Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session N8: Transport and Optical Phenomena in Carbon Nanotubes |
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Sponsoring Units: DMP Chair: Dan Prober, Yale University Room: 307 |
Wednesday, March 20, 2013 11:15AM - 11:27AM |
N8.00001: Terahertz Detection as a Probe of Luttinger-Liquid Behavior in an Individual Single-Walled Carbon Nanotube Joel D. Chudow, Chris B. McKitterick, Daniel E. Prober, Daniel F. Santavicca, Philip Kim Carbon nanotubes (CNTs) serve as an experimental system for verification of physical models of one-dimensional (1-D) conduction, in particular the Luttinger-liquid theory. We describe measurements of terahertz (THz) absorption in individual single-walled carbon nanotubes and distinguish between two response mechanisms: bolometric detection due to heating a CNT with a temperature-dependent resistance and the response due to non-thermal electrical contact nonlinearities. The effect of the contact nonlinearity is not significantly decreased at THz frequencies, allowing for analysis of the parallel contact capacitance to an individual CNT.[1] We study high-frequency charge excitations in a CNT as a probe of the strength of the electron-electron interactions due to the lack of screening in this 1-D system. This is achieved by exciting terahertz standing wave resonances along the length of a CNT, observed using the nonlinear detection mechanism. We exploit this experimental technique to test predictions of the Luttinger-liquid model. $\backslash \backslash $[4pt] [1] J.D. Chudow, D.F. Santavicca, C.B. McKitterick, D.E. Prober and P. Kim, \textit{Appl. Phys. Lett.} \textbf{100}, 163503 (2012). [Preview Abstract] |
Wednesday, March 20, 2013 11:27AM - 11:39AM |
N8.00002: Determination of absorption cross-section in suspended single-walled carbon nanotubes Xiaoping Hong, Kaihui Liu, Sangkook Choi, Steven Louie, Feng Wang Quantitative determination of optical absorption cross-section at single tube level was performed for over 50 suspended single-walled carbon nanotubes (SWCNTs). The structures of the nanotubes are independently identified by electron diffraction, which allows a chirality-dependent study of the nanotube absorption cross-section. We will discuss the absorption strength as well as the linewidth of the optical resonances in both semiconducting and metallic nanotubes of different diameters. [Preview Abstract] |
Wednesday, March 20, 2013 11:39AM - 11:51AM |
N8.00003: Triplet-triplet exciton interactions and delayed fluorescence in single-wall carbon nanotubes Tobias Hertel, Florian Spath, Dominik Stich, Hannes Kraus, Andreas Sperlich, Vladimir Dyakonov We present pump-probe-, time-correlated single photon counting and spin-sensitive photoluminescence studies of semiconducting single-wall carbon nanotubes (SWNTs) which unambiguously identify triplet-triplet annihilation as the mechanism underlying a long-lived delayed fluorescence (DF) signal. DF decays with a $t^{-0.9}$ power-law, characteristic of diffusion-limited annihilation reactions in 1-dimensional systems. The experiments allow to determine triplet diffusion constants in SWNTs to be on the order of $1\, {\rm cm^2s^{-1}}$ and the triplet lifetime which is found to be $60\pm30\, {\rm \mu s}$. The experiments indicate that the rate of diffusion-limited photo-reactions, here exemplified by triplet-triplet annihilation, can be reduced by one-dimensional confinement. A comparison of optical transients in aqueous and organic solvent environments also indicates how polaron pair dynamics can be influenced by the environment. [Preview Abstract] |
Wednesday, March 20, 2013 11:51AM - 12:03PM |
N8.00004: Nonequilibrium Tunneling Spectroscopy of Carbon Nanotubes Nicholas Bronn, Nadya Mason We have used nonequilibrium tunneling spectroscopy to elucidate the nature of electron-electron interactions in carbon nanotubes. Due to their reduced dimensionality, carbon nanotubes are thought to be described by Luttinger liquid theory, where electron-electron interactions play a considerable role. Superconducting tunnel probes are used to measure the electron energy distribution functions, whose shape can be related to electronic energy relaxation and scattering. We measure the dependence of the electron distribution function on nonequilibrium bias, position along the nanotube, and temperature. [Preview Abstract] |
Wednesday, March 20, 2013 12:03PM - 12:15PM |
