Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session W18: Focus Session: Carbon Nanotubes: Electronic and Optical Properties III |
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Sponsoring Units: DMP Chair: Gordana Dukovic, Columbia University Room: Baltimore Convention Center 315 |
Thursday, March 16, 2006 2:30PM - 3:06PM |
W18.00001: Phonon sideband in optical spectra of C13 carbon nanotubes Invited Speaker: Photoluminescence (PL) of single-walled carbon nanotubes (SWNTs) has been widely used for the measurement of chirality distribution of single-walled carbon nanotubes (SWNTs). However, there are unassigned peaks in the 2-D photoluminescence map plotted as a function of emission and excitation photon energy. In order to clarify the origin of these peaks, we have studied photoluminescence (PL) and resonant Raman scattering of single-walled carbon nanotubes (SWNTs) consisting of carbon-13 (SW$^{13}$CNTs) synthesized from a small amount of isotopically modified ethanol [1]. There was almost no change in the Raman spectra shape for SW$^{13}$CNTs except for a downshift of the Raman shift frequency by the square-root of the mass ratio 12/13. By comparing photoluminescence excitation (PLE) spectra of SW$^{13}$CNTs and normal SWNTs, the excitonic phonon sideband due to strong exciton-phonon interaction was clearly identified with the expected isotope shift [2]. The PLE line shape and energy difference from E$_{ii}$ are remarkably similar to the excitonic phonon sideband predicted by Perebeinos \textit{et al.} for (7, 5) and (6, 5) nanotubes. In addition to these phonon sideband features, we also found low-intensity `pure electronic' features whose origin has never been elucidated. In order to examine these `pure electronic' features, polarized PLE measurements on individually-dispersed SWNTs aligned in a gelatin-based thin film. By comparing optical transitions of SWNTs for incident light parallel or perpendicularly polarized to the nanotube axis, we have attributed these features to excitation by perpendicularly polarized light to the nanotube axis. The measured absorption energies of perpendicularly polarized light are compared with cross-polarized version of the Kataura plot. References: [1] S. Maruyama and Y. Miyauchi, AIP Conf. Proc. 786, 2005, 100-105. [2] Y. Miyauchi and S. Maruyama, cond-mat/0508232. [Preview Abstract] |
Thursday, March 16, 2006 3:06PM - 3:18PM |
W18.00002: Raman Studies of Exciton-Phonon Coupling in Single-Walled Carbon Nanotubes Stephen Doorn, Serguei Goupalov, Satishkumar Chikkannanavar Significant chirality-dependent effects on nanotube Raman intensities have recently been observed whose origins lie in the chirality dependence of exciton-phonon coupling. We present resonance Raman excitation data that demonstrates this dependence in radial breathing mode (RBM) intensities for both E11 and E22 excitation. For E22 excitation, intensities for (n- m)mod 3 = -1 chiralities are significantly more intense than for (n-m)mod 3 = +1, with more complex behavior in E11 excitation. We discuss the results in terms of a new theoretical analysis of exciton-phonon coupling that accurately describes the observations with simple intuitive analytical expressions. Relative intensities can be easily predicted using a newly introduced parameter that is also able to explain a number of anomalies in the observations. We also present the first direct comparison of E11 vs. E22 intensities for a number of chiralities. This comparison yields the ratio of the decay rates for the excited and ground excitonic states serving as intermediate states in the Raman process under E22 and E11 excitations, respectively. [Preview Abstract] |
Thursday, March 16, 2006 3:18PM - 3:30PM |
W18.00003: Resonance Raman Spectroscopy of $1.2 $< d_t < 2.0$\,nm Diameter Single Wall Carbon Nanotubes in the $E_{33}^S$ and $E_{44}^S$ Optical Range Paulo A.T. Ara\'{u}jo, S.K. Doorn, A.G. Souza Filho, J. Jiang, R. Saito, S. Maruyama, M.A. Pimenta, A. Jorio This work uses Resonant Raman Spectroscopy with excitation laser energy from 1.26 to 2.98 eV to measure the $E_{33}^S$ and $E_{44}^S$ optical transition energies, for single wall carbon nanotubes (SWNTs) with diameters in the range$1.2 < d_t < 2.0 $\,nm.We identify the families of $(2n+m) =$ constant and analyse the radial breathing mode (RBM) frequencies, the $E_{33} ^S$ and $E_{44}^S$ energies and intensities as a function of $(n,m)$. The excitonic effects are weaker in the $E_{33}^S$ and $E_{44}^S$, the energies being blue-shifted when compared with earlier predictions. We also study the relation between the RBM intensity and tube chirality, clearly showing that the RBM Raman spectrum is less intense for armchair tubes. [Preview Abstract] |
