Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session J31: Transport in Carbon Nanotubes: Experiment |
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Sponsoring Units: DCMP Chair: Bhupesh Chandra, Columbia University Room: Colorado Convention Center 401 |
Tuesday, March 6, 2007 11:15AM - 11:27AM |
J31.00001: Transport in Carbon Nanotube -- Polymer Field Emission Cathodes. David Carey, Richard Smith Embedding carbon nanotubes in host polymer matrices is an attractive way to control the nanotube density and provides a way to protect the nanotube emitter. Field emission from individual carbon nanotubes is usually discussed in terms of the field enhancement factor and electrostatic screening. The field enhancement factor can be regarded as the most important factor for efficient emission when transport of electrons is not the rate limiting step. Large area emission characterisation of cathodes tends to produce an ensemble average of the enhancement factor with sites with the lowest local turn on field emitting. We show that in nanotube polymer composites charge transfer through the composite and the effects of fluctuation induced tunneling due to variable nanotube-nanotube separation are important considerations. [Preview Abstract] |
Tuesday, March 6, 2007 11:27AM - 11:39AM |
J31.00002: A comparative study of transport properties between low- and high-resistance nanotube field-effect transistors Swastik Kar, Aravind Vijayaraghavan, Caterina Soldano, Pulickel Ajayan A large amount of fundamental work has been done in demonstrating the possibilities of using carbon nanotubes in future nanoscale devices. A primary concern in these devices has been the nature of transport mechanism in carbon nanotubes, especially semiconducting nanotubes where the conductance can be modulated significantly using a gate voltage, giving rise to a nanotube field-effect transistor. The quality of the metal-nanotube interface plays a significant role in determining the characteristics of field-effect transistors fabricated using single-wall carbon nanotubes. When contact-resistance is high due to a large Schottky barrier, the transistor characteristics are dominated by this barrier. When the barrier height is low, the intrinsic nanotube electronic properties determine the transistor characteristics. In this work, we compare and contrast the significant features of the transistor characteristics for the two types of devices. [Preview Abstract] |
Tuesday, March 6, 2007 11:39AM - 11:51AM |
J31.00003: Transport properties of metallic nanocluster impregnated multi wall carbon nanotubes Caterina Soldano, Swastik Kar, Saikat Talapatra, Saroj Nayak, Pulickle Ajayan Artificially engineered low-dimensional heterostructures form a class of extremely exciting new materials for fundamental and applied research. One such very interesting system is the formation of arrays of metallic nanoclusters confined to one-dimension, within the scaffolding of another one dimensional material. A good example of this kind of a system is metal-nanocluster-impregnated carbon nanotubes. In this work, we report the fabrication of nanoscale heterostructures in the form of ferromagnetic metal nanocluster array impregnated multi wall carbon nanotubes. The nanoclusters can be impregnated into the nanotubes by a simple electrochemical technique. Two and four terminal devices with such individual nanoarchitectures have been fabricated using a combination of photo- and focused ion beam lithography. The systems form extremely exciting platforms for investigating charge and spin transport in confined geometries. We present preliminary data on the electrical properties of these novel systems at room and low temperatures. [Preview Abstract] |
Tuesday, March 6, 2007 11:51AM - 12:03PM |
J31.00004: Electronic transport in loops comprised of individual carbon nanotubes Jinseong Heo, Gil Refael, Marc Bockrath We discuss electronic transport in loops comprised of individual carbon nanotubes. The conductance versus gate voltage shows oscillations with a number of periods. These oscillations persist up to temperatures $\sim $50 K. We compare our results with a model [Dear APS organizers: please note the theoretical talk on the same subject given by Gil Refael. We would like to reference this talk if possible in this abstract.] that accounts \newline for the interference of counterpropagating electron waves around the loop, analogous to a Sagnac interferometer in optics. In this model, the different velocities for right and left movers in the two carbon nanotube bands produce large energy scale interference oscillations. We find semi-quantitiative agreement between our data and the theory. These results may enable phase coherence in nanotubes to be studied up to temperatures much higher than the cutoff imposed by thermal smearing. [Preview Abstract] |
Tuesday, March 6, 2007 12:03PM - 12:15PM |
J31.00005: Sagnac interference in Carbon nanotube loops Gil Refael, Jinseong Heo, Marc Bockrath Some of the most pronounced manifestations of electron interference effects occur in carbon-nanotubes. When a nanotube is made to form a loop, a new large-period mode of interference appears in the conductance measured as a function of gate-voltage or source-drain voltage. The periodicity of the fringes is determined by the velocity detuning between right- and left-moving electrons, thus the nanotube loop forms a Sagnac interferometer which precisely measures this detuning. In our work we explore this effect in strongly interacting Carbon nanotubes, and carefully consider the response to the gate and source-drain voltages. [Preview Abstract] |
