Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session J27: Focus Session: Carbon Nanotubes: Electronic Properties II |
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Sponsoring Units: DMP Chair: Michael Fuhrer, UMD Room: LACC 501C |
Tuesday, March 22, 2005 11:15AM - 11:27AM |
J27.00001: Suppression mechanism of inter-tube transfer in double-wall carbon nanotubes Seiji Uryu, Tsuneya Ando Double-wall carbon nanotubes have incommensurate lattice structure and are quasi-periodic[1,2]. Therefore, inter-tube transfer of electrons between incommensurate tubes is the key to understanding of double-wall tubes. Although some theoretical studies reported suppression of inter-tube transfer in multiwall tubes[3], the mechanism has not been well understood. The purpose of this paper is to clarify effects of inter-tube transfer in double-wall tubes. Using a tight-binding model length-dependence of conductance due to inter-tube transfer is calculated. The conductance is negligibly small in comparison to the conductance quantum and oscillates around an average which is approximately independent of the length. It is revealed based on the first-order perturbation theory that the result is attributed to quasi-periodic oscillation of position dependence of small local effective inter-tube coupling. [1] M. Kociak, K. Suenaga, K. Hirahara, Y. Saito, T. Nakahira, and S. Iijima, Phys. Rev. Lett. {\bf 89} (2002) 155501. [2] J. M. Zuo, I. Vartanyants, M. Gao, R. Zhang, and L. A. Nagahara, Science {\bf 300} (2003) 1419. [3] Y.-G. Yoon, P. Delaney, and S. G. Louie, Phys. Rev. B {\bf 66} (2002) 073407. [Preview Abstract] |
Tuesday, March 22, 2005 11:27AM - 11:39AM |
J27.00002: Electrical Properties of Defects in Carbon Nanotubes Brett Goldsmith, Philip G. Collins Unmodified single-walled carbon nanotubes are generally considered to be defect free conductors, even though most synthesis and fabrication techniques introduce non-zero defect densities. Primarily using scanned probe microscopies, we have investigated a number of electronic devices in which defects play important, if not primary, roles. For example, defects in otherwise metallic nanotubes can lead to switching behaviors in a field-effect transistor geometry, leading to the misidentification of such tubes from transport measurements alone. Furthermore, defect sites also contribute disproportionally to the device resistance of a metallic nanotube. In semiconducting nanotubes, field-induced switching has different signatures depending on whether the contacts, the bulk nanotube, or a defect site dominates the behavior. We will present data and measurements from a variety of samples demonstrating the characteristics and frequency of such effects in typical nanotube devices. This work has been supported by NSF-DMR. [Preview Abstract] |
Tuesday, March 22, 2005 11:39AM - 11:51AM |
J27.00003: Effects of Disorder on the Conductance of Semiconducting Carbon Nanotubes D. Areshkin, C.T. White The single parameter graphene sheet model for single-wall carbon nanotubes has been used to successfully explain many of their fundamental properties. However, even within this simple tight-binding approach calculations of nanotube conductance are typically restricted to the achiral armchair and zig-zag tubes because of the relatively small number of atoms in their translational unit cells. By taking advantage of helical symmetry we have overcome this limitation. This Green function based approach allows ready treatment of the effects of disorder on conductance without regard to the tube's chirality. Results for the effects of residual disorder on the conductance of a series of chiral semiconducting nanotubes will be presented. [Preview Abstract] |
Tuesday, March 22, 2005 11:51AM - 12:27PM |
