Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session W28: Focus Session: Carbon Nanotubes: Transport and Thin Films |
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Sponsoring Units: DMP Chair: Yuri Zuev, Columbia University Room: Colorado Convention Center 302 |
Thursday, March 8, 2007 2:30PM - 2:42PM |
W28.00001: Hall Effect and Magnetoresistance of Single-walled Carbon Nanotubes S. H. Jhang, S. H. Lee, U. Dettlaff, D. S. Lee, S. Roth, Y. W. Park, C. Strunk We report Hall coefficient and magnetoresistance measurements on films and networks of single-walled carbon nanotubes (SWNTs). Four different types of SWNTs are prepared as films; Purified SWNTs synthesized either by HiPCO (High-Pressure CO Conversion) process or by laser ablation method (laser SWNTs), and HiPCO and laser SWNTs chemically treated by SOCl$_{2}$. SOCl$_{2}$-modified SWNTs show higher conductivity due to doping effect. The measured Hall voltages are linear for all samples in fields up to 6 T. The carrier density of SWNTs is determined to be $\sim $10$^{22}$ cm$^{-3}$ for HiPCO and SOCl$_{2}$-modified SWNTs, and $\sim $10$^{21}$ cm$^{-3 }$for laser SWNTs. Considering that theoretically predicted carrier density of metallic SWNT is $\sim $10$^{22}$ cm$^{-3}$ and that of semiconducting SWNT is $\sim $10$^{20}$ cm$^{-3}$, the difference in carrier density between HiPCO and laser SWNTs can be originated from the difference in the ratio of metallic and semiconducting SWNTs in both films. While Hall coefficient is positive in the whole temperature range of 1.4 - 300 K for HiPCO and SOCl$_{2}$-modified SWNTs, the Hall coefficient of laser SWNTs interestingly shows a sign change around at T = 15 K. The magnetoresistance of SWNTs studied in high magnetic fields up to 33 T, and in a temperature range of 0.4 - 300 K will be also presented. [Preview Abstract] |
Thursday, March 8, 2007 2:42PM - 2:54PM |
W28.00002: ABSTRACT WITHDRAWN |
Thursday, March 8, 2007 2:54PM - 3:06PM |
W28.00003: Energy Anomaly and Polarizability of Carbon Nanotubes Dmitry Novikov, Leonid Levitov Electron properties of carbon nanotubes can change qualitatively by applying a strong perpendicular electric field. In metallic tubes the sign of Fermi velocity can be reversed by a sufficiently strong field, while in semiconducting tubes the effective mass can change sign. Changes in the spectrum manifest themselves in a breakup of the Fermi surface and in the energy gap suppression, respectively. The effect is controlled by the field inside the tube which is screened due to the polarization induced on the tube. The theory of screening is linked to the chiral anomaly for 1D fermions that reveals universality and scale invariance of the response dominated by $\pi$ electrons. [Phys. Rev. Lett. {\bf 96}, 036402 (2006)] [Preview Abstract] |
Thursday, March 8, 2007 3:06PM - 3:42PM |
W28.00004: Massive Integration of Nanotube/Nanowire-based Devices Invited Speaker: Although nanotube (NT)/nanowire (NW)-based devices are drawing an attention as next generation device architecture, a lack of massive assembly method has been holding back their practical applications. In this talk, we will present a massive integration strategy of NT/NW-based devices, where surface molecular patterns guide the `selective assembly' and `alignment' of various NTs/NWs (e.g. carbon NT, vanadium oxide NWs, etc) on virtually general substrates (e.g. Au, silicon oxide, Si, Al, etc). Interestingly, NT/NW adsorbed on solid substrates exhibit `2-dimensional sliding motions' on the substrates to form desired device structures. This strategy is named here as `surface-programmed assembly' in the sense that entire assembly process can be programmed by surface molecular patterns. This process is utilized for wafer-scale fabrication of NT/NW-based devices such as high-performance transistors and bio-sensors. Importantly, since entire processing steps can be done using only conventional microfabrication facilities without any high-temperature processing, the strategy is readily accessible for conventional device industry and may open up new `NT/NW-silicon hybrid device industry' in the future. [REF: Nature 425, 26 (2003); Nature Nanotechnology 1, 66 (2006)] [Preview Abstract] |
Thursday, March 8, 2007 3:42PM - 3:54PM |
W28.00005: Quantum capacitance and gate coupling in NT array field effect devices Slava V. Rotkin, John A. Rogers Modern electronics may essentially benefit on a new approach to fabricating nanotube field-effect thin film transistors (NT-TFT) that consist of parallel NT arrays with high uniformity of inter-tube spacing and orientation of neighbor NTs. The large density of NTs per channel area allows to improve such device characteristics as drain current and transconductance. Here we address theoretically the issue of a quantum capacitance as a unique feature of the single-wall NT material and its role in transport in the dense or sparse array NT-TFTs. We present a complete electrostatic model joined with the quantum theory of the NT response to investigate the capacitance coupling to the backgate and/or the top gate for the broad range of the TFT device geometry. We vary the NT density, uniformity of the array, dielectric substrate and the top-gate dielectric to study the factors possibly limiting performance of the NT-array TFT. We found that due to the effect of strong electrostatic coupling between neighbor NTs in the TFT channel the device characteristics, such as gate coupling and the conductance related to the latter, are robust even to significant deviations from an ideal geometry. This is discussed with respect to the problem of fabrication of devices with good uniformity at the system level despite of some disorder at the subsystem level of discrete elements. [Supported by NSF-0403489] [Preview Abstract] |
