Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session W7: Focus Session: Carbon Nanotubes: Optical Properties |
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Sponsoring Units: DMP Room: 303 |
Thursday, March 21, 2013 2:30PM - 2:42PM |
W7.00001: Tailoring of optoelectronic properties in nanotube-chromophore energy transfer complexes Friederike Ernst, Timm Heek, Antonio Setaro, Rainer Haag, Stephanie Reich The formation of nanotube-chromophore energy transfer complexes is of great interest for a number of applications, in particular for energy conversion. Certain chromophores can $\pi$ - $\pi$ stack on the nanotube wall: when they are radiatively excited an exciton is formed, which subsequently passes into the carbon nanotube. In the carbon nanotube it can radiatively recombine, emitting a photon characteristic for that nanotube's chirality, or, by applying a voltage, the exciton can be split into an electron and a hole, generating a photocurrent. We demonstrate that the chromophore may be incorporated directly into a surfactant molecule, which then serves two distinct purposes: constituting the photon collecting half of the energy transfer complex, and solubilizing said complexes (Ernst et al., Adv. Funct. Mat 2012). This approach results in temporally stable, biologically compatible solutions which are functional in a wide range of pHs. Alternatively, nanotubes suspended in surfactant micelles can be functionalized with dyes in organic media through micelle swelling. Both processes yield functional nanotube-chromophore complexes with tunable optoelectronic properties, paving the way for scalable optoelectronic devices. [Preview Abstract] |
Thursday, March 21, 2013 2:42PM - 2:54PM |
W7.00002: Optical transitions of small-diameter carbon nanotubes Takashi Koretsune, Koichiro Kato, Susumu Saito The optical properties for most of carbon nanotubes have been well understood based on the band structure of graphene with some curvature effects. In small-diameter nanotubes, however, it is well known that the curvature drastically affects the electronic structures. Thus, to clarify the optical properties of these small-diameter tubes from first principles, we theoretically study all the small-diameter nanotubes including chiral ones using the density-functional theory, and predict the absorption and emission properties within the single-particle picture. It is found that the wavefunction that originates from M point in the hexagonal Brillouin zone of the graphene plays an key role to understand the optical properties of small-diameter nanotubes. [Preview Abstract] |
Thursday, March 21, 2013 2:54PM - 3:06PM |
W7.00003: Probing the Free Carrier Doping Effects in Individual Carbon Nanotubes by Optical Spectroscopy Kaihui Liu, Xiaoping Hong, Feng Wang The free carrier (electron or hole) doping in carbon nanotubes will shift their Fermi level, which has dramatically effects in the nanotube electrical transport properties. At the same time, the free carrier doping will also significantly modify the nanotube optical properties. Here we report the development of a new optical spectroscopy method to measure the field-induced change of optical transitions in individual semiconducting and metallic nanotubes. We will discuss the important role of electron-electron interactions to explain our results. [Preview Abstract] |
Thursday, March 21, 2013 3:06PM - 3:18PM |
W7.00004: Non-Adiabatic/Adiabatic Phase Transitions in Ultra-Clean Suspended Carbon Nanotubes Rohan Dhall, Shun-Wen Chang, Zuwei Liu, Stephen Cronin We have recently reported pronounced electron-phonon interactions in suspended, nearly defect-free metallic carbon nanotubes, observed through a Kohn anomaly of greater strength than theoretically predicted. This Kohn Anomaly is accompanied by a gate-induced modulation of the G band Raman intensity. In a systematic study of over 20 quasi-metallic carbon nanotubes devices, we have established a quantitative correlation between the strength of the non-adiabatic Kohn anomaly and the modulation of Raman intensity, indicating that the underlying cause that leads to both these effects is the same. We find that metallic nanotubes can switch between a regime in which the non-adiabatic Kohn anomaly is clearly observed and a regime where the non-adiabatic Kohn anomaly is absent, by varying temperature. In the non-adiabatic regime, an enhancement of the Raman intensity is observed under electrostatic gating. However, in the regime where the non-adiabatic Kohn anomaly is not observed, suppression of the Raman intensity with gating is observed. [Preview Abstract] |
