Computational study of the shift of the G band of double-walled carbon nanotubes due to interlayer interactions

The interactions between the layers of double-walled carbon nanotubes induce measurable shift of the G bands relative to the isolated layers. While experimental data on this shift in free-standing double-walled carbon nanotubes has been reported in the past several years, comprehensive theoretical description of the observed shift is still lacking. The prediction of this shift is important for supporting the assignment of the measured double-walled nanotubes to particular nanotube types. Here, we report a computational study of the G-band shift as a function of the semiconducting inner layer radius and interlayer separation. We find that with increasing interlayer separation, the G band shift decreases, passes through zero and becomes negative, and further increases in absolute value for the wide range of considered inner layer radii. The theoretical predictions are shown to agree with the available experimental data within the experimental uncertainty

Efficient Inner-to-Outer Wall Energy Transfer in Highly Pure Double-Wall Carbon Nanotubes Revealed by Detailed Spectroscopy

The coaxial stacking of two single-wall carbon nanotubes (SWCNTs) into a double-wall carbon nanotube (DWCNT), forming a so-called one-dimensional van der Waals structure, leads to synergetic effects that dramatically affect the optical and electronic properties of both layers. In this work, we explore these effects in purified DWCNT samples by combining absorption, wavelength-dependent infrared fluorescence–excitation (PLE), and wavelength-dependent resonant Raman scattering (RRS) spectroscopy. Purified DWCNTs are obtained by careful solubilization that strictly avoids ultrasonication or by electronic-type sorting, both followed by a density gradient ultracentrifugation to remove unwanted SWCNTs that could obscure the DWCNT characterization. Chirality-dependent shifts of the radial breathing mode vibrational frequencies and transition energies of the inner and outer DWCNT walls with respect to their SWCNT analogues are determined by advanced two-dimensional fitting of RRS and PLE data of DWCNT and their reference SWCNT samples. This exhaustive data set verifies that fluorescence from the inner DWCNT walls of well-purified samples is severely quenched through efficient energy transfer from the inner to the outer DWCNT walls. Combined analysis of the PLE and RRS results further reveals that this transfer is dependent on the inner and outer wall chirality, and we identify the specific combinations dominant in our DWCNT samples. These obtained results demonstrate the necessity and value of a combined structural characterization approach including PLE and RRS spectroscopy for bulk DWCNT samples

Experimental evidence of a mechanical coupling between layers in an individual double-walled carbon nanotube

We perform transmission electron microscopy, electron diffraction, and Raman scattering experiments on an individual suspended double-walled carbon nanotube (DWCNT). The first two techniques allow the unambiguous determination of the DWCNT structure: (12,8)@(16,14). However, the low-frequency features in the Raman spectra cannot be connected to the derived layer diameters d by means of the 1/d power law, widely used for the diameter dependence of the radial-breathing mode of single-walled nanotubes. We discuss this disagreement in terms of mechanical coupling between the layers of the DWCNT, which results in collective vibrational modes. Theoretical predictions for the breathing-like modes of the DWCNT, originating from the radial-breathing modes of the layers, are in a very good agreement with the observed Raman spectra. Moreover, the mechanical coupling qualitatively explains the observation of Raman lines of breathing-like modes, whenever only one of the layers is in resonance with the laser energy.This work has been done in the framework of the GDR-E No 2756 “Science and Application of the Nanotubes-NANO-E”. The authors acknowledge financial support from ANR Excitubes, TRAIN2 network, and French Russian PICS No. 4818. V.N.P. acknowledges financial support from University of Montpellier 2.Peer reviewe

Modes Raman des nanotubes de carbone individuels mono et multi parois de structure identifiée

