Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session X20: Focus Session: Carbon Nanotubes: Optical Studies |
Hide Abstracts |
Sponsoring Units: DMP Chair: Steve Cronin, University of Southern California Room: C120-C122 |
Thursday, March 18, 2010 2:30PM - 2:42PM |
X20.00001: Magnetic Susceptibility Anisotropy of Metallic Carbon Nanotubes T.A. Searles, J. Kono, Y. Imanaka, T. Takamasu, J.A. Fagan, E.K. Hobbie, H. Ajiki Metallic single-walled carbon nanotubes (SWNTs) are predicted to possess exotic orbital magnetism, arising from Aharonov-Bohm-phase-induced gap opening (in a parallel field) in addition to the large graphite-like diamagnetism (in a perpendicular field). Their magnetic susceptibilities are calculated to be a sensitive function of the applied magnetic field, the Fermi energy, and the field orientation. Here, through magnetic linear dichorism spectroscopy in high magnetic fields, we have determined the magnetic susceptibility anisotropy of metallic SWNTs for the first time and found it to be 2-4 times greater than values for semiconducting SWNTs. The measurements were made on length-sorted, (6,5)-enriched CoMoCAT SWNTs in magnetic fields up to 35~T. The observed large magnetic anisotropy, consistent with theoretical predictions, is due to the large orbital paramagnetism of electrons in metallic nanotubes in a parallel magnetic field. We also compared our values with those obtained in previous work for semiconducting nanotubes, which confirm a break from the prediction that the magnetic susceptibility anisotropy increases linearly with the diameter. [Preview Abstract] |
Thursday, March 18, 2010 2:42PM - 2:54PM |
X20.00002: Polarization-dependent coherent phonon spectroscopy of single-walled carbon nanotubes G. D. Sanders, C. J. Stanton, L. G. Booshehri, C. L. Pint, E. H. Haroz, R. H. Hauge, J. Kono, Y.-S. Lim, J.-H. Kim, K.-J. Yee To extend our previous studies\footnote{Nano Lett.~{\bf 6}, 2696 (2006); Phys.~Rev.~Lett.~{\bf 102}, 037402 (2009); Phys.~Rev.~B {\bf 79}, 205434 (2009).} of coherent phonon (CP) dymaincs in single-walled carbon nanotubes (SWNTs), we investigate the polarization anisotropy of the radial breathing mode (RBM) in highly-aligned SWNTs. We measure RBM CPs as a function of both the angle between the tube axis and the pump polarization ($\theta_1$) and the angle between the pump and probe polarizations ($\theta_2$), observing complete quenching of the RBM when $\theta_1$ = 90$^\circ$. We simulate CP dynamics varying both $\theta_1$ and $\theta_2$ and find that the CP signal decreases as $\theta_1$ goes from 0$^\circ$ (parallel to the tube) to 90$^\circ$. We compare theory with experiment for RBM CPs created by pumping at the $E_{44}$ optical transition in an ensemble of SWNTs with a diameter distribution centered around 3~nm. [Preview Abstract] |
Thursday, March 18, 2010 2:54PM - 3:06PM |
X20.00003: Spin-orbit coupling and curvature effects on the static polarizability of single-wall carbon nanotubes S. E. Ulloa, G. S. Diniz Carbon nanotubes (CNTs) are known to exhibit metallic or insulating behavior for different chiral vectors. Application of external electric fields and the presence of spin-orbit interaction (SOI) result in modification of the energy level structure of CNTs and their electrical response functions. SOI is known to significantly couple spin and orbital degrees of freedom in these nanostructures [1], and we consider interesting related effects. In particular, we present here calculations of the static dielectric response of different single-wall CNTs in the long-wavelength limit regime when subjected to uniform external electric fields both along and across the longitudinal direction (parallel to the nanotube axis). Our calculation uses a four-orbital tight-binding following the Slater-Koster formalism and includes the effect of finite curvature on the CNT. We consider Rashba and intrinsic SOIs, and use a random phase approximation to evaluate $\epsilon(q\rightarrow 0, \omega=0)$. We find that the metallic-to-semiconductor transition induced by the intrinsic SOI is suppressed as the Rashba field is taken into account. We further show that this behavior has a clear signature on measurable quantities, such as the static polarizability. We discuss the dependence of these effects on nanotube size, field strenghs, and curvature.\\ $[1]$ F. Kuemmeth et al., Nature 452, 448-452 (2008). [Preview Abstract] |
Thursday, March 18, 2010 3:06PM - 3:42PM |
X20.00004: Ultrafast measurement of electron phonon coupling in CNTs (optical, ultrafast) Invited Speaker: |
Thursday, March 18, 2010 3:42PM - 3:54PM |
