Enrichment of Armchair Carbon Nanotubes <i>via</i> Density Gradient Ultracentrifugation: Raman Spectroscopy Evidence

Hároz, Erik H.; Rice, William; Lu, Benjamin Y.; Ghosh, Souparno; Hauge, Robert H.; Weisman, R. Bruce; Doorn, Stephen K.; Kono, Junichiro

doi:10.1021/nn901908n

Cited by 82 publications

(107 citation statements)

References 30 publications

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“…The RBM frequencies found for the (8,8), (7,7), and (6,6), are 219, 248, and 287 cm −1 , respectively and match those found in previous work 7,19,20,26,27 . The (5,5) RBM frequency is found here to be 338 cm −1 .…”

Section: Resultssupporting

confidence: 89%

“…Additionally, enrichment of the (5,5) (from CoMoCAT SG65EX source material) and (8,8) (from Rice-produced HiPco 107.1r source material) structures was provided via the recently introduced aqueous two-phase extraction technique (ATPE) [21][22][23] . Complementary results obtained on samples enriched from HiPco source material (batch HPR 189.2) using a density gradient ultracentrifugation (DGU) approach 19,24 are presented in the supporting material 25 . In all cases, extensive ultrasonication during processing prior to separation generates samples that are predominantly waterfilled.…”

Section: Methodsmentioning

confidence: 95%

“…This is now possible for specific metallic species as a result of recent advances in separation techniques that yield samples enriched in armchair structures [19][20][21] . Here, we present resonance Raman excitation spectra for the radial breathing mode (RBM) and G-band phonons for the (5,5), (6,6), (7,7), and (8,8) armchair nanotubes.…”

Section: Introductionmentioning

confidence: 99%

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Asymmetric excitation profiles in the resonance Raman response of armchair carbon nanotubes

et al. 2015

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We performed tunable resonance Raman spectroscopy on samples highly enriched in the (5,5), (6,6), (7,7), and (8,8) armchair structures of metallic single-wall carbon nanotubes. We present Raman excitation profiles (REPs) for both the radial breathing mode and G-band phonons of these species. G-band excitation profiles are shown to resolve the expected incoming and outgoing resonances of the scattering process. Notably, the profiles are highly asymmetric, with the higherenergy outgoing resonance weaker than the incoming resonance. These results are comparable to the asymmetric excitation profiles observed previously in semiconducting nanotubes, introduce a new electronic type, and broaden the structural range over which the asymmetry is found to exist. Modeling of the behavior with a third-order quantum model that accounts for the k -dependence in energies and matrix elements, without including excitonic effects, is found to be insufficient for reproducing the observed asymmetry. We introduce an alternative fifth-order model in which the REP asymmetry arises from quantum interference introduced by phonon-mediated state-mixing between the E M 11 and K-momentum excitons. Such state-mixing effectively introduces a nuclear coordinate dependence in the transition dipole moment and thus may be viewed as a non-Condon effect from a molecular perspective. This result unifies a molecular-like picture of nanotube transitions (introduced by their excitonic nature) with a condensed matter approach for describing their behavior.

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Section: Resultssupporting

confidence: 89%

Section: Methodsmentioning

confidence: 95%

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Asymmetric excitation profiles in the resonance Raman response of armchair carbon nanotubes

et al. 2015

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“…117,118 Motivated by these advancements in separation science and also the lack of specific (n, m) composition information in metal-enriched materials, we focused our approach to produce metal-enriched SWCNT material that could be identified as a function of (n, m) composition. We employed a three-surfactant DGU method similar to that of Yanagi et al 69 and described in detail in Hároz et al 119 for HiPco SWCNTs (batch 188.2). For SWCNT material produced by other synthesis methods such as CoMoCAT, other HiPco batches, laser ablation, and arcdischarge material, similar gradient parameters were used as described in Hároz et al 57 Figure 4 shows a photograph of typical, unsorted SWCNT material appearing black on the left side and the resulting metal-enriched layers from CoMoCAT, three different HiPco batches, laser ablation, and arc-discharge materials appearing yellow, orange, pink, purple, cyan, and green, respectively, on the right side.…”

