The Experts below are selected from a list of 201 Experts worldwide ranked by ideXlab platform
Philippe Lambin - One of the best experts on this subject based on the ideXlab platform.
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Theoretical 2D Raman Band of strained graphene
Physical Review B, 2013Co-Authors: Valentin N. Popov, Philippe LambinAbstract:We study the 2D Raman Band of in-plane uniaxially strained graphene within a non-orthogonal tight-binding model. At non-zero strain, the obtained 2D Band splits into two subBands at strain angles $0^{\circ}$ and $30^{\circ}$ or into three subBands at intermediate angles. The evolution of the 2D subBands is calculated systematically in the range of the accessible strains from -1% to 3% and for the commonly used laser photon energy from 1.5 eV to 3.0 eV. The strain rate and dispersion rate of the 2D subBands are derived and tabulated. In particular, these two quantities show large variations up to 50%. The results on the 2D subBands can be used for detecting and monitoring strain in graphene for nanoelectronics applications.
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Theoretical 2D Raman Band of strained graphene
Physical Review B, 2013Co-Authors: Valentin N. Popov, Philippe LambinAbstract:We study the 2$D$ Raman Band of in-plane uniaxially strained graphene within a nonorthogonal tight-binding model. At nonzero strain, the obtained 2$D$ Band splits into two subBands at strain angles ${0}^{\ensuremath{\circ}}$ and ${30}^{\ensuremath{\circ}}$ or into three subBands at intermediate angles. The evolution of the 2$D$ subBands is calculated systematically in the range of the accessible strains from $\ensuremath{-}1%$ to $3%$ and for the commonly used laser photon energy from 1.5 to $3.0$ eV. The strain rate and dispersion rate of the 2$D$ subBands are derived and tabulated. In particular, these two quantities show large variations up to $50%$. The results on the 2$D$ subBands can be used for detecting and monitoring strain in graphene for nanoelectronics applications.
Valentin N. Popov - One of the best experts on this subject based on the ideXlab platform.
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2D Raman Band of single-layer and bilayer graphene
Journal of Physics: Conference Series, 2016Co-Authors: Valentin N. PopovAbstract:We present a computational study of the 2D Raman Band of single-layer and bilayer graphene within a density-functional-based non-orthogonal tight-binding model. The phonon dispersion is derived perturbatively and the 2D Band intensity is calculated in fourth-order quantum perturbation theory within this model. The 2D Band intensity is enhanced through resonant processes in which the laser excitation matches an electronic transition and the energy and momentum of the scattered phonons match the difference of those of pairs of electronic states. As a result, the 2D Band is dispersive, i.e., its position depends on the laser excitation. Here, we calculate the shift and shape, as well as the dispersion rate, of the 2D Band for both single-layer graphene and bilayer graphene. The results are compared to available experimental data.
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Two-phonon Raman Bands of bilayer graphene: Revisited
Carbon, 2015Co-Authors: Valentin N. PopovAbstract:Abstract We present complete calculations of the two-phonon Raman Bands of bilayer graphene, including all overtone and combination modes, within a density-functional tight-binding model. Based on our results, we assign unambiguously the observed two-phonon Raman Bands to two-phonon modes, thus resolving the existing controversies. In particular, we show that both overtone and combination modes have essential contribution to the 2D Band, bringing about specific modifications of the Band shape. We argue that a mid-range two-phonon Raman Band, previously assigned to the 2ZO mode, should be assigned to the TOZO′ mode. We find that the Raman Band, usually assigned to the LOLA mode, has significant contribution from the TOZO mode. The predicted Raman Bands can be used for assignment of the observed ones in the Raman spectra of bilayer graphene for the needs of sample characterization for future technological applications.
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Theoretical 2D Raman Band of strained graphene
Physical Review B, 2013Co-Authors: Valentin N. Popov, Philippe LambinAbstract:We study the 2D Raman Band of in-plane uniaxially strained graphene within a non-orthogonal tight-binding model. At non-zero strain, the obtained 2D Band splits into two subBands at strain angles $0^{\circ}$ and $30^{\circ}$ or into three subBands at intermediate angles. The evolution of the 2D subBands is calculated systematically in the range of the accessible strains from -1% to 3% and for the commonly used laser photon energy from 1.5 eV to 3.0 eV. The strain rate and dispersion rate of the 2D subBands are derived and tabulated. In particular, these two quantities show large variations up to 50%. The results on the 2D subBands can be used for detecting and monitoring strain in graphene for nanoelectronics applications.