N8.00005: Ultrafast Spectral Diffusion of the First Subband Exciton in Single-Wall Carbon Nanotubes Daniel Schilling, Tobias Hertel The width of optical transitions in semiconductors is determined by homogeneous and inhomogeneous contributions. Here, we report on the determination of homogeneous linewidths for the first exciton subband transition and the dynamics of spectral diffusion in single-wall carbon nanotubes (SWNTs) using one- and two-dimensional time resolved spectral hole burning spectroscopy. Our investigation of highly purified semiconducting (6,5)-SWNTs suggests that room temperature homogeneous linewidths are on the order of 4~meV and are rapidly broadened by an ultrafast sub-ps spectral diffusion process. These findings are supported by our off-resonant excitation experiments where we observe sub-ps population transfer reflecting the thermal distribution of energy levels around the first subband exciton transition. The results of temperature-dependent spectral hole burning experiments between 17~K and 293~K suggest that homogeneous linewidths are due to exciton interaction with low energy optical phonons, most likely of the radial breathing mode type. In contrast, we find that inhomogeneous broadening is determined by an electronic degree of freedom such as ultrafast intra-tube exciton diffusion which is characteristic and unique for excitons in these one-dimensional semiconductors. [Preview Abstract] |
Wednesday, March 20, 2013 12:15PM - 12:27PM |
N8.00006: Free Carrier Dynamics in Photoexcited Semiconducting Carbon Nanotube / C$_{60}$ Planar Heterojunctions Dominick Bindl, Meng-Yin Wu, Andrew Ferguson, Nikos Kopidakis, Jeffrey Blackburn, Michael Arnold Semiconducting single walled carbon nanotubes (s-SWCNTs) have remarkable photophysical properties and are appealing for use as principal absorbers in photovoltaics. We have previously demonstrated the collection of photocurrent from thin s-SWCNT films with efficiencies approaching 100{\%} at C$_{60}$ interfaces. Exploiting this interface in high efficiency photovoltaics requires collecting free carriers from optically dense s-SWCNT/C$_{60}$ films with negligible recombination losses, and therefore, an understanding of free carrier recombination kinetics and mechanisms. Time resolved microwave conductivity (TRMC) is a technique which monitors free carrier generation and decay transients in response to a spectrally tunable pump. Here, we report TRMC studies of free carrier dynamics in s-SWCNT thin films and in heterojunctions with C$_{60}$. We have found that free carrier generation yields increase by nearly an order of magnitude and lifetimes increase up to 850ns following introduction of a C$_{60}$ interface, with free carrier lifetimes and generation yields strongly dependent on excited s-SWCNT diameter. We discuss yields, kinetics, and provide insight into relevant charge transfer and recombination mechanisms. [Preview Abstract] |
Wednesday, March 20, 2013 12:27PM - 12:39PM |
N8.00007: p-n junction photodetectors based on macroscopic single-walled carbon nanotube films Xiaowei He, S\'ebastien Nanot, Robert H. Hauge, Junichiro Kono Single-Wall carbon nanotubes (SWCNTs) are promising in use of solar technology and photodetection. There have been many reports about photovoltaic effect in nanoelectronic devices based on individual SWCNTs, but they are limited by miniscule absorption. There has been a growing trend for merging SWNTs into mico- and macroscopic devices to provide more practical applications. Here we report p-n junction photodetectors based on macroscopic SWCNTs film. Factors affecting the PV amplitude and response time have been studied, including substrates, doping level. The maximal responsivity $\sim $ 1 V/W was observed with samples on Teflon tapes, while a fast response time $\sim $ 80 $\mu $s was observed with samples on AlN substrates. Hence an optimal combination of photoresponse time and amplitude can be found by choosing proper substrates. We found that the PV amplitude increases nonlinearly with increasing n-doping concentration, indicating the existence of an optimal doping concentration. Finally, we checked photoresponse in a wide wavelength range (360 to 900 nm), and PV was observed throughout, indicating that the device could potential be used as a broadband photodetector. [Preview Abstract] |
Wednesday, March 20, 2013 12:39PM - 12:51PM |
N8.00008: Energies of higher optical transitions in semiconductor carbon nanotubes Serguei Goupalov We show that short-range electron interactions in semiconductor carbon nanotubes promote inter-subband coupling. This coupling is revealed in a significant alteration of energies of E$_{33}$ and E$_{44}$ optical transitions with respect to the predictions of the non-interacting model. The influence of the short-range electron interactions is traced analytically and numerically, by switching it off entirely or partly while calculating optical absorption spectra. [Preview Abstract] |
Wednesday, March 20, 2013 12:51PM - 1:03PM |
