Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session D27: Focus Session: Carbon Nanotubes: Raman Spectroscopy |
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Sponsoring Units: DMP Chair: Pehr Pehrson, Naval Research Lab Room: LACC 501C |
Monday, March 21, 2005 2:30PM - 2:42PM |
D27.00001: Theory of Resonance Raman Scattering in Carbon Nanotubes using Excitonic Intermediate States Jose Menendez, Eric Chang, Giovanni Bussi, Alice Ruini, Elisa Molinari Optical transition energies in carbon nanotubes can be obtained with high precision from Raman excitation profiles (REPs) measured with continuously tunable laser sources. In the case of Raman scattering by the radial breathing mode (RBM), the measured frequency of this mode makes it possible to associate the optical transition energies with a particular tube diameter, a unique feature of the Raman approach. The theoretical interpretation of REPs has been so far limited to free-electron-hole pairs. However, large excitonic binding energies are expected in quasi one-dimensional systems, and this expectation has been recently confirmed by detailed first principles calculations. Here we present an extension of the ab initio approach to the computation of REPs in semiconducting tubes. A many-body method based on the GW approximation and the Bethe-Salpeter equation is developed to compute the REP for RBMs. This approach yields REPs that take into account the electron-hole interaction and excitonic effects. The method has been applied to the (4,2) tube. The calculated REP iscompared with predictions for the case of free electron-hole pairs as well as with the theoretical optical absorption. Such a comparison makes it possible to identify the relative advantages of these two different optical techniques. [Preview Abstract] |
Monday, March 21, 2005 2:42PM - 2:54PM |
D27.00002: In-situ Raman Spectroscopy of Optically Trapped Single-Walled Carbon Nanotubes Herman A. Lopez, Shida Tan, Michael P. Stewart, Yuegang Zhang In-situ Raman spectroscopy was demonstrated to provide direct evidence of optical trapping of individual single-walled carbon nanotubes (SWNTs) and used to investigate the possibility of using tunable laser tweezers (514 nm - 1455 nm) to selectively manipulate and sort nanotubes. The in-situ Raman and optical trapping system consists of two lasers, allowing selection of a Raman probing wavelength in resonance with the desired SWNTs and a separate optical trapping wavelength to control the interaction with the tubes. The Raman probe (633 nm or 785 nm probing wavelength) is capable of detecting structural information of both metallic and semiconducting SWNTs. This provides direct evidence of the local SWNTs concentration variation and chirality distribution in the optical trap. The Raman probe can also be moved independent to the optical trap, allowing spatial profiling. This work will discuss the evidence of optical trapping of SWNTs, determination of the trapping threshold and trapping volume profile, and results of tube type selectivity by the laser tweezers. [Preview Abstract] |
Monday, March 21, 2005 2:54PM - 3:06PM |
D27.00003: Tunable resonance Raman on individual, suspended single wall carbon nanotubes Y. Yin, A.G. Walsh, S.B. Cronin, A.K. Swan, A. Stolyarov, W.S. Bacsa, M. Tinkham, M.S. Unlu, B.B. Goldberg Resonance Raman studies are performed with a tunable excitation laser on single wall carbon nanotubes (SWNTs) suspended in air over trenches. Radial breathing mode (RBM) Stokes intensity excitation profiles (REP) are symmetric in shape and fitted to find lifetime broadenings and locations of the resonant electronic states. The simultaneous Anti-Stokes data are well fitted with the identical parameters. A comparison of REP and PL excitation profiles will be discussed. Tens of measurements show a narrow line broadening of 15-20 meV and a red shift of E{\_}22 compared to suspended SWNTs in solutions. Similar results are found for REPs of the G band Raman mode. This shift can be explained by an exciton binding energy shift in two different dielectric media. This study also suggests that environmental effects, or other inhomogeneous differences for nanotubes, can significantly change sub-band transition energies. The measured differences between individual tubes fall within the inhomogeneously broadened experimental results reported for NT bundles. [Preview Abstract] |
