Raman Spectroscopic Investigation of Individual Single-Walled

Subscriber access provided by UNIV OF ARIZONA

Article

Raman Spectroscopic Investigation of Individual Single-Walled Carbon Nanotubes Helically Wrapped by Ionic, Semiconducting Polymers Sebastien Bonhommeau, Pravas Deria, Mary G. Glesner, David Talaga, Samar Najjar, Colette Belin, Leopold Auneau, Sebastien Trainini, Michael J. Therien, and Vincent Rodriguez J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/jp4037606 • Publication Date (Web): 20 Jun 2013 Downloaded from http://pubs.acs.org on June 24, 2013

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

The Journal of Physical Chemistry C is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 35

The Journal of Physical Chemistry

20 June 2013 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Raman Spectroscopic Investigation of Individual SingleWalled Carbon Nanotubes Helically Wrapped by Ionic, Semiconducting Polymers Sébastien Bonhommeau,*,† Pravas Deria,‡ Mary G. Glesner,‡ David Talaga,† Samar Najjar,† Colette Belin,† Léopold Auneau,† Sébastien Trainini,† Michael J. Therien,‡ and Vincent Rodriguez† †

Université de Bordeaux, Institut des Sciences Moléculaires, CNRS UMR 5255, F-33400 Talence, France, and ‡Department of Chemistry, French Family Science Center, 124 Science Drive, Duke University, Durham, North Carolina 27708, USA.

*To whom correspondence should be addressed. E-mail: [email protected] RECEIVED DATE (to be automatically inserted after your manuscript is accepted if required according to the journal that you are submitting your paper to)

ABSTRACT Raman-active vibrational modes of (6,5) chirality-enriched single-walled carbon nanotubes

(SWNTs),

helically

wrapped

by

semiconducting

poly[2,6-{1,5-bis(3-

propoxysulfonicacidsodiumsalt)}naphthylene]ethynylene (PNES), are described in great detail. At an irradiation wavelength of 568.2 nm, the extent to which the environment impacts the nanotube vibrational signature can be probed; in particular, the absence of a G band shift for PNES-[(6,5) SWNT] samples relative to benchmark surfactant-coated nanotubes indicates the lack of any significant charge transfer between the PNES strand and the SWNT skeleton, but electronic spectra provide compelling evidence for polymer-to-SWNT energy transfer. At an irradiation wavelength of 457.9 nm, vibrational ACS Paragon Plus Environment

1


Page 2 of 35

20 June 2013 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

modes associated with PNES chains that wrap (6,5) SWNTs are conspicuously enhanced. Under 514.5 nm irradiation, PNES-[(6,5) SWNTs] are not excited in resonance but G and G’ bands associated with these nanohybrids are strongly enhanced, reflecting the excitation of a multiphonon-mediated vibronic transition of the (6,5) SWNT backbone. At a 488.0 nm irradiation wavelength, Raman spectral signatures of both the PNES polymer and the vibronically-excited (6,5) SWNT skeleton through onephonon-assisted processes are pronounced, demonstrating that a specific SWNT chirality and the corresponding semiconducting polymer helically wrapped about its surface can be probed using an excitation wavelength that does not resonantly excite the SWNT structure.

KEYWORDS Single-walled carbon nanotube, Raman and electronic spectroscopy, atomic force microscopy. 1. INTRODUCTION Single-walled carbon nanotubes (SWNTs)1,2 possess many atypical mechanical,3-7 optical,8-11 electrical,12-16 magnetic,17-19 and thermal20,21 properties that open the way to the elaboration of a wide range of promising functional materials. Strong van der Waals interactions between nanotubes impede however interrogation of individualized SWNTs.16 Noncovalent solubilization strategies, that have exploited a wide range of surfactants, small molecules, and polymers, are currently employed to diminish the extent of nanotube-nanotube noncovalent associative interactions.22,23 Among these dispersive agents, conjugated polymers have attracted considerable attention24-31 as such systems offer the additional opportunity to tailor new types of SWNT-based electro-optic functionalities.32-36 In particular, SWNTs dispersed via interaction with the highly charged semiconducting poly[2,6-{1,5bis(3-propoxysulfonicacidsodiumsalt)}naphthylene]ethynylene

(PNES),

provide

noncovalently

modified SWNT samples in which a polymer monolayer helically wraps the nanotube surface at periodic and constant morphology (helical pitch length = 10 ± 2 nm).24-27

ACS Paragon Plus Environment

2

Page 3 of 35


20 June 2013 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Spectral characterization of polymer-SWNT hybrids have been carried out using a plethora of techniques that include electronic absorption, emission, and vibrational spectroscopies.24-27,30,31,35-38 These techniques have been used to track changes in transition energies, spectral breadths, and oscillator strengths associated with the polymer-SWNT interaction,8,39,40 and the extent to which the polymer impedes SWNT bundling. In addition, these methods have been utilized to distinguish metallic and semiconducting SWNTs, and signatures associated with specific SWNT chiralities. Raman spectroscopy, in particular, represents a very powerful technique to scrutinize charge transfer between the carbon skeleton and the surrounding molecules as well as the nature of SWNT distortions relative to an idealized structure.35,37,38,41 Sometimes it allows the spectral signature of both the SWNT backbone and these molecules to be identified at the same irradiation wavelength.38,42 However, in order to obtain a Raman signal of sufficient intensity, SWNT resonant light excitation is typically required, which often prevents concomitant spectral detection of molecular structures that may be associated with the nanotube.37,43 Here, we report confocal Raman microscopic, electronic, and combined confocal Raman and atomic force microscopy (AFM) spectroscopic investigations of PNES-wrapped (6,5) chirality-enriched SWNTs (PNES-[(6,5) SWNTs]), obtained in >85% purity through a combination of linear and nonlinear density gradient ultracentrifugation methods, in aqueous solution (Scheme 1) and as drop-cast high- and low-density (monolayer) films. These studies: (i) examine the extent to which the PNES electronic structure impacts nanotube Raman-active vibrational modes in these self-assembled helical polymer-SWNT superstructures and (ii) demonstrate that a specific SWNT chirality and the corresponding semiconducting polymer helically wrapped about its surface can be probed at the same excitation wavelength without the constraint to resonantly excite the SWNT structure.

2. EXPERIMENTAL DETAILS 2.1 Sample preparation ACS Paragon Plus Environment

3


Page 4 of 35

20 June 2013 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The PNES polymer, PNES-SWNT, and SC (sodium cholate)-SWNT suspensions in water were prepared following procedures described in detail elsewhere.24-27 These suspensions were prepared from HiPco nanotubes and enriched with (6,5) chirality SWNTs via a two-cycle, density gradient ultracentrifuge (DGU) separation technique yielding a final solution containing ~85% (mass percentage) (6,5) chirality-enriched SWNTs with a 15% mass residue dominated by (7,5), (7,6) and (9,1) chiralities. In order to prepare the SC-[(6,5) SWNTs]/H2O sample, a DGU-separated (6,5) SWNT solution (2 mL) was passed through a short desalting column (ZebaTM, molecular weight cut-off = 3000; presaturated with 1% SC in H2O) using 1% SC in H2O as eluant. The purple colored SC-[(6,5) SWNTs]/H2O suspension was collected in a clean vial; the resulting suspension had an optical density (OD) of 1.23 at 982 nm in a 2 mm-thick cuvette, which corresponded to a SWNT concentration of ~85 µg/mL. Likewise, the SC-[(6,5) SWNTs]/D2O sample was obtained by using 1% SC in D2O instead of H2O solvent, and the resulting suspension (OD = 2.02 at 982 nm in a 2 mm-thick cuvette) was diluted with 1% SC in D2O to an OD of 0.74 at 982 nm for spectroscopic studies. In order to prepare the PNES-[(6,5) SWNTs]/H2O sample, an aqueous solution of PNES was mixed with 2 mL of DGU-separated, surfactant (mixed sodiumdodecylsulfate (SDS) and SC) coated (6,5) SWNT solution. This mixture was stirred overnight and subsequently dialyzed against deionized water using a 10000 MWCO membrane. After extracting surfactant and iodixanol (used as the DG medium during the (6,5) chirality enrichment process), the PNES-wrapped (6,5) SWNT suspension was filtered through a 100-nm pore cellulose membrane to remove excess/free polymer. The concentrated PNES[(6,5) SWNT] suspension was washed with H2O several times until the filtrate became void of free polymer. The concentrated solution was then centrifuged at 26000g for 25 min. The upper 80% of the supernatant was carefully harvested, and centrifuged again at 33000g for 25 min. The upper 60% of the supernatant was carefully collected and transferred to a clean vial. The pH of the solution was adjusted to 7.5 with NaOH. The resulting suspension had an OD of 0.44 at 1002 nm in a 2 mm-thick cuvette, which corresponds to a SWNT concentration of ~35 µg/mL. Likewise, the corresponding PNES-[(6,5) ACS Paragon Plus Environment

4

Page 5 of 35


20 June 2013 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

SWNT]/D2O sample was prepared by filtering and washing a PNES-wrapped (6,5) SWNT suspension in H2O through a 100-nm pore cellulose membrane with D2O (5x3 mL). The concentrated solution in D2O solvent was then centrifuged at 26000g for 30 min. The upper 80% of the supernatant was carefully harvested and centrifuged again at 33000g for 30 min. The upper 60% of the supernatant was carefully collected and transferred to a clean vial. The pH of the solution was adjusted to 9.3. The resulting suspension (OD = 0.87 at 1002 nm in a 2 mm-thick cuvette) was diluted with D2O to an OD of 0.58 at 1002 nm for spectroscopic studies.

