Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session D30: Focus Session: Carbon Nanotubes and Related Materials V: Nanotube Transport |
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Sponsoring Units: DMP Chair: Oleg Prezhdo, University of Washington at Seattle Room: Morial Convention Center 222 |
Monday, March 10, 2008 2:30PM - 3:06PM |
D30.00001: Electrical, Mechanical, and Optical Studies of Carbon Nanotubes of Known Chiral Index. Invited Speaker: Because small changes in the crystal structure (chirality) of carbon nanotubes can produce large changes in their electrical properties, it is important to understand the relationship between structure and transport properties, both for basic science and for applications. We have developed a unique set of tools for characterizing and manipulating nanotubes that allow for detailed studies of the properties of known-chirality nanotubes. Completed and ongoing studies include: structure-correlated optical properties; tube-tube interactions; variable electron-phonon coupling; electromechanical properties; structure-correlated electrical transport; nanotube intermolecular heterojunctions; and mechanical stiffness and strength. [Preview Abstract] |
Monday, March 10, 2008 3:06PM - 3:18PM |
D30.00002: Electron field emission from Carbon Nanotube Composites: Transport and Local Electric Fields David Carey, Thomas Connolly, Richard Smith, Jonathan Coleman Electron field emission characterisation of carbon nanotube polymer composites has been performed where emission at low nanotube mass fractions ($<$10{\%}) has been observed. Nanotubes have been embedded in two different types of polymer: PmPV, a conjugated polymer and PVA, polyvinyl alcohol. It shown that for nanotubes embedded in PmPV, the field emission is strongly influenced by charge transport through the film. For nanotubes in PVA a transition from bulk transport to a Fowler-Nordheim emission mechanism is seen as the mass fraction exceeds about 1-2{\%}. Estimates of the local field as a function of mass fraction are also shown. The potential role of nanotube -- polymer composites produced by solution processing to large area cathodes with a controllable mass fraction will be discussed. [Preview Abstract] |
Monday, March 10, 2008 3:18PM - 3:30PM |
D30.00003: Metal-Semiconductor-Metal (MSM) Photodetectors with Single-walled Carbon Nanotube Film Schottky Electrodes on GaAs Ashkan Behnam, Jason Johnson, Yongho Choi, Leila Noriega, G\"unhan Ertosun, Zhuangchun Wu, Andrew Rinzler, Pawan Kapur, Krishna Saraswat, Ant Ural We fabricate and experimentally characterize the dark and photocurrent in metal-semiconductor-metal (MSM) photodetectors with transparent and conductive single-walled carbon nanotube (CNT) film electrodes on GaAs. The dark current measurements of MSM structures reveal that the CNT film forms a Schottky contact on GaAs substrates. The Schottky barrier height and the CNT film workfunction are extracted to be approximately 0.55 and 4.6 eV, respectively, based on dark current measurements as a function of temperature. We also study the effect of device geometry on the dark current of the CNT film-GaAs MSM devices. Furthermore, we find that CNT film MSM devices exhibit a significantly lower dark current and higher normalized photo-to-dark current ratio compared to metal control samples. We explain these observations by comparing the interfaces in these structures. This work opens up the possibility of integrating CNT films as Schottky electrodes in conventional semiconductor electronic and optoelectronic devices. [Preview Abstract] |
Monday, March 10, 2008 3:30PM - 3:42PM |
D30.00004: Anomalous Coulomb oscillation in crossed carbon nanotubes Seung Jae Baek, Dongsu Lee, Seung Joo Park, Yung Woo Park, Johannes Svensson, Mats Jonson, Eleanor E. B. Campbell Single-walled carbon nanotube (SWCNT) crossed junctions separated by an insulating layer were fabricated to investigate the double quantum dot modulated by a single gate (DQD-sG). Anomalous Coulomb oscillations were observed on the lower CNT at low temperature, where the behavior was interpreted by the concept of a double quantum dot (DQD) system http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal\&id =APPLAB000089000023233107000001\&idtype=cvips\&gifs=yes [1]. To understand it more clearly, we have intentionally fabricated crossed CNTs without oxide layer in between. The observed anomalous Coulomb oscillations indicate that the contact resistance between the two tubes becomes a potential barrier splitting the initial single QD into the DQD, and the back-gate modulates the energy levels of the DQD. [Preview Abstract] |
Monday, March 10, 2008 3:42PM - 3:54PM |