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Theoretical 2D Raman Band of strained graphene
Physical Review B, 2013Co-Authors: Valentin N. Popov, Philippe LambinAbstract:We study the 2$D$ Raman Band of in-plane uniaxially strained graphene within a nonorthogonal tight-binding model. At nonzero strain, the obtained 2$D$ Band splits into two subBands at strain angles ${0}^{\ensuremath{\circ}}$ and ${30}^{\ensuremath{\circ}}$ or into three subBands at intermediate angles. The evolution of the 2$D$ subBands is calculated systematically in the range of the accessible strains from $\ensuremath{-}1%$ to $3%$ and for the commonly used laser photon energy from 1.5 to $3.0$ eV. The strain rate and dispersion rate of the 2$D$ subBands are derived and tabulated. In particular, these two quantities show large variations up to $50%$. The results on the 2$D$ subBands can be used for detecting and monitoring strain in graphene for nanoelectronics applications.
Ray L. Frost - One of the best experts on this subject based on the ideXlab platform.
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a vibrational spectroscopic study of the silicate mineral pectolite naca2si3o8 oh
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2015Co-Authors: Ray L. Frost, Antonio Wilson Romano, Andrés López, Frederick L Theiss, Ricardo ScholzAbstract:Abstract The mineral pectolite NaCa 2 Si 3 O 8 (OH) is a crystalline sodium calcium silicate which has the potential to be used in plaster boards and in other industrial applications. Raman Bands at 974 and 1026 cm −1 are assigned to the SiO stretching vibrations of linked units of Si 3 O 8 units. Raman Bands at 974 and 998 cm −1 serve to identify Si 3 O 8 units. The broad Raman Band at around 936 cm −1 is attributed to hydroxyl deformation modes. Intense Raman Band at 653 cm −1 is assigned to OSiO bending vibration. Intense Raman Bands in the 2700–3000 cm −1 spectral range are assigned to OH stretching vibrations of the OH units in pectolite. Infrared spectra are in harmony with the Raman spectra. Raman spectroscopy with complimentary infrared spectroscopy enables the characterisation of the silicate mineral pectolite.
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Vibrational Spectroscopy of the Borate Mineral Priceite—Implications for the Molecular Structure
Spectroscopy Letters, 2014Co-Authors: Ray L. Frost, Ricardo Scholz, Andrés López, Yunfei XiAbstract:ABSTRACT Priceite is a calcium borate mineral and occurs as white crystals in the monoclinic pyramidal crystal system. We have used a combination of Raman spectroscopy with complimentary infrared spectroscopy and scanning electron microscopy with Energy-dispersive X-ray Spectroscopy (EDS) to study the mineral priceite. Chemical analysis shows a pure phase consisting of B and Ca only. Raman Bands at 956, 974, 991, and 1019 cm−1 are assigned to the BO stretching vibration of the B10O19 units. Raman Bands at 1071, 1100, 1127, 1169, and 1211 cm−1 are attributed to the BOH in-plane bending modes. The intense infrared Band at 805 cm−1 is assigned to the trigonal borate stretching modes. The Raman Band at 674 cm−1 together with Bands at 689, 697, 736, and 602 cm−1 are assigned to the trigonal and tetrahedral borate bending modes. Raman spectroscopy in the hydroxyl stretching region shows a series of Bands with intense Raman Band at 3555 cm−1 with a distinct shoulder at 3568 cm−1. Other Bands in this spectral reg...