Monday, March 21, 2005 3:06PM - 3:18PM |
D27.00004: Signal Enhancement in Resonant Raman Spectra from Suspended Carbon Nanotubes A. Walsh, Y. Yin, B. Goldberg, S. Cronin, S. Stolyarov, M. Tinkham, A. Swan, S. Unlu, W Bacsa Suspended SWNTs are grown over trenches on a quartz substrate. Resonance Raman spectra from individual tubes or small bundles are mapped spatially, near resonance, using a tunable Ti:Sappire laser. A strong signal is found either exclusively over the trench or with a factor of 5-10 enhancement compared to the substrate. This effect is observed in the radial breathing modes (RBM) Stokes, anti-Stokes, and G-band Stokes processes, and is too large to be ascribed to an electric-field standing-wave enhancement over the trench. Several resonant tubes are indicated by the presence of more than one RBM. Occasionally, in addition to a RBM in the range of 180-250 cm-1, a low energy phonon mode is observed in the range 350-410 cm-1 with the same spatial extent and resonance maxima as the RBM. RBMs with these phonon energies are unlikely to be produced by the chemical vapor deposition growth process with an iron catalyst. This implies that tube-tube interactions, higher order, or other symmetry allowed Raman modes might be responsible. [Preview Abstract] |
Monday, March 21, 2005 3:18PM - 3:30PM |
D27.00005: $(n,m)$ dependent effects on the Resonance Raman Spectroscopy for small diameter single-wall carbon nanotubes A. Jorio, C. Fantini, M. A. Pimenta, R. B. Capaz, Ge. G. Samsonidze, G. Dresselhaus, M. S. Dresselhaus, J. Jiang, N. Kobayashi, A. Gr\"{u}neis, R. Saito We discuss accurate analysis of the electronic transition
energies $E_{22}^S$ and $E_{11}^M$ and the radial breathing mode
frequencies $\omega_{\rm RBM}$ from 40 small diameter single-
wall carbon nanotubes (SWNTs) in the diameter range $0.7 |
Monday, March 21, 2005 3:30PM - 3:42PM |
D27.00006: Effects of the Non-linearity of the Electronic Bands on the Double-Resonance Raman Features of Graphite and Carbon Nanotubes Eduardo Barros, Antonio Souza Filho, Josue Mendes Filho, Luis Gustavo Cancado, Ado Jorio, Georgii Samsonidze, Gene Dresselhaus, Mildred Dresselhaus The second-order Raman feature that is observed for graphite at $\sim $2450 cm$^{-1}$ for 2.41 eV excitation energy (E$_{L})$ has been explained by considering a double-resonance Raman process originating from a near-K-point phonon. [1] However, the negative dispersion with laser energy ($\partial \omega $/$\partial $E$_{L})$ observed for this peak has not yet been successfully explained. In the present work, we explain the negative dispersion of the 2450 cm$^{-1}$ peak with laser energy by considering a non-linear energy dispersion for the electrons close to the K-point of the Brillouin zone. Also, the slope of the dispersion of the 2450cm$^{-1}$ feature with laser energy is shown to be associated with the presence of a Kohn anomaly at the K-point of the phonon dispersion associated with both the G'-band and this $\sim $2450 cm$^{-1}$ peak [2]. Therefore, the results obtained in this work provide indirect experimental evidence for the presence of the Kohn anomaly in graphite and enables a measurement of the electron-phonon coupling. The discussion is extended to the effects of the Kohn anomaly and the non-linear electronic dispersion on the electronic and vibrational properties of carbon nanotubes. [1] Shimada et al. Carbon, \textit{submitted } [2] Piscanec et al. Phys. Rev. Lett., \textit{accepted} [Preview Abstract] |
Monday, March 21, 2005 3:42PM - 3:54PM |
D27.00007: Surfactant Effects on Single-Walled Carbon Nanotube Raman Spectroscopy Lars Ericson, Pehr Pehrsson Raman spectroscopy is a common tool used to characterize the composition of nanotube devices and probe the effectiveness of electronic separation schemes. Raman spectroscopy of samples made from single-walled carbon nanotubes (SWNTs) suspended in various common aqueous surfactants has been performed. Changes in the radial breathing modes, disorder mode, and tangential mode have been explored as a function of aggregate state, surfactant presence, and sample deposition, including dielectrophoretic deposition (DEP). The nature of these changes has been analyzed in the context of resonance shifts, charge transfer effects, and SWNT electronic separation. The metallic SWNT selectivity of DEP has been examined in the presence of surfactant. [Preview Abstract] |