N8.00009: Effect of Disorder on AC Response of Metallic Carbon Nanotubes Daisuke Hirai, Takahiro Yamamoto, Satoshi Watanabe Metallic carbon nanotubes (M-CNTs) have long coherent lengths. In fact, the Anderson localization has been observed in M-CNTs with defects at room temperature [1]. In considering the AC response, not only the understanding of DC conductance behavior but also that of phase-difference between electric current and bias voltage are important. At present, however, the influence of disorder on the AC response remains unclear. In this study, we calculated the AC response of M-CNTs with disorder based on the nonequilibrium Green's function method combined with nearest-neighbor $\pi $-orbital tight-binding approximation and wide-band-limit approximation. In our simulation, disorder potential is described as $V=\Sigma_{i}V_{i}$, \textit{\textbar V}$_{i}$\textit{\textbar }$\le W$, where $V_{i}$ and $W$ are localized potential at $i$th carbon atom and strength of disorder, respectively. We found that the DC conductance decreases with the CNT length, while the behaviors of phase-difference are drastically different by the disorder strength: for a small disorder the phase-difference always behaves inductive, while for a large disorder the phase-difference transits from inductive response to capacitive one with increase of the CNT length. Moreover, we clarified that inductive-capacitive transition universally occurs at the same value of DC conductance. [1] C. Gomez-Navarro et al., Nature 4, 534 (2005). [Preview Abstract] |
Wednesday, March 20, 2013 1:03PM - 1:15PM |
N8.00010: An explicit formula for optical oscillator strength of excitons in semiconducting single-walled carbon nanotubes: family behavior Sangkook Choi, Jack Deslippe, Rodrigo B. Capaz, Steven G. Louie The sensitive structural dependence of the optical properties of single-walled carbon nanotubes (SWCNTs), which are dominated by excitons and tunable by changing diameter and chirality, makes them excellent candidates for optical devices. Because of strong many-electron interaction effects, the detailed dependence of the optical oscillator strength of excitons on nanotube diameter $d$, chiral angle $\theta $, and electronic subband index P (the so called family behavior) however has been unclear. Based on results from an extended Hubbard Hamiltonian with parameters derived from \textit{ab initio} GW-BSE calculations, we have obtained an explicit formula for the family behavior of the oscillator strengths of excitons in semiconducting SWCNTs, incorporating environmental screening. The formula explains well recent measurements, and is expected to be useful in the understanding and design of possible SWCNT optical and optoelectronic devices. This work was supported by NSF grant No. DMR10-1006184 and U.S. DOE under Contract No. DE-AC02-05CH11231. Computational resources have been provided by NERSC and Teragrid. [Preview Abstract] |
Wednesday, March 20, 2013 1:15PM - 1:27PM |
N8.00011: Theory of coherent phonons in carbon nanotubes and graphene nanoribbons G.D. Sanders, C.J. Stanton, A.R.T. Nugraha, R. Saito We have performed theoretical studies on generating and detecting coherent radial breathing mode (RBM) phonons in single-walled carbon nanotubes and coherent radial breathing like mode (RBLM) phonons in graphene nanoribbons. A microscopic theory incorporating electronic states, phonon modes, optical matrix elements, and electron-phonon interaction matrix elements allows us to calculate the coherent phonon spectrum. The coherent phonon amplitudes satisfy a driven oscillator equation with a driving term that depends on photoexcited carrier density. We study the coherent phonon spectrum for nanotubes of different chirality and for armchair and zigzag graphene nanoribbons. We compare our results with a simpler, effective mass theory where we find reasonable agreement with the main features of our computed coherent phonon spectrum. [Preview Abstract] |
Wednesday, March 20, 2013 1:27PM - 1:39PM |
N8.00012: Nonlinear motion of cantilevered SWNT and Its Meaning to Phonon Dynamics Heeyuen Koh, James Cannon, Shohei Chiashi, Junichiro Shiomi, Shigeo Maruyama Based on the finding that the lowest frequency mode of cantilevered SWNT is described by the continuum beam theory in frequency domain, we considered its effect of the symmetric structure for the coupling of orthogonal transverse modes to explain the nonlinear motion of free thermal vibration. This nonlinear motion calculated by our molecular dynamics simulation, once regarded as noise, is observed to have the periodic order with duffing and beating, which is dependent on aspect ratio and temperature. It could be dictated by the governing equation from the Green Lagrangian strain tensor. The nonlinear beam equation from strain tensor described the motion well for various models which has different aspect ratio in molecular dynamics simulation. Since this motion is nothing but the interaction between 2nd mode of radial, tangential mode and 1st longitudinal mode, it was found that Green Lagrangian strain tensor is capable to deal such coupling. The free thermal motion of suspended SWNT is also considered without temperature gradient. The Q factor measured by this theoretical analysis will be discussed. [Preview Abstract] |