Thursday, March 21, 2013 3:18PM - 3:30PM |
W7.00005: The Double Resonance Raman Behavior of the Carbon Nanotube 2-D Mode Observed in Samples Enriched in a Single Chirality Stephen Doorn, Hagen Telg, Juan Duque, Janina Maultzsch, Xiaomin Tu, Ming Zheng Access to carbon nanotube samples enriched in single chiralities allows the observation of new photophysical behaviors obscured or difficult to demonstrate in mixed-chirality ensembles. Recent examples include the observation of strongly asymmetric G-band excitation profiles [1] and the unambiguous demonstration of Raman interference effects [2]. Likewise, the complex response expected for the CNT 2-D mode has not yet been clearly defined because of similar limitations. We present results on the dispersive and resonance behaviors of the 2-D mode obtained from samples enriched in a single chirality. The response will be discussed in the context of the interplay of dispersive effects and resonance with the E11 and E22 transitions. The results will be compared to simulations that include all relevant electronic and phonon bands tied to the double-resonance process. 1. J.G. Duque, et. al., ACS Nano, 5, 5233 (2011). 2. J. G. Duque, et. al., Phys. Rev. Lett., 108, 117404 (2012). [Preview Abstract] |
Thursday, March 21, 2013 3:30PM - 3:42PM |
W7.00006: Observation and Spectroscopy of a Two-Electron Wigner Molecule in Ultra-Clean Carbon Nanotubes Sharon Pecker, Ferdinand Kuemmeth, Andrea Secchi, Massimo Rontani, Dan Ralph, Paul McEuen, Shahal Ilani Coulomb interactions can have a decisive effect on the ground state of electronic systems. The simplest system in which interactions can play an interesting role is that of two electrons on a string. In the presence of strong interactions the two electrons are predicted to form a Wigner molecule, separating to the ends of the string due to their mutual repulsion. This spatial structure is believed to be clearly imprinted on the energy spectrum, yet to date a direct measurement of such a spectrum in a controllable one-dimensional setting is still missing. Here we use an ultra-clean suspended carbon nanotube to realize this strongly-correlated system in a tunable potential. Using tunneling spectroscopy we measure the excitation spectra of two interacting carriers, electrons or holes. Seven quantum states are identified, characterized by their spin and isospin quantum numbers. These states are seen to fall into two distinctive multiplets according to their exchange symmetries. Interestingly, we find that the splitting between multiplets is quenched by an order of magnitude compared to the non-interacting value. This quenching is shown to be a direct manifestation of the formation of a strongly-interacting Wigner-molecule ground state. [Preview Abstract] |
Thursday, March 21, 2013 3:42PM - 3:54PM |
W7.00007: Raman Studies on Chirality Purified Nanotubes: the Chirality Dependence of the G Modes in Semiconducting and Metallic Carbon Nanotubes Hagen Telg, Juan G. Duque, Xiaomin Tu, Erik H. Haroz, Junichiro Kono, Ming Zheng, Stephen K. Doorn We present results from resonant Raman experiments on nanotube samples which are highly enriched in particular chiralities (n,m). Our study includes 14 different semiconducting tube species and 5 different types of metallic armchair (n,n) carbon nanotubes. Results from G peak positions of semiconducting tubes show a significant dependence on tube diameter, chiral angle and family. Considering theoretical predictions we discuss the origin of these dependences with respect to rehybridization of the carbon orbitals, confinement, and electron-electron interactions.\footnote{H. Telg et al., ACS Nano 6, 904 (2012)} As all armchair nanotubes have the same chiral angle and family, results from these samples are restricted to a diameter dependence, which, however, strongly deviates from the diameter dependence of semiconducting tubes. This deviation has been predicted to be associated with non-adiabatic effects and the Kohn-anomaly in metallic carbon nanotubes. We discuss the contribution of these effects on the peak positions of armchair carbon nanotubes based on electro-chemical doping experiments. [Preview Abstract] |
Thursday, March 21, 2013 3:54PM - 4:06PM |
