Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session V28: Focus Session: Carbon Nanotubes and Related Materials: Devices III |
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Sponsoring Units: DMP Chair: Ralph Krupke, Karlsruhe Institute of Technology, Germany Room: C156 |
Thursday, March 24, 2011 8:00AM - 8:12AM |
V28.00001: High Frequency Rectification by Carbon Nanotube Schottky Diodes Enrique D. Cobas, Steven M. Anlage, Michael S. Fuhrer Carbon nanotubes (CNTs) display many properties that make them appealing for RF electronics, including room-temperature mean- free paths approaching 1 $\mu$m and a carrier mobility of 10$^5$ cm$^2$ / Vs. Further, small junction capacitances on the order of 10 aF promise cut-off frequencies approaching 1 THz, but high impedances make microwave measurements of individual CNTs challenging. We have fabricated single and few-tube CNT Schottky diodes on high-frequency compatible substrates and measured their ac rectification as a function of dc bias, ac power and frequency, up to 40 GHz. The bias dependence of the cut-off frequency is used to extract the effective junction capacitance for diodes of various channel lengths. This capacitance is found to have a weak dependence on applied bias and a strong relation to channel length. Electrostatic simulations corroborate that stray capacitance from the 1D channel to the metal electrode dominates over the effect of carrier depletion near the junction. The results demonstrate that chottky rectification is a viable method of probing transport in high-impedance semiconducting nanostructures. [Preview Abstract] |
Thursday, March 24, 2011 8:12AM - 8:24AM |
V28.00002: Logarithmic time response of carbon nanotube field-effect transistors Andrew Tunnell, Vince Ballarotto, Merijntje Bronsgeest, John Cumings When observing the source-drain current of a carbon nanotube field effect transistor (FET) held at constant bias, several different processes can produce a time response of the current, including fluctuations due to current noise, heating of contacts, and releasing of trapped charges in the gate dielectric. This third phenomenon is investigated by pulsing voltages on the gate and observing the source-drain current over time. Instead of a typical exponential decay with one or a few time constants, the current was observed to decrease linearly with the logarithm of time, possibly indicating exponential decay with multiple time constants. This trend was seen to continue for over 20 hours, which spans five orders of magnitude in time with respect to the measurement resolution. This trend of scaling logarithmically with time is also seen with the rate of current change with respect to a gate voltage pulse width. This behavior has been investigated in various FET geometries and different materials, all with comparable results. These measurements may be a new way to investigate and characterize the hysteresis in carbon nanotube FETs and the materials used in their fabrication. [Preview Abstract] |
Thursday, March 24, 2011 8:24AM - 8:36AM |
V28.00003: Mirage Effect From Thermally-Modulated Transparent Carbon Nanotube Sheet Ali Aliev, Ray Baughman The single beam mirage effect, also known as photothermal deflection, is studied using a free-standing, highly-aligned carbon nanotube sheet as a heat source whose temperature can be modulated over a wide frequency range. The extremely low thermal capacitance and high heat transfer ability of these transparent forest-drawn carbon nanotube sheets enables high frequency modulation of sheet temperature over an enormous temperature range, thereby providing a sharp, rapidly changing gradient of refractive index in surrounding liquid or gas. The advantages of temperature modulation using carbon nanotube sheets are multiple: in inert gases the temperature can reach $>$2500 K; the obtained frequency range for photothermal modulation is $\sim $100 kHz in gases and over 100 Hz in high refractive index liquids; and the heat source is transparent for optical and acoustical waves. The remarkable light deflection in gases and liquids suggests possible application of carbon nanotube sheets for large laser projectors and cloaking systems. [Preview Abstract] |