Section: A Density Gradient Ultracentrifugationmentioning

confidence: 99%

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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“…3), (5,5) and (6,6) armchairs absorb strongly in the blue, resulting in a yellow-colored suspension. Armchair-enriched laser ablation SWCNT material absorbs strongly in the red due to (9,9) and (10,10), producing a cyan-colored suspension. Armchairenriched samples #3 and #4, which are produced from HiPco material, absorb mainly in the green region, producing suspensions that are colored magenta to purple, depending on the varying amounts of (7,7), (8,8), and (9,9) absorbed.…”

Section: Introductionmentioning

confidence: 99%

Unique Origin of Colors of Armchair Carbon Nanotubes

Hároz

Duque

et al. 2012

J. Am. Chem. Soc.

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ABSTRACT:The colors of suspended metallic colloidal particles are determined by their size-dependent plasma resonance, while those of semiconducting colloidal particles are determined by their size-dependent band gap. Here, we present a novel case for armchair carbon nanotubes, suspended in aqueous medium, for which the color depends on their sizedependent excitonic resonance, even though the individual particles are metallic. We observe distinct colors of a series of armchair-enriched nanotube suspensions, highlighting the unique coloration mechanism of these one-dimensional metals.The size-dependent colors of suspended colloidal particles have fascinated researchers, engineers, and artists for centuries. While quantum confinement always plays a fundamental role, the coloration mechanism can differ depending on whether the particles are metallic or semiconducting. For metallic nanoparticles, their colors are determined by the freecarrier plasma resonance whose frequency depends on the electron density as well as the particle size and shape. 1 For semiconducting nanoparticles, the key parameter is the sizedependent fundamental band gap, i.e., the separation between the top of the valence band (HOMO) and the bottom of the conduction band (LUMO), which sensitively changes with quantum confinement, i.e., size. 2 Here, we present a novel case for armchair single-walled carbon nanotubes (SWCNTs), suspended in aqueous medium, for which the origin of their color depends on the interband excitonic resonance even though the individual particles are gapless, i.e., metallic. Armchair nanotubes enjoy a rather special status among the SWCNT family. The structure of each member, or species, of the family is uniquely specified by a pair of integers, (n,m), resulting in different species possessing different diameters, chiral angles, and electronic types (semiconducting or metallic). 3 Armchair SWCNTs are characterized by the simple relation n = m, i.e., (n,n), and they are known to be the only truly gapless species with excellent electrical properties, exhibiting ballistic conduction even at room temperature. 4 At the same time, their one-dimensional characteristics combined with their linear band dispersions have attracted much fundamental interest for exploring many-body phenomena. 5 However, systematic studies of macroscopic ensembles of armchair nanotubes have been impossible due to the coexistence of different (n,m) species of nanotubes in asgrown samples.Recent years have seen impressive progress in post-growth separation of SWCNTs using a variety of methods. One of the most successful methods has been density gradient ultracentrifugation (DGU), 6-10 which can sort out different species of SWCNTs in bulk quantities according to their diameters, chiralities, and electronic types, enabling studies of (n,m)-dependent properties using standard macroscopic characterization measurements. In a recent report, 10 we provided unambiguous evidence of bulk enrichment of armchair nanotubes through DGU by utilizing wavelength-dependen...

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Enrichment of Armchair Carbon Nanotubes via Density Gradient Ultracentrifugation: Raman Spectroscopy Evidence

Cited by 82 publications

References 30 publications

Asymmetric excitation profiles in the resonance Raman response of armchair carbon nanotubes

Asymmetric excitation profiles in the resonance Raman response of armchair carbon nanotubes

Fundamental optical processes in armchair carbon nanotubes

Unique Origin of Colors of Armchair Carbon Nanotubes

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