Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session Y22: Focus Session: Carbon Nanotubes: Optical, Mechanical, Magnetic & Other Properties |
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Sponsoring Units: DMP Chair: Michael S. Arnold, University of Wisconsin-Madison Room: 202A |
Friday, March 6, 2015 8:00AM - 8:12AM |
Y22.00001: Stark effect of excitons in individual air-suspended carbon nanotubes Masahiro Yoshida, Yusuke Kumamoto, Akihiro Ishii, Akio Yokoyama, Yuichiro K. Kato We investigate electric-field induced redshifts of photoluminescence from individual single-walled carbon nanotubes.\footnote{M. Yoshida, Y. Kumamoto, A. Ishii, A. Yokoyama, and Y. K. Kato, Appl. Phys. Lett. 105, 161104 (2014).} Photoluminescence spectra of air-suspended nanotubes within field-effect transistor structures are collected under an application of symmetric bias voltages on source and drain contacts.\footnote{Y. Kumamoto, M. Yoshida, A. Ishii, A. Yokoyama, T. Shimada, and Y. K. Kato, Phys. Rev. Lett. 112, 117401 (2014).} We find that redshifts scale quadratically with field, while measurements with different excitation powers and energies show that effects from heating and relaxation pathways are small. We attribute the shifts to the Stark effect, and characterize nanotubes with different chiralities. By taking into account exciton binding energies for air-suspended tubes, we find that theoretical predictions are in quantitative agreement. [Preview Abstract] |
Friday, March 6, 2015 8:12AM - 8:24AM |
Y22.00002: ABSTRACT WITHDRAWN |
Friday, March 6, 2015 8:24AM - 8:36AM |
Y22.00003: In-situ TEM study of collapsing, reinflating and twisting of multi-walled carbon nanotubes Aiming Yan, Hamid Barzegar, Claudia Ojeda-Aristizabal, Gabriel Dunn, Thomas Wagberg, Alex Zettl Since the first observation of collapsed carbon nanotubes (CCNTs) by Chopra et al., CCNTs have attracted a lot of attention due to their potentially modified electrical properties caused by structural changes compared to their tubular counterparts. We study the transition of multi-walled carbon nanotubes (MWCNTs) from tubular to collapsed form and the reverse process in-situ by Transmission Electron Microscope (TEM) and monitor the whole process by imaging and electron diffraction. We show that we are able to collapse the tubular CNT by extracting the inner core of the tube and reinflate the collapsed carbon nanotube by applying a voltage at the tip of the CNT. We also observe the twisting of the collapsed multi-walled CNT in-situ. The nano-scale manipulation of carbon nanotubes inside TEM enables us to tailor the transition between tubular and collapsed forms of a CNT. [Preview Abstract] |
Friday, March 6, 2015 8:36AM - 9:12AM |
Y22.00004: Optoelectronic Properties and Electromechanical Resonance Behavior in Individual Suspended Carbon Nanotube pn-Junctions and Devices Invited Speaker: Stephen Cronin In carbon nanotubes \textit{pn}-junctions, we observe Zener tunneling behavior and photocurrent generation in quasi-metallic nanotubes [1], which have smaller band gaps than most known bulk semiconductors. These carbon nanotube-based devices deviate from conventional bulk semiconductor device behavior due to their low dimensional nature. We observe rectifying behavior based on Zener tunneling of ballistic carriers instead of ideal diode behavior, as limited by the diffusive transport of carriers. We observe substantial photocurrents at room temperature, suggesting that these quasi-metallic pn-devices may have a broader impact in optoelectronic devices. We also explore the role of weak clamping forces, typically assumed to be infinite, in the electromechanical resonance behavior of these suspended carbon nanotubes [2]. Due to these forces, we observe a hysteretic clamping and unclamping of the nanotube device that results in a discrete drop in the mechanical resonance frequency on the order of 5$-$20 MHz, when the temperature is cycled between 340 and 375 K. This instability in the resonant frequency results from the nanotube unpinning from the electrode/trench sidewall where it is bound weakly by van der Waals forces. Interestingly, this unpinning does not