Thursday, March 16, 2006 3:30PM - 3:42PM |
W18.00004: Raman spectroscopy and imaging of surface and suspended carbon nanotubes Kate Kaminska, Jacques Lefebvre, D. Guy Austing, Jeffery Bond, Paul Finnie Freely suspended single walled carbon nanotubes show enhanced photoluminescence and Raman signals compared with those from nanotubes on surfaces. We prepared suspended carbon nanotubes by chemical vapor deposition on lithographically patterned substrates. The nanotubes were of the order of 100 microns in length with suspended segments ranging from 1 to 20 microns. Individual nanotubes and bundles were characterized with both Raman spectroscopy and scanning electron microscopy. Raman signals from suspended and non-suspended segments of the same nanotube were detected with up to a tenfold signal enhancement observed for the suspended segments. The effect of suspension is clearly illustrated in spatially resolved confocal images of nanotubes extending over many microns. [Preview Abstract] |
Thursday, March 16, 2006 3:42PM - 3:54PM |
W18.00005: Effects of collective excitations on the G-band and RBM modes in the Raman spectra of metallic unfilled and filled carbon nanotubes Saurabh Gayen, Surjyo Behera, Shyamalendu Bose The Raman spectra of a single-wall carbon nanotube (SWNT) consist of three types of modes; (i) the high frequency G-mode arising out of tangential oscillations of carbon atoms, (ii) D-mode due to the defects in the nanotube and (iii) the low frequency radial breathing mode (RBM) resulting out of radial oscillations of the carbon atoms. In this paper we theoretically investigate the effects of collective oscillations of electrons (plasmons) on the G and RBM modes in the Raman spectra of a filled and unfilled metallic SWNT. Inclusion of plasmon and the filling (rattler) atom produces four peaks in the Raman spectra in general. The positions and relative strengths of the Raman peaks [1] depend upon phonon frequencies of the nanotube and that of the filling atoms, the plasmon frequency, the strength of the electron-phonon interaction, strength of the interactions between the nanotube phonons and rattler phonon and radius of the nanotube [2]. Usually the intensity of the G-mode is higher than that of RBM. For heavier filling atoms the frequency of the rattler phonon is lower in value, which may broaden the peak to such an extent that it may disappear in the background spectrum altogether. 1.S.M. Bose et al., Physica B \textbf{351}, 129 (2004) 2. S.M. Bose, S.Gayen and S. Behera, Phys. Rev. B \textbf{72}, 153402 (2005). [Preview Abstract] |
Thursday, March 16, 2006 3:54PM - 4:06PM |
W18.00006: Chirality dependence of Raman intensity of single wall cabon nanotubes Riichiro Saito, Jie Jiang, Kentaro Sato, Ado Jorio, Georgii Samsonidze, Grace Chou, Gene Dresselhaus, Mildred Dresselhaus We present calculated Raman intensity of radial breathing modes (RBM), and other first and second order Raman signals as a function of (n,m) with exciton wavefunctions. Because of strong k dependent electron-phonon and electron-photon matrix elements, the Raman intensity shows (2n+m) family pattern. Within the extended tight binding calculation, we make exciton Kataura-plot for RBM. The Raman intensity is enhanced by localized wavefunction of the bright exciton which decreases with increasing energy and diameter. We will further discuss disorder induced D-band Raman intensity with some experimental results. [Preview Abstract] |
Thursday, March 16, 2006 4:06PM - 4:18PM |
W18.00007: Carbon Nanotube Population Analysis from Raman and Photoluminescence Intensities Ado Jorio, C. Fantini, P.A.T. Araujo, M.A. Pimenta, D.A. Heller, M.S. Strano, M.S. Dresselhaus, Y. Oyama, J. Jiang, R. Saito Large efforts are now being directed to developing synthesis or manipulation processes able to generate single-wall carbon nanotubes (SWNT) with well-defined geometric structure, i.e. $(n,m)$ indices. The $(n,m)$ population in a SWNT sample can be obtained from intensity analysis of photoluminescence excitation (PLE) and Resonance Raman spectroscopy (RRS) experiments, after the information is corrected to account for the $(n,m)$ dependence of the RRS and