X20.00005: Third-order Coherent Optical Spectroscopy of Individual Carbon Nanotubes Tatyana Sheps, Philip G. Collins, Eric Potma Single walled carbon nanotubes (SWCNTs) are low dimensional conductors with unique electronic and electro-optic properties. To probe these properties, we investigate the third-order, coherent anti-stokes (CAS) response of individual SWCNTs using a dual color, four-wave-mixing technique. Despite being nanoscale objects much smaller than the wavelength of light, the CAS response allows single SWCNTs to be optically imaged with good spatial resolution and high signal-to-noise [1]. The absence of any Raman signature shows that the CAS response is dominated by electronic, rather than vibrational, dynamics, which suggests a method for straightforward optical discrimination between metallic and semiconducting SWCNTs. Furthermore, electrically-connected SWCNTs in a field effect transistor geometry enable additional investigation of the dependence of the CAS signal on charge carrier densities. We observe changes in the CAS signal that depend on contact resistances and on physiochemical effects that change the effective SWCNT Fermi level.\\[0pt] [1] H. Kim et al, Nano Lett. 9 2991-2995 (2009). [Preview Abstract] |
Thursday, March 18, 2010 3:54PM - 4:06PM |
X20.00006: Control of specific vibrational modes in carbon nanotubes and fullerenes responding to fast intense laser pulses Roland Allen, Chenwei Jiang, Xiang Zhou This talk will review the results of Xiang Zhou [1] and Chenwei Jiang [2] for the response of carbon nanotubes and fullerenes to ultrafast laser pulses. For carbon nanotubes at low temperature, it is predicted [1] that laser pulses with \textit{optimized durations} will excite particular vibrational modes with high specificity. This prediction results from a simple analytical model, and is confirmed by completely independent and detailed supercomputer simulations using semiclassical electron-radiation-ion dynamics, which are in remarkably precise agreement with the analytical solution. Similarly, for fullerenes at low temperature it is predicted [2] that a sequence of laser pulses with an \textit{optimized delay} between pulses will excite a specifically chosen vibrational mode. In addition, vibrational modes can be suppressed and more generally controlled by an additional pulse. [1] X. Zhou, C. Jiang, and R. E. Allen, to be published. [2] C. Jiang, X. Zhou, R. H. Xie, F. L. Li, and R. E. Allen, to be published. [Preview Abstract] |
Thursday, March 18, 2010 4:06PM - 4:18PM |
X20.00007: Resonant Raman Spectroscopy of Chirality-Enriched Semiconducting Single Walled Carbon Nanotubes Juan G. Duque, Hang Chen, Anna Swan, Xiaomin Tu, Ming Zheng, Stephen K. Doorn Recent advances in carbon nanotube separations science are providing access to samples highly enriched in single chiralities. We present a Raman spectroscopic investigation of enriched semiconducting samples generated from ion chromatography of DNA-functionalized nanotubes. We will present results on the resonance Raman excitation profile behavior of RBM, G-band, and G' spectra from isolated SWNT samples. RBM profiles show very good separation of single chirality semiconducting fractions with very low cross-contamination from other nanotubes. G-band profiles allow testing of different models for the Raman scattering process and reveal new evidence for the importance of non-Condon effects in the Raman response. Investigations into the G' mode enabled us to map the band structure of the different isolated chiralities and to probe variable coupling in the vicinity of the E22 transition. These results demonstrate the important role that chirality-enriched samples have to play in revealing new SWNT photophysical behaviors. [Preview Abstract] |
Thursday, March 18, 2010 4:18PM - 4:30PM |
X20.00008: Observation of Heat Exchange between Different Gas Molecules and Suspended Carbon Nanotubes with Raman Spectroscopy I-Kai Hsu, Michael T. Pettes, Mehmet Aykol, Li Shi, Stephen Cronin We observe different heat dissipation behavior of individual, suspended carbon nanotubes (CNTs) in different gas environments based on their temperature profiles as measured by micro-Raman spectroscopy under various electrical heating powers. The heat transfer coefficient between gas molecules and CNTs is determined by comparing the temperature profiles along each individual CNT measured in vacuum and in different ambient gas environments. Our results show that heat taken away by gas molecules from the hot CNT surface is approximately 3 times larger than the heat transported though the CNT itself, indicating the significant influence of gas molecules in the thermal transport of CNTs. This result is encouraging for thermal management solutions for future CNT-based electronic applications. Moreover, the heat transfer coefficient is found to be inversely proportional to the temperature of the CNT, which implies that the heat removal rate from the CNT by gas molecules might also be limited by the decreased thermal conductivity of the CNT at higher temperatures. [Preview Abstract] |
Thursday, March 18, 2010 4:30PM - 4:42PM |
