graphite like carbon at 11 GPa which is completed at 16 GPa. This transition is reversible on decompression.
Mildred S. Dresselhaus - One of the best experts on this subject based on the ideXlab platform.
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The possible way to evaluate the purity of double-walled carbon nanotubes over single wall carbon nanotubes by chemical doping
Chemical Physics Letters, 2006Co-Authors: Yoong Ahm Kim, Hiroyuki Muramatsu, Masahito Kojima, Takuya Hayashi, Morinobu Endo, Mauricio Terrones, Mildred S. DresselhausAbstract:Here, we carried out Raman study on chemically doped single wall carbon nanotube (SWNT)/double-walled carbon nanotube (DWNT) mixed bucky-papers. Their highly different Raman responses (e.g., a large upshift of Tangential Mode of SWNT and no large changes in the frequencies of Tangential Mode assigned to the outer tubes of the DWNT) upon doping with the sulfuric acid could be used as a qualitative indicator of the purity of the DWNT samples with the concentration of its SWNTs contents.
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Characterizing carbon nanotube samples with resonance Raman scattering
New Journal of Physics, 2003Co-Authors: Anouar Jorio, A. G. Souza Filho, R. Saito, Gene Dresselhaus, M A Pimenta, Mildred S. DresselhausAbstract:The basic concepts and characteristics ofRaman spectra from carbon nanotubes (both isolated and bundled) are presented. The general characteristics of the radial breathing Mode, Tangential Mode (G band), disorder-induced Mode (D-band) and other Raman features are presented, with the focus directed toward their use for carbon nanotube characterization. Polarization analysis, surface enhanced Raman spectroscopy and complementary optical techniques are also discussed in terms of their advantages and limitations. 6
Lothar Dunsch - One of the best experts on this subject based on the ideXlab platform.
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In situ Raman spectroelectrochemistry of SWCNT bundles: Development of the Tangential Mode during electrochemical charging in different electrolyte solutions
Diamond and Related Materials, 2009Co-Authors: Martin Kalbac, Ladislav Kavan, Lothar DunschAbstract:Abstract The Raman spectra of metallic tubes in SWCNTs (Single wall carbon nanotubes) bundles during electrochemical doping have been investigated using three different electrolyte solutions: LiClO 4 /CH 3 CN, LiClO 4 /propylenecarbonate/poly(methyl methacrylate) and LiClO 4 /polyethyleneimine. Precise control of the electrochemical charging enabled us to follow the detailed development of the Tangential displacement (TG) Mode of SWCNT bundles in dependence on the electrode potential. The response of the TG Mode to electrode potential was dependent on electrolyte used as a consequence of different doping efficiency. We demonstrate that the liquid electrolyte solution (LiClO 4 /CH 3 CN) has superior doping efficiency to those of both the tested polymer electrolytes.
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Development of the Tangential Mode in the Raman spectra of SWCNT bundles during electrochemical charging.
Nano letters, 2008Co-Authors: Martin Kalbac, Ladislav Kavan, Lothar Dunsch, M. S. DresselhausAbstract:The detailed analysis of the in situ Raman spectroelectrochemical behavior of single walled carbon nanotube (SWCNT) bundles is presented. The Raman Modes of metallic SWCNTs exhibit striking changes even before the potential of the first van Hove singularity is achieved. Special attention has been paid to the development of the Tangential (TG) Mode broadening, which subsequently vanishes if the potential is shifted away from V = 0. The Tangential Mode band has been fitted by four components. During the electrochemical doping, three components of the Tangential Mode follow the predictions of a theoretical Model for the LO Modes of metallic tubes based on the Kohn anomaly. On the other hand, the behavior of the fourth component is consistent with a Model based on electron-plasmon coupling. The TO Mode of metallic tubes has been identified only at a doping level corresponding to 1.0 V or above. Our results also indicate an asymmetry in the behavior of the TG Mode for positive electrode potentials relative to negative ones.
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Distinct Redox Doping of Core/Shell Nanostructures: Double Wall Carbon Nanotubes
AIP Conference Proceedings, 2004Co-Authors: Ladislav Kavan, Martin Kalbac, Markéta Zukalová, Matthias Krause, Hiromichi Kataura, Lothar DunschAbstract:Double wall carbon nanotubes (DWCNT) were prepared by pyrolysis of C60, C70 and C78 peapods. Redox doping was followed by electrochemistry in acetonitrile electrolyte solutions and in ionic liquids. The doping‐driven bleaching of optical transitions between Van Hove singularities causes reversible quenching of resonance Raman scattering of the tube related Modes. The outer tube of DWCNT is more sensitive to doping‐induced loss of Raman resonance. The inner tube is effectively screened from the double‐layer charging and only available to doping after charging of the outer tube. Electrochemical p‐doping of DWCNT allows deconvolution of the Tangential Mode features, which normally overlap each other in pristine DWCNT.
M. S. Dresselhaus - One of the best experts on this subject based on the ideXlab platform.
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Development of the Tangential Mode in the Raman spectra of SWCNT bundles during electrochemical charging.