Tuesday, March 6, 2007 12:15PM - 12:27PM |
J31.00006: Electronic transport across a Carbon nanotube Heterojunction: Experimental observations of high temperature Coulomb Charging and level spacing. Bhupesh Chandra, Yang Wu, Meninder Purewal, Mingyuan Huang, Hugen Yan, Limin Huang, Stephen Brien, Tony Heinz, Philip Kim, James Hone We present electrical transport measurements of individual a single-wall carbon nanotube in which the chiral indices (n, m) are not fixed along the nanotube length. These kinds of structures are known to show strong rectifying behavior in current voltage characteristics. At low temperatures the device essentially behaves like a quantum dot with very high charging energy and level-spacing. These features can be seen till 70K also, making it a high temperature single electron transistor. [Preview Abstract] |
Tuesday, March 6, 2007 12:27PM - 12:39PM |
J31.00007: Thermomagnetic Measurements of Transport in Single Walled Carbon Nanotubes J. P. Heremans, C. M. Thrush, V. Jovovic, J. West The thermomagnetic transport properties of single walled carbon nanotubes bundles and mats in high magnetic fields have been measured in vacuum and in the presence of noble gases. They are used to determine mechanism responsible for change in thermopower and resistivity in the presence of gases with respect to one measured in high vacuum. The thermopower and its change in a magnetic field is recorded in Ne, Ar, Xe atmospheres. The variation of the zero-field thermopower with the presence of noble gases is consistent with that observed recently [1]. The magnetothermopower in a saturating magnetic field is only 0.2{\%} larger than the zero-field thermopower. As the magnetothermopower in high field is independent of the scattering mechanism, this result argues in favor of diffusion mechanism as responsible for variations in transport properties, and against the recently suggested concept that collisions between gas molecules and the nanotubes are responsible for the changes in thermopower. \newline \newline [1] H. E. Romero, K. Bolton, A. Tosen and P. C. Eklund, Atom Collision-induced Resistivity of Carbon Nanotubes, Science 307 89 (2005) [Preview Abstract] |
Tuesday, March 6, 2007 12:39PM - 12:51PM |
J31.00008: Observation of unusual structure in the low-temperature conductance of carbon nanotubes Jeffrey D. Stephens, Jerome C. Licini, A.T. Charlie Johnson, Douglas R. Strachan, Sam Khamis, Danvers E. Johnston Carbon nanotubes grown by chemical vapor deposition on a oxidized silicon substrate were contacted to form a gated sample consisting of a pair of tubes in parallel. The sample was tested at low temperature and high magnetic field using a dilution refrigerator and superconducting magnet. The current versus bias voltage graph shows a general trend consistent with the linear relationship except at low voltage. Further investigation is done by computing the differential conductance (dI/dV) and investigating how it varies with bias voltage. Here we see some intriguing behavior including a substantial increase in conductivity near zero voltage and a pronounced asymmetry with bias voltage. The temperature dependence of the zero field peak and asymmetry show that they appear at low temperatures and receding quickly by 3.0K. However, the magnetic field dependence is less intuitive. There are apparent shifts and possible splits that seem to develop but they are not followed in a manner consistent with simple theory. [Preview Abstract] |
Tuesday, March 6, 2007 12:51PM - 1:03PM |
J31.00009: Low temperature electron transport measurements of dielectrophoretically assembled single wall carbon nanotube Paul Stokes, Liwei Liu, Saiful Khondaker Dielectrophoretic (DEP) assembly of carbon nanotube (CNT) has attracted tremendous interests because of its usefulness in assembling CNT at selected positions in nanoelectronic circuits with high yield. Although DEP technique has been used to fabricate nanoelectronic devices, the effect of contact resistance and nanotube buckling at the electrode-substrate interface has not been examined. Here, we present electronic transport measurements of DEP assembled single wall carbon nanotubes from room temperature to 1.5 K to examine the contact resistance and nanotube buckling. The nanotubes were suspended in dimethylformamide (DMF) and assembled between gold or palladium electrodes by the application of an AC electric field. A fundamental understanding of the contact resistance and buckling behavior will lead to improved designing of DEP assembled devices. [Preview Abstract] |
Tuesday, March 6, 2007 1:03PM - 1:15PM |
J31.00010: Electrical transport through tunable pn junctions in suspended carbon nanotubes Ferdinand Kuemmeth, Shahal Ilani, P. L. McEuen, D. C. Ralph Energy barriers play a crucial role within many carbon nanotube electronic devices, but their properties are often complicated by disorder induced by a substrate. Here we study well-controlled pn junctions in suspended carbon nanotubes whose transparency and position can be tuned using electrostatic gates. To achieve this we suspend individual single walled nanotubes above two separate gate electrodes and monitor the tube's conductance while changing the gate voltages in various ways; by varying the voltage difference between both gates we can tune the pn junction's width, whereas offsetting both gates by a common voltage controls its position. In small bandgap nanotubes we can additionally tune the junction's transparency by axial magnetic fields. At low temperature, these devices allow measurements of quantum dots with a tunable length and coupling to the leads. [Preview Abstract] |