2.2 Spectroscopic techniques and microscopy methods Raman measurements were carried out in backscattering geometry using two commercial (Horiba Jobin Yvon) confocal Raman spectrometers, a long focal length (f = 800 mm) Labram HR800, and a Labram II instrument (motorized xyz stage, 1800 grooves/mm and 600 grooves/mm gratings, two shortworking-distance (100× and 50×) and two long-working-distance (20× and 10×) objectives with numerical apertures (NA) of 0.90, 0.75, 0.35 and 0.25). The 1800 grooves/mm grating was selected to reach a high spectral resolution (∼ 1-2 cm-1) when studying subtle peak shifts. Short-working-distance objectives were appropriate to investigate PNES and SC solids as well as PNES-[(6,5) SWNT] and SC[(6,5) SWNT] films obtained via drop-casting on borosilicate glass coverslips (Electron Microscopy Sciences). The 20× long-working-distance objective was dedicated to liquid samples contained within 120 µL quartz cuvettes. The 10× objective was devoted to rough sample positioning. Irradiation wavelengths (568.2, 514.5, 488.0 and 457.9 nm) correspond to the emission lines of Ar+ and Kr+ lasers. In order to avoid sample damage, all the measurements carried out on solids (PNES and SC powders and drop-cast suspensions) were performed with laser powers ranging between 10 and 100 µW, while higher laser powers up to 9 mW were employed for liquid samples. A DuoScan device composed of two mirrors was activated, whenever needed, in order to prevent any sample degradation, allowing the


5


Page 6 of 35

20 June 2013 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

excitation beam to scan micron-sized areas in the confocal regime instead of being fixed on a single spot. An apparatus combining atomic force microscopy (AFM) and Raman spectroscopy was used to realize the topographic and chemical characterization of single nanostructures.44 In brief, this instrument features a commercial Raman spectrometer (Horiba Jobin Yvon, Labram HR800) coupled with an inverted optical microscope (Olympus IX 71) and a commercial atomic force microscope (Bruker, Bioscope II). This instrument enabled on-axis AFM and Raman measurements in backscattering geometry using a 60× short-working-distance water immersion objective (NA = 1.20). A 600 grooves/mm grating, providing good spectral resolution (∼ 3 cm-1), was employed in this system. Irradiation at 568.2 nm was carried out using an Ar+/Kr+ laser. AFM was undertaken in tapping mode using commercial tips (Nanosensors PPP-NCHR, silicon tips, 350 kHz resonance frequency, 70N/m force constant). Note that the AFM tip was systematically lifted up by 5 µm from the nanotube surface before collecting the Raman scattered signal in order to avert mechanical perturbations on the SWNT sidewalls.7 To optimize dispersion of SWNTs, as-prepared solutions of PNES-[(6,5) SWNTs] were diluted 10 fold (final concentration ~ 3 µg/mL) and drop-cast on a borosilicate glass coverslip preexposed to UV light (254 nm; mercury lamp NIQ 60/35XL, Heraeus Noblelight, France) for 30 min, in order to increase its hydrophilic character by creating terminal Si-OH functionality on the borosilicate glass. This procedure was utilized to produce the low-density films. Electronic absorption spectral measurements of as-prepared SC-[(6,5) SWNT] and PNES-[(6,5) SWNT] suspensions in water were carried out with a double beam spectrometer (SAFAS Monaco 190 DES) over the 250-750 nm range at 2-nm spectral resolution. Visible-near infrared micro-absorption measurements of high-density drop-cast films (10 µL of the aforementioned SC-[(6,5) SWNT] and PNES-[(6,5) SWNT] solutions dripped onto a borosilicate glass slide) were carried out over the 400950 nm spectral range using a tailor-made experimental setup45 equipped with a deuterium tungstenhalogen fiber optic light source and a Mikropack dh-2000 excitation source. In this experimental ACS Paragon Plus Environment

6

Page 7 of 35


20 June 2013 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

system, light was guided by an optical fiber having a 100 µm core diameter, collimated by a 10× objective, and finally focused onto the sample using a 20× objective. The spot size at the sample was 50 µm. The transmitted light was collected using a 10× objective and analyzed by a Horiba Jobin Yvon HR800 confocal spectrometer. This spectrometer, equipped with a 150 grooves/mm grating and a Symphony detector, provided a spectral resolution of 2 nm. The absorbance A was inferred from the relation A=log10(I0/I), where I and I0 are respectively the transmitted intensities through a coated and uncoated area on a glass slide. SC-[(6,5) SWNT] and PNES-[(6,5) SWNT] emission and excitation spectra were recorded on an Edinburgh FLSP920 steady state luminescence instrument that utilizes a Xe lamp for excitation and a Hamamatsu H10330-75 (900-1700 nm) PMT detector. Emission spectra were recorded over a 940-1300 nm spectral range (1 nm steps; integration time = 0.5 s) by exciting the E S22 transition (~580 nm) of the [(6,5) SWNT] samples. A 5 nm slit width was used for both the excitation and emission beams; the excitation beam was passed through a 550 nm long-pass filter to remove second order scattering light from the lamp and grating, and an 830 nm long-pass filter was used on the emission side to eliminate scattered light. The final emission spectra were obtained by averaging data collected over 5 scans and correcting for variations in detector response as a function of wavelength using correction files supplied by the National Bureau of Standards. Excitation spectra for [(6,5) SWNT] samples, probed at λem = 982 and 1009 nm, were recorded over the 300-700 nm spectral domain in two segments: the 300-550 nm segment was collected without any filter for the excitation light beam, while the 480-700 nm segment utilized a 455 nm long-pass filter for the excitation beam. These two spectral segments, for each sample, were appended at 515 nm, averaged over 5 scans, and then corrected for variations in photomultiplier response as a function of wavelength using correction files generated from the spectral output of a calibrated light source supplied by the National Bureau of Standards. For excitation-emission spectral maps, the excitation wavelength was varied from 300 to 700 nm at 5 nm increments over the spectral segments noted above; emission spectra were compiled over the 950 to 1300 nm spectral domain (1 nm ACS Paragon Plus Environment

7


Page 8 of 35

20 June 2013 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

steps; integration time = 0.5 s). These two sets of excitation-emission data (300-520 nm, 500-700 nm) were corrected and merged using Origin 7.5 software to construct excitation-emission spectral maps. All spectroscopic measurements were carried out at 23 ± 1 °C.