J27.00004: Probing Scattering in Single-Walled Carbon Nanotubes Invited Speaker: Transport measurements and atomic force microscopy were used to study electron scattering rates in metallic single-walled carbon nanotubes. From scaling of the resistance of the same nanotube with length in the low and high bias regimes, the mean free paths for both regimes are inferred. The observed scattering rates are consistent with calculations for acoustic phonon scattering at low biases and zone boundary/optical phonon scattering at high biases. We have also developed techniques to probe the high frequency transport properties of nanotube transistors. We have used the nanotube transistor as a microwave mixer operating at frequencies up to 50 GHz. The long-term goal is to directly measure the fundamental excitations and scattering rates. The author would like to acknowledge Ji-Yong Park, Yuval Yaish, Vera Sazonova, Xinjian Zhou, Hao Lin, Hande Ustunel, Stephan Braig, T.A. Arias, Piet W. Brower, Sandip Tiwari and Paul L. McEuen of Cornell University for their contributions to this work. [Preview Abstract] |
Tuesday, March 22, 2005 12:27PM - 12:39PM |
J27.00005: Velocity Saturation in Semiconducting Carbon Nanotubes Yung-Fu Chen, M. S. Fuhrer Charge transport in individual semiconducting single-walled nanotubes (SWNTs) with Schottky barrier contacts has been studied at high bias voltages. We observe nearly symmetric ambipolar transport, and find that both electron and hole currents may significantly exceed 25 $\mu $A, thought to be the limiting current in metallic SWNTs due to optical phonon emission. The current for a ballistic ambipolar nanotube field-effect transistor has been calculated carefully, treating the potential and the charge of the nanotube self-consistently, and including electron-hole recombination. The result is directly compared with the experimental transport data, and it is found that the current may be as high as one-fifth that expected for a ballistic nanotube field-effect transistor, even for nanotubes with lengths of tens of microns. The high-bias behavior in semiconducting nanotubes is better explained by velocity saturation, rather than current saturation. We propose a charge-controlled current model of transistor operation, with maximum saturation velocity $v_{s}$ of 1.8 $\times $ 10$^{7}$ cm/s, which explains the magnitude of both the differential conductance under symmetric bias and the transconductance. [Preview Abstract] |
Tuesday, March 22, 2005 12:39PM - 12:51PM |
J27.00006: Electrical generation and absorption of phonons in carbon nanotubes B.J. LeRoy, S.G. Lemay, V. Pahilwani, J. Kong, I. Heller, C. Dekker We have performed low temperature scanning tunneling spectroscopy on individual single-wall carbon nanotubes freely suspended over trenches. Spatially resolved spectroscopy shows a Coulomb-staircase behavior superimposed on the local density of states. In addition to the Coulomb peaks from the addition of electrons, side peaks appear due to phonon-assisted tunneling. Electrons inelastically tunneling into the nanotube cause a non-equilibrium phonon occupation, leading to both emission and absorption of phonons by successive tunneling electrons. The addition of a gate electrode into our STM configuration allows further validation of this interpretation. These observations represent a new class of electrical transport phenomena, namely a current induced non-equilibrium phonon distribution and its influence on transport through a molecule. [Preview Abstract] |
Tuesday, March 22, 2005 12:51PM - 1:03PM |
J27.00007: Adsorbed monolayers on individual single-walled carbon nanotubes Zenghui Wang, Jiang Wei, Michael Shimogawa, Oscar Vilches, David Cobden We have built devices and apparatus to search for the effects of adsorbed monolayers on electrical transport through single-walled carbon nanotubes. The nanotubes, grown by chemical vapor deposition, are contacted by shadow evaporation for cleanliness, and placed in a controlled pressure and temperature environment where an external magnetic field can be applied. We concentrate on atoms and molecules which are likely to influence the electronic properties. Our eventual aim is to extend earlier work on the two-dimensional phases of matter on pyrolytic graphite to the nearly one-dimensional regime presented by cylindrical monolayers on a nanotube surface. We report preliminary results on oxygen, which is thought to dope nanotubes, and which exhibits magnetic order in low temperature 2D monolayers. [Preview Abstract] |
Tuesday, March 22, 2005 1:03PM - 1:15PM |