W7.00008: Surface-enhanced Raman scattering study using metal oxide nanowires grown by chemical vapor deposition Hae-Young Shin, Hayoung Jung, Myung Hwa Kim, Seokhyun Yoon We present surface-enhanced Raman scattering (SERS) results using templates made of metal oxide nanowires such as IrO$_{2}$ and RuO$_{2\, }$that were grown by chemical vapor deposition. SERS has been attracting great attention due to its interesting optical behavior and great potential for applications such as chemical sensor, optoelectronic devices, etc. For promising applications utilizing SERS effect, however, there are crucial issues to be resolved. One is to find a way to systematically control `hot spots' of enhancement and the other is to fully understand the enhancement mechanism. In addition to the well-known two dominant mechanisms, i.e., electromagnetic enhancement mechanism and charge transfer mechanism, we observed that the enhancement greatly depends on the geometry of the nanowires that could suggest another mechanism for SERS. Our results were compared to the FDTD simulations. Our finding may lead us to a way to systematically create, or control hot spots for enhancement of light field using one dimensional nanostructures. [Preview Abstract] |
Thursday, March 21, 2013 4:06PM - 4:18PM |
W7.00009: Deformations and nanomechanical energy storage in twisted carbon nanotube ropes David Tomanek, Zacharias G. Fthenakis, Gotthard Seifert, David Teich We determine the deformation energetics and energy density of twisted carbon nanotube ropes that effectively constitute a torsional spring. Due to the unprecedented stiffness and resilience of constituent carbon nanotubes, a twisted nanotube rope becomes an efficient energy carrier. Using {\em ab initio} and parameterized density functional calculations, we identify structural changes in these systems and determine their elastic limits. The deformation energy of twisted nanotube ropes contains contributions associated not only with twisting, but also with stretching, bending and compression of individual nanotubes. We quantify these energy contributions and show that their relative role changes with the number of nanotubes in the rope. The calculated reversible nanomechanical energy storage capacity of carbon nanotube ropes surpasses that of advanced Li-ion batteries by up to a factor of ten. [Preview Abstract] |
Thursday, March 21, 2013 4:18PM - 4:30PM |
W7.00010: Probing Mechanical Resonances in Cantilevered Coiled Carbon Nanowires Deepika Saini, Doyl Dickel, Herbert Behlow, Balu Pillai, Keqin Yang, Malcolm Skove, Steven Serkiz, Apparao Rao Helically coiled carbon nanowires (CCNW) and nanotubes are promising elements for use in MEMS/NEMS devices and nanorobotics, as nano-inductors and sensors, and for impact protection (e.g. Bell \textit{et al.} 2007 IEEE International Conference, J. Appl. Phys. \textbf{100}, 064309 (2006)). Understanding and characterizing their mechanical resonance behavior is essential for the reliability in applications. In this study, we have electrically actuated an individual CCNW in a diving-board cantilever configuration inside a scanning electron microscope, and electrically detected its mechanical resonance modes. By oscillation at low frequency we confirmed the induced-charge actuation mechanism. Among the modes we observed, some appeared to have both axial and lateral components. We also observed closely spaced resonance modes which we attribute to the splitting of degenerate modes, consistent with our COMSOL simulations. We suggest that the helical morphology facilitates inter-mode coupling that results in the observed complex resonance behavior. [Preview Abstract] |
Thursday, March 21, 2013 4:30PM - 4:42PM |
W7.00011: A Novel Multidirectional, Non-Contact Strain-Sensing Nanocomposite Paul Withey, Srivishnu Vemuru, Sergei Bachilo, Satish Nagarajaiah, R. Bruce Weisman Single-walled carbon nanotubes (SWCNTs) have been successfully dispersed in a polymeric host resulting in the development of a novel strain-sensitive nanocomposite material with promise for scalability. Dubbed ``strain paint'' this new material when coated onto a surface becomes a smart-skin sensor that can detect strain through load transfer from the polymeric host to embedded SWCNTs. Strain is easily measured in a non-contact manner via laser excitation and detection of the unique near-infrared (NIR) fluorescence spectrum of semiconducting SWCNTs. When strained, each ($n,m)$ SWCNT type exhibits a predictable shift in its NIR