affect the Q-factor of the resonance, since the clamping is still governed by van der Waals forces above and below the unpinning. For a 1 $\mu $m device, the drop observed in resonance frequency corresponds to a change in nanotube length of approximately 50$-$65 nm. On the basis of these findings, we introduce a new model, which includes a finite tension around zero gate voltage due to van der Waals forces and shows better agreement with the experimental data than the perfect clamping model. From the gate dependence of the mechanical resonance frequency, we extract the van der Waals clamping force to be 1.8 pN. The mechanical resonance frequency exhibits a striking temperature dependence below 200 K attributed to a temperature-dependent slack arising from the competition between the van der Waals force and the thermal fluctuations in the suspended nanotube.\\[4pt] [1] Amer, M.R., S.-W. Chang, R. Dhall, J. Qiu and S. Cronin, ``Zener Tunneling and Photocurrent Generation in Quasi-Metallic Carbon Nanotube pn-Devices'' Nano Letters, 13, 5129 (2013).\\[0pt] [2] Mehmet Aykol, Bingya Hou, Rohan Dhall, Shun-Wen Chang, William Branham, Jing Qiu, and Stephen Cronin, ``Clamping Instability and van der Waals Forces in Carbon Nanotube Mechanical Resonators'' Nano Letters, 14, 2426-2430 (2014).\\[0pt] [3] Shun-Wen Chang, Kevin Bergemann, Rohan Dhall, Jeramy Zimmerman, Stephen Forrest, Stephen Cronin, ``Non-ideal Diode Behavior and Band Gap Renormalization in Carbon Nanotube P-N Junctions'' IEEE Transactions on Nanotechnology, 13, 41 (2014). [Preview Abstract] |
Friday, March 6, 2015 9:12AM - 9:24AM |
Y22.00005: Near-field optical study of individual single-walled carbon nanotubes Zhiwen Shi, Xiaoping Hong, Hans Bechtel, Michael Martin, Yuen-Ron Shen, Feng Wang Quantum-confined electrons in one dimension (1D) behave as Luttinger liquid, a strongly correlated electronic matter distinctly different from Fermi liquid. Metallic single-walled carbon nanotubes (SWNTs), with their strong quantum confinement and structural simplicity, provide the ideal model system for Luttinger liquid. Direct experimental observation of Luttinger liquid in SWNTs, however, proves to be surprisingly challenging. Through near-field optical study, we demonstrated conclusively a robust Luttinger liquid in metallic SWNTs at room temperature. [Preview Abstract] |
Friday, March 6, 2015 9:24AM - 9:36AM |
Y22.00006: Photoluminescence Dynamics of Covalent Dopant-Induced Trap States in Single Wall Carbon Nanotubes Stephen Doorn, Nicolai Hartmann, Sibel Yalcin, Xuedan Ma, Han Htoon Recent advances in low level covalent functionalization of carbon nanotubes is receiving significant attention due to new emitting states being introduced by chemically stable oxygen [1,2] and aryl diazonium dopants [3] that increase photoluminescence quantum yields. Recent low-temperature studies have furthermore elucidated the associated chemical and electronic structure.[4] We report here photoluminescence studies of dynamic behaviors of the dopant sites. Relevant to their potential uses in imaging and as novel photon sources, we demonstrate blinking behaviors and discuss a range of response as a function of dopant species. We also report photoluminescence decay dynamics obtained at the ensemble and single tube levels. We find that localization of excitons at dopant sites dramatically increases photoluminescence lifetimes, indicating the importance of exciton trapping as a route to limiting non-radiative decay pathways arising from exciton mobility. [1] S. Ghosh, et al., Science, 330, 1656 (2010). [2] Y. Piao, et al., Nature Chem., 5, 840 (2013). [3] Y. Miyauchi, et al., Nature Photon., 7, 715 (2013). [4] X. Ma, et al., ACS Nano, 8, 10782 (2014). [Preview Abstract] |
Friday, March 6, 2015 9:36AM - 9:48AM |
