Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session D26: Focus Session: Nanotubes and Nanowires: Electronic Properties |
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Sponsoring Units: DMP Chair: Chongwu Zhou, USC Room: LACC 501B |
Monday, March 21, 2005 2:30PM - 3:06PM |
D26.00001: Measurements of electronics transport properties of single walled carbon nanotubes Invited Speaker: The aim of the talk is to discuss the electronic transport properties of metallic single walled nanotubes when defects are present. Two different type of defects will be considered: the first one is a strong localized defect produced by squashing the nanotube with the tip of an atomic force microscope. The radial deformation so induced produces a gap opening that decrease the low voltage conductance up to one order of magnitude. The second type of defects are weak defects uniformly distributed along the length of the nanotube . Consecutive ion irradiation doses are applied to nanotubes producing the uniform density of defects. After each dose the electrical characteristics of the same carbon nanotube are measured by using a conductive atomic force microscopy. Theoretical simulations demonstrate that only di-vacancies are relevant to explain the conductance drop induced by the irradiation. The data show that only a 0.1 {\%} of defects cause the resistance of a 400 nm length nanotube to increase three orders of magnitude. [Preview Abstract] |
Monday, March 21, 2005 3:06PM - 3:18PM |
D26.00002: Tunable tunnel barriers in carbon nanotubes as a probe of electron-electron interactions in one-dimensional systems Joseph Sulpizio, Charis Quay, Zvonimir Bandic, David Goldhaber-Gordon We fabricate carbon nanotube devices with single tunable tunnel barriers using lithographically defined narrow metal gate electrodes. By measuring the end-to-end transport across the tunnel barriers in these one-dimensional structures, we aim to probe electron-electron interactions and test the predictions of Luttinger liquid theory. [Preview Abstract] |
Monday, March 21, 2005 3:18PM - 3:30PM |
D26.00003: Carbon Nanotube Gated Lateral Resonant Tunneling Field-Effect Transistor D. P. Wang, B. R. Perkins, A. Zaslavsky, A. J. Yin, J. M. Xu Carbon nanotubes have generated a great deal of interest for use in novel devices due to their small size and high current densities. We have produced a new type of lateral resonant tunneling field-effect transistor using a Y-junction multiwalled carbon nanotube as the dual gate on a narrow wire etched from a modulation-doped GaAs/AlGaAs heterostructure. The two branches of the Y-junction nanotube produced in an alumina nanotemplate array \footnote{Li, J., Papadopoulos, C. and Xu, J. M., ``Growing Y- Junction Carbon Nanotubes" Nature 402, 253-254, 2000.} are used as gates to produce a voltage-tunable double-barrier potential for the carriers traveling from source to drain along the wire. The three terminal I-V characteristics of the device have been measured at 4.2K. Conductance oscillation is observed as a function of dual gate potential, indicating electron resonant tunneling through the energy states between the barriers. Detailed measurement and comparison with self-consistent potential simulations will be presented. [Preview Abstract] |
Monday, March 21, 2005 3:30PM - 3:42PM |
D26.00004: Excitation spectrum of carbon nanotube quantum dots Sami Sapmaz, Pablo Jarillo-Herrero, Jing Kong, Cees Dekker, Leo P. Kouwenhoven, Herre S.J. van der Zant We have studied the excitation spectrum of nanotube quantum dots. At low temperatures, the stability diagrams show very regular Coulomb blockade diamonds. We have observed four-fold shell structure both in the electron addition and excitation energy spectrum. The measured nanotube spectra are in good agreement with theoretical predictions based on the nanotube band structure. In suspended nanotubes, additional harmonic excitations appear at low energies that we attribute to phonon assisted tunneling in the nanotube quantum dot. Our results permit the complete identification of the electron quantum states in nanotube quantum dots. [Preview Abstract] |
Monday, March 21, 2005 3:42PM - 3:54PM |
