Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session H27: Focus Session: Carbon Nanotubes: Electronic Properties I |
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Sponsoring Units: DMP Chair: Tony Heinz, Columbia University Room: LACC 501C |
Tuesday, March 22, 2005 8:00AM - 8:36AM |
H27.00001: Spin Transport in Carbon Nanotubes Invited Speaker: We report on spin transport in carbon nanotubes. First, spin injection in arc-discharge grown multi-walled carbon nanotubes (MWNTs) is achieved by using a ferromagnetic PdNi alloy as contact material. The two contacts, i.e. source and drain, have different shape rendering different magnetic switching fields. Typical two-terminal resistances are in the range of 5-100 kOhm. We find a tunneling magneto resistance (TMR) signal amounting to 2.5-3{\%}. Secondly, we explore the TMR signal as a function of temperature T, source-drain voltage Vsd, and gate voltage Vg. As expected the TMR signal decays with T and Vsd. Remarkably, however, we find a sign change in the spin signal (the TMR signal) as a function of both Vsd and Vg. This work has been done in collaboration with: S. Sahoo and T. Kontos (Univ. of Basel), C. S\"{u}rgers (Univ. of Karlsruhe), and L. Forro (EPFL Lausanne). [Preview Abstract] |
Tuesday, March 22, 2005 8:36AM - 8:48AM |
H27.00002: Electron Transport in Ferromagnetically-Contacted Single-Walled Carbon Nanotubes Chris Merchant, Soo-Hyung Lee, Jeffrey Wasserman, Nina Markovic We present low-temperature electron transport measurements on ferromagnetically-contacted single-walled carbon nanotubes in the Coulomb blockade regime. The carbon nanotubes were grown by the chemical vapor deposition method and end-contacted with cobalt leads spaced less than 500 nm apart. Due to the Coulomb blockade effects, conduction occurs via either single-electron tunneling or higher-order processes, which can involve spin modulation. The effect of Coulomb blockade on magnetoresistance is investigated and discussed in terms of spin transport. [Preview Abstract] |
Tuesday, March 22, 2005 8:48AM - 9:00AM |
H27.00003: Characterization of noise and dynamic fluctuations in carbon nanotubes Derek Kingrey, Philip G. Collins Carbon nanotubes (CNTs) are promising realizations of nanoscale electronics except for the dominant excess noise at low frequencies, which remains poorly understood. A full characterization of this noise on CNT transistor devices has been completed in the temperature range of 77 -- 500K. The noise power spectral density (PSD) exhibits a combination of features, including strong deviations from 1/f behavior at the phase transitions of common contaminants including nitrogen and water. This indicates these adsorbates play key roles in CNT conduction even in high vacuum after high temperature degassing. We will present a comparison of measurements performed in air and in vacuum and further compare the noise to what can be achieved using encapsulated, forming-gas annealed devices. [Preview Abstract] |
Tuesday, March 22, 2005 9:00AM - 9:12AM |
H27.00004: Quantum Shot Noise Suppression in Single-walled Carbon Nanotubes Na Young Kim, Jing Kong, William Oliver, Hongjie Dai, Yoshihisa Yamamoto We investigate the nonequilibrium transport properties of individual single-walled carbon nanotubes via differential conductance and the low frequency current fluctuations at liquid helium temperature. Both the conductance and the shot noise show two distinct regimes separated by the size of the applied voltage relative to one-dimensional subband energy spacing. While the Fabry-Perot interference pattern in the differential conductance as evidence of ballistic transport in the tube device is clearly visible for low bias voltages, the pattern dies out as the bias voltage increases. In addition, the shot noise of the tubes is strongly suppressed for high bias voltages, and the degree of reduction exceeds the predicted estimate for a non-interaction electron system. Experimental results suggest the electron interactions in one-dimensional quantum wires play an important role. [Preview Abstract] |
Tuesday, March 22, 2005 9:12AM - 9:24AM |
H27.00005: Coulomb Oscillations and Hall Effect in Quasi-2D Graphite Quantum Dots Scott Bunch, Yuval Yaish, Markus Brink, Kirill Bolotin, Paul McEuen We perform low temperature electrical transport measurements on gated, quasi-2D graphite quantum dots. In devices with low contact resistances, we use longitudinal and Hall resistances to extract carrier densities of 9.2-13 x 10$^{12}$ cm$^{-2}$ and mobilities of 200-1900 cm$^{2}$/V-s. In devices with high resistance contacts, we observe Coulomb blockade phenomena and infer the charging energies and capacitive couplings. These experiments demonstrate that electrons in mesoscopic graphite pieces are delocalized over nearly the whole graphite piece down to low temperatures. [Preview Abstract] |
Tuesday, March 22, 2005 9:24AM - 9:36AM |
H27.00006: Persistent Four-Electron Shell Filling in Carbon Nanotubes Alexander Makarovski, Alexey Zhukov, Jie Liu, Gleb Finkelstein We report on our measurements of electron conductivity in single-walled carbon nanotube devices in the Coulomb Blockade regime. Persistent four-fold grouping of the Coulomb blockade peaks was observed over an extended range of gate voltages. This grouping reflects the four-fold degeneracy of the electron levels (two spin directions and two valleys). We discuss the energy levels, excited states, and inelastic co-tunneling events extracted from the I(V) spectroscopy of the system. [Preview Abstract] |
Tuesday, March 22, 2005 9:36AM - 9:48AM |