D30.00005: Strain Tuning of the Photocurrent Spectrum in Single wall Carbon Nanotubes Prasanth Gopinath, A. Mohite, H. Shah, J. Lin, B. Nagabhirava, T. Bansal, B. Alphenaar The electronic structure of a single-wall nanotube (SWNT) can be substantially modified by the application of uniaxial strain. We use displacement photocurrent spectroscopy to study the effect of uniaxial strain on the optical transitions of a SWNT in the energy range 0.5eV-3eV. This broad energy range allows us to compare the strain dependence of the lowest (E11) and higher order (E22 and E33) optical transitions of semiconducting SWNT's. As predicted by a simple non-interacting model, we observe an energy shift of each transition with increasing strain. By fitting the model to the magnitude and slope of the energy shift for the lowest energy transition (E11) the nanotube chirality can be identified uniquely. For the higher energy transitions, the data deviates significantly from the non-interacting model, presumably because of the influence of the excitonic binding energy. Finally, we observe a large reversible increase in the magnitude of the photocurrent around the ground state (E11) energy regime with an applied strain of 0.01{\%}. We attribute this to reversible strain induced defect states opening up within the bandgap of the SWNT. [Preview Abstract] |
Monday, March 10, 2008 3:54PM - 4:06PM |
D30.00006: Negative magneto resistance in carbon nanotubes: A first principle study Li Chen, Saroj Nayak We have studied spin transport through single wall carbon nanotube (SWNT) with nickel contacts using \textit{ab initio} density functional theory and green's function based Landauer B\"{u}ttiker formalism. Our results show enhanced current for anti-parallel alignment compared to that obtained for parallel alignment. This non Julli\'{e}re's model results due to finite size effect and this talk will present a detailed atomic level mechanism of such phenomena. Our results will be discussed in the light of recent experimental studies. [Preview Abstract] |
Monday, March 10, 2008 4:06PM - 4:18PM |
D30.00007: Observation of Spin-Orbit Coupling in Clean Carbon Nanotubes Ferdinand Kuemmeth, Shahal Ilani, Paul McEuen, Dan Ralph The electronic states in defect-free carbon nanotubes (NTs) are widely believed to be four-fold degenerate, due to independent spin and orbital symmetries, and also to possess electron-hole symmetry. We report measurements demonstrating that in clean NTs the spin and orbital motion of electrons are coupled, thereby breaking all of these symmetries. This spin-orbit coupling is directly observed as a splitting of the four-fold degeneracy of a single electron in an ultra-clean quantum dot. Application of a parallel magnetic field reveals that the coupling favours parallel alignment of the orbital and spin magnetic moments for electrons and anti-parallel alignment for holes. We further show that SO coupling determines the filling order in the many-electron ground states, in a way different than that expected from electron-electron interactions. At low magnetic fields we find that the two-electron ground state is neither a spin-triplet nor a spin-singlet, but a Slater determinant in which the spin and orbital wavefunction are entangled. Our findings have important implications for spintronic applications in NTs and provide a mechanism for all-electrical control of spins. [Preview Abstract] |
Monday, March 10, 2008 4:18PM - 4:30PM |
D30.00008: Infrared Photoconductivity of Individual Carbon Nanotubes Using Fourier-Transform Spectroscopy Sami Rosenblatt, Matthew Sfeir, Yang Wu, Hugen Yan, Christophe Voisin, Bhupesh Chandra, Robert Caldwell, Yuyao Shan, Tony F. Heinz, James Hone, G. Larry Carr, James A. Misewich We have developed a novel infrared spectroscopy technique for studying the photocurrent response of individual semiconducting carbon nanotubes. We use a synchrotron-based, broadband infrared light source coupled to a Fourier-transform spectrometer and microscope to induce currents in electrically biased nanotubes. This approach enables the rapid acquisition of high-resolution photocurrent spectra near the bandgap of the larger diameter ($>$ 1.7 nm) nanotubes commonly produced by synthesis using chemical vapor deposition. We have recorded optical transitions with energies as low as 0.4 eV for individual nanotubes. The structures used in these measurements consisted of isolated nanotubes with well-separated metal contacts on a Si back gate. In addition to describing the experimental approach and results, we will discuss the sensitive dependence of the measured photocurrent on the electrical biasing conditions. [Preview Abstract] |
Monday, March 10, 2008 4:30PM - 4:42PM |
D30.00009: Conductance enhancement of carbon nanotubes through metallization Caterina Soldano, Li Chen, Swastik Kar, Saikat Talapatra, Robert Vajtai, Saroj Nayak, Pulickel Ajayan A novel method for building high-conductance device using carbon nanotubes is presented. The process involves a systematic, repeatable and controllable enhancement of the conductance using a rapid high-voltage cycling conducted in vacuum; this process leads to orders of magnitude drop in the two-terminal resistance. Electron microscopy analysis indicates that the high-bias cycling of nanotubes causes sufficient Joule heating for the platinum to migrate from the contact regions and decorate the outer surface of the nanotubes, giving rise to enhanced metallization. Pre- and post-metallization characterization is presented. It is believed that the conductance enhancement is due to a combination of a decrease in disorder density in the tube and an increase in the number of available channels for conductance. Those outcomes are investigated in the light of recently predicted theoretical models. [Preview Abstract] |