The main objective of this work is the fundamental physical study of individual isolated carbon nanostructures in order to address their intrinsic vibrational and optical properties and also to estimate and quantify the environmental effects. For these purposes, we synthesized individual single- and multi-walled carbon nanotubes by chemical vapour deposition method on dedicated substrates. The main aspect of the work involves the combined use of different experimental probes on the same individual nanostructures. We performed a complete structure analysis by electron diffraction and high-resolution electron microscopy and the measurement of the Raman spectra on these individual nanostructures. Several important environmental effects were evidenced for the first time, e.g. the effect of mechanical coupling (van-der-Waals interaction) between the layers of double-walled carbon nanotubes leading to the change in the low-frequency Raman modes and the optical resonance conditions. Moreover the behaviour of high-frequency modes of double-walled tubes was also analysed and described. As a result of this work several experimental criteria for structure diagnostics of multi-walled carbon nanotubes were proposed.L'objectif principal de ce travail est l'étude fondamentale de nanostructures à base de carbone individuelles dans le but d'améliorer la compréhension de leurs propriétés vibrationnelles et optiques intrinsèques ainsi que d'estimer et de quantifier les effets d'environnement. Dans ce but, nous avons synthétisé des nanotubes de carbone mono- et multi-feuillets par décomposition catalytique en phase vapeur sur des substrats dédiés. L'aspect principal du travail est basé sur l'utilisation combinée de plusieurs sondes expérimentales sur la même nanostructure carbonée individuelle. Nous avons effectué une analyse structurale complète par diffraction électronique et microscopie électronique haute résolution et mesuré les spectres Raman de ces nanostructures individuelles. Plusieurs effets environnementaux importants ont été mis en évidence pour la première fois, comme par exemple l'effet d'un couplage mécanique (due à l'interaction de van-der-Waals) entre les parois des nanotubes bi-feuillets conduisant à une modification des modes Raman de basse fréquence et des conditions de résonances optiques. De plus, le comportement des modes de haute fréquence des nanotubes bi-feuillets a été analysé. Suite à ce travail plusieurs critères expérimentaux permettant un diagnostic de la structure des nanotubes multi-feuillets ont été proposés

Modes Raman des nanotubes de carbone individuels mono et multi parois de structure identifiée

L'objectif principal de ce travail est l'étude fondamentale de nanostructures à base de carbone individuelles dans le but d'améliorer la compréhension de leurs propriétés vibrationnelles et optiques intrinsèques ainsi que d'estimer et de quantifier les effets d'environnement. Dans ce but, nous avons synthétisé des nanotubes de carbone mono- et multi-feuillets par décomposition catalytique en phase vapeur sur des substrats dédiés. L'aspect principal du travail est basé sur l'utilisation combinée de plusieurs sondes expérimentales sur la même nanostructure carbonée individuelle. Nous avons effectué une analyse structurale complète par diffraction électronique et microscopie électronique haute résolution et mesuré les spectres Raman de ces nanostructures individuelles. Plusieurs effets environnementaux importants ont été mis en évidence pour la première fois, comme par exemple l'effet d'un couplage mécanique (due à l'interaction de van-der-Waals) entre les parois des nanotubes bi-feuillets conduisant à une modification des modes Raman de basse fréquence et des conditions de résonances optiques. De plus, le comportement des modes de haute fréquence des nanotubes bi-feuillets a été analysé. Suite à ce travail plusieurs critères expérimentaux permettant un diagnostic de la structure des nanotubes multi-feuillets ont été proposés.The main objective of this work is the fundamental physical study of individual isolated carbon nanostructures in order to address their intrinsic vibrational and optical properties and also to estimate and quantify the environmental effects. For these purposes, we synthesized individual single- and multi-walled carbon nanotubes by chemical vapour deposition method on dedicated substrates. The main aspect of the work involves the combined use of different experimental probes on the same individual nanostructures. We performed a complete structure analysis by electron diffraction and high-resolution electron microscopy and the measurement of the Raman spectra on these individual nanostructures. Several important environmental effects were evidenced for the first time, e.g. the effect of mechanical coupling (van-der-Waals interaction) between the layers of double-walled carbon nanotubes leading to the change in the low-frequency Raman modes and the optical resonance conditions. Moreover the behaviour of high-frequency modes of double-walled tubes was also analysed and described. As a result of this work several experimental criteria for structure diagnostics of multi-walled carbon nanotubes were proposed.MONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF

Role of Mechanical van der Waals Coupling in the G-Band Splitting of Individual Multiwall Carbon Nanotubes

Characterization of multiwalled carbon nanotubes (MWCNT) by Raman spectroscopy is challenging due to their structural complexity, inhomogeneity, and complicated interlayer van der Waals (vdW) interactions. These latter effects can be however well investigated in individual MWCNTs, prepared by the on-chip purification of arc-discharge (AD) MWCNT powder, combining atomic force microscopy, polarized Raman imaging, and spectroscopy. In this work, we reveal the inhomogeneity of the Raman signal from individual AD-MWCNTs and attribute it to the extraction of inner layers during the sonication stage of the dispersion procedure. We report the splitting of the Raman-active G-band, describing it in terms of the variation of interlayer mechanical vdW coupling as a function of diameter and interlayer distance in the probed AD-MWCNTs. Finally, we present a practical method for investigating the polarization behavior of MWCNTs with a nonuniform Raman response based on Raman mapping and advanced data fitting. Our work gives additional insights into the characterization of structurally nonuniform MWCNTs and allows distinguishing between these MWCNTs and 1D moiré crystals based on collapsed SWCNTs or studying telescopic 1D vdW heterostructures with Raman spectroscopy.peerReviewe

Role of mechanical van der Waals coupling in the G-band splitting of individual multiwall carbon nanotubes

Characterization of multiwalled carbon nanotubes (MWCNT) by Raman spectroscopy is challenging due to their structural complexity, inhomogeneity, and complicated interlayer van der Waals (vdW) interactions. These latter effects can be however well investigated in individual MWCNTs, prepared by the on-chip purification of arc-discharge (AD) MWCNT powder, combining atomic force microscopy, polarized Raman imaging, and spectroscopy. In this work, we reveal the inhomogeneity of the Raman signal from individual AD-MWCNTs and attribute it to the extraction of inner layers during the sonication stage of the dispersion procedure. We report the splitting of the Raman-active G-band, describing it in terms of the variation of interlayer mechanical vdW coupling as a function of diameter and interlayer distance in the probed AD-MWCNTs. Finally, we present a practical method for investigating the polarization behavior of MWCNTs with a nonuniform Raman response based on Raman mapping and advanced data fitting. Our work gives additional insights into the characterization of structurally nonuniform MWCNTs and allows distinguishing between these MWCNTs and 1D moiré crystals based on collapsed SWCNTs or studying telescopic 1D vdW heterostructures with Raman spectroscopy.peerReviewe

Probing the Intrinsic Vibrational and Optical Properties ofIndividual Chirality-Identified Carbon Nanotubes by Raman Spectroscopy

International audienceThe goal of this chapter is to review the main information derived from Raman spectroscopy on individual suspended (free-standing) chiralityidentified single-wall carbon nanotubes (SWCNTs) and double-wall carbonnanotubes (DWCNTs) with a special focus on the characteristics of their radial breathing modes and G modes, including their resonance conditions. ForSWCNTs, the different relationships between the radial breathing mode frequency and the inverse of the diameter illustrate the high sensitivity of individual suspended SWCNTs to their environmental conditions. The intrinsicprofiles of the optical longitudinal (LO) and transverse (TO) G modes are unambiguously identified both for metallic and semiconducting chiral and achiral SWCNTs, and the diameter dependence of the LO and TO frequencies are established. In DWCNTs, the intertube coupling, originating from the van der Waals interaction between the inner and outer tubes, plays an important role in determining the features/characteristics of the collectiveradial breathing-like modes and G modes