Monday, March 21, 2005 3:54PM - 4:06PM |
D27.00008: Resonance Raman intensity excitation spectra of single wall carbon nanotubes Riichiro Saito, Jie Jiang, Alexander Gruneis, Shin Grace Chou, Georgii Samsonidze, Ado Jorio, Gene Dresselhaus, Mildred S. Dresselhaus Raman intensity of RBM and G-band of single wall carbon nanotubes (SWNTs) is calculated as a function of excaition laser energy. Depending on type (mod(2n+m,3)=1 or 2 for (n,m) SWNT) of semiconducting SWNTs and on trigonal warping effect of metallic SWNTs, Raman excitation spectra show a variety of excitation spectra features. The physical origin of these specra can be understood by (1) strong k dependence of electron- phonon interaction, (2) interepherence effect between Raman processes and (3) broadening factor in the resonance processes. We comapred with the experimental results of Raman excitation profile with use of tunable laser, which is consistent with the theoretical prediction. [Preview Abstract] |
Monday, March 21, 2005 4:06PM - 4:18PM |
D27.00009: Intermediate frequency modes in resonance Raman spectra of single-wall carbon nanotubes Cristiano Fantini, Ado Jorio, Mauricio Souza, Riichiro Saito, Georgii Samsonidze, Mildred Dresselhaus, Marcos Pimenta Intermediate frequency modes (IFMs) appear in resonance Raman spectra of single-wall carbon nanotubes (SWNTs) in the spectral range between 600 to 1100 cm$^{-1}$. Early studies indicated that IFMs exhibit dispersion with excitation wavelength. Recently, we conducted an extensive study of IFMs with many laser excitation wavelengths on SWNT samples prepared by electric arc discharge. This study revealed the step-like nature of the IFM dispersion for $E_{33}^S$ and $E_{44}^S$ transitions in semiconducting SWNTs, that was attributed to a phonon assisted electronic resonance mechanism that is highly selective of IFM excitation from low chiral angle (zigzag-like) SWNTs. In the present work we perform similar measurements on HiPco SWNT samples featuring $E_{11}^M$ transitions in metallic SWNTs, observing similar step-like dispersive behavior, thus allowing us to further confirm and refine the theory of IFMs. The new theory of IFMs enhances the potential of using resonance Raman spectroscopy for SWNT sample characterization. [Preview Abstract] |
Monday, March 21, 2005 4:18PM - 4:30PM |
D27.00010: Exciton Effects in the Optical Spectra of Single-Walled Carbon Nanotubes Angela Hight Walker, Danilo Romero We investigate excitonic effects in the optical spectra of single-walled carbon nanotubes (SWCNT) by means of resonant Raman and photocurrent spectroscopies. The measurements are carried out with the newly built confocal Raman microscope at the NIST-Optical Technology Division. The microscope is capable of working over a wide range of temperatures (T = 4.2-300 K) and magnetic fields (H = 0-8 T). Resonance enhancement of the Raman scattering intensity of the radial breathing modes and the photocurrent spectra in SWCNTs is probed with tunable laser excitation sources. The influence of an applied magnetic field on the exciton spectra at low temperatures will be presented in this talk. [Preview Abstract] |
Monday, March 21, 2005 4:30PM - 4:42PM |
D27.00011: Raman and IR Spectroscopy of Chemically-Processed Single-Walled Carbon Nanotubes C. A. Furtado, U. J. Kim, X. Liu, H. R. Gutierrez, G. Chen, A. Gupta, P. C. Eklund We have used IR and Raman spectroscopy to study the evolution of the vibrational spectrum of bundled single-walled carbon nanotubes (SWNTs) during the purification process needed to remove metal catalyst and amorphous carbon from arc-derived soot and after high temperature annealing. We have carried out a systematic study to define the different outcomes stemming from different purification protocols, e.g., DO, DO/HCl, DO/HNO$_{3}$, H$_{2}$O$_{2}$, H$_{2}$O$_{2}$/HCl, where the first step is either dry oxidation (DO) in flowing air or wet oxidation in refluxing H$_{2}$O$_{2}$ to remove amorphous carbon. The second step is an acid reflux step to remove the residual growth catalyst (Ni-Y). Using IR transmission through thin films of nanotubes, we resolve structure due to functional groups, which are present in the as-prepared material (e.g., -COC-), and groups added through the chemical processing (e.g., -COOH, -OH). After high temperature vacuum annealing at 1100$^{o}$C, most of oxygen-containing groups were removed. $^{\dag }$This work was supported, in part, by the NSF NIRT program (DMR- 0304178). [Preview Abstract] |