Monday, March 10, 2008 4:42PM - 4:54PM |
D30.00010: Carbon nanotubes as tunable Luttinger liquids Wade DeGottardi, Tzu-Chieh Wei, Smitha Vishveshwara We investigate the properties of single-walled carbon nanotubes in transverse electric and magnetic fields. We find via band structure calculations that these fields can break particle- hole symmetry as well as that of the two Dirac points. Additionally, the speed of the left and right movers is generally different in the presence of both electric and magnetic fields. We consider the effect of these fields on Coulomb interactions within the tube and show that they can be used to tune the interaction parameter K associated with the Luttinger liquid properties of the tube. Finally, we discuss finite size effects and Coulomb blockade physics in this context. [Preview Abstract] |
Monday, March 10, 2008 4:54PM - 5:06PM |
D30.00011: Massively Parallel Imaging and Electrical Characterization of Carbon Nanotube Transistors with Scanning Thermocurrent Microscopy Adam Tsen, Huseyin Kurt, Luke Donev, LiHong Herman, Jiwoong Park Electrical characterization of individual carbon nanotubes (CNTs) is a painstaking and time-consuming process, requiring a serial study of individual CNT devices. We present a novel method utilizing a laser-based setup$^{1}$ to simultaneously image and electrically characterize a multitude of CNTs in a parallel transistor array geometry, foregoing the need to create individual CNT devices in the study of their electronic transport. The diffraction-limited laser spot induces local heating of the CNT and affects overall conductance under applied bias, presenting a spatially-resolved visual image of the CNT in our measurement scheme. Furthermore, this change in conductance displays gate dependence similar to that of overall conductance of the CNT, allowing us to probe the local electronic properties of the CNT simultaneously. Using this technique we are then able to both image with diffraction-limited resolution and electrically characterize up to hundreds of CNTs rapidly in the simplest of device geometries. 1. Y. H. Ahn, A. W. Tsen, B. Kim, Y. W. Park, and J. Park, ``Photocurrent Imaging of p-n Junctions in Amibipolar Carbon Nanotube Transistors,'' \textit{Nano Letters}, vol. 7, no. 11, pp. 3320-3323, 2007. [Preview Abstract] |
Monday, March 10, 2008 5:06PM - 5:18PM |
D30.00012: Modeling Nanotube Networks For Semiconductor Channels and Sensors Meg Noah, Young-Kyun Kwon We present a model to characterize ensembles of NT networks using properties of individual from measurement and from ab initio computations, and including changes in the presence of gases like NH$_{3}$, pressure, or external fields. From these, we simulate networks for user-specified channel shape, size and inhomogeneous NT mixtures. For example, the ensemble \textit{IVg }characteristics of 2 by 2 micron network can readily be compared to ensembles of 20 by 40 micron networks or annular networks with 1 micron and 3 micron radii for a mixure of nanotubes characterized by independent length distributions for each chirality and then compared subjected to different environmental conditions. Validation with experimental data resulting from inhomogeneous NT mixtures is presented. Our goal is to optimize nanomanufacturing parameters like channel size for a user-defined application be it gas sensor, pressure actuator, or semiconductor answering questions like: ``What is the statistical conductivity enhancement in the presence of NO$_{2}$?'' ``What radii yield the most semiconducting for 1 micron SWNT?'' and ``How does conductivity change as a function of gas density?'' We focus on the fundamental understanding of nanocomposites. [Preview Abstract] |
Monday, March 10, 2008 5:18PM - 5:30PM |
D30.00013: The Control of Electron Transport Related Defects in \textit{In situ} Fabricated Single Wall Carbon Nanotube Devices Zhixian Zhou, Alaska Subedi, Gyula Eres, Rongying Jin, David Mandrus Metallic single wall carbon nanotube (SWNT) devices were characterized using low temperature transport measurements to study how the growth conditions affect defect formation in carbon nanotubes. Suspended carbon nanotube devices were grown \textit{in situ} by a molecular beam growth method on a pair of catalyst islands located on opposing Au electrodes fabricated by electron beam lithography. We present experimental evidence that transport related defect formation in carbon nanotubes, in addition to the well known growth temperature dependence, is also affected by the nature and the composition of the carbon growth gases. [Zhou \textit{et al}., Appl. Phys. Lett. 89, 133124 (2006)] We have also investigated how the transport related defects affect the performance of SWNT field-effect-transistors, revealing significantly different impacts of the defects on semiconducting SWNT devices with Schottky and Ohmic contacts. [Zhou \textit{et al}., unpublished] [Preview Abstract] |
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