Excitation and chirality dependence of the exciton-phonon coupling in carbon nanotubes

Goupalov, S. V.; Satishkumar, B. C.; Doorn, Stephen K.

doi:10.1103/physrevb.73.115401

Cited by 40 publications

(88 citation statements)

References 18 publications

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“…In general, as the chiral angle increases within the same family of nanotubes, the M ph values decrease, in agreement with previous reported results. 16,21,22,24,25,30,41 While we obtain fewer M ph values for aggregated SWNTs, a similar trend in M ph vs is observed as for the individually dispersed nanotubes. This confirms an earlier assumption that, to a first approximation, the chiralangle dependence of M ph is preserved upon bundling.…”

Section: ͑5͒supporting

confidence: 80%

“…Primarily, nanotubes of mod-2 type ͓defined as mod͑n − m ,3͒ =2͔ are observed, due to their stronger excitonphonon interaction matrix elements in comparison to their mod͑n-m ,3͒ =1 ͑or mod-1͒ counterparts. 21,23,26,30 Similar data were acquired over the full excitation range on aggregated ͑bundled͒ samples. In the intermediate Raman shift region ͑380-650 cm −1 ͒, we observed two types of peaks: ͑i͒ asymmetric peaks exhibiting sharp edges on the low frequency side and tails toward higher frequencies, and ͑ii͒ symmetric peaks.…”

Section: Resultsmentioning

confidence: 99%

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Bundling effects on the intensities of second-order Raman modes in semiconducting single-walled carbon nanotubes

2008

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The second-order Raman modes in the range of 380-650 cm −1 were investigated for individually dispersed and aggregated HiPco single-walled carbon nanotubes ͑SWNTs͒ using a 700-985 nm tunable laser source. For individually dispersed SWNTs, this Raman region displays relatively weak response from both intermediate frequency modes ͑IFMs͒ and the overtones of the radial breathing mode ͑RBM͒, with the latter dominating. In contrast, for aggregated SWNTs, the IFMs dominate and gain significant intensity relative to the RBM fundamental. Utilizing the correlation between RBM overtone and RBM fundamental intensity ratio as a function of laser energy, we derived Huang-Rhys factors for several ͑n , m͒ nanotube species in both individually dispersed and aggregated states. These values were further used to obtain the corresponding absolute values of the exciton-phonon interaction matrix element for these nanotube species. It is demonstrated that the chiral-angle dependence of exciton-phonon coupling parameters is similar for dispersed and bundled samples. However, we find that bundling results in a decrease in the exciton-phonon coupling for the RBM, while the IFMs display the opposite behavior. These findings are particularly relevant for further clarifying the factors that govern Raman intensities and provide a tool for the selective characterization of various mod͑n − m ,3͒ =2 ͑n , m͒-SWNTs as a function of their aggregation state.

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Section: ͑5͒supporting

confidence: 80%

Section: Resultsmentioning

confidence: 99%

Bundling effects on the intensities of second-order Raman modes in semiconducting single-walled carbon nanotubes

2008

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“…In fact, the zigzag or (3n,0) species can possess as much as an order of magnitude larger M e−ph than the armchair species, for the same 2n+m family. 128,130,131 Combining both matrix element behaviors together, Jiang et al and Sato et al observe (as shown in Fig. 12) an increase in Raman intensity I RRS with decreasing diameter and decreasing chiral angle for metallic species, illustrating the need for correcting experimentally determined, integrated Raman intensities for (n, m)-dependent Raman cross-sections to compare each chiral species fairly for the purposes of measuring relative abundances.…”