3. RESULTS AND DISCUSSION SWNTs evince densities of electronic states typified by the presence of van Hove singularities in the conduction and valence bands for all (n,m) chiralities, where n and m indices are positive or null integers.40 Interband transitions between these singularities render possible absorption of visible light and emission in the near-infrared (NIR) range.8,9 Figure 1 shows absorption spectra of PNES-[(6,5) SWNT] and SC-[(6,5) SWNT] aqueous solutions as well as PNES-[(6,5) SWNT] and SC-[(6,5) SWNT] high-density films on glass slides. SC-[(6,5) SWNTs] are considered an experimental benchmark in these studies, as it is commonly accepted that ionic surfactants impede nanotube aggregation and that SWNT electronic properties and Raman spectral profiles remain largely unaltered as a function of surfactant.46 Marked absorption bands are observed at 573 nm for SC-[(6,5) SWNTs] and at 580 nm for PNES-[(6,5) SWNTs], irrespective of the sample liquid or solid state. These transition wavelengths lie very close to the measured E S22 transition of (6,5) nanotubes dispersed in aqueous SDS suspension (567 nm).8 Figures 2A and 2E present Raman spectra obtained for a PNES-[(6,5) SWNT] solution using a 568.2 nm excitation wavelength (top spectra). The 568.2 nm laser wavelength excites (6,5) nanotubes near resonance,8 and characteristic SWNT spectral bands are easily distinguished. The radial breathing modes (RBMs) emerge at 309 cm-1 for (6,5) SWNTs and at 336 cm-1 for (6,4) SWNTs (Figure S1A), congruent with literature.8 Spectral contributions of (9,1), (7,5) and (7,6) nanotubes are absent, as SWNTs of these chiralities feature E S22 transitions that are not resonant with the excitation wavelength.8 The tangential G band derived from the graphite-like in-plane mode is located at 1587 cm-1. This band usually consists of two main components, namely the G+ and G- bands, associated respectively with ACS Paragon Plus Environment

8

Page 9 of 35


20 June 2013 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

axially and radially directed vibrations.40 In these PNES-SWNT samples, the G band region can be decomposed into a sum of three Lorentzians: the G- band at the lowest frequency,47 the G+ band at the highest frequency, and an intermediate Raman-active mode tentatively tied to E2 symmetry48 (Figure S1C). These bands emerge at 1526, 1587, and 1546 cm-1, respectively, in liquid suspensions. The disorder-induced D band is observed at 1311 cm-1 (Figure S1B), while its second-order harmonic (the G’ band) is centered at 2630 cm-1 (Figures 2E and S1D). For liquid samples, the Raman band of water can be discerned as well at ~3200 cm-1 (not shown in Figure 2). Multiple (12) isolated individual PNES-[(6,5) SWNT] superstructures, selected on low-density films in diverse orientations with respect to the laser light polarization (tilted by 23° relative to the y-axis, Figure 2C), were interrogated using AFM/Raman measurements that utilized 568.2 nm excitation. All the Raman spectra showed a silicon optical phonon peak of the AFM tip at ∼521 cm-1, as well as broad marker bands of the glass substrate near 433 and 925 cm-1 (Figure 2A). Furthermore, no Raman features that are associated with SWNTs can be distinguished when moving the laser spot to a region void of SWNTs, demonstrating that the alignment between the laser, the tip and the sample is preserved and optimized. Characteristic D, G-, E2, G+ and G’ bands are centered at 1311, 1525, 1544, 1587 and 2620 cm-1, respectively (Figures 2A and 2E). Note that the band located at 632 cm-1 is related to the SWNT skeleton, as its intensity grows in parallel with that of the D and G bands and diminishes upon irradiation of a glass substrate region void of SWNTs (Figure 2A). We assign this peak to be an intermediate frequency mode (IFM), known to range from 600 to 1100 cm-1; such IFMs are considered to be combination modes thought to derive from double-resonance processes.49,50 RBMs can be discerned at about 311 cm-1 for these isolated (6,5) SWNTs, close to the value observed for PNES-[(6,5) SWNTs] in solution (Figure 2A). The cross-section of an isolated individual SWNT along the drawn dashed line (Figure 2C) shows that the nanotube is 1.3 nm high (Figure 2D). Since the diameter of pristine (6,5) SWNTs is expected to be 0.76 nm,8 this height nicely reflects the 1.3 nm diameter of a


9


Page 10 of 35

20 June 2013 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

helically wrapped (6,5) nanotube.24 The 15 nm lateral width mirrors the SWNT breadth convolved with the tip apex curvature radius (10-20 nm) of the AFM tip. Key differences can be discerned in the Raman spectra of individual isolated PNES-[(6,5) SWNTs] relative to corresponding liquid samples; these include enhancements of IFM, D and G’ band intensities, and a downshift of the G’ band frequency. Note that the consistent ID/IG ratio (~0.6) measured for 12 nanotubes (Figure 2B), where ID and IG are the integrated intensities of D and G+ bands respectively, underscores the reproducibility of these observations. A sample-to-sample increase in the D band intensity is generally ascribed to an increased sp2 disorder. In pristine SWNTs, sp2 disorder can be related to the presence of defects such as missing atoms (vacancy defects), non-hexagonal carbon rings (Stone-Wales or topological defects) or sp2 to sp3 rehybridization.51 Vacancy defects can appear in nanotubes during purification or as a result of electron/ion irradiation.51,52 Topological defects can be created during the SWNT growth at high temperature (> 1,000 K).53,54 Rehybridization defects can be produced by conversion of an sp2 C to an sp3 C on the nanotube surface via SWNT covalent modification.55 All of these mechanisms that cause disorder in the SWNT sp2 framework cannot result from deposition onto a glass slide, and thus cannot account for the D band enhancements observed for isolated PNES-SWNTs relative to corresponding conventional solution-dispersed samples. Nanotube bending can also be ruled out as a possible cause, since the stretching of C-C bonds in the bent region causes a downshift of the G+ band56 and modifies the band gap of semiconducting SWNTs.57 As IFM, D and G’ bands are all double-resonance spectral features,49 we presume that this spectral anomaly is tied to a double-resonance effect that is enhanced by the (6,5) van Hove singularity. It has been suggested that the D band intensity may show a sharp maximum when a van Hove singularity is matched in the joint density of states by either the incoming or outgoing scattered light.58 Such a specific enhancement mechanism would imply at least a weak electronic perturbation of PNES-[(6,5) SWNTs] after desolvation, since it does not occur for PNES-[(6,5) SWNT] liquid suspensions (Figure 2A). Such a weak electronic perturbation is perhaps indicated by the slightly increased RBM intensity for isolated ACS Paragon Plus Environment

10

Page 11 of 35


20 June 2013 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

PNES-[(6,5) SWNTs] on a glass slide (Figure 2A) relative to solution, and the ∼10 cm-1 downshift of the G’ band frequency that occurs with desolvation (Figure 2E). The G’ band, which is a Ramanallowed second-order feature observed for all sp2 carbon materials, is indeed known to be extremely sensitive to the SWNT π-electronic structure. For example, this band has been used to assess the number of layers in graphene samples despite the fact that the interaction between layers is very weak,59 and to study the influence of p and n doping on bare SWNTs.60 From these AFM/Raman measurements carried out using an irradiation wavelength of 568.2 nm, we have been able to excite specifically PNES-[(6,5) SWNTs], and probe their Raman spectral signature. Such spectroscopic measurements cannot be carried out in liquid suspensions and films using conventional confocal Raman microscopy, since (6,4) superstructures can also be resonantly excited (Figures 2 and S1), which are present in trace quantities even in highly (6,5)-enriched samples. Considering the scattering cross-section of SDS-[(6,4) SWNTs] is ∼7-fold higher relative to that for (6,5) species,61 the low-intensity RBM band corresponding to the (6,4) chirality as shown in Figure S1 suggests the presence of only ∼1.7% PNES-[(6,4) SWNTs] in these liquid suspensions. This work thus shows that chiralities of high scattering cross-section can be detected at low concentrations; the presence of such SWNT heterogeneity is problematic when precise descriptions of the spectroscopic features characteristic of a single SWNT chirality is desired if only aqueous suspensions are interrogated, especially in the G band region where the Raman signals for each nanotube chirality would overlap. Likewise, a similar problem will occur with 647.1 nm excitation, as this wavelength excites resonantly (7,5) and (7,6) chiralities that have significantly different scattering cross-sections.8,61

Moreover,

studying isolated nanotubes is particularly crucial when using non-chirality-enriched polymer-wrapped samples since both semiconducting and metallic species may be excited in resonance (e.g., metallic (12,3) and semiconducting (6,5) and (6,4) SWNTs can be excited with 568.2 nm irradiation).8,39 Raman spectra associated with PNES-[(6,5) SWNTs] and SC-[(6,5) SWNTs] present RBMs with analogous full width at half maximum (FWHM, assessed from Lorentzian fitting) of ∼4-6 cm-1 ACS Paragon Plus Environment