D26.00005: Superconducting proximity effect in superconductor / semiconducting-carbon-nanotube / superconductor junctions. Paola Barbara, Kyle Hatton, Alexander Tselev, Jian Zhang We measure the proximity effect in devices made of two superconducting electrodes bridged by a 3-micrometer long semiconducting carbon nanotube. The electrodes are made of a Pd/Nb bilayer and the junctions are fabricated by using standard photolithography [1]. The superconducting proximity effect manifests itself with a peak in the low-bias differential conductance due to Andreev reflection at the superconductor/carbon nanotube interfaces. Application of a gate voltage allows the transparency of the junction to be tuned from high (Andreev reflection) to low (tunneling) [2]. We have studied the temperature dependence of the features in each regime. This work is supported by the NSF (DMR-0239721) and by the Research Corporation. [1] A. Tselev, K. Hatton, M. S. Fuhrer, M. Paranjape and P. Barbara, Nanotechnology 15, 1475 (2004). [2] A. F. Morpurgo, J. Kong, C. M. Marcus, and H. Dai, Science 286, 263 (1999). [Preview Abstract] |
Monday, March 21, 2005 3:54PM - 4:06PM |
D26.00006: Instabilities in electrical properties of carbon nanotube FETs with superconducting Pd/Nb electrodes Alexander Tselev, Jian Zhang, Kyle Hatton, Paola Barbara We investigate low-temperature transport properties of carbon nanotube FETs with the source and drain electrodes made of a Pd/Nb bilayers. The samples are fabricated on overdoped Si wafers covered by thermally grown 500 nm-thick silicon dioxide using photolithographic techniques. The substrates serve as back gates of the FETs. Below the superconducting transition of the electrodes and at large negative gate voltages, about -50 V, the differential conductance is highest, and Andreev-reflection-like features can be observed as a peak at zero bias in differential conductance vs. bias voltage curves. Both metallic and semiconducting nanotubes show such features. At a fixed gate voltage, the differential conductance vs. bias voltage was found to be unstable, with features evolving in time from high transparency Andreev-reflection-like to low-transparency tunneling-like. The instabilities are probably caused by mobile charges within and on the surface of the gate oxide. This work is supported by the NSF (DMR-0239721) and by the Research Corporation. [Preview Abstract] |
Monday, March 21, 2005 4:06PM - 4:18PM |
D26.00007: The Aharonov-Bohm Interference and Beating in Single-Walled Carbon Nanotube Interferometers Jien Cao, Qian Wang, Hongjie Dai A hallmark of the Aharonov-Bohm (AB) effect is conductance oscillations of metallic rings or cylinders as a function of enclosed magnetic flux with a period on the order of the flux quantum \textit{$\Phi $}$_{0}=h/e$ due to quantum interference. Carbon nanotubes are chemically derived cylinders with atomically well-defined structures. Multi-walled nanotubes (MWNT) have radius $r \quad \sim $ 10 nm and in magnetic fields parallel to the tube axis, conductance modulations with a period of $B_{0}$\textit{=$\Phi $}$_{0}$\textit{ /$\pi $ r }$^{2} \quad \sim $ 10T in magnetic field have been seen. Single-walled nanotubes (SWNT) are ultra-small with $r \quad \sim $ 1 nm and the magnetic field needed to approach 1\textit{$\Phi $}$_{0}$ flux through the nanotube cross section is $B_{0} \quad \sim $ 1000T, far beyond reach by experiments. We show here that in the Fabry-Perot interference regime, beating in the AB-interference between two modes of spiraling electrons with non-degenerate wave-vectors causes conductance modulations under fields much smaller than that needed to reach 1\textit{$\Phi $}$_{0.}$ Single-walled nanotubes hence represent the smallest cylinders exhibiting the AB effect with rich interference and beating phenomena arising from well-defined molecular orbitals reflective of the nanotube chirality. The observation of quantum beats for the AB effect is to our knowledge unprecedented in mesoscopic systems and is a result of well-defined molecular orbitals of nanotubes in magnetic fields. [Preview Abstract] |
Monday, March 21, 2005 4:18PM - 4:30PM |
D26.00008: Geometry dependence of electrical breakdown in multi-walled carbon nanotubes Hsin-Ying Chiu, Vikram Deshpande, Marc Bockrath We compare the results of electrical breakdown experiments on multi-walled carbon nanotubes for substrate-supported and free-standing geometries. At a threshold power typically $\sim $50 $\mu $W, the resistance of most free-standing samples drops dramatically until it is typically $\sim $10 k$\Omega $, while this occurs only rarely in the substrate-supported geometry. This enables the electrical breakdown to occur even in samples that have a high initial contact resistance, giving a high yield to the breakdown process for free-standing tubes. Furthermore, the length of the removed shells is generally shorter for free-standing tubes. We use a model of thermal transport to account for our observations, which demonstrate that the local temperature plays an important role in the breakdown process and the decrease in conductance. Finally, breaking all the shells creates devices with nano-scaled gaps of 3-20 nm. We will discuss their electromechanical properties. [Preview Abstract] |