Section: Resonant Raman Scattering Spectroscopy Of Armchair-enricmentioning

confidence: 90%

Fundamental optical processes in armchair carbon nanotubes

Hároz

Duque

et al. 2013

Nanoscale

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Single-wall carbon nanotubes provide ideal model 1-D condensed matter systems in which to address fundamental questions in many-body physics, while, at the same time, they are leading candidates for building blocks in nanoscale optoelectronic circuits. Much attention has been recently paid to their optical properties, arising from 1-D excitons and phonons, which have been revealed via photoluminescence, Raman scattering, and ultrafast optical spectroscopy of semiconducting carbon nanotubes. On the contrary, dynamical properties of metallic nanotubes have been poorly explored, although they are expected to provide a novel setting for the study of electron-hole pairs in the presence of degenerate 1-D electrons. In particular, (n,n)-chirality, or armchair, metallic nanotubes are truly gapless with massless carriers, ideally suited for dynamical studies of Tomonaga-Luttinger liquids. Unfortunately, progress towards such studies has been slowed by the inherent problem of nanotube synthesis whereby both semiconducting and metallic nanotubes are produced. Here, we use post-synthesis separation methods based on density gradient ultracentrifugation and DNAbased ion-exchange chromatography to produce aqueous suspensions strongly enriched in armchair nanotubes. Through resonant Raman spectroscopy of the radial breathing mode phonons, we provide macroscopic and unambiguous evidence that density gradient ultracentrifugation can enrich armchair nanotubes. Furthermore, using conventional, optical absorption spectroscopy in the nearinfrared and visible range, we show that interband absorption in armchair nanotubes is strongly excitonic. Lastly, by examining the G-band mode in Raman spectra, we determine that observation of the broad, lower frequency (G − ) feature is a result of resonance with non-armchair "metallic" nanotubes. These findings regarding the fundamental optical absorption and scattering processes in metallic carbon nanotubes lay the foundation for further spectroscopic studies to probe many-body physical phenomena in one dimension.

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“…Recent tight-binding calculations predicts a strong chirality and family dependence of the eph coupling of the radial breathing mode (RBM) in carbon nanotubes [15,16]. The relative strengths of the e-ph couplings are supported by Raman intensity measurements from a CNT ensemble, assuming a uniform chirality distribution [15].…”

mentioning

confidence: 93%

Optical Determination of Electron-Phonon Coupling in Carbon Nanotubes

et al. 2007

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We report on an optical method to directly measure electron-phonon coupling in carbon nanotubes by correlating the first and second harmonic of the resonant Raman excitation profile. The method is applicable to 1D and 0D systems and is not limited to materials that exhibit photoluminescence. Experimental results for electron-phonon coupling with the radial breathing mode in 5 different nanotubes show coupling strengths from 3-11 meV, depending on chirality. The results are in good agreement with the chirality and diameter dependence calculated by Goupalov et al. PACS: 73.63.Fg, 63.22.+m The intrinsic coupling between the electronic and atomic degrees of freedom is fundamental to many transport and optical properties of condensed matter. Here we examine carbon nanotubes, a prototypical one-dimensional (1D) system under intense study for both fundamental physical properties and potential applications as transistors, sensors and optoelectronic devices. The electron-phonon (e-ph) coupling in carbon nanotubes (CNTs) is a key coupling parameter in the electronic band structure, controls Raman scattering [1], heat and electron conductivity [2], and sets an upper limit to ballistic transport [3,4]. In polar semiconductors, multi-phonon replicas in luminescence have been used to measure the Fröhlich e-ph coupling with longitudinal optical (LO) phonons in good agreement with theory [5,6]. In low dimensional systems, the electron and phonon confinement complicates the situation, with conflicting experimental results [7][8][9][10], and requiring model-dependent interpretation to extract the e-ph interaction. E-ph interactions in CNTs are due to the deformation-potential interaction, generally weaker than Fröhlich interaction in polar materials. Nonetheless, evidence of e-ph coupling in CNTs are observed in photoluminescence phonon replicas [11], the Kohn anomaly manifested in the phonon dispersion and line-widths in metallic nanotubes [12] and temperature dependence of optical transition energies [13,14]. However, direct measurements of e-ph coupling in CNTs are lacking.

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Excitation and chirality dependence of the exciton-phonon coupling in carbon nanotubes

Cited by 40 publications

References 18 publications

Bundling effects on the intensities of second-order Raman modes in semiconducting single-walled carbon nanotubes

Bundling effects on the intensities of second-order Raman modes in semiconducting single-walled carbon nanotubes

Fundamental optical processes in armchair carbon nanotubes

Optical Determination of Electron-Phonon Coupling in Carbon Nanotubes

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