Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session B20: Focus Session: Carbon Nanotubes: Superconductivity, Electrical Properties |
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Sponsoring Units: DMP Chair: Nathaniel Gabor, Cornell University Room: C120-C122 |
Monday, March 15, 2010 11:15AM - 11:51AM |
B20.00001: Modifying inter-tube bonding, and doping, in carbon nanotubes Invited Speaker: Doping carbon nanotubes is essential for tuning their physical properties. Improved $\it{in-situ}$ and post-synthesis methods have succeeded in preparing carbon nanotubes with novel electronic, vibrational, thermal and mechanical properties. For example, we have recently reported a superconducting transition temperature of $\sim$ 12 K in thin films of boron-doped single-walled carbon nanotubes. Detailed Raman studies showed the presence of charged defects in the nanotube framework which leads to modified electron and phonon energies. In this talk, we present evidence for the formation of inter-tube bonding in nanotubes when subjected to the spark plasma sintering (SPS) process. The combined results of x-ray powder diffraction, Raman spectroscopy, scanning electron microscopy and high resolution transmission electron microscopy show that the nanotubes largely retain their individual tubular morphology. In turn, these inter-tube connections influence the overall electrical resistivity, thermoelectric power and thermal conductivity of the SPS-ed samples. In particular, the magnitude of the electrical resistivity as a function of SPS temperature exhibits a percolative behavior while the low temperature lattice thermal conductivity shows a crossover in the sample dimensionality. These results are discussed in terms of the quasi 1D metallic nature of carbon nanotubes, the packing density and the electron-phonon coupling. Results for SPS-ed samples in the presence of dopants (such as boron) will also be discussed. [Preview Abstract] |
Monday, March 15, 2010 11:51AM - 12:03PM |
B20.00002: 1D Superconducting behavior in 4-Angstrom carbon nanotube-zeolite composite Wu Shi, Zhe Wang, Hang Xie, Ting Zhang, Ning Wang, Zikang Tang, Xixiang Zhang, Rolf Lortz, Ping Sheng We report 4-probe electrical measurements on a sample of 4-Angstrom carbon nanotubes-zeolite composite that exhibit 1D superconducting behavior. The resistance displays a smooth decrease as a function of temperature that is characteristic of the phase slip fluctuation effects, and the differential resistance measured as a function of current shows a quasigap that is characteristic of the fluctuating condensate. Both data sets show very little variation upon the application of a magnetic field, up to 9 Tesla. These behaviors are explainable in terms of the Langer-Ambegaokar-McCumber-Halperin (LAMH) theory of phase slips. We also show and discuss an interesting phenomenon in which a sharp zero current (bias) peak appears in the differential resistance above 3 K. [Preview Abstract] |
Monday, March 15, 2010 12:03PM - 12:15PM |
B20.00003: Electronic and Magnetic Properties of Partially Open Carbon Nanotubes Bing Huang, Young-Woo Son, Gunn Kim, Wenhui Duan, Jisoon Ihm We demonstrate that partially open carbon nanotubes (CNTs) observed in recent experiments have rich electronic and magnetic properties which depend on the degree of the opening. A partially open armchair CNT is converted from a metal to a semiconductor and then to a spin-polarized semiconductor by increasing the length of the opening on the wall. Some partially open zigzag CNT superlattices are by themselves giant magnetoresistive devices. In addition, external electric fields or chemical modifications are usable to control the electronic and magnetic properties of partially open CNTs. We show that half-metallicity may be achieved and the spin current may be controlled by external electric fields or by asymmetric functionalization of the edges of the opening. [Preview Abstract] |
Monday, March 15, 2010 12:15PM - 12:27PM |
B20.00004: Bangap opening in metallic carbon nanotubes due to silicon impurities Branden Kappes, Cristian Ciobanu Controlling the bandgap of carbon nanostructures is key to the development and mainstream applications of carbon-based nanoelectronic devices. We report density functional theory calculations of the effect of silicon impurities on the electronic properties of carbon nanotubes (CNTs). We have found that silicon adatoms can open up a bandgap in intrinsically metallic CNTs. Even when the linear density of Si atoms is low enough that they do not create a bonded adatom chain, the bandgap opened in metallic CNTs can range between 0.10 eV and 0.47 eV, depending on adsorption site, linear density of Si atoms, and on the chirality of the nanotube. [Preview Abstract] |
Monday, March 15, 2010 12:27PM - 12:39PM |
B20.00005: Carbon nanotubes interactions: effects of chirality Lilia Woods, Adrian Popescu, Igor Bondarev Calculations of the pressures on the surfaces of two concentric carbon nanotubes in vacuum are presented. The approach is based on quantizing the electromagnetic field and on the dyadic Green function method. Carbon nanotubes are described as dielectric bodies characterized by a spatially varying permittivity that is a complex function of frequency. The effects of the tubes chiralities on the strength of their mutual interactions are discussed. Furthermore, the results are compared with those obtained with a classical approach, where the carbon nanotubes interaction is described by using a pairwise additive type of interatomic potential. [Preview Abstract] |
Monday, March 15, 2010 12:39PM - 12:51PM |
B20.00006: Study of low energy excitations of carbon nanotubes with DMRG Alexander Struck, Sebastian A. Reyes, Sebastian Eggert We examine the low-energy properties of impure carbon nanotubes including short-ranged electron-electron interactions. In particular, we calculate the local density of states (LDOS) close to selected impurities such as Stone-Wales defect and half-fullerene caps at the tube ends using the density matrix renormalization group (DMRG). We discuss the possibility to identify interaction strength and range from LDOS patterns, which reveal the interplay of electron interactions and impurities. [Preview Abstract] |
Monday, March 15, 2010 12:51PM - 1:03PM |