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Infrared and Raman Spectroscopic Characterization of the Silicate Mineral Gilalite Cu5Si6O17 · 7H2O
Spectroscopy Letters, 2014Co-Authors: Andrés Lópes, Ricardo Scholz, Yunfei Xi, Ray L. Frost, Aline AmaralAbstract:ABSTRACT Gilalite is a copper silicate mineral with a general formula of Cu5Si6O17 · 7H2O. The mineral is often found in association with another copper silicate mineral, apachite, Cu9Si10O29 · 11H2O. Raman and infrared spectroscopy have been used to characterize the molecular structure of gilalite. The structure of the mineral shows disorder, which is reflected in the difficulty of obtaining quality Raman spectra. Raman spectroscopy clearly shows the absence of OH units in the gilalite structure. Intense Raman Bands are observed at 1066, 1083, and 1160 cm−1. The Raman Band at 853 cm−1 is assigned to the –SiO3 symmetrical stretching vibration and the low-intensity Raman Bands at 914, 953, and 964 cm−1 may be ascribed to the antisymmetric SiO stretching vibrations. An intense Raman Band at 673 cm−1 with a shoulder at 663 cm−1 is assigned to the ν4 Si-O-Si bending modes. Raman spectroscopy complemented with infrared spectroscopy enabled a better understanding of the molecular structure of gilalite.
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Infrared and Raman spectroscopic characterization of the silicate mineral gilalite Cu5Si6O17.7H2O
Science & Engineering Faculty, 2014Co-Authors: Andres Lopez Toro, Ricardo Scholz, Yunfei Xi, Ray L. Frost, Aline AmaralAbstract:Gilalite is a copper silicate mineral with a general formula of Cu5Si6O17 · 7H2O. The mineral is often found in association with another copper silicate mineral, apachite, Cu9Si10O29 · 11H2O. Raman and infrared spectroscopy have been used to characterize the molecular structure of gilalite. The structure of the mineral shows disorder, which is reflected in the difficulty of obtaining quality Raman spectra. Raman spectroscopy clearly shows the absence of OH units in the gilalite structure. Intense Raman Bands are observed at 1066, 1083, and 1160 cm−1. The Raman Band at 853 cm−1 is assigned to the –SiO3 symmetrical stretching vibration and the low-intensity Raman Bands at 914, 953, and 964 cm−1 may be ascribed to the antisymmetric SiO stretching vibrations. An intense Raman Band at 673 cm−1 with a shoulder at 663 cm−1 is assigned to the ν4 Si-O-Si bending modes. Raman spectroscopy complemented with infrared spectroscopy enabled a better understanding of the molecular structure of gilalite.
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Raman spectroscopic study of the antimonate mineral roméite
Spectrochimica acta. Part A Molecular and biomolecular spectroscopy, 2009Co-Authors: Silmarilly Bahfenne, Ray L. FrostAbstract:Raman spectroscopy has been sued to study the antimony containing mineral romeite Ca(2)Sb(2)O(6)(OH,F,O) from three different origins. Romeite is a calcium antimonate mineral of the pyrochlore group. An intense Raman Band at approximately 518 cm(-1) for romeite is assigned to the SbO nu(1) symmetric stretching mode and the Band at 466 cm(-1) to the SbO nu(3) antisymmetric stretching mode. The Raman Band at 303 cm(-1) is attributed to the OSbO bending mode. Some variation in Band positions is observed and is attributed to the variation in composition between the three mineral samples.
Kamal Kumar - One of the best experts on this subject based on the ideXlab platform.
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Solvent dependent analysis of isotropic Raman Band shape of CO stretching vibration
Spectrochimica acta. Part A Molecular and biomolecular spectroscopy, 2002Co-Authors: Arpita Das, Radhendu Das, Kamal KumarAbstract:The isotropic Raman Band shape corresponding to C=O stretching vibration of some molecules has been studied in neat liquids and as a function of solvent concentration using both polar and non-polar solvents. The Raman Band shape was analyzed on the basis of correlation with the Lorentzian line shape by employinga simple method of linear curve fitting. In neat liquids and in low solvent concentration region, the Band shape was found to be non-Lorentzian. With the gradual increase in solvent concentration the Band shape approaches a Lorentzian function. The plot of the correlation coefficient for a Lorentzian shape shows a discontinuity in the intermediate range of solvent concentration. The influence of the structural characteristics of the solute and the solvent systems on the reference mode and various multipolar interactions together with the time varying spatial distribution of solvent molecules with respect to the reference molecule are expected to govern the microenvironmental fluctuations. This may be responsible for the discontinuity in the intermediate solvent concentration region.