Thursday, March 24, 2011 8:36AM - 8:48AM |
V28.00004: Application of Carbon Nanotube Assemblies for Sound Generation and Heat Dissipation Mikhail Kozlov, Carter Haines, Jiyoung Oh, Marcio Lima, Shaoli Fang Nanotech approaches were explored for the efficient transformation of an electrical signal into sound, heat, cooling action, and mechanical strain. The studies are based on the aligned arrays of multi-walled carbon nanotubes (MWNT forests) that can be grown on various substrates using a conventional CVD technique. They form a three-dimensional conductive network that possesses uncommon electrical, thermal, acoustic and mechanical properties. When heated with an alternating current or a near-IR laser modulated in 0.01--20 kHz range, the nanotube forests produce loud, audible sound. High generated sound pressure and broad frequency response (beyond 20 kHz) show that the forests act as efficient thermo-acoustic (TA) transducers. They can generate intense third and fourth TA harmonics that reveal peculiar interference-like patterns from ac-dc voltage scans. A strong dependence of the patterns on forest height can be used for characterization of carbon nanotube assemblies and for evaluation of properties of thermal interfaces. Because of good coupling with surrounding air, the forests provide excellent dissipation of heat produced by IC chips. Thermoacoustic converters based on forests can be used for thermo- and photo-acoustic sound generation, amplification and noise cancellation. [Preview Abstract] |
Thursday, March 24, 2011 8:48AM - 9:00AM |
V28.00005: Thermoelectric Transport Through Arrays Of Carbon Nanotube Junctions Irma Kuljanishvili, Jim Choe, Venkat Chandrasekhar, Serhii Shafraniuk The work addresses the voltage-controlled thermal flow and electric current through the carbon nanotube (CNT) junction arrays. The CNT thermoelectric generation (TEG) promises a high efficiency for thermal and electric energy conversion in a variety of applications. [1] The energy generation had been studied using advanced methods of the condensed matter physics and nanotechnology. We will outline our experimental findings based on CNTs - TEG devices. We will report on our results that involve TEG-CNTs devices in array and /or single CNTs junctions geometries. We will describe fabrications protocols for preferential CVD growth of CNTs and nanoscale precision patterning of the catalyst on predefined device architectures. Electronic transport and optical properties of the CNTs-TEG nanostructures will also be discussed. I.K. and S.S. acknowledge support from the U.S. Army CECOM Acquisition Center {\#}W909MY-10-C-0032. I.K. acknowledge collaboration with NanoInk Inc. [Preview Abstract] |
Thursday, March 24, 2011 9:00AM - 9:12AM |
V28.00006: Carbon nanotube quantum dot in a dissipative environment Henok Mebrahtu, Ivan Borzenets, Yuriy Bomze, Alex Smirnov, Gleb Finkelstein We study conductance through a resonant level in a single-walled carbon nanotube quantum dot embedded in a dissipative environment. The dissipation is provided by environmental modes in the nanotube leads and the strength of the dissipation is experimentally controlled in several samples. At base temperature, dissipation suppresses the resonant tunneling peak height while maintaining resonant level width. We also observe a regime where the height and the width of a conductance peak demonstrate qualitatively different energy scaling. [Preview Abstract] |
Thursday, March 24, 2011 9:12AM - 9:48AM |
V28.00007: Energy Dissipation and Transport in Carbon Nanotube Devices Invited Speaker: Power consumption is a significant challenge in electronics, often limiting the performance of integrated circuits from mobile devices to massive data centers. Carbon nanotubes have emerged as potentially energy-efficient future devices and interconnects, with both large mobility and thermal conductivity. This talk will focus on understanding and controlling energy dissipation [1-3] and transport [4-6] in carbon nanotubes, with applications to low-energy devices, interconnects, heat sinks, and memory elements [7]. Experiments have been used to gain new insight into the fundamental behavior of such devices, and to better inform practical device models. The results suggest much room for energy optimization in nanoelectronics through the design of geometry, interfaces, and materials. \\[4pt] [1]. E. Pop, ``Energy Dissipation and Transport in Nanoscale Devices,'' Nano Research 3, 147 (2010). \\[0pt] [2]. Z.