11


Page 12 of 35

20 June 2013 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

irrespective of the physical state of the sample (liquid solution, low-density or high-density films; Figures 2A, 4A and S1A). These FWHM values match the estimated natural line width of ∼3 cm-1 for RBMs associated with pristine SWNTs grown on a Si/SiO2 substrate through chemical vapor deposition (CVD).37,62 Unlike RBMs, the FWHM of the G+ band varies depending on the sample state of SC-[(6,5) SWNTs] and PNES-[(6,5) SWNTs]; for liquid suspensions and low-density films, a FWHM of ∼10 cm-1 (Figures 2A and S1C) is observed, which is close to the estimated natural line width of ∼5 cm-1, as inferred from the G+ Raman feature associated with pristine SWNTs grown on a Si/SiO2 substrate by CVD.37,59 For high-density films, however, the G+ band line width doubles to ∼20 cm-1 (Figures 4A and S1C), which likely results from SWNT-SWNT distances that are less than the laser irradiation wavelength.62,63 Note that the presence of closely-spaced SWNTs in these high-density films is not correlated with nanotube bundle formation, as the E S22 electronic transition observed for high-density films is neither red-shifted nor broadened relative to its counterpart in aqueous solution (Figure 1).9,64 Congruent with this reasoning, such a red-shift of the E S22 transition would also cause the laser excitation wavelength to move further out of resonance with SC-[(6,5) SWNTs] and PNES-[(6,5) SWNTs], and thereby diminish strongly the observed RBM intensity, which is not observed; SWNT bundling thus does not play a role in the enhancement of the G+ band line width in high-density PNESSWNT films. In practice, an analysis of energy shifts of the G band should allow the extent of any polymer-SWNT charge transfer interactions in these PNES-[(6,5) SWNT] nanohybrids to be assessed. SWNT charge transfer is known to prompt shifts of the G band, up to several tens of cm-1,42 with SWNT-electronacceptor complexes causing G band upshifts and SWNT-electron-donor interactions driving G band downshifts.37 Note that the downshift (upshift) in the G band is consistent with in-plane C-C bond length expansion (contraction) expected upon reduction (oxidation) of the SWNT structure.37 In our samples however, no G band shift has been observed for PNES-[(6,5) SWNT] relative to benchmark SC-[(6,5) SWNT] samples, which precludes the occurrence of any significant charge transfer between ACS Paragon Plus Environment

12

Page 13 of 35


20 June 2013 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

PNES and the SWNT backbone. Note that PNES-[(6,5) SWNTs] exhibit small 1-4 cm-1 RBM frequency upshifts with respect to SC-[(6,5) SWNTs]. The magnitude of these PNES-[(6,5) SWNTs] RBM spectral shifts are thus likely associated with modulation of the SWNT local dielectric environment37 or the impact of PNES helical wrapping of the SWNT surface upon the breathing frequency. Indeed, the impact of polymer wrapping on the SWNT RBM frequency has also been observed for DNA-[(6,5) SWNTs], for which RBMs were found to upshift by 2 cm-1 relative to SDS-[(6,5) SWNTs].65 Laser excitation at 568.2 nm does not allow Raman marker bands associated with the PNES polymer to be identified (Figure 4A). Figure 3B indicates that the PNES-[(6,5) SWNT] electronic spectrum acquired over the 300-700 nm range features a broadband absorption centered at ∼400 nm that is associated with the PNES polymer (see PNES absorption and excitation spectra, Figures S2 and S3), and the E S22 (∼570 nm) and E S33 (∼346 nm) bands characteristic of the (6,5) SWNT backbone. Raman experiments that utilized shorter wavelength excitation (488.0 and 457.9 nm, Figures 4C-D), provide spectra that display enhancement of polymer-specific modes. Irradiation of PNES and PNES-[(6,5) SWNT] high-density solid samples at 457.9 nm (Figure 4D, top and middle spectra) excites the tail of the PNES visible absorption band (Figures 3B and S2). At this irradiation wavelength, Raman bands of this polymer are strongly enhanced. We tentatively assign bands observed at 2996/2795 cm-1, 2195 cm-1, 1608/1586/1554 cm-1, 1455 cm-1, 1397/1384 cm-1, 1213 cm-1 and 1191 cm-1 to respective aliphatic C-H stretching, C≡C stretching, C=C-C aromatic ring stretching, C-H scissoring, C-O stretching, aliphatic C-C stretching, and C-SO3- stretching vibrations (Scheme 1); as the PNES solid and PNES-[(6,5) SWNT] hybrids display almost the same spectral signatures between 500 and 2500 cm-1, with analogous Raman frequencies and relative peak intensities, it is clear that the polymer, which is noncovalently bound to the carbon skeleton, remains largely unperturbed by the underlying SWNT structure. Note that a large emission background (Figure S4) has been subtracted in order to obtain the Raman spectrum of the PNES solid (Figure 4D). Such a background is expected when exciting PNES at 457.9 nm but not for resonant Raman experiments that ACS Paragon Plus Environment

13


Page 14 of 35

20 June 2013 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

interrogate PNES-[(6,5) SWNTs] at 568.2 nm (Figure S3). Under 457.9 nm irradiation, the polymer emission bands of PNES and PNES-[(6,5) SWNTs] in aqueous solution attain maximum intensity at ∼520 nm, but also remain significant at 568.2 nm, where [(6,5) SWNTs], wrapped with PNES, can absorb. Excitation-emission mapping spectra of PNES-[(6,5) SWNT] samples in aqueous solvent also reveal a prominent emission of the (6,5) SWNT skeleton probed at 1009 nm upon PNES excitation (∼430 nm), indicative of polymer-to-[(6,5) SWNT] energy transfer (Figure 3A). With 457.9 nm irradiation, two RBMs can be discerned at 287 and 306 cm-1 in the Raman spectrum of PNES-[(6,5) SWNTs] (Figure 4D). As RBMs are also observed at 287 and 305 cm-1 for SC-[(6,5) SWNTs] (Figure 4D, bottom spectrum), polymer-to-[(6,5) SWNT] energy transfer cannot play a role in the observed enhancement of the intensities of these bands. We posit that these intensified RBMs observed for 457.9 nm irradiation arise from excitation of metallic PNES-[(6,6) SWNTs] and PNESM M [(7,4) SWNTs], both of which possess E 11 transitions near 457.9 nm ( E 11 = 476.3 nm for 0.83 nmMM+ diameter (6,6) SWNTs; E 11 = 448.4 and E 11 = 478.3 nm for 0.77 nm-diameter (7,4) SWNTs, where MM+ M E 11 and E 11 reflect the expected peak splitting of the E 11 transition of metallic (n≠m) nanotubes with

M negative and positive deviations from the E 11 transition associated with their armchair (n=m)

counterparts).39 The stronger RBM intensity observed at 305 cm-1 is congruent with the fact that the 457.9 nm irradiation wavelength lies closer in energy to the (7,4) SWNT resonance. Despite the minority character of metallic chiralities in our samples, we are able to detect a weak electronic absorption at ∼465 nm for SC-[(6,5) SWNTs] (Figures 1 and S2), which can be ascribed to transitions M transition of (6,6) SWNTs (∼460 nm) has from metallic (7,4) and (6,6) nanotubes. Note that the E 11

been determined from spectroscopic studies of enriched [(6,6) SWNT] samples prepared from the same starting material used in the present study.66 For PNES-[(6,5) SWNTs] however, absorption features related to the (7,4) and (6,6) chiralities lie under the PNES absorption band (Figures 1 and S2).