PLE efficiency. In the absence of standard single-wall carbon nanotube samples with well-known (n,m) population, we provide both a photoluminescence excitation (PLE) and resonance Raman scattering (RRS) analysis that together can be used to check the calculations for PLE and RRS efficiency. We show that available models describe well the chirality dependence of the intensity ratio, confirming the differences between type 1 and type 2 semiconducting tubes and the existence of a node in the radial breathing mode intensity for type 2 carbon nanotubes with chiral angles between 20$^{\circ}$ and 25$^{\circ}$. The method is used to characterize SWNT samples grown by the CoMoCAT, HiPco and alcohol-CVD processes. [Preview Abstract] |
Thursday, March 16, 2006 4:18PM - 4:30PM |
W18.00008: Optical studies of finite length effects in short DNA-wrapped carbon nanotubes Shin Grace Chou, H. Son, Eduardo Barros, Georgii G. Samsonidze, Ming Zheng, Riichiro Saito, Gene Dresselhaus, Mildred Dresselhaus In this study, a systematic resonance Raman study was carried out on samples of DNA-wrapped SWNTs with average lengths between 50 and 100nm using multiple laser excitation energies. The different Raman features have been studied in detail as a function of nanotube length and laser excitation energies. The ratio of the D-band to G-band intensities has been found to increase with decreasing average SWNT length and decreasing laser excitation energy. As the nanotubes becomes much shorter than 1/4 wavelength of light, distinct finite length effects are also observed in overtone and intermediate frequency modes between 400 and 1500cm$^{-1}$. The MIT authors acknowledge supports under the Dupont-MIT Alliance, and NSF Grant DMR 04-05538. [Preview Abstract] |
Thursday, March 16, 2006 4:30PM - 4:42PM |
W18.00009: ($n$,$m)$-dependent environmental effect on photoluminescence of single-walled carbon nanotubes Yutaka Ohno, Shinya Iwasaki, Yoichi Murakami, Shigeru Kishimoto, Shigeru Maruyama, Takashi Mizutani The photoluminescence (PL) map was measured for 20 chiralities of single-walled carbon nanotubes (SWNTs) suspended in air, and the $E_{11}$ and $E_{22}$ were compared to the results reported for SDS-wrapped SWNTs [1]. The $E_{11}$ and $E_{22}$ are mostly blueshifted by a few tens of meV, except for $E_{22}$ of type-II near zigzag SWNTs which show a redshift. The energy shifts of $E_{11}$ and $E_{22}$ from those of SDS-wrapped SWNTs, $\Delta E_{11}$ and $\Delta E_{22}$, show clear dependence on the chirality, in particular on the chiral angle rather than the diameter. $E_{11}$ and $E_{22}$ show different dependences on the chiral angle between type-I and type-II SWNTs. In the case of type-I SWNTs, $\Delta E_{11}$ is lager for the larger chiral angle whereas $\Delta E_{22}$ is smaller for the larger chiral angle. In contrast, type-II SWNTs shows the opposite dependences. The difference between type-I and type-II disappears for the SWNTs with the chirality near armchair. The chiral angle dependence of environmental effect can be explained by difference in effective mass. [1] R. B. Weisman \textit{et al}. \textit{Nano Lett. }\textbf{3 }1235(2003). [Preview Abstract] |
Thursday, March 16, 2006 4:42PM - 4:54PM |
W18.00010: Raman Scattering from few-layer Graphene Films A. Gupta, P. Joshi, T. Srinivas, Peter Eklund Few layer-graphene sheet ($n$GL's) films, where n is the number of graphene layers, are new two-dimensional sp$^{2}$ carbon systems that have been shown to produce exciting Fractional Quantum Hall phenomena. We report here on the first Raman scattering (RS) results of $n$GLs. $n$GLs with lateral dimensions of $\sim $1-3 $\mu $m were prepared by chemical delamination of graphite flake or HOPG and then transferred from solution onto substrates (mica, pyrex,In/pyrex and Au/pyrex). RS spectra have been collected on $n$GL's with n=1, 2, 3 and compared with the graphite. Graphite exhibits two E$_{2g}$ interlayer modes at 42 cm$^{-1}$ and 1582 cm$^{-1}$. The Raman spectra of (n=1-3) $n$GLs were found to exhibit peaks at 1350 cm$^{-1}$ and 1620 cm$^{-1}$, i.e., near frequencies associated with high phonon density of states. The high frequency E$_{2g}$ band is found to split into two bands when the $n$GL is supported on metallic substrates (In,Au). In both these cases, we observe bands at 1583 cm$^{-1}$, $\sim $1592 cm$^{-1}$ rather than one band at 1581 cm$^{-1 }$when the nGL is on insulating pyrex. The splitting of the interlayer band when on metallic substrates is identified with charge transfer between the nGL and the substrate. The phonon density of states scattering observed does not appear to be due to disorder in the basal plane. [Preview Abstract] |