Thursday, March 8, 2007 3:54PM - 4:06PM |
W28.00006: Self-assembled Monolayers of Carbon Nanotubes and Their Properties Vladimir Samuilov, Jaseung Koo, Jean Galibert, Vitaly Ksenevich, Nikolaj Poklonski Electronic and thermal transport properties of carbon nanotubes are of particular interest due to their potential use as components in nano electronics applications. Applications of the \textit{individual} nanotubes are progressing rapidly. However, the electrical and thermal conductivity transport properties of the 2-D layers still fall far short of the properties of the individual carbon nanotubes. We have developed a new method of self-assembling of carbon nanotubes (CNT) into high-density 2-D arrays without prior functionalization based on modified Langmuir-Blodgett technique. The method shows several major advantages over the conventional method of CNT monolayers formation. The electrical, thermal conductivity and magneto-transport properties of the monolayers (arrays) of multi-wall and single-wall carbon nanotubes in the temperature range 1.8-300K and in magnetic fields up to 35 T have been tested. Gas sensing properties of the self-assembled arrays of CNTs are discussed. [Preview Abstract] |
Thursday, March 8, 2007 4:06PM - 4:18PM |
W28.00007: Towards an optimal nanotube dispersion for transparent conductive coatings Matthew Garrett, Ilia Ivanov, Bin Zhao, Alex Puretzky, David Geohegan Thin films of carbon nanotubes have been investigated as a potential material for transparent conductive coatings. There is a range of transmission and resistance that must be met to make the film useful for technological applications, down to 10 $\Omega $/Square at over 80{\%}T. When nanotubes in solution are made into thin films, the electro-optical properties of the film is dependent on the method of dispersion of the tubes used to make the film, in addition to the quality of the starting material used to make the dispersion. At 90{\%}T, the method of dispersion can cause nearly a factor of ten difference, 15000 $\Omega $/Square, in the resulting film's resistance. Aggregates can cause scattering from the film, detracting from its transmission. The length and purity of the tubes affects the overall resistance of the film. The extent of tube bundling also plays an important role in the electro-optical properties of these films. Methods of quantifying the nature of tubes in solution can yield much insight into the quality of the film which will result from the solution. We have shown how a thorough characterization of the tubes during dispersion as well as after deposition is helpful in determining how to achieve the desirable attributes of a transparent conductive film of nanotubes. [Preview Abstract] |
Thursday, March 8, 2007 4:18PM - 4:30PM |
W28.00008: Ambient Formation of Aligned Carbon Nanotube Networks Marcus Lay, Pornnipa Vichchulada Nano-scale electronic materials will play a roll of great significance in electronic devices of the near future. Carbon nanotubes (CNTs), in particular, show great technological promise. Yet, major obstacles to the incorporation of CNTs into practical electronic devices remain; one such challenge is the lack of a method to form ordered constructs of individual carbon nanotubes on a large scale. 2-dimensional networks of CNTs show potential as a method of circumventing the difficulties associates with lack of control over the physical and electrical properties of individual CNTs; for a random distribution of CNTs, the density of the network is the major factor controlling device properties, as fluctuations in characteristics of individual CNTs become less important. Therefore, a 2-D network composed of a mixture of metallic and semiconducting CNTs behaves as a semiconductor above the percolation threshold for semiconducting nanotubes. A novel method of creating ordered arrays of purified CNTs has been developed to attain a higher level of control over reproducibility in CNT-based applications. This method uses unidirectional airflow to order CNTs in aqueous suspension and deposit them on a prepared surface. The result is an electrically continuous array of highly aligned CNTs. These ordered arrays of CNTs exhibit electrical conductivity over macroscopic lengths (up to 3$''$), and have shown promise in field-effect transistor (FET) applications. [Preview Abstract] |
Thursday, March 8, 2007 4:30PM - 4:42PM |