14

Page 15 of 35


20 June 2013 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The RBM assignments ascribed to metallic SWNTs are corroborated by the presence of a prominent Breit-Wigner-Fano (BWF) lineshape of the G- band centered at 1530 cm-1 in the SC-[(6,5) SWNT] sample. Such a broad and intense G- feature has been noted as a spectral fingerprint of metallic SWNTs.67 The intensity of this BWF-broadened G- band is very low for the PNES-[(6,5) SWNT] sample due to the strong Raman contribution of the PNES polymer (Figure 4D) and the relatively insignificant amount of metallic SWNT structures present in these samples. While the G- band emerges at a frequency lower than that noted in previous reports (1550 and 1560 cm-1 for 1.3 and 1.5 nmdiameter nanotubes) that examined larger-diameter SWNTs,37 it is commonly accepted that the frequency of the BWF-broadened G- band for metallic nanotubes decreases as the diameter decreases, while its line width and intensity increases.40 Under 514.5 nm irradiation, RBM intensities are extremely weak for all samples (Figure 4B), contrasting analogous spectral signatures acquired using the resonant 568.2 nm wavelength (Figure 4A). Two RBMs are barely distinguishable at 310 and 318 cm-1 for the PNES-[(6,5) SWNT] sample; these modes can be assigned to semiconducting PNES-[(6,5) SWNTs] and a sparse metallic PNES-[(8,2) M+ = 490.7 nm).39 Small M and iTOLA SWNT] population which is excited near resonance ( E 11

(combination of two phonons from the in-plane Transverse Optical and the Longitudinal Acoustic branches) bands are also indicated, in accordance with literature.49,68 Surprisingly, despite the resonant excitation of the minority PNES-[(8,2) SWNT] species, only the G+ band at 1590 cm-1 and the G’ band at 2625 cm-1 exhibit prominent intensities. As the G band is not BWF-broadened, it likely traces its genesis to the excitation of PNES-[(6,5) SWNTs]: RBM, G and G’ features associated with the (6,5) chirality appear thus arise under non-resonant 514.5nm irradiation. In Figure 3B, the excitation spectra of PNES-[(6,5) SWNTs] and SC-[(6,5) SWNTs] probed at 1009 and 982 nm respectively, show a band centered at ∼520 nm (∼2.39 eV), blue to the [(6,5) SWNT] E S22 transition by 50-60 nm (∼0.24 eV). This sideband cannot be ascribed to a contribution from the PNES polymer (Figure S2). It furthermore cannot reflect the presence of (8,5) or (9,3) chiralities either ACS Paragon Plus Environment

15


Page 16 of 35

20 June 2013 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

M+ (resonant at E 11 = 423.8 and 526.1 nm,39 respectively), since their characteristic RBM features do not

appear in the Raman spectrum (Figure 4B). However, from photoluminescence investigations of surfactant-wrapped

13

C-enriched [(6,5) SWNTs], the vibronic nature of this sideband has been

unequivocally demonstrated.69 This absorptive phonon sideband is precisely centered at the energy expected for the so-called +X sideband (∼2.4 eV).70 Proposed excitation mechanisms of such an absorptive band require a two-phonon process that becomes favorable through involvement of Kmomentum dark (dipole forbidden) exciton states.71,72 In particular, time-resolved electronic spectroscopy of surfactant-dispersed [(6,5) SWNTs] reveal that the +X→ E S22 population transfer involved multiple-phonon (G band, RBM) emission in order to satisfy energy-momentum conservation.70 Under 488.0 nm irradiation, RBMs centered at 307 and 317 cm-1 are observed for PNES-[(6,5) SWNT] and SC-[(6,5) SWNT] samples (Figure 4C); these bands derive from the presence of a small population of metallic PNES-[(7,4) SWNTs] and PNES-[(8,2) SWNTs] which are excited near resonance.39 As the diameter of (8,2) SWNTs (∼0.73 nm) is smaller than that for (7,4) and (6,6) SWNTs, the intensity ratio of the BWF-broadened G- and the G+ bands should be higher for (8,2) species.40 The slight BWF line shape of the G- band at 1530 cm-1, which can be identified in the SC[(6,5) SWNT] sample, reflects the relative scarcity of metallic nanotubes that are resonantly excited at 488 nm (∼2.54 eV). This hints that the prominent G+ band arises from the excitation of the +2G phonon sideband centered at 2.55 eV for the E S22 transition associated with PNES-[(6,5) SWNTs], where +2G indicates the second-order harmonic of the G band.70 In contrast, the intense G’ band at 2633 cm-1 likely originates from excitation of the +G’ phonon sideband centered at ∼2.5 eV.70 At 488.0 nm irradiation, the spectral signature of the PNES polymer (Figure 4D) is also evident, as this wavelength allows both the PNES polymer and the (6,5) SWNT skeleton to be probed simultaneously (Figures 3B and S2).

4. CONCLUSIONS ACS Paragon Plus Environment

16

Page 17 of 35


20 June 2013 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Individual single-walled carbon nanotubes (SWNTs), helically wrapped by semiconducting poly[2,6{1,5-bis(3-propoxysulfonicacidsodiumsalt)}naphthylene]ethynylene (PNES) and enriched in the (6,5) chirality, have been investigated in aqueous solution and as high-density drop-cast films on borosilicate substrates by micro-Raman and electronic spectroscopies, and as isolated species through a combination of confocal Raman and atomic force microscopic experiments. These studies examine for the first time the Raman signatures of self-assembled helical polymer-SWNT superstructures, and reveal: subtle electronic effects upon single and double-resonance features, excitation conditions that give rise to polymer-to-[(6,5) SWNT] energy transfer, and an absence of any detectable charge transfer between the PNES polymer and the SWNT skeleton. By varying the laser excitation wavelength, diverse SWNT chiralities, present in minute concentration, were identified through resonant excitation: these included semiconducting (6,4) (λex = 568.2 nm) and (6,5) SWNT chiralities (λex = 568.2 and 514.5 nm), as well as metallic (8,2) (λex = 514.5 and 488.0 nm), (7,4) (λex = 488.0 and 457.9 nm) and (6,6) (λex = 457.9 nm) SWNT chiralities. Excitation into the PNES absorption band (λex = 488.0 and 457.9 nm) makes prominent the polymer Raman signature; in contrast, at a 514.5 nm irradiation wavelength, PNES-[(6,5) SWNTs] are not excited in resonance but RBM, G and G’ bands associated with these nanohybrids are strongly enhanced, reflecting the excitation of a vibronic transition of the (6,5) SWNT backbone, which involves RBM, G, and D phonons. Using 488.0 nm irradiation, Raman spectral signatures of both the PNES polymer and the vibronically-excited (6,5) SWNT skeleton are pronounced, demonstrating that a specific SWNT chirality and the corresponding semiconducting polymer helically wrapped about its surface can be probed using an excitation wavelength that does not resonantly excite the SWNT structure. This work underscores the utility of confocal Raman microscopy used in combination with conventional solution-phase Raman to probe the electronic interactions between a semiconducting polymer and a SWNT in self-assembled helical polymer-SWNT superstructures; such methods should thus illuminate the extent of the electronic coupling in polymer-SWNT superstructures in which the electronic nature of the semiconducting polymer is systematically modulated. ACS Paragon Plus Environment

17


Page 18 of 35

20 June 2013 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACKNOWLEDGMENT We gratefully acknowledge J.L. Bruneel, Dr. N. Daugey, Dr. G. Le Bourdon and Dr. L. Vellutini for technical assistance. This work was supported through equipment grants from the Aquitaine Region, the University of Bordeaux, and the CNRS (Centre National de la Recherche Scientifique) through the chair of excellence awarded to S.B. P.D., M.G.G., and M.J.T. acknowledge research support from the Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences, of the U.S. Department of Energy, through Grant DE-SC0001517.

SUPPORTING INFORMATION Magnification of RBM-, D-, G-, and G’ band spectral regions associated with PNES-[(6,5) SWNT] aqueous suspensions, and high-density and low-density films; electronic absorption spectra of PNES[(6,5) SWNT], SC-[(6,5) SWNT] and PNES samples in aqueous solvent; emission spectra of PNES and PNES-[(6,5) SWNT] aqueous solutions, and an excitation spectrum of a PNES aqueous solution; Raman spectra of: (i) the PNES solid, λex = 457.9 nm; and (ii) a sodium cholate powder sample, λex = 457.9 nm. This material is available free of charge via the Internet at http://pubs.acs.org.