fluorescence peak. SWCNTs with high intensity are easily detected in the bulk fluorescence spectrum of raw, unsorted SWCNTs embedded in the polymer. Thin films of the polymer/SWCNT nanocomposite were spin-coated onto substrates, strains typically up to 1{\%} were applied, and strain magnitudes were determined by resistive strain gauges bonded to the coating and substrate. Spectral shifts reveal a linear response to strain with little hysteresis. Two SWCNT types exhibiting opposite spectral shifts with strain were used to improve sensitivity. Strain along any direction is determined simply by adjusting the polarization of the excitation laser. [Preview Abstract] |
Thursday, March 21, 2013 4:42PM - 4:54PM |
W7.00012: Strong electromechanical coupling in ultra-short carbon nanotube quantum dots A.C. McRae, V. Tayari, J.O. Island, A.R. Champagne We study electromechanical coupling in suspended single-wall carbon nanotubes using low-temperature electron transport. Using a feedback-controlled electromigration method $[1]$, we create gate-tuneable single quantum dots whose lengths range from tens of nm down to $\approx$ 3 nm. We observe current suppression of low bias stretching vibron sidebands due to the Franck-Condon blockade, and extract the electron-vibron coupling strength, $g$, both in the electron and hole doped regimes in the same devices. We observe strong $g$ and are exploring its dependence on mechanical strain in the tube. Due to a positive feedback mechanism between tunneling electrons and bending mode vibrations of the nanotubes, we observe bending mode frequencies up to the 100 GHz range $[2]$. The bending mode frequency is found to be tuneable by a factor of two by applying electrostatic strain. \\ $[1]$ J.O. Island \textit{et al}. Appl. Phys. Lett. \textbf{99}, 243106 (2011) \\ $[2]$ J.O. Island \textit{et al}. Nano. Lett. \textbf{12}, 4564 (2012) [Preview Abstract] |
Thursday, March 21, 2013 4:54PM - 5:06PM |
W7.00013: Origin of Compressive Strain Induced Electromechanical Oscillations in Multiwalled Carbon Nanotubes Swastibrata Bhattacharyya, Laishram Singh, Karuna Nanda, Abhishek Singh We show by the application of compressive strain, the electrical conductance of multiwalled carbon nanotubes can be increased monotonically. The strain induces oscillations in electrical conductance, which can have potential applications in many electromechanical nanodevices. While the monotonic increase in the conduction is due to the intra-wall interaction of the nanotubes, the oscillations are caused by the transition from \textit{sp}$^{2}$ to \textit{sp}$^{3}$ hybridization of the carbon atoms, promoted by the interwall interaction. A series of experimental and theoretical analyses based on density functional tight binding method were performed to confirm this finding. These results opens up a possibility of enhancing the conductance of carbon nanotubes by controlling applied strains. [Preview Abstract] |
Thursday, March 21, 2013 5:06PM - 5:18PM |
W7.00014: Movement of solid iron nanocrystal through a constriction in the multiwall carbon nanotube Sinisa Coh, Will Gannett, Alex Zettl, Marvin L. Cohen, Steven G. Louie It has been known for some time that iron (and some other metals) can move inside multiwall carbon nanotube under the application of an external electrical current to the nanotube (B.C. Regan et al, Nature 428, 924 (2004)). Here we report on finding that a solid piece of iron nanocrystal can move through a constriction in the multiwall carbon nanotube that has a smaller cross-sectional area than the nanocrystal itself. Furthermore, we find that during this entire process the core of the nanocrystal remains solid and that the carbon in the nanotube does not chemically interact with iron. We performed kinetic Monte Carlo simulation based on a first principles density functional theory calculation which can reproduce this experimental finding. Additionally, we discuss the nature of the movement of the iron nanocrystal in our simulation and show why the nanocrystal is able to go through a constriction. Also, we compare the dependence of the nanocrystal speed on applied current with available experimental data. From this comparison we are able to estimate the experimental temperature and infer the magnitude of the electromigration force experienced by individual iron atoms for given applied external current. [Preview Abstract] |
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