Y22.00007: Plasmon enhanced Raman scattering effect for an atom near a carbon nanotube Alex Gulyuk, Igor Bondarev A quantum theory of the resonance Raman scattering is developed for a two-level dipole emitter, two-level system (TLS), coupled to a low-energy inter-band plasmon resonance of a carbon nanotube (CN). This resonance Raman scattering is a manifestation of the general Surface Enhanced Raman Scattering (SERS) effect received much of attention due to a very broad range of its applications in nanophotonics, biochemistry, and medicine. Here[1], the SERS effect comes about as a near-field effect in which strong local-field enhancement occurs due to the inter-band plasmon excitation when the TLS is located near the CN surface and its transition energy matches the plasmon resonance energy of the CN. Raman cross-section derived covers both weak and strong TLS-plasmon coupling, and shows a dramatic increase by a factor $\sim 10^{3}$ in the strong coupling regime. The effect may be used to detect individual atomic type objects trapped near CNs. More advanced applications, which require further theoretical development, may include highly efficient CN based SERS substrates for single molecule/atom/ion detection, precision spontaneous emission control, and manipulation. -- [1]I.V.Bondarev, arXiv1407.5142 [Preview Abstract] |
Friday, March 6, 2015 9:48AM - 10:00AM |
Y22.00008: Optical Field Enhancement by Semiconducting Graphene Nanoribbons Yoshiyuki Miyamoto, Hong Zhang Graphene nano-ribbons are known to have energy gap depending on direction of ribbon edge and ribbon width having optical property different from that derived from Dirac cone of the graphene. When the edges are in armchair direction, the ribbons are semiconducting with energy gaps at their $\Gamma$ points. In this presentation, we report an enhancement of an optical electric field (E-field) by an armchair graphene nano-ribbon by means of the first-principles simulation. The polarization of the E-field was set as parallel to the graphene sheet and perpendicular to ribbon axis. By performing the time-dependent density functional theory (TDDFT) simulation under dynamical E-field, an enhancement of E-field was seen with optical frequencies near the resonance of absorption peaks of the nano-ribbon. The enhancement was not persistent but showed an amplitude modulation with frequencies of few (tens) terahertz depending on E-field frequencies. In this presentation, we discuss mechanisms of field-enhancement and possible applications. [Preview Abstract] |
Friday, March 6, 2015 10:00AM - 10:12AM |
Y22.00009: Novel quasi-1D Y-junction carbon with anisotropic conductance and changeable magnetization Bhalchandra Pujari, Andrey Tokarev We propose two conformations of a novel quasi-1D carbon allotrope designed by tailoring three graphene nanoribbons to form a Y-shaped junction. The armchair and zigzag conformations arise due to chirality of underlying ribbons. While armchair Y-junction carbon (YjC) is formed by three identical ``arms'' of the graphene nanoribbons the zigzag conformation has one distinguishable arm. The result in the later configuration is the broken symmetry of the structure, in which the arms are no longer separated by 120$^{\circ}$ each. Interestingly the broken structural symmetry of zigzag YjC is also associated with magnetic moment. It is shown that the magnetism is due to underlying nanoribbons and not symmetry breaking. Moreover the magnetism is also affected by the nature of edge passivation. Based on the analysis of density of states, we conjecture that the mixture of sp$^{3}$- and sp$^{2}$ bonded atoms results three conducting ribbons joined together by the insulating carbon chain. Thus making the structure an anisotropic conductor, with conductivity of armchair conformation being higher than that of zigzag. Armchair and zigzag conformations are energetically extremely stable with binding energy of 11.44 eV/atom and 8.39 eV/atom respectively. [Preview Abstract] |
Friday, March 6, 2015 10:12AM - 10:24AM |
Y22.00010: Non-saturating Linear Magnetoresistance in 3-dimensional Carbon Nanostructure Lei Wang, Ming Yin, Fouzi Arammash, Timir Datta Magneto-transport of carbon nanostructure with periodic spherical voids was investigated in magnetic field up to 9.4T in the temperatures range from 2K to 50K. With increase of magnetic field, transverse magnetoresistance crosses over from quadratic to a non-saturating linear dependence. Furthermore, longitudinal magnetoresistance which is negligible in most materials exhibits the same value as transverse magnetoresistance in our system. We demonstrate linear magnetoresistance (LMR) is proportional to the carrier mobility. Over the entire B-T phase region studied, MR data is observed to be a universal function of B/T. Orientation independent linear response is an attractive feature for applications. [Preview Abstract] |