Tuesday, March 6, 2007 1:15PM - 1:27PM |
J31.00011: Scaling of Resistance with Channel Length in Single Walled Carbon Nanotubes. Meninder Purewal, Byung Hee Hong, Aniruddh Ravi, Bhupesh Chandra, James Hone, Philip Kim We report on the scaling of resistance with channel length in single walled carbon nanotubes (SWNTs) with multiple Pd Ohmic contacts. The channel lengths range from 100nm to 400um. The intrinsic 1-D resistivity of individual SWNTs are measured from the slope of the linear dependence of resistance and length. The temperature dependent electron mean free length can be obtained from these data. While the mean free length ranges 100-500 nm at room temperature, the low temperature saturated value shows values as high as $\sim $10um. In addition, we will discuss possible mechanisms for the deviation from linear scaling behavior, as seen in long length scales ($>$100um). Finally, we will report unusual strong suppression of conductance outside of the band gap regions of several SWNTs deviating from typical small and large band gap semiconducting SWNTs. [Preview Abstract] |
Tuesday, March 6, 2007 1:27PM - 1:39PM |
J31.00012: Magnetic and Transport Properties of Carbon Nanotube-Based One-Dimensional Nanocomposite Materials Adam Friedman, Latika Menon, Jesse Silverberg, Yung Joon Jung Carbon nanotubes (CNTs) prove to be extremely well suited for the investigation of electron conduction in one-dimensional materials. CNTs have been shown to conduct in the ballistic regime according to Landauer's formula. When placed in electromagnetic fields and at low temperatures where the mean free path is smaller than the diameter of the tube, CNTs been shown to be the perfect platform to study Luttinger liquid behavior, the Kondo effect and quantum fluctuations, electron coherence, and the Aharonov-Bohm effect. These unique properties can be further enhanced by inserting materials into the cavities of the CNTs. In this work, we use anodized porous alumina templates as a substrate for the controlled growth of CNTs by means of chemical vapor depostion. AC electrodeposition is then used to deposit Fe, Ni, Co, as well as semiconductor nanowires inside the tubes. The magnetic and electrical properties of such nanotube-nanowire composites (both single and bundled) in the presence of applied magnetic fields upto 5.5T and at low temperatures down to 4.2K are studied and preliminary results will be reported. [Preview Abstract] |
Tuesday, March 6, 2007 1:39PM - 1:51PM |
J31.00013: One-Dimensional Carbon Nanotube Electrodes Carla Aguirre, Benoit St. Antoine, Mathieu Paillet, Patrick Desjardins, Richard Martel The study of the transport properties of organic semiconducting materials has been limited by the lack of suitable electrical contacts. Inappropriate charge injection at the electrode - organic semiconductor interface results in large contact resistances that often dominate device performance. We describe a strategy for circumventing charge injection barriers by using 1D metallic carbon nanotube electrodes. The favorable electrostatics at the tip of an individual carbon nanotube allows for efficient field assisted charge injection into organic semiconducting layers. A detailed finite element numerical study has allowed us to determine the scaling parameters required to optimize the performance of carbon nanotube electrodes. We present experimental results for pentacene organic thin-film transistors connected using individual metallic carbon nanotube source and drain contacts. Different gate oxide thicknesses (20 - 100 nm), channel lengths ( 2 - 100 nm) and carbon nanotube diameters (1 - 3 nm) were explored using experimental and numerical techniques. [Preview Abstract] |
Tuesday, March 6, 2007 1:51PM - 2:03PM |
J31.00014: Heat Transport in Carbon Nanotubes Measured using Raman Spectroscopy I-Kai Hsu, Michael Pettes, Rajay Kumar, Li Shi, Stephen Cronin We investigate thermal transport in suspended carbon nanotubes on micromachined heating devices using Raman spectroscopy. Individual carbon nanotubes suspended between two membranes with integrated heaters and thermometers are characterized using micro-Raman spectroscopy. The temperature dependent shifts of the Raman mode frequencies are used to quantify the heating along the length of the nanotube. We find that results vary depending on the number of defects in the nanotube. The results are understood on the basis of a diffusive thermal transport model. [Preview Abstract] |
Tuesday, March 6, 2007 2:03PM - 2:15PM |
J31.00015: Breakdown of Fourier's law in nanotube thermal conductors Chih-Wei Chang, David Okawa, Henry Garcia, Arunava Majumdar, Alex Zettl We present experimental evidence that the room temperature thermal conductivity ($\kappa )$ of individual multiwall carbon nanotubes and boron-nitride nanotubes does not obey Fourier's law as do ordinary thermal conductors. By varying the length (L) of the nanotube, we find that $\kappa $ diverges as L$^{0.6\sim 0.9}$. Our results show that Fourier's law is violated despite the fact that the ballistic phonon condition is not satisfied and large isotopic disorder is present. [Preview Abstract] |
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