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Microenvironment dependence of vibrational relaxation in p-methyl acetophenone
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 1998Co-Authors: Arpita Das, Kamal KumarAbstract:Abstract The Raman Band shape analysis and vibrational relaxation studies of the CO stretching mode of vibration of p-methyl acetophenone reveals that macroscopic considerations are not sufficient to analyse the Raman anisotropy shift and the linewidth of the isotropic component observed in complex molecular systems. The Band shape analysis was therefore attempted at a microscopic level by taking into account the concept of microenvironment. The solvent dependent study of the anisotropy shift shows that the repulsive potential may be playing a major role in the vibrational relaxation process.
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Microviscosity dependence of the Raman Band shape of methyl-isobutyl ketone
Spectrochimica Acta Part A: Molecular Spectroscopy, 1991Co-Authors: Anusree Purkayastha, Radhendu Das, Kamal KumarAbstract:Abstract The Raman Band shape analysis of the CO stretching mode of vibration of methyl-isobutyl ketone in solution phase reveals that macroscopic consideration of hydrodynamic force is not sufficient to correlate the vibrational relaxation rate (τ v −1 ) with parameter ƒ(ϱ, η, n ), involving dynamic viscosity (η). The Band shape analysis was therefore attempted taking the microscopic parameter, microviscosity (η m ) into account through a modified parameter ƒ m . The correlation of τ v −1 with ƒ m is reported.
Mauro C. C. Ribeiro - One of the best experts on this subject based on the ideXlab platform.
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Raman Band shape analysis of cyanate-anion ionic liquids
Journal of Molecular Liquids, 2015Co-Authors: Tatiana C. Penna, Luiz F. O. Faria, Mauro C. C. RibeiroAbstract:Abstract Raman Band shape analysis of the C ≡ N stretching mode was carried out for ionic liquids based on [SCN] − , [N(CN) 2 ] − , [C(CN) 3 ] − , and [B(CN) 4 ] − , with a common cation, 1-ethyl-3-methylimidazolium, [C 2 C 1 im] + . Vibrational and reorientational time correlation functions were obtained by Fourier transforming isotropic and anisotropic Raman spectra. Comparison is provided between results for [C 2 C 1 im][SCN] and literature data available for molten alkali thiocyanates. Vibrational dephasing of the ω CN mode in [C 2 C 1 im][SCN] belongs to the regime of inhomogeneous broadening as it is determined by the distribution of vibrational frequencies, ω 2 >. Vibrational dephasing in [N(CN) 2 ] − , [C(CN) 3 ] − , and [B(CN) 4 ] − , depends on both the ω 2 > and the correlation time of frequency fluctuation. Decay rates of reorientational time correlation functions within the range of 1.0 ps do not correlate with the viscosity of these ionic liquids. Molecular dynamics simulations of these ionic liquids provide support to the experimental finding that the reorientational time correlation function of [SCN] − decays faster than the other anions. The Raman Band shape analysis suggests that the short-time dynamics of these ionic liquids is structure-limited because of steric hindrance.
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Raman Band shape analysis of a low temperature molten salt
The Journal of Chemical Physics, 2003Co-Authors: Ary O. Cavalcante, Mauro C. C. RibeiroAbstract:The salt tetra(n-butyl)ammonium croconate, [(n-C4H9)4N]2C5O5⋅4H2O, (TBCR), is a very viscous glassforming liquid which undergoes a glass transition at room-temperature. Raman Band shape analysis of the totally symmetric ring breathing mode of the croconate dianion, C5O52−, was performed by Fourier analysis. The vibrational time correlation functions obtained from the isotropic Raman spectra were modelled with well-known models for vibrational dephasing. The time correlation functions of pure TBCR and of TBCR in acetonitrile solutions were compared with previous results for the simple salt Li2C5O5 in aqueous solution. It has been found remarkable changes of the dynamic parameters characterizing the vibrational dephasing of C5O52− in these different environments. Discontinuous temperature dependence of the dephasing parameters was observed at the glass transition temperature of pure TBCR. In glassy TBCR, however, common models for vibrational dephasing are not strictly valid because the Raman Bands display ...