Monday, March 21, 2005 4:42PM - 4:54PM |
D27.00012: Characterization of Isolated Single-Wall Carbon Nanotubes by Raman Spectroscopy and Transmission Electron Microscopy on the Same Nanotube Antonio Souza Filho, Eduardo Barros, Josue Mendes Filho, HyungBin Son, Jing Kong, Gene Dresselhaus, Mildred Dresselhaus The correlation between the structural and the vibrational properties of isolated single wall carbon nanotubes (SWNTs) is studied in this work by combined Transmission Electron Microscopy (TEM) and Raman spectroscopy experiments on the same nanotube and at the single nanotube level. The SWNTs were grown on coated TEM grids by the CVD method. Isolated SWNTs were selected and their locations mapped by using low-magnification TEM. Structural information and the electronic and vibrational properties of the selected nanotubes were obtained by a Raman spectroscopy study. High-resolution TEM measurements were used to characterize the same selected nanotubes in order to compare the structural information obtained by the two different methods and to relate it to the electronic and vibrational properties of nanotubes. [Preview Abstract] |
Monday, March 21, 2005 4:54PM - 5:06PM |
D27.00013: Infrared-ActiveVibrational Modes of Single-Walled Carbon Nanotubes†U. J. Kim, X. Liu, C. A. Furtado, G. Chen, R. Saito, J. Jiang, M. S. Dresselhaus, P. C. Eklund We believe we have observed the IR-active vibrational modes of single-walled carbon nanotubes (SWNTs) for the first time. They were observed by optical transmission through thin films of bundled nanotubes. Because IR-active chemical functional groups, e.g., -COOH,-OH, might also be attached to the tube walls and contribute additional spectral features, we have also studied the effects of chemical purification and long-term high-temperature vacuum annealing on the IR spectrum. Through comparison with theory, we are able to assign much of the sharp stucture observed in our SWNT IR spectra. {\dag}This work was supported, in part, by the NSF NIRT program (DMR- 0304178). [Preview Abstract] |
Monday, March 21, 2005 5:06PM - 5:18PM |
D27.00014: Vibrational and Electron Energy Spectrum of Double Wall Carbon Nanotubes Aditya Mohite, Bruce Alphenaar, Gamini Sumanasekera Using Raman and photocurrent spectroscopy, we are able to distinguish between inner and outer tube features in both the vibrational and electron energy spectrums of double wall carbon nanotubes (DWNTs). DWNTs are synthesized using the ``peapod'' fabrication method. The inner hollow space of single wall nanotubes (SWNTs) is filled with C$_{60}$ molecules by vapor phase reaction at 400$^{o}$C, creating nanotube peapods. Annealing the peapods at 1200$^{o}$C in high vacuum transforms the C$_{60}$ molecules into the inner shell of the DWNT. Transmission electron microscopy measurements reveal that highly uniform DWNTs are formed with average outer and inner diameters of 1.4 nm and 0.9 nm, respectively. The Raman spectrum of the DWNTs contains a series of peaks not observed in the SWNTs or peapods. One of these peaks at 335 cm$^{-1}$ can be attributed to the radial vibrational mode of the inner nanotube. The photocurrent spectrum of the DWNTs contains two extra peaks not observed in SWNTs. Based on the tube diameters, these are associated with the S11 and S22 transitions for the inner nanotube. \textit{Supported by the NSF ( ECS-0224114) and NASA (NCC5- 571).} [Preview Abstract] |
Monday, March 21, 2005 5:18PM - 5:30PM |
D27.00015: Study of the Atomic Structure of Graphite Edges Using Raman Spectroscopy Marcos Pimenta, Luiz Gustavo Can\c{c}ado, Bernardo Neves, Maria Sylvia Dantas, Ado Jorio A study of step edges in graphite with different atomic structures combining Raman spectroscopy and scanning probe microscopy is presented. The orientation of the carbon hexagons with respect to the edge axis, in the so-called armchair or zigzag arrangements, is distinguished spectroscopically by the intensity of a disorder-induced Raman D-band. This effect is explained by applying the double resonance theory to a semi-infinite graphite crystal and by considering the one-dimensional character of the defect and the anisotropy in the optical absorption of graphite. [Preview Abstract] |
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