18

Page 19 of 35


20 June 2013 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

FIGURE CAPTIONS

Scheme 1. Structural schematic of PNES-wrapped SWNTs (PNES-SWNTs). Figure 1. Electronic absorption spectra of as-prepared PNES-[(6,5) SWNT] (black solid line) and SC[(6,5) SWNT] (red solid line) suspensions in H2O solvent, and micro-absorption measurements of similar PNES-[(6,5) SWNT] (black dashed line) and SC-[(6,5) SWNT] (red dashed line) high-density samples drop-cast on glass slides. Absorbance spectra have been shifted vertically with respect to each other for clarity. Arrows pinpoint the maximal absorbance assigned to PNES-[(6,5) SWNTs] and SC[(6,5) SWNTs]. Figure 2. (A) Raman spectra of PNES-[(6,5) SWNTs] in aqueous solution (top), of an isolated individual PNES-[(6,5) SWNT] (middle) and of its underlying glass substrate in a region void of PNES[(6,5) SWNTs] (bottom) obtained using 568.2 nm irradiation. The two upper spectra are normalized to each other with respect to the G band intensity. (B) ID/IG ratio for N=12 different nanotubes, where ID and IG are the integrated intensities of D and G+ bands respectively. (C) Typical topographic tapping mode AFM image of an isolated individual PNES-[(6,5) SWNT]. (D) Cross-section of the PNES-[(6,5) SWNT] reported on Figure 2C along the indicated white dashed line. The x, y, and z directions correspond to the reference frame highlighted in Figure 2C. (E) G’ band region of the experimental Raman spectra associated with PNES-[(6,5) SWNT] liquid suspensions (top) and an isolated individual PNES-[(6,5) SWNT] (bottom). Arrows pinpoint G’ bands maxima. Figure 3. (A) Excitation-emission mapping spectra of a PNES-[(6,5) SWNT] sample in D2O solvent. A prominent [(6,5) SWNT] emission (λem = 1009 nm) is evident with PNES excitation (~430 nm) and marked with an arrow, indicating polymer-to-[(6,5) SWNT] energy transfer. (B) An excitation spectrum (left y-axis, λem = 1009 nm; see dashed line in the panel A data) of a PNES-[(6,5) SWNT] sample (black line) in D2O solvent. The labeled spectral peaks [PNES (arrow), E S33 , and E S22 ] in the excitation and ACS Paragon Plus Environment

19


Page 20 of 35

20 June 2013 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

scaled absorption spectrum (right y-axis) of the PNES-[(6,5) SWNT] sample (dashed line) indicate polymer- and nanotube-localized excitations that give rise to 1009 nm emission in the panel A excitation-emission map. A normalized excitation spectrum of a SC-[(6,5) SWNT] sample (red spectrum, (λem = 982 nm) in aqueous solvent is shown for reference). Experimental conditions: 5x5 mm path-length cell, 23 0C. Figure 4. (A) Raman spectra of PNES-[(6,5) SWNT] and SC-[(6,5) SWNT] high-density films obtained using 568.2 nm excitation. RBM, D, G+, G’, M and iTOLA bands are labeled.49 (B) Raman spectra of PNES-[(6,5) SWNT] and SC-[(6,5) SWNT] high-density films obtained using 514.5 nm excitation. The inset displays a magnification of the spectral window near 300 cm-1. (C) Raman spectra of PNES-[(6,5) SWNT] and SC-[(6,5) SWNT] high-density films obtained using 488.0 nm excitation. The inset displays a magnification of the spectral window near 1600 cm-1. (D) Raman spectra of a PNES powder, PNES-[(6,5) SWNT] and SC-[(6,5) SWNT] high-density films obtained using 457.9 nm excitation. The PNES solid emission background has been subtracted for clarity. The inset displays a magnification of the spectral window near 1600 cm-1 for the PNES and PNES-[(6,5) SWNT] samples. These films were prepared by drop-casting 10 µL of the as-prepared PNES-[(6,5) SWNT] and SC-[(6,5) SWNT] suspensions on a glass slide in which the respective SWNT concentration corresponded to 35 and 85 µg/mL.


20

Page 21 of 35


20 June 2013 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Scheme 1.


21


Page 22 of 35

20 June 2013 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 1.


22

Page 23 of 35


20 June 2013 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 2.


23


Page 24 of 35

20 June 2013 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 3.


24

Page 25 of 35


20 June 2013 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 4.


25


Page 26 of 35

20 June 2013 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

REFERENCES (1) Iijima, S.; Ichihashi, T. Single-Shell Carbon Nanotubes of 1-nm Diameter. Nature 1993, 363, 603605. (2) Bethune, D.S. ; Klang, C.H. ; de Vries, M.S. ; Gorman, G. ; Savoy, R. ; Vazquez, J. ; Beyers, R. Cobalt-Catalyzed Growth of Carbon Nanotubes with Single-Atomic-Layer Walls. Nature 1993, 363, 605-607. (3) Ajayan, P.M. ; Stephan, O. ; Colliex, C.; Trauth, D. Aligned Carbon Nanotubes Arrays Formed by Cutting a Polymer Resin-Nanotube Composite. Science 1994, 265, 1212-1214. (4) Baughman, R.H.; Cui, C.; Zakhidov, A.A. ; Iqbal, Z. ; Barisci, J.N.; Spinks, G.M.; Wallace, G.G.; Mazzoldi, A.; De Rossi, D.; Rinzler, A.G.; et al. Carbon Nanotube Actuators. Science 1999, 284, 1340-1344. (5) Kim, P.; Lieber, C.M. Nanotube Nanotweezers. Science 1999, 286, 2148-2150. (6) Yu, M.-F.; Files, B.S.; Arepalli, S.; Ruoff, R.S. Tensile Loading of Ropes of Single Wall Carbon Nanotubes and their Mechanical Properties. Phys. Rev. Lett. 2000, 84, 5552-5555. (7) Tombler, T.W.; Zhou, C.; Alexseyev, L.; Kong, J.; Dai, H.J.; Liu, L.; Jayanthi, C.S.; Tang, M.; Wu, S.-Y. Reversible Electromechanical Characteristics of Carbon Nanotubes under Local-Probe Manipulation. Nature 2000, 405, 769-772. (8) Bachilo, S.M. ; Strano, M.S. ; Kittrell, C. ; Hauge, R.H.; Smalley, R.E.; Weisman, R.B. StructureAssigned Optical Spectra of Single-Walled Carbon Nanotubes. Science 2002, 298, 2361-2366. (9) O’Connell, M.J.; Bachilo, S.M.; Huffman, C.B.; Moore, V.C.; Strano, M.S.; Haroz, E.H.; Rialon, K.L.; Boul, P.J.; Noon, W.H.; Kittrell, C.; et al. Band Gap Fluorescence from Individual SingleWalled Carbon Nanotubes. Science 2002, 297, 593-596. ACS Paragon Plus Environment

26

Page 27 of 35


20 June 2013 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(10) Misewich, J.A.; Martel, R.; Avouris, P. ; Tsang, J.C. ; Heinze, S. ; Tersoff, J. Electrically Induced Optical Emission from a Carbon Nanotube FET. Science 2003, 300, 783-786. (11) Wang, F.; Dukovic, G. ; Brus, L.E.; Heinz, T.F. The Optical Resonances in Carbon Nanotubes Arise from Excitons. Science 2005, 308, 838-841. (12) Dai, H.; Wong, E.W.; Lieber, C.M. Probing Electrical Transport in Nanomaterials: Conductivity of Individual Carbon Nanotubes. Science 1996, 272, 523-526. (13) Bockrath, M.; Cobden, D.H.; McEuen, P.L.; Chopra, N.G.; Zettl, A.; Thess, A.; Smalley, R.E. Single-Electron Transport in Ropes of Carbon Nanotubes. Science 1997, 275, 1922-1925. (14) Tans, S.J.; Verschueren, A.R.M.; Dekker, C. Room-Temperature Transistor Based on a Single Carbon Nanotube. Nature 1998, 393, 49-52. (15) Liang, W.; Bockrath, M.; Bozovic, D.; Hafner, J.H.; Tinkham, M.; Park, H. Fabry-Perot Interference in a Nanotube Electron Waveguide. Nature 2001, 411, 665-669. (16) Baughman, R.H.; Zakhidov, A.A.; de Heer, W.A. Carbon nanotubes - the route toward applications. Science 2002, 297, 787-792. (17) Walters, D.A.; Casavant, M.J.; Qin, X.C.; Huffman, C.B.; Boul, P.J.; Ericson, L.M.; Haroz, E.H.; O’Connell, M.J.; Smith, K.; Colbert, D.T.; et al. In-Plane-Aligned Membranes of Carbon Nanotubes. Chem. Phys. Lett. 2001, 338, 14-20. (18) Zaric, S.; Ostojic, G.N.; Kono, J.; Shaver, J.; Moore, V.C.; Hauge, R.H.; Smalley, R.E.; Wei, X. Estimation

of

Magnetic

Susceptibility

Anisotropy

of

Carbon

Nanotubes

Using

Magnetophotoluminescence. Nano Lett. 2004, 4, 2219-2221. (19) Man, H.T.; Morpurgo, A.F. Sample-Specific and Ensemble-Averaged Magnetoconductance of Individual Single-Wall Carbon Nanotubes. Phys. Rev. Lett. 2005, 95, 026801. ACS Paragon Plus Environment