Thursday, March 16, 2006 4:54PM - 5:06PM |
W18.00011: Resonance Raman Study of Linear Carbon Chains Formed by the Heat Treatment of Double-Wall Carbon Nanotubes C. Fantini, E. Cruz, A. Jorio, M. Terrones, H. Terrones, G. Van Lier, J-C. Charlier, M. S. Dresselhaus, R. Saito, Y. A. Kim, T. Hayashi, M. Maramatsu, M. Endo, M. A. Pimenta The Raman spectra of carbon nanotubes exhibit weak features in the spectral range between 1600 and 2000 cm$^{-1}$ that are ascribed to a second-order Raman process. However, the observation of unusual and strong spectral features around 1850\,cm$^{-1}$ have been reported recently in the Raman spectra of carbon nanotube systems, and have been ascribed to the vibration of one-dimensional chains of carbon atoms. We study the resonance behavior of the unusual Raman feature known as the coalescence-inducing mode (CIM), observed at $\sim$1850\,cm$^{-1}$, in samples of double-wall carbon nanotubes annealed at high temperatures. Resonance Raman spectra taken with many different laser energies show that the intensity of the CIM band exhibits a maximum around 2.20 eV. By comparing the experimental results with first principles calculations for the vibrational frequency and the energy gap, we propose that the CIM feature is associated with short carbon chains with an odd number of atoms, interconnecting the nanotube surfaces. [Preview Abstract] |
Thursday, March 16, 2006 5:06PM - 5:18PM |
W18.00012: Raman Scattering Study of the Thermal Conversion of SWNTs into Graphitic NanoRibbons. U.J. Kim, H.R. Guti\'{e}rrez, Peter Eklund Thermal processing of purified bundled SWNTs in vacuum at high temperatures has been found to lead to a series of important structural transformations: SWNT coalescence (1400 \r{ }C-1600 \r{ }C), formation of MWNTs ($\sim $1600-1800 \r{ }C) and the formation of a new filamentary allotrope, i.e., Graphitic Nanoribbons (GNRs). HRTEM indicates that GNRs are collapsed MWNTS. ARC and HiPCO SWNTs go through the first two transformations, but only ARC material transforms to GNRs. At the highest temperatures, the ARC material is almost completely transformed into GNRs. Here we present the results of Raman scattering experiments on these carbon filaments after high temperature heat treatment (HTT) for $\sim $ 6 hr. For coalesced SWNTs, the structural order in the tube walls is sufficient to observe new low frequency radial (R) Raman modes ($\sim $100 cm$^{-1})$ identified with the diameter-doubled tubes. We can conclude that small diameter tubes (d$<$ 1.4 nm) are preferentially lost in the range HTT$\sim $1600-1800 \r{ }C. After HTT$\sim $1800 \r{ }C, the formation of MWNTs occurs via massive bond rearrangement of coalesced SWNTs, and this transformation is observed in Raman as a broadening of the high frequency bands and a loss of R-band intensity. A few isolated SWNTs with d $\sim $ 1.3-1.5 nm were found to survive HTT$\sim $2000 \r{ }C, but not HTT$\sim $2200 \r{ }C. [Preview Abstract] |
Thursday, March 16, 2006 5:18PM - 5:30PM |
W18.00013: Coherent phonon oscillations from micelle-suspended single-walled carbon nanotubes E. Haroz, J. Shaver, J. Kono, R. Hauge, R. Smalley, Y.S. Lim, K.J. Lee, J.H. Kim, S. Doorn Time-domain oscillations were generated via degenerate pump- probe spectroscopy from individual single-walled carbon nanotubes (SWNTs) dispersed in aqueous media using ultrafast excitation pulses from a Ti:sapphire laser over the range of 710- 860 nm. Fast Fourier transform of such oscillations reveals the observation of coherent phonons (CP) corresponding to the radial breathing mode (RBMs) of 16 distinct (n,m) SWNTs. Comparison to Resonance Raman scattering (RRS) experiments indicates excellent agreement with observed RBMs, with significantly narrower linewidths seen for CP. Additionally, different RBM intensity behavior is observed within 2n+m families compared to RRS. Finally, we have directly observed two-peak maxima, separated by tens of meV, in the excitation profile for a given RBM. A possible origin of this two-peak structure is discussed. This technique represents a novel method for (n,m) characterization as well as electronic structure probing. [Preview Abstract] |
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