Wednesday, March 20, 2013 1:39PM - 1:51PM |
N8.00013: Heat Pulse Propagation in Carbon Nanotube Peapods Mohamed Osman Earlier studies of heat pulse propagation in single and double wall nanotubes at very low temperatures have shown that the heat pulse generated wave packets that moved at the speed of sound corresponding to LA and TW phonon modes, second sound waves and diffusive components [1,2]. The energy content of LA mode wave packets in SWNT was significantly smaller than the TW mode. The energy of the leading LA mode wavepacket in DWNT had a significant increase in the energy content compared to SWNT LA mode. Additionally, an increase simple strain within the LA mode was higher in DWNT compared to SWNT was also reported in [1]. This has motivated us to examine heat pulse propagation in carbon nanopeapods and the coupling between the (10,10) SWNT nanotube and the C60 fullerenes enclosed. The major coupling frequency between the C60 and the (10,10) occurs at 4.88 THz which correspond to the radial breathing mode frequency. We will discuss these results and report on the major phonon modes involved in heat pulse propagation in the (10,10) SWNT-C60 nanopeapod.\\[4pt] [1] T. Kim and M.A Osman, C. Richards, R. Richards, D. Bahr, Phys. Rev. B 76, 155424 (2007)\\[0pt] [2] M.A. Osman and D. Srivastava, Phys. Rev. B 72, 125413 (2005) [Preview Abstract] |
Wednesday, March 20, 2013 1:51PM - 2:03PM |
N8.00014: Microstructural characterization of nanoporous carbon fiber as determined by neutron scattering Lilin He, Yuri Melnichenko, Sofiane Baukhalfa, Gleb Yushin We have applied small angle neutron scattering (SANS) technique to investigate the microstructure of nanoporous carbon fiber. The scattering curves were fitted to various models, which allowed us to estimate the structural parameters (i.e. total radii of gyration of pores as well as cross sectional radius of gyration, physical radius and lengths of cylindrical pores) in the studied samples. Chord length analysis was performed to estimate the average sizes of pores and solid matrix. The information obtained from SANS data is in general agreement with independent measurements of surface area using gas sorption carried out in this study. SANS data obtained from carbons saturated with contrast matching liquid (D$_{\mathrm{2}}$O) indicate that the scattering with power law decay of I(Q) in the low Q domain originates from outer surface of carbon fibers. Lower than anticipated decrease in scattering intensity in the high Q domain suggests that a certain amount of nanopores are not accessible to D$_{\mathrm{2}}$O molecules. The investigation of the isotope effect on the pore filling suggests that the H$_{\mathrm{2}}$O is more penetrated than D$_{\mathrm{2}}$O, which is attributed to the stronger bond network among deuterium atoms than that in hydrogen atoms. [Preview Abstract] |
Wednesday, March 20, 2013 2:03PM - 2:15PM |
N8.00015: Optical Characterization of Natural Nontoxic Nanomaterials Devulapalli Rao, Chandra Yelleswarapu Synthetic nanomaterials -- carbon nanotubes, semiconductor nanoparticles, nanowires and nanorods, metal clusters in polymer films -- are extensively studied for potential photonic applications. Naturally occurring halloysite nanotubes offer additional advantages of high tensile strength, nontoxcity and biocompatibility. Halloysite is receiving lot of attention for application as low cost nanoscale container for encapsulation of biologically active molecules, drugs, and anticorrosion agents. We studied the optical properties of halloysite nanotube samples of length $\sim$1000 nm with 50 nm external diameter and 15 nm internal diameter. The hollysite sample was provided by Prof. Yuri Lvov, Institute for Micromanufacturing, Louisiana Tech. The sample suspended in water at a concentration 2.5 mg/ml exhibits a broad optical absorption band in the visible region with a peak $\sim$600 nm. Z-scan studies are carried out, with 3 nsec laser pulses of frequency doubled Nd:YAG laser, using 1 mm glass cell containing the sample suspended in acetone at a concentration 0.66 mg/ml. Open aperture z-scan measurements indicate two-photon absorption. Closed aperture z-scan measurements exhibit a positive nonlinear refractive index. Results of photoacoustic z-scan currently in progress will also be presented. [Preview Abstract] |
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