27


Page 28 of 35

20 June 2013 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(20) Hone, J.; Llaguno, M.C.; Biercuk, M.J.; Johnson, A.T.; Batlogg, B.; Benes, Z.; Fischer, J.E. Thermal Properties of Carbon Nanotubes and Nanotube-Based Materials. Appl. Phys. A 2002, 74, 339-343. (21) Pop, E.; Mann, D.; Wang, Q.; Goodson, K.; Dai, H. Thermal Conductance of an Individual Single-Wall Carbon Nanotube above Room Temperature. Nano Lett. 2006, 6, 96-100. (22) Bartelmess, J.; Ballesteros, B.; de la Torre, G.; Kiessling, D. ; Campidelli, S. ; Prato, M. ; Torres, T. ; Guldi, D.M. Phthalocyanine-Pyrene Conjugates: A Powerful Approach toward Carbon Nanotube Solar Cell. J. Am. Chem. Soc. 2010, 132, 16202-16211. (23) Britz, D.A.; Khlobystov, A.N. Noncovalent Interactions of Molecules with Single Walled Carbon Nanotubes. Chem. Soc. Rev. 2006, 35, 637-659. (24) Deria, P.; Sinks, L.E.; Park, T.-H.; Tomezsko, D.M.; Brukman, M.J.; Bonnell, D.A.; Therien, M.J. Phase Transfer Catalysts Drive Diverse Organic Solvent Solubility of Single-Walled Carbon Nanotubes Helically Wrapped by Ionic, Semiconducting Polymers. Nano Lett. 2010, 10, 41924199. (25) Park, J.; Deria, P.; Therien, M.J. Dynamics and Transient Absorption Spectral Signatures of the Single-Wall Carbon Nanotube Electronically Excited Triplet State. J. Am. Chem. Soc. 2011, 133, 17156–17159. (26) Larsen, B.A.; Deria, P.; Holt, J.M.; Stanton, I.N.; Heben, M.J.; Therien, M.J.; Blackburn, J.L. Effect of Solvent Polarity and Electrophilicity on Quantum Yields and Solvatochromic Shifts of Single-Walled Carbon Nanotube Photoluminescence. J. Am. Chem. Soc. 2012, 134, 12485−12491. (27) Rosario-Canales, M.R.; Deria, P.; Therien, M.J.; Santiago-Avilés, J.J. Composite Electronic Materials

Based

on

Poly(3,4-propylenedioxythiophene)

and

Highly

Charged


28

Page 29 of 35


20 June 2013 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Poly(aryleneethynylene)-Wrapped Carbon Nanotubes for Supercapacitors. ACS Appl. Mater. Interfaces 2012, 4, 102−109. (28) Rice, N.A.; Soper, K.; Zhou, N.; Merschrod, E.; Zhao, Y. Dispersing as-Prepared Single-Walled Carbon Nanotube Powders with Linear Conjugated Polymers. Chem. Commun. 2006, 4937-4939. (29) Nish, A.; Hwang, J.-Y.; Doig, J.; Nicholas, R.J. Highly Selective Dispersion of Single-Walled Carbon Nanotubes Using Aromatic Polymers. Nat. Nanotechnol. 2007, 2, 640-646. (30) Hwang, J.-Y.; Nish, A.; Doig, J.; Douven, S.; Chen, C.-W.; Chen, L.-C.; Nicholas, R.J. Polymer Structure and Solvent Effects on the Selective Dispersion of Single-Walled Carbon Nanotubes. J. Am. Chem. Soc. 2008, 130, 3543-3553. (31) Kang, Y.K.; Lee, O.-S.; Deria, P.; Kim, S.H.; Park, T.-H.; Bonnell, D.A.; Saven, J.G.; Therien, M.J. Helical Wrapping of Single-Walled Carbon Nanotubes by Water Soluble Poly(pphenyleneethynylene). Nano Lett. 2009, 9, 1414-1418. (32) Kymakis, E.; Amaratunga, G.A.J. Single-Wall Carbon Nanotube/Conjugated Polymer Photovoltaic Devices. Appl. Phys. Lett. 2002, 80, 112-114. (33) Hur, S.-H.; Khang, D.-Y. ; Kocabas, C.; Roger, J.A. Nanotransfer Printing by Use of Nonconvalent Surface Forces: Applications to Thin-Film Transistors that Use Single-Wall Carbon Nanotube Networks and Semiconducting Polymers. Appl. Phys. Lett. 2004, 85, 5730-5732. (34) Geng, J.; Zeng, J. Influence of Single-Walled Carbon Nanotubes Induced Crystallinity Enhancement and Morphology Change on Polymer Photovoltaic Devices. J. Am. Chem. Soc. 2006, 128, 16827-16833.


29


Page 30 of 35

20 June 2013 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(35) Geng, J.; Kong, B.-S.; Yang, S.B. ; Youn, S.C. ; Park, S. ; Joo, T.; Jung, H.-T. Effect of SWNT Defects on the Electron Transfer Properties in P3HT/SWNT Hybrid Materials. Adv. Func. Mater. 2008, 18, 2659-2665. (36) Schuettfort, T.; Nish, A.; Nicholas, R.J. Observation of a Type II Heterojunction in a Highly Ordered Polymer-Carbon Nanotube Nanohybrid Structure. Nano Lett. 2009, 9, 3871-3876. (37) Shim, M.; Ozel, T.; Gaur, A.; Wang, C. Insights on Charge Transfer Doping and Intrinsic Phonon Line Shape of Carbon Nanotubes by Simple Polymer Adsorption. J. Am. Chem. Soc. 2006, 128, 7522-7530. (38) do Nascimento, G.M.; Silva, T.B.; Corio, P.; Dresselhaus, M.S. Charge Transfer Behavior of Polyaniline Single Wall Carbon Nanotubes Nanocomposites Monitored by Resonance Raman Spectroscopy. J. Raman Spectrosc. 2010, 41, 1587-1593. (39) Strano, M.S.; Doorn, S.K.; Haroz, E.K.; Kittrell, C.; Hauge, R.H.; Smalley, R.E. Assignment of (n,m) Raman and Optical Features of Metallic Single-Walled Carbon Nanotubes. Nano Lett. 2003, 3, 1091-1096. (40) Dresselhaus, M.S. ; Dresselhaus, G. ; Jorio, A. ; Souza Filho, A.G. ; Saito, R. Raman Spectroscopy on Isolated Single Wall Carbon Nanotubes. Carbon 2002, 40, 2043-2061. (41) Liu, Z.; Zhang, J.; Gao, B. Raman Spectroscopy of Strained Single-Walled Carbon Nanotubes. Chem. Commun. 2009, 6902-6918. (42) Rao, A.M.; Eklund, P.C.; Bandow, S.; Thess, A.; Smalley, R.E. Evidence for Charge Transfer in Doped Carbon Nanotube Bundles from Raman Scattering. Nature 1997, 388, 257-259.


30

Page 31 of 35


20 June 2013 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(43) Shoda, M.; Bandow, S.; Maruyama, Y.; Iijima, S. Probing Interaction between ssDNA and Carbon Nanotubes by Raman Scattering and Electron Microscopy. J. Phys. Chem. C 2009, 113, 6033-6036. (44) Najjar, S.; Talaga, D.; Coffinier, Y.; Szunerits, S.; Boukherroub, R.; Servant, L.; Couzi, M.; Bonhommeau, S. Characterization of Single Transition Metal Oxide Nanorods by Combining Atomic Force Microscopy and Polarized Micro-Raman Spectroscopy. Chem. Phys. Lett. 2011, 514, 128-133. (45) Bonhommeau, S.; Lacroix, P.G.; Talaga, D.; Bousseksou, A.; Seredyuk, M.; Fritsky, I.O.; Rodriguez, V. Magnetism and Molecular Nonlinear Optical Second-Order Response Meet in a Spin-Crossover Complex. J. Phys. Chem. C 2012, 116, 11251-11255. (46) Moore, V.C.; Strano, M.S.; Haroz, E.H.; Hauge, R.H.; Smalley, R.E. Individually Suspended Single-Walled Carbon Nanotubes in Various Surfactants. Nano Lett. 2003, 3, 1379-1382. (47) Jorio, A.; Souza Filho, A.G.; Dresselhaus, G.; Dresselhaus, M.S.; Swan, A.K.; Ünlü, M.S.; Goldberg, B.B.; Pimenta, M.A.; Hafner, J.H.; Lieber, C.M.; Saito, R. G-Band Resonant Raman Study of 62 Isolated Single-Wall Carbon Nanotubes. Phys. Rev. B 2002, 65, 155412. (48) Paillet, M.; Langlois, S.; Sauvajol, J.-L.; Marty, L.; Iaia, A.; Naud, C.; Bouchiat, V.; Bonnot, A.M. Raman Spectroscopy of Free-Standing Individual Semiconducting Single-Wall Carbon Nanotubes. J. Phys. Chem. B 2006, 110, 164-169. (49) Dresselhaus, M.S. ; Dresselhaus, G. ; Saito, R.; Jorio, A. Raman Spectroscopy of Carbon Nanotubes. Phys. Rep. 2005, 409, 47-99. (50) Fantini, C.; Jorio, A.; Souza, M.; Ladeira, L.O. ; Souza Filho, A.G. ; Saito, R. ; Samsonidze, Ge.G. ; Dresselhaus, G.; Dresselhaus, M.S.; Pimenta, M.A. One-Dimensional Character of