B20.00007: Noise in single-wall carbon nanotubes under high electric field stress Curt Richter, Oana Jurchescu, Xuelei Liang, David Gundlach, Albert Liao, Eric Pop We characterized the noise properties of field effect transistors made from individual semiconducting single-walled carbon nanotubes (CNTs) under high electric field stress to probe scattering mechanisms during avalanche and self-heating conditions. Single-walled CNTs were grown from patterned Fe catalyst by CVD on oxidized p-doped Si wafers which serve as a back gate. Pd source/drain (S/D) contacts were used to form devices ranging in length from 1 $\mu $m to 4$\mu $m. 1/ $f $noise measured at room temperature in air shows conventional changes in amplitude as a function of gate voltage and low S/D voltages. As the S/D bias on the CNTs increases, we observe an unexpected increase in noise at $\approx $3 V. This change occurs at fields and voltages below those necessary to induce avalanche generation of free electrons and holes. Thermal modeling reveals that the average temperature of the CNTs reaches $\approx $370 K when the noise behavior increases, which is consistent with oxygen desorption. Thus, our measurements and modeling provide insight into noise at high field in CNTs, uncovering the role of changes in doping and threshold voltage at high operating temperature. [Preview Abstract] |
Monday, March 15, 2010 1:03PM - 1:15PM |
B20.00008: Electron beam induced flicker noise in carbon nanotubes Jack Chan, Brian Burke, Chong Hu, Joe Campbell, Lloyd Harriott, Keith Williams Discrete current switching is induced in carbon nanotubes by low dosage electron beam irradiation. Switching is observed at room temperature. Switching is created by electron beam. Change in noise power spectral density following electron beam exposure will be discussed. The observed flicker noise is attributed to charge traps created by electron beam irradiation in silicon oxide. [Preview Abstract] |
Monday, March 15, 2010 1:15PM - 1:27PM |
B20.00009: Measurement of scattering cross section of long-range and short-range scatters on single-walled carbon nanotubes Ryuichi Tsuchikawa, Masahiro Ishigami Impacts of long-range and short-range scattering potentials on transport properties of carbon nanotubes are expected to be radically different. We measured adsorbate- induced resistance while varying adsorbate density in ultra high vacuum environment. We used cesium for exerting long-range coulomb potential and atomic hydrogen for inducing short-range scattering potential. We have determined the resistance of individual scattering sites as a function of the scattering potential. We will discuss our results on both nanotube network and individual nanotube devices and compare our results to previous theoretical investigations. [Preview Abstract] |
Monday, March 15, 2010 1:27PM - 1:39PM |
B20.00010: The effect of carbon vacancies on the electrical conductance of carbon nanotubes Alex Taekyung Lee, Yong-Ju Kang, Kee Joo Chang Defects such as carbon vacancy strongly affect the electronic properties of graphene and carbon nanotubes. It is known that divacancies are one of the most common defects generated under ion irradiation. Based on first-principles matrix Green's function calculations, we study the effect of various carbon vacancies on the electrical conductance of (5,5) and (9,0) carbon nanotubes. For vacancy clusters V$_{n}$ ($n \quad \le $ 4), where $n$ is the number of missing atoms, conductance generally decreases due to the formation of topological defects. When vacancies are randomly distributed, resistances exhibit the localization behavior. The localization lengths are found to be smaller for vacancies with $n$ = even integer due to scattering by the 7- or 8-membered ring. This length is also reduced in the zigzag tube as defect levels lie closer to the Fermi point, as compared to the armchair tube. For large vacancy clusters with $n \quad \ge $ 5, the electrical conductance is mainly affected by the local gap opening induced by the tube shrinkage. The overall behavior of electrical conductance in zigzag tubes is similar to that of armchair tubes. [Preview Abstract] |
Monday, March 15, 2010 1:39PM - 1:51PM |
B20.00011: First principles study of defects in nanotubes Jessica Gallagher, Ethan Minot, Guenter Schneider, David Roundy Engineered defects in carbon nanotubes (CNTs) have proven useful in electrical device applications such as self-assembled CNT circuits, gas sensors and single molecule sensors. In many cases the nature of the defects is largely unknown. We present an \emph{ab initio} study investigating the effects of several varieties of defects on the electronic structure of single walled carbon nanotubes. The defects studied include the single-carbon vacancy, a single-carbon vacancy passivated with hydrogen, and a single $sp^3$-bonded carbon. Within the framework of density-functional theory in the local density approximation, we have investigated the effect of these vacancies and other defects on the local band gap and speculate as to their effects as scattering centers. [Preview Abstract] |
Monday, March 15, 2010 1:51PM - 2:03PM |
B20.00012: ABSTRACT WITHDRAWN |
Monday, March 15, 2010 2:03PM - 2:15PM |
B20.00013: Noise conductance of carbon nanotube transistors Emiliano Pallecchi, Bernard Placais, Julien Chaste, Pascal Morfin, Gwendal Feve, Takis Kontos, Jean-Marc Berroir, Pertti Hakonen We report on radio-frequency transmission and noise measurements of high-transconductance carbon nanotube transistors. Gate capacitance $C_g$, drain conductance $g_d$, transconductance $g_m$ and current-noise data are analyzed with a ballistic 1-dimensional nano-transistor model where the nanotube channel is described by a quantum capacitance $C_q$. Current is thermally activated with a transconductance controlled by a bias-dependent electronic temperature. Shot-noise is a thermal noise with a noise conductance $g_n$ different from the drain conductance $g_d$. The 1-dimensional model gives a simple formula $g_n-g_d=g_m(C_q/2C_g)$ which is verified in the nanotube transistor. Finally we estimate the charge resolution of nanotube devices for applications as fast single-shot electron detectors. [Preview Abstract] |
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