X20.00009: Raman Spectroscopy of Individual Suspended Carbon Nanotubes under Immense Strains Chia-Chi Chang, I-Kai Hsu, Mehmet Akyol, Stephen B. Cronin Suspended carbon nanotubes with long nanotube-substrate contacts grown by chemical vapor deposition enable us to explore carbon nanotubes up to strains of 13.6{\%}. Here, Raman spectroscopy is utilized to observe strain-induced changes in the $G$ band vibrational modes, which have a linear and pronounced response to the extension of the C-C bonds under various degrees of strain. The $G$ band is found to downshift at rates ranging from -6.2 to -23.6cm$^{-1}$/{\%} strain among the different nanotubes measured in this study. Despite this wide range of downshift coefficient, we observe broadening of the $G$ band linewidth (FWHM) at a universal threshold downshift of $\Delta \omega _{G }>$ 75cm$^{-1}$. The $G$ band is observed to downshift by up to 157cm$^{-1}$ (from 1592 to 1435cm$^{-1})$ under immense strains without any noticeable $D$ band. Our measurements show that carbon nanotubes remain intact up to 13.6{\%} strain with no slippage, breakage, or defect formation. [Preview Abstract] |
Thursday, March 18, 2010 4:42PM - 4:54PM |
X20.00010: Coupled Radial Breathing Modes in Double-Walled Carbon Nanotubes Kaihui Liu, Xiaoping Hong, Wenlong Wang, Enge Wang, Feng Wang Radial breathing modes (RBM) phonon vibrations of chirality-resolved, individual double-walled nanotubes (DWNT) were studied by combined electron diffraction and Raman scattering techniques. The chiral-indices of both the inner- and outer-wall nanotubes are determined directly by TEM diffraction. We found that the RBM phonons of each shell in DWNTs, compared to the isolated SWNTs with the same (n, m), were modified by the intershell interactions. The RBM vibration frequency shift varies significantly with specific DWNT shell atomic structures. We will compare the results to a continuously model for two coupled nanomechanical oscillators. [Preview Abstract] |
Thursday, March 18, 2010 4:54PM - 5:06PM |
X20.00011: Dynamic AC Conductivity and Radiative Dipole Coupling of Carbon Nanotubes Daniel Joh Rayleigh scattering spectroscopy has recently emerged as a powerful technique for probing CNTs at optical frequencies, but quantitative understanding of the electrical properties of CNTs, most importantly the dynamic AC conductivity \textit{$\sigma $}(\textit{$\omega $}), at optical frequencies is currently missing. Using a new Rayleigh imaging technique, we are able to measure the elastic scattering intensity of individual carbon nanotubes while we vary the excitation wavelength, and for the first time, we show that the AC conductivity is uniform over many different CNTs for different resonances. We explain this surprising discovery using a model that includes energy dependent electron-(acoustic) phonon scattering. Finally, we present evidence of long-range radiative coupling between parallel CNTs, which suggests that a transfer of electric dipole is possible over a large distance ($>$300nm) when there is a significant resonance overlap. [Preview Abstract] |
Thursday, March 18, 2010 5:06PM - 5:18PM |
X20.00012: Spectral Rayleigh Imaging of Carbon Nanotubes Using Darkfield Microscopy with Index-Matching Media Lihong Herman, Daniel Joh, Jiwoong Park We present a novel technique for investigating the elastic scattering of carbon nanotubes (CNTs) with high signal-to-noise ratio by using a modified darkfield microscope. Our method allows for high-throughput imaging of CNTs directly on a solid substrate with diffraction-limited optical and spectral resolution, enabling us to determine key resonance parameters such as resonance wavelength, intensity, and peak widths for their respective Rayleigh spectra. In conjunction with AFM measurements, this technique permits us to assign specific sub-band transitions, and even identify structural ($n, m)$ values.~ By characterizing many CNTs in parallel, we can furthermore determine metallic to semiconducting ratios and the density of chirality-changing events for a given sample. [Preview Abstract] |
Thursday, March 18, 2010 5:18PM - 5:30PM |
X20.00013: Simultaneous Measurement of Raman and Rayleigh Spectroscopy for Probing Carbon Nanostructures Properties Sang-Yong Ju, Jiwoong Park Carbon nanotubes (CNTs) have demonstrated a promising candidate due to excellent electrical and mechanical properties originating from their one dimensionality. In order to fully utilize these characteristics in a novel electronic and optoelectronic device geometry, one must find and exploit their chiral information (i.e. ($n, m))$ as well as their electronic type. However, the elucidation of such information on the substrate remains challenging and the characterization of many nanotubes in parallel is even daunting. Recently, Rayleigh imaging debuts to characterize CNTs and shows a potential use for uncovering the aforementioned key parameters with aid of other technique. Here, we shows that the simultaneous measurement of Raman and Rayleigh signals shows excellent tool to measure the unequivocal chiral information of CNTs on a substrate. Our technique can probe a large number of CNTs, altogether with their spatial information on a substrate. This technique can provide a venue to fabricate CNT devices with ``known'' chiral indices and, therefore, correlate them with their electronic and optoelectronic properties. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700