J27.00008: Electrical Breakdown of Carbon Nanotubes in Ultrahigh Vacuum Amy L. Perlman, Alexander D. Schwab, Walter F. Smith, James Hone, Nathan C. Keim It has been shown$^{1}$ that the current-induced breakdown of multiwall carbon nanotubes occurs at a higher voltage in high vacuum than in air, and that the size of the resulting gap is smaller. It is believed that the breakdown is due to joule heating and oxidation. Therefore, we expect that the maximum voltage and current would be higher in an oxygen-free environment, and that these conditions would allow study of the fundamental limits of current density in nanotubes. Further, it is reasonable to expect that the resulting gap would be smaller, and perhaps more suitable for making electrical contacts to other target molecules.$^{2}$ We present measurements on single wall nanotubes taken in a vacuum better than 1 x 10$^{-10}$ Torr, so that less than one oxygen molecule impinges on a nanotube over a several hour experiment. $^{1}$P.G. Collins \textit{et al}, Phys. Rev. Lett. \textbf{86}, 3128 (2001)$.$ $^{2}$ K. Tsukagoshi, I. Yagi, and Y. Aoyagi, Appl. Phys. Lett. \textbf{85}, 1021 (2004). [Preview Abstract] |
Tuesday, March 22, 2005 1:15PM - 1:27PM |
J27.00009: High Temperature Conductivity and Reactivity of Carbon Nanotube Electronic Circuits Alexander Kane, Philip G. Collins At sufficiently high temperatures, carbon nanotubes (CNTs) begin to react with their immediate environment. For example, adsorbates first desorb, then the carbon may react with connective electrodes, and ultimately Stone-Wales defects become mobile and can be annealed. We have designed and built an apparatus to study electronic transport in individual CNTs under these extreme conditions. Our apparatus provides continuous, four probe measurements of impedance and transimpedance from room temperature to 1500 K in an ultrahigh vacuum (UHV) system. By heating the devices to such temperatures, we are able to study the onset and progress of reactions, and the UHV environment allows for precise control of the local surface chemistry. Furthermore, the devices can be heated either resistively or radiatively at rates exceeding 100 K/min, allowing for pulsed thermal processing and an investigation of photoinduced chemistries. We will present results on the high temperature resistance of CNT devices in a UHV environment, and preliminary results indicating irreversible chemical changes which occur at high temperatures. [Preview Abstract] |
Tuesday, March 22, 2005 1:27PM - 1:39PM |
J27.00010: Equivalent Circuit Modeling for Carbon Nanotube Schottky Barrier Modulation in Polarized Gases Toshishige Yamada We study the carbon nanotube Schottky barrier (SB) at the metallic electrode interface in polarized gases using an equivalent circuit model. The gas-nanotube interaction is often weak and very little charge transfer is expected [1]. This is the case with oxygen, but the gas- electrode interaction is appreciable and makes the oxygen molecules negatively charged. In the closed circuit condition, screening positive charges appear in the nanotube as well as in the electrode, and the SB is modulated due to the resultant electrostatic effects [2]. In the case of ammonia, both the gas-nanotube and gas-electrode interactions are weak, but the SB can still be modulated since the molecules are polarized and align in the preferred orientation within the gap between the electrode and nanotube in the open circuit condition (dipole layer formation). In the closed circuit condition, an electric field appears in the gap and strengthens or weakens the preferred dipole alignment reflecting the nanotube Fermi level. The resultant dipole field modulates the SB. The modulation is visible when the nanotube depletion mode is involved, and the required dipole density is as low as 2 x 10 $^{13}$ dipoles/cm$^{2}$, which is quite feasible experimentally. [1] Bauschlicher and Ricca, Phys. Rev. B 70, 115409 (2004). [2] Yamada, Phys. Rev. B 69, 125408 (2004). [Preview Abstract] |
Tuesday, March 22, 2005 1:39PM - 1:51PM |