31


Page 32 of 35

20 June 2013 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Combination Modes in the Resonance Raman Scattering of Carbon Nanotubes. Phys. Rev. Lett. 2004, 93, 087401. (51) Kulathunga, D.D.T.K.; Ang, K.K.; Reddy, J.N. Molecular Dynamics Analysis on Buckling of Defective Carbon Nanotubes. J. Phys.: Condens. Matter 2010, 22, 345301. (52) Sammalkorpi, M.; Krasheninnikov, A.; Kuronen, A.; Nordlund, K.; Kaski, K. Mechanical Properties of Carbon Nanotubes with Vacancies and Related Defects. Phys. Rev. B 2004, 70, 245416. (53) Suenaga, K.; Wakabayashi, H.; Koshino, M.; Sato, Y.; Urita, K.; Iijima, S. Imaging Active Topological Defects in Carbon Nanotubes. Nat. Nanotechnol. 2007, 2, 358-360. (54) Yudasaka, M.; Kataura, H.; Ichihashi, T. ; Qin, L.C.; Kar, S.; Iijima, S. Diameter Enlargement of HiPco Single-Wall Carbon Nanotubes by Heat Treatment. Nano. Lett. 2001, 9, 487-489. (55) Strano, M.S.; Dyke, C.A.; Usrey, M.L.; Barone, P.W.; Allen, M.J.; Shan, H.; Kittrell, C.; Hauge, R.H.; Tour, J.M.; Smalley, R.E. Electronic Structure Control of Single-Walled Carbon Nanotube Functionalization. Science 2003, 301, 1519-1522. (56) Ko, H.; Pikus, Y.; Jiang, C.; Jauss, A.; Hollricher, O.; Tsukruk, V.V. High-Resolution Raman Microscopy of Curled Carbon Nanotubes. Appl. Phys. Lett. 2004, 85, 2598-2600. (57) Minot, E.D.; Yaish, Y.; Sazanova, V.; Park, J.-Y.; Brink, M.; McEuen, P.L. Tuning Carbon Nanotube Band Gaps with Strain. Phys. Rev. Lett. 2003, 90, 156401. (58) Kürti, J.; Zólyomi, V.; Grüneis, A.; Kuzmany, H. Double Resonant Raman Phenomena Enhanced by Van Hove Singularities in Single-Wall Carbon Nanotubes. Phys. Rev. B 2002, 65, 165433.


32

Page 33 of 35


20 June 2013 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(59) Graf, D.; Molitor, F.; Ensslin, K.; Stampfer, C.; Jungen, A.; Hierold, C.; Wirtz, L. Spatially Resolved Raman Spectroscopy of Single- and Few-Layer Graphene. Nano Lett. 2007, 7, 238-242. (60) Maciel, I.O.; Anderson, N.; Pimenta, M.A.; Hartschuh, A.; Qian, H.; Terrones, M.; Terrones, H.; Campos-Delgado, J.; Rao, A.M.; Novotny, L.; et al. Electron and Phonon Renormalization near Charged Defects in Carbon Nanotubes. Nat. Mater. 2008, 7, 878-883. (61) Jorio, A.; Santos, A.P.; Ribeiro, H.B.; Fantini, C.; Souza, M.; Vieira, J.P.M.; Furtado, C.A.; Jiang, J.; Saito, R.; Balzano, L.; et al. Quantifying Carbon-Nanotube Species Phys. Rev. B 2005, 72, 075207. (62) Jorio, A.; Fantini, C.; Dantas, M.S.S.; Pimenta, M.A.; Souza, A.G.; Samsonidze, Ge.G.; Brar, V.W. ; Dresselhaus, G. ; Dresselhaus, M.S.; Swan, A.K.; et al. Linewidth of the Raman Features of Individual Single-Wall Carbon Nanotubes. Phys. Rev. B 2002, 66, 115411. (63) Jorio, A.; Souza Filho, A.G.; Brar, V.W.; Swan, A.K.; Ünlü, M.S.; Goldberg, B.B.; Righi, A.; Hafner, J.H.; Lieber, C.M.; Saito, R.; et al. Polarized Resonant Raman Study of Isolated SingleWall Carbon Nanotubes: Symmetry Selection Rules, Dipolar and Multipolar Antenna Effects. Phys Rev. B 2002, 65, 121402. (64) O’Connell, M.J.; Sivaram, S.; Doorn, S.K. Near-Infrared Resonance Raman Excitation Profile Studies of Single-Walled Carbon Nanotube Intertube Interactions: A Direct Comparison of Bundled and Individually Dispersed HiPco Nanotubes. Phys. Rev. B 2004, 69, 235415. (65) Fantini, C.; Jorio, A.; Santos, A.P. ; Peressinotto, V.S.T. ; Pimenta, M.A. Characterization of DNA-Wrapped Carbon Nanotubes by Resonance Raman and Optical Absorption Spectroscopies. Chem. Phys. Lett. 2007, 439, 138-142.


33


Page 34 of 35

20 June 2013 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(66) Hároz, E.H.; Duque, J.G.; Lu, B.J.; Nikolaev, P.; Arepalli, S.; Hauge, R.H.; Doorn, S.K.; Kono, J. Unique Origin of Colors of Armchair Carbon Nanotubes. J. Am. Chem. Soc. 2012, 134, 44614464. (67) Nguyen, K.T.; Gaur, A.; Shim, M. Fano Lineshape and Phonon Softening in Single Isolated Metallic Carbon Nanotubes. Phys. Rev. Lett. 2007, 98, 145504. (68) Brar, V.W.; Samsonidze, Ge. G.; Dresselhaus, M.S.; Dresselhaus, G.; Saito, R.; Swan, A.K.; Ünlü, M.S.; Goldberg, B.B.; Souza Filho, A.G.; Jorio, A. Second-Order Harmonic and Combination Modes in Graphite , Single-Wall Carbon Nanotube Bundles, and Isolated SingleWall Carbon Nanotubes Phys. Rev. B 2002, 66, 155418. (69) Miyauchi, Y.; Maruyama, S. Identification of an Excitonic Phonon Sideband by Photoluminescence Spectroscopy of Single-Walled Carbon-13 Nanotubes. Phys. Rev. B 2006, 74, 035415. (70) Graham, M.W. ; Calhoun, T.R. ; Green, A.A. ; Hersam, M.C. ; Fleming, G.R. Two-Dimensional Electronic Spectroscopy Reveals the Dynamics of Phonon-Mediated Excitation Pathways in Semiconducting Single-Walled Carbon Nanotubes. Nano Lett. 2012, 12, 813-819. (71) Torrens, O.N. ; Zheng, M. ; Kikkawa, J.M. Energy of K-Momentum Dark Excitons in Carbon Nanotubes by Optical Spectroscopy. Phys. Rev. Lett. 2008, 101, 157401. (72) Blackburn, J.L.; Holt, J.M.; Irurzun, V.M.; Resasco, D.E.; Rumbles, G. Confirmation of KMomentum Dark Exciton Vibronic Sidebands Using C-13-labeled, Highly Enriched (6,5) SingleWalled Carbon Nanotubes. Nano Lett. 2012, 12, 1398-1403.


34

Page 35 of 35


20 June 2013 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

SYNOPSIS TOC


35

Raman Spectroscopic Investigation of Individual Single-Walled

Recommend Documents