Friday, March 6, 2015 10:24AM - 10:36AM |
Y22.00011: Anomalous magnetization of a carbon nanotube as an excitonic insulator Massimo Rontani We show theoretically that an undoped carbon nanotube might be an excitonic insulator---the long-sought phase of matter proposed by Keldysh, Kohn, and others fifty years ago. We predict that the condensation of triplet excitons, driven by intervalley exchange interaction, spontaneously occurs at equilibrium if the tube radius is sufficiently small [1]. The signatures of exciton condensation are its sizable contributions to both the energy gap and the magnetic moment per electron. The increase of the gap might have already been measured, albeit with a different explanation [2]. The enhancement of the quasiparticle magnetic moment is a pair-breaking effect that counteracts the weak paramagnetism of the ground-state condensate of excitons. This property could rationalize the anomalous magnitude of magnetic moments recently observed in different devices close to charge neutrality. [1] M. Rontani, Phys. Rev. B {\bf 90,} 195415 (2014). [2] V. V. Deshpande {\it et al.}, Science {\bf 323,} 106 (2009). [Preview Abstract] |
Friday, March 6, 2015 10:36AM - 10:48AM |
Y22.00012: Carbon nanotubes coupled to superconducting impedance matching circuits Schonenberger Christian, Minkyung Jung, Vishal Ranjan, Gabriel Puebla-Hellmann, Thomas Hasler, Andreas Nunnenkamp, Matthias Muoth, Christofer Hierold, Andreas Wallraff Coupling carbon nanotube devices to microwave circuits offers a significant increase in bandwidth and signal-to-noise ratio. These facilitate fast non-invasive readouts important for quantum optics, shot noise and correlation measurements. Here, we successfully couple a carbon nanotube (CNT) double quantum dot to a GHz superconducting matching circuit using a mechanical transfer technique. The device shows a tunable bipolar double dot behavior, reaching the few-electron/hole regime. The resonance response reflected by the matching circuit is a sensitive probe of the charge state of the device, allowing a determination of the absolute charge number. The resonance response at the interdot charge transitions enables quantitative parameter extraction. Presented results open the path for novel studies of microwave photons interacting with electrons in carbon nanotubes. [Preview Abstract] |
Friday, March 6, 2015 10:48AM - 11:00AM |
Y22.00013: Interplay of Magnetism of Superconductivity in Graphitic Nanostructures Yao An, Robert Meulenberg The main foci in modern high temperature superconductivity (HTS) research are two-fold: (a) in conventional HTS finding new machinable materials necessary for any real world applications and (b) discovering new materials for that elusive room temperature superconductivity (RTS). It is quite evident that the potential applications for HTS or RTS are immense, and could show tremendous cost savings in various industries. To date, most reports of RTS have been eventually disproved; however, recent work has suggested that graphite flakes can exhibit RTS when treated with water. This extraordinary claim, if true, offers a wide range of stimulating physics to be studied in RTS. A main obstacle toward RTS in carbon based materials is ruling out whether one is truly observing superconductivity, or simply magnetism. In this talk, we will discuss effects of solution exfoliation of graphite powders. Not surprisingly, drastic changes to the graphite powder are observed. These changes, mainly in the form of graphene sheet exfoliation and defect formation, suggest a form of magnetism and not superconductivity in the treated powders via SQUID magnetometry measurements. A method for preparing graphitic monoliths that allow for transport measurements will be presented. [Preview Abstract] |
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