J27.00011: Two-dimensional Percolation Effects of Transparent, Conductive Carbon Nanotube Films Liangbing Hu, David Hecht, George Gruner Ultra-thin, uniform single-walled carbon nanotube films of varying densities have been made at room temperature by a vacuum filtration method. Measurements of the sheet conductance as a function of nanotube network density show 2D percolation behavior. In addition, the network transparency in the visible spectral range was examined and the results are in agreement with a standard thin-film model: fits to the standard theory at 550 nm. Transparency measurements also indicate the usefulness of nanotube network films as a transparent, conductive coating. [Preview Abstract] |
Tuesday, March 22, 2005 1:51PM - 2:03PM |
J27.00012: Measurements of nonlinear transport and interactions in single-walled carbon nanotubes Michael Shimogawa, Jiang Wei, Zenghui Wang, Iuliana Radu, David Cobden It has recently been emphasized that the nonlinear two-terminal conductance of a piece of material can be used to measure the strength of electron-electron interactions in that material. More precisely, contributions to the current which are quadratic in voltage bias and proportional to the applied magnetic field should be proportional to the interaction constant at low temperatures and to the interaction constant squared at high temperatures. The question of what role interactions and correlations play in one-dimensional conductors such as single-walled carbon nanotubes remains open, although it is generally agreed that the degenerate electron system in a pure nanotube behaves as a Luttinger liquid. With this in mind we have measured these nonlinear terms in single-walled carbon nanotubes, in both semiconducting and metallic regimes, and at high and low temperatures. [Preview Abstract] |
Tuesday, March 22, 2005 2:03PM - 2:15PM |
J27.00013: Tomonaga-Luttinger liquid related superconductivity in end-bonded carbon nanotubes Junji Haruyama, Izumi Takesue, Naoki Kobayashi, Shohei Chiashi, Shigeo Maruyama, Toshiki Sugai, Hisanori Shinohara Is it possible to find superconductivity in one-dimensional (1D) systems? It is well known that 1D systems have some obstructions that prevent emergence of superconductivity, e.g. Tomonaga-Luttinger liquid (TLL), spin fluctuation, van-Hove singularity, Peierls transition, and charge-density waves. Carbon nanotube (CN) is a good candidate to investigate this possibility. Although a variety of intriguing quantum phenomena has been reported in CNs, only two groups reported intrinsic superconductivity without reproducibility by other researchers. As well, the transition temperature (Tc) was as low as 0.2K in suspended ropes of SWNTs. Although Tc of 15K was found in thin SWNTs, it was identified only from the Meissner effect. No correlation with 1D phenomena, in particular with TLL arising from 1D electron-electron interaction, was also clarified. Here, we report superconductivity with the onset Tc as high as 12K and T=7.8K, at which resistance drops to zero ohm, for the highest case in end-bonded CNs, which were packed into nanopores of alumina templates. The transition temperatures were approximately 25-times and 40-times larger than those in a past report, respectively. We find that end-bonding the CNs by an electrode is the crucial factor for realizing superconductivity that overcomes TLL. [Preview Abstract] |
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J27.00014: Suppressed Conductance of Individual Single Walled Carbon Nanotube/Polypyrole Composite Nanowires and Their Sensing Applications Xiaolei Liu, James Ly, Song Han, Hao Chen, Hao Zhou, Daihua Zhang, Zhicheng Luo, Mark Thompson, Chongwu Zhou We present synthesis of individual single walled carbon nanotube/polypyrrole composite nanowire by chemical vapor deposition followed by electrochemical deposition for the first time. The transport properties of the composite nanowire were studied and suppression in conduction through carbon nanotube channels was discovered and discussed. Moreover, we also demonstrated the composite nanowire devices can serve as chemical sensors, which responses to oxidizing and reducing gases. The studies on the transport of the composite and their sensing applications shed light on the interaction between the nanotubes and the electrochemically coated polymers and also opens the way toward high performance chemical/bio sensors with high selectivity. [Preview Abstract] |
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