Nano letters, 2008Co-Authors: Martin Kalbac, Ladislav Kavan, Lothar Dunsch, M. S. DresselhausAbstract:The detailed analysis of the in situ Raman spectroelectrochemical behavior of single walled carbon nanotube (SWCNT) bundles is presented. The Raman Modes of metallic SWCNTs exhibit striking changes even before the potential of the first van Hove singularity is achieved. Special attention has been paid to the development of the Tangential (TG) Mode broadening, which subsequently vanishes if the potential is shifted away from V = 0. The Tangential Mode band has been fitted by four components. During the electrochemical doping, three components of the Tangential Mode follow the predictions of a theoretical Model for the LO Modes of metallic tubes based on the Kohn anomaly. On the other hand, the behavior of the fourth component is consistent with a Model based on electron-plasmon coupling. The TO Mode of metallic tubes has been identified only at a doping level corresponding to 1.0 V or above. Our results also indicate an asymmetry in the behavior of the TG Mode for positive electrode potentials relative to negative ones.
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First and Second-Order Resonant Raman Spectra of Single-Walled Carbon Nanotubes
Fundamental Materials Research, 1Co-Authors: M. S. Dresselhaus, Marcos A. Pimenta, Katrin Kneipp, S. D. M. Brown, P. Corio, A. Marucci, G. DresselhausAbstract:In summary, overtones and combination Modes have been identified in the second-order spectra for the two dominant features in the first-order spectra (the radial breathing Mode and the Tangential Mode) that are associated with the resonant Raman enhancement process arising from the 1D electronic density of states. Just as for the case of the first-order spectra, the resonant contributions to the second-order spectra also involve a different set of (n, m) nanotubes at each laser excitation energy Elaser. A second-order analog is observed for the broad spectral band identified with contributions from metallic nanotubes to the first-order Tangential Mode spectra. The unique feature of the second-order Tangential overtone band shows a larger Elaser range over which the metallic nanotubes contribute, and this effect is attributed to the large (ħωphononc04eV) energy of these phonons. Combination Modes associated with (ωtang+ωRBM) and (ωtang+2ωRBM) have been identified. These combination Modes show behaviors as a function ofElaser that are consistent with the behavior of their first-order constituents, namely that different nanotubes contribute to the spectra at each value of Elaser. The behavior of the ‘D-band’ and G-band features show a very large phonon frequency dependence on Elaser and show a resonant 2D behavior when the electron and phonon wave vectors coincide, as also occurs in other sp2 carbons.
Martin Kalbac - One of the best experts on this subject based on the ideXlab platform.
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In situ Raman spectroelectrochemistry of SWCNT bundles: Development of the Tangential Mode during electrochemical charging in different electrolyte solutions
Diamond and Related Materials, 2009Co-Authors: Martin Kalbac, Ladislav Kavan, Lothar DunschAbstract:Abstract The Raman spectra of metallic tubes in SWCNTs (Single wall carbon nanotubes) bundles during electrochemical doping have been investigated using three different electrolyte solutions: LiClO 4 /CH 3 CN, LiClO 4 /propylenecarbonate/poly(methyl methacrylate) and LiClO 4 /polyethyleneimine. Precise control of the electrochemical charging enabled us to follow the detailed development of the Tangential displacement (TG) Mode of SWCNT bundles in dependence on the electrode potential. The response of the TG Mode to electrode potential was dependent on electrolyte used as a consequence of different doping efficiency. We demonstrate that the liquid electrolyte solution (LiClO 4 /CH 3 CN) has superior doping efficiency to those of both the tested polymer electrolytes.
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Development of the Tangential Mode in the Raman spectra of SWCNT bundles during electrochemical charging.
Nano letters, 2008Co-Authors: Martin Kalbac, Ladislav Kavan, Lothar Dunsch, M. S. DresselhausAbstract:The detailed analysis of the in situ Raman spectroelectrochemical behavior of single walled carbon nanotube (SWCNT) bundles is presented. The Raman Modes of metallic SWCNTs exhibit striking changes even before the potential of the first van Hove singularity is achieved. Special attention has been paid to the development of the Tangential (TG) Mode broadening, which subsequently vanishes if the potential is shifted away from V = 0. The Tangential Mode band has been fitted by four components. During the electrochemical doping, three components of the Tangential Mode follow the predictions of a theoretical Model for the LO Modes of metallic tubes based on the Kohn anomaly. On the other hand, the behavior of the fourth component is consistent with a Model based on electron-plasmon coupling. The TO Mode of metallic tubes has been identified only at a doping level corresponding to 1.0 V or above. Our results also indicate an asymmetry in the behavior of the TG Mode for positive electrode potentials relative to negative ones.
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Distinct Redox Doping of Core/Shell Nanostructures: Double Wall Carbon Nanotubes
AIP Conference Proceedings, 2004Co-Authors: Ladislav Kavan, Martin Kalbac, Markéta Zukalová, Matthias Krause, Hiromichi Kataura, Lothar DunschAbstract:Double wall carbon nanotubes (DWCNT) were prepared by pyrolysis of C60, C70 and C78 peapods. Redox doping was followed by electrochemistry in acetonitrile electrolyte solutions and in ionic liquids. The doping‐driven bleaching of optical transitions between Van Hove singularities causes reversible quenching of resonance Raman scattering of the tube related Modes. The outer tube of DWCNT is more sensitive to doping‐induced loss of Raman resonance. The inner tube is effectively screened from the double‐layer charging and only available to doping after charging of the outer tube. Electrochemical p‐doping of DWCNT allows deconvolution of the Tangential Mode features, which normally overlap each other in pristine DWCNT.