H27.00007: Probing the Conductivity of Single-Walled Carbon Nanotubes by THz Time-Domain Spectroscopy Yang Wu, Feng Wang, Gordana Dukovic, Michael Loy, Louis Brus, Tony Heinz Terahertz time-domain spectroscopy has been applied to examine the transient conductivity of single-walled carbon nanotubes (SWNTs). The sample, consisting of isolated SWNTs in a polymer matrix, was interrogated by a freely propagating THz electromagnetic transient after excitation by a femtosecond laser pulse. The photo-induced change of the SWNTs is characterized by an increase in the THz absorption. This behavior suggests that the dominant contribution to the signal arises from free charge carriers, rather than strongly bound states like excitons. The decay of the THz conductivity occurs on the time scale of picoseconds, comparable to that observed for fluorescence emission.$^{1-3}$ The THz response shows a nonlinear dependence on the excitation laser fluence, with strong saturation for fluences above 0.1 J/m$^{2}$. The implications of these results for carrier dynamics in SWNTs will be considered. $^{1 }$F. Wang et al., Phys. Rev. Lett. \textbf{92}, 177401 (2004). $^{2 }$Y. Z. Ma et al., J. Chem. Phys. \textbf{120}, 3368 (2004). $^{3 }$F. Wang et al., Phys. Rev. B (in press). [Preview Abstract] |
Tuesday, March 22, 2005 9:48AM - 10:24AM |
H27.00008: Local Gate Control in Carbon Nanotube Quantum Devices Invited Speaker: Carbon nanotubes exhibit many properties which make them ideal candidates for applications in coherent electronic devices for quantum computation.We have made significant technological advancements in device fabrication,for the creation of multiple spatially localized electrostatic gates on a single nanotube device. These advancements permit a previously unattainable level of device control in the quantum regime, essential forelectronic logic operations. Our measurements have demonstrated independent gate control in nanotube double quantum dots defined by naturally occurring tunnel barriers [1], as well as the controllable formation of intratube quantum point contacts [2]. In these devices conductance quantization is evident in units of e2/h, suggesting that both band and spin degeneracies may be lifted at zero magnetic field. Local gating has also permitted the fabrication of fully gate-defined intratube quantum dots with gate-tunable tunnel barriers. Multiple quantum dots with independent control over charge number and tunneling rates have been demonstrated [3], raising the functionality of carbon nanotube devices to match that of standard semiconductor heterostructures. New devices incorporating integrated RF-SETs, and microwave studies of gate-defined intratube quantum dots will be discussed.$\backslash $[1] Science 303 p.655, 20042] PRL in press, cond-mat/04066523] To be published [Preview Abstract] |
Tuesday, March 22, 2005 10:24AM - 10:36AM |
H27.00009: Frequency-Modulation Imaging of Quantum Dots in Carbon Nanotubes Markus Brink, J. Zhu, Paul L. McEuen We use Frequency-Modulation Imaging (FM-AFM) at 4K to probe single electron charging events of quantum dots in semiconducting carbon nanotubes. This technique does not require conduction across the carbon nanotube device, thereby enabling us to image the first few charge states of the dots. The charging energy can be extracted from the amplitude of the frequency modulation signal. In addition, we observe avoided crossings in the charging spectrum of neighboring dots due to coupling. [Preview Abstract] |
Tuesday, March 22, 2005 10:36AM - 10:48AM |
H27.00010: Electrical properties of 0.4 cm long single walled nanotubes Zhen Yu, Christopher Rutherglen, Shengdong Li, Peter Burke Centimeter scale aligned carbon nanotube arrays are grown from nanoparticle/metal catalyst pads[1]. We find the nanotubes grow both with and ``against the wind.'' A metal underlayer provides in-situ electrical contact to these long nanotubes with no post growth processing needed. Using the electrically contacted nanotubes, we study electrical transport of 0.4 cm long nanotubes[2]. Using this data, we are able to determine the resistance of a nanotube as a function of length quantitatively, since the contact resistance is negligible in these long nanotubes. The source drain I-V curves are quantitatively described by a classical, diffusive model. Our measurements show that the outstanding transport properties of nanotubes can be extended to the cm scale and open the door to large scale integrated nanotube circuits with macroscopic dimensions. These are the longest electrically contacted single walled nanotubes measured to date. [1] Zhen Yu, Shengdong Li, Peter J. Burke, ``Synthesis of Aligned Arrays of Millimeter Long, Straight Single-Walled Carbon Nanotubes,'' Chemistry of Materials, 16(18), 3414-3416 (2004). [2] Shengdong Li, Zhen Yu, Christopher Rutherglen, Peter J. Burke, ``Electrical properties of 0.4 cm long single-walled carbon nanotubes'' Nano Letters, 4(10), 2003-2007 (2004). [Preview Abstract] |
Tuesday, March 22, 2005 10:48AM - 11:00AM |
H27.00011: Electrical and thermal transport in metallic carbon nanotubes Marcelo Kuroda, Jean-Pierre Leburton The interpretation of the non-linear I-V characteristics of metallic single wall carbon nanotubes under electric stress has been particularly puzzling because the role played by Joule heating remains an open question [1]. In this talk, we present an electron transport model, which takes into account thermal heating in metallic single wall carbon nanotubes. The model is based on the solution of the Boltzmann equation in presence of electron-(optical)phonon scattering, in which heat production/dissipation determines self-consistently the local temperature in the nanotube. Not only does our model reproduce the features of the IV characteristics as a function of tube length but also predicts the electrical breakdown of the nanotube. This work is supported by the Beckman Institute and NSF through the National Computation Network at Purdue University. [1] P.G. Collins et al, Phys. Rev. Lett. 86, 3128 (2001) [Preview Abstract] |
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