Monday, March 21, 2005 4:30PM - 4:42PM |
D26.00009: Annealing of Multiwalled Carbon Nanotubes an in-situ TEM study Shaul Aloni, William Mickelson, Brian Christopher Regan, Steve Konsek, Alex Zettl 1D Nanostructures in general and nanotubes in particular are often containing substantial amount of defects. The defects may are present in as grown tubes, may stem from extensive processing or being induced by electron beam. In previous reports heating above 1500C was required to anneal defects in bulk multiwalled nanotubes. In this work we report a simple procedure to anneal the tubes by passing an electrical current through suspended nanotubes in-situ inside a TEM. The experiments were performed both in a two terminal configuration as well as in free standing nanotubes attached to an in-situ nano-manipulator. As a result of local heating the defects are annealed resulting in near perfect tubular structures free of defects. In related experiments, low energy structural defects can be induced by the electrical current. [Preview Abstract] |
Monday, March 21, 2005 4:42PM - 4:54PM |
D26.00010: Failure Modes in Carbon Nanotube Devices S.L. Konsek, Shaul Aloni, B.C. Regan, Alex Zettl We study the electrical breakdown of multiwall carbon nanotube transistor devices. Electrical transport measurements are preformed in a transmission electron microscope, allowing real-time nanometer scale imaging of device breakdown. Failure modes are correlated to changes in nanotube device behavior. [Preview Abstract] |
Monday, March 21, 2005 4:54PM - 5:06PM |
D26.00011: Nano-mechanical relay device using multi-walled nanotubes as linear bearings Vikram Deshpande, Hsin-Ying Chiu, Henk Postma, Marc Bockrath Electrical breakdown of free-standing multi-walled carbon nanotube (MWNT) devices leads to gaps $\sim $3-20 nm, which are insulating at low biases. By applying sufficient voltage ($\sim $5-10 V) the inner shells extend due to electrostatic attraction and the gaps close, restoring a non- zero conductance. This demonstrates that the low-friction sliding between shells of a MWNT can be utilized to create a nano-mechanical relay. The observed threshold voltages along with approximate models for the capacitance between the nanotube segments yield a typical electrostatic actuation force $\sim $0.5 nN. We will compare our observed actuation forces to the expected inner-shell retraction force based on the constant-force spring model of Cumings and Zettl [1]. Finally, recent data indicates that the low conductance state can be restored via the application of a gate voltage, enabling the reversible operation of the device. We will discuss our latest results and interpretations. [1] Cumings, J. {\&} Zettl, A., \textit{Science} \textbf{289}, 602-604 (2000) [Preview Abstract] |
Monday, March 21, 2005 5:06PM - 5:18PM |
D26.00012: Detecting the mechanical vibrations of carbon nanotubes using tunnel gap modulation spectroscopy Joel Therrien, Chun Lan, Ron Reifenberger The natural vibrational frequencies of multiwalled carbon nanotubes are measured as a function of length using a novel tunnel gap modulation technique. The method, which works well under ambient conditions, requires fixing one end of the nanotube to an STM tip. When the free end of the nanotube is brought within tunneling range of a conducting substrate, the nanotube's thermal vibrations modulate the size of the tunnel gap, leading to an oscillatory component in the tunnel current at the natural frequency of the nanotube. The frequency of the oscillation can be easily adjusted by tailoring the length, diameter and elastic properties of the nanotube. In principle, a spectroscopy based on tunnel gap modulation can measure the frequencies of vibrational modes of any structure in the path of the tunnel current; for the case of nanotubes attached to tips, frequencies approaching 300 GHz should be realizable using single walled nanotubes. Coupled with the high lateral resolution of STM, tunnel gap modulation spectroscopy enables a new probe of the vibrational properties of substrates with nanometer resolution. [Preview Abstract] |
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