W28.00009: Geometry-dependent resistivity scaling in single-walled carbon nanotube films Ashkan Behnam, Ant Ural We study the resistivity scaling in transparent and conductive carbon nanotube films as a function of nanotube and device parameters. First, we observe experimentally that the nanotube film resistivity exhibits an inverse power law dependence on device width below a critical width of 2 microns. We then use Monte Carlo simulations to model this behavior and to study the effect of four parameters, namely tube-tube contact to nanotube resistance ratio, nanotube density, length, and alignment on resistivity and its scaling with device width. We observe stronger resistivity scaling with device width when the transport characteristics in the film are dominated by tube-tube contact resistance, or when the nanotube density, length, or alignment is increased. We also observe that, near the percolation threshold, the resistivity of the nanotube film exhibits an inverse power law dependence on all of these parameters, which is a distinct signature of percolating conduction. However, the strength of resistivity scaling for each parameter is different. We explain these observations, which are in agreement with experimental work, by simple physical and geometrical arguments. Nanoscale study of percolating transport mechanisms in nanotube films is essential for understanding and characterizing their performance in submicron devices. [Preview Abstract] |
Thursday, March 8, 2007 4:42PM - 4:54PM |
W28.00010: Modeling of Nanotube Network Semiconductors Meg Noah, Young-Kyun Kwon Novel modeling techniques are used to characterize the structural, electronic and optical properties of nanocomposite network semiconductors. Ab initio computations of the structural properties of ensembles of nanotubes on a variety of substrates are presented. We use Monte Carlo and percolation simulations to predict manufacturing success rates given semiconductor design and processing constraints. The performance impact of flattening of nanotubes and topological defects on nanotubes will also be presented. The purpose of this study is to assist experimentalists and to stream-line and optimize nanomanufacturing. Our research focuses on the fundamental understanding of nanostructured materials and their application to molecular electronic devices. [Preview Abstract] |
Thursday, March 8, 2007 4:54PM - 5:06PM |
W28.00011: Microwave Conductivity of Single Wall Carbon Nanotube Arrays C. Highstrete, E.A. Shaner, Mark Lee, F.E. Jones, P.M. Dentinger, A.A. Talin We have measured the microwave conductivity spectra of carbon nanotube (CNT) parallel arrays from room temperature to 4K. Single wall CNTs were assembled by AC dielectrophoresis into parallel arrays of individual CNTs and ropes spanning the electrodes of coplanar waveguides (CPWs). The CPW complex reflection and transmission coefficients were measured from 0.1 to 50 GHz. Measurements of identical bare CPWs were utilized to calculate the frequency dependent complex conductivity and power dissipation of the CNT arrays and provide estimates of these quantities for individual CNTs in this configuration. Small loss due to the CNT arrays is consistently measured and increases with frequency. [Preview Abstract] |
Thursday, March 8, 2007 5:06PM - 5:18PM |
W28.00012: Kohn anomalies and non-adiabaticity in doped carbon nanotubes A. Marco Saitta, Nicolas Caudal, Michele Lazzeri, Francesco Mauri The tangential vibrational modes of metallic single-walled carbon nanotubes (SWNTs) are thought to be characterized by Kohn anomalies resulting from the combination of their intrinsic one-dimensional nature and a significant electron- phonon coupling. These properties are modified by the doping- induced tuning of the Fermi energy level $\epsilon_F$, obtained through the intercalation of SWNTs with alkali atoms or the application of a gate potential. We present a Density- Functional Theory (DFT) study of the vibrational properties of a (n,n) metallic SWNT as a function of electronic doping. For such study, we use, as in standard DFT calculations of vibrational properties, the Born-Oppenheimer (BO) approximation, but we also use time-dependent perturbation theory to explore non-adiabatic effects beyond this approximation. We compare our results with existing measurements and suggest features to be explored in future experiments. [Preview Abstract] |
Thursday, March 8, 2007 5:18PM - 5:30PM |
W28.00013: Radiation Protection Materials for Space Missions and Industries Ram Tripathi NASA has a new vision for space exploration in the 21st Century encompassing a broad range of human and robotic missions including missions to Moon, Mars and beyond. Exposure from the hazards of severe space radiation in deep space long duration missions is ``the show stopper.'' The great cost of added radiation shielding is a potential limiting factor in deep space missions. In the enabling technology, we have developed methodology and concomitant technology for optimized shield design over multi-segmented missions involving multiple work and living areas in the transport and duty phase of space missions. The total shield mass over all pieces of equipment and habitats is optimized subject to career dose and dose rate constraints. Studies have been made for various missions. Current technology is adequate for low earth orbit missions. Revolutionary materials need to be developed for career astronauts and deep space missions. The details of this new technology and its impact on space missions and other technologies will be discussed. [Preview Abstract] |
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