-Y. Ong and E. Pop, ``Molecular Dynamics Simulation of Interfacial Thermal Resistance between Single-Wall Carbon Nanotubes and SiO2,'' Phys. Rev. B 81, 155408 (2010). \\[0pt] [3]. A. Liao, R. Alizadegan, Z.-Y. Ong, S. Dutta, F. Xiong, K. J. Hsia, E. Pop, ``Thermal Dissipation and Variability in Electrical Breakdown of Carbon Nanotube Devices,'' Phys. Rev. B 82, 205406 (2010). \\[0pt] [4]. A. Liao, Y. Zhao, E. Pop, ``Avalanche-Induced Current Enhancement in Semiconducting Single-Walled Carbon Nanotubes,'' Phys. Rev. Lett. 101, 256804 (2008). \\[0pt] [5]. Y. Zhao, A. Liao, E. Pop, ``Multiband Mobility in Semiconducting Carbon Nanotubes,'' IEEE Elec. Dev. Lett. 30, 1078 (2009). \\[0pt] [6]. D. Estrada, A. Liao, S. Dutta, E. Pop, ``Reduction of Hysteresis for Carbon Nanotube Mobility Measurements Using Pulsed Characterization,'' Nanotechnology 21, 085702 (2010). \\[0pt] [7]. F. Xiong, A. Liao, E. Pop, ``Inducing Chalcogenide Phase Change with Ultra-Narrow Carbon Nanotube Heaters,'' Appl. Phys. Lett. 95, 243103 (2009). [Preview Abstract] |
Thursday, March 24, 2011 9:48AM - 10:00AM |
V28.00008: Proximal heating by a current-carrying nanotube Kamal H. Baloch, Norvik Voskanian, Merijntje S. Bronsgeest, John Cumings The 1D nature of carbon nanotubes makes them an excellent candidate for thermal management and thermal logic devices. Using an established thermal measurement technique based on the melting of indium islands [1], we have studied the thermal characteristics of Joule-heated MWNTs. Our experimental observations contradict prevailing theoretical models for heat dissipation in CNT. Despite the high thermal contact resistance between the CNT and the substrate we observe that a current-carrying nanotube dissipates power readily into the substrate, suggesting an alternate mode of heat transport based on scattering of hot electrons in the CNT from the substrate phonons. Experimental results, simulations, and a review of the experimental technique will be presented in this talk. \\[4pt] [1] T. Brintlinger, et al., Nano Lett. \textbf{8}, 582 (2008). [Preview Abstract] |
Thursday, March 24, 2011 10:00AM - 10:12AM |
V28.00009: Correlated breakdown of carbon nanotubes in an ultra-high density aligned array Shashank Shekhar, Mikhail Erementchouk, Michael Leuenberger, Saiful Khondaker Many proposed applications of single walled carbon nanotubes (SWNTs) require a massively parallel array and selective removal of metallic pathways from the array via electrical breakdown. Since experimental and theoretical studies of individual SWNTs demonstrate that the breakdown is due to Joule heating which occurs at defect sites, a straightforward extrapolation to an array would suggest that the breakdown would occur at random point inside each SWNT. Here we demonstrate that in a densely packed aligned array of SWNTs containing up to 30 SWNT/$\mu $m, the breakdown of one of the SWNTs leads to a highly correlated breakdown of neighboring SWNTs, thereby producing a ``nano fissure'' shaped pattern. We show theoretically that the correlated breakdown is due to the electrostatic field of broken nanotubes that produces locally inhomogeneous current distributions in the neighboring nanotubes triggering their breakdowns in the vicinity of the broken nanotubes. Our results suggest that the densely aligned array works like a correlated solid and have strong implications in the future development of fault-tolerant nano-electronic circuits based on SWNT array. [Preview Abstract] |
Thursday, March 24, 2011 10:12AM - 10:24AM |
V28.00010: Thermionic Emission Properties of Surface modified conical carbon nano tubes (CCNT) Andriy Sherehiy, Gamini Sumanasekera, Santoshrupa Dumpala, Mahendra Sunkara, Robert Cohn We have studied field emission and thermionic emission properties of surface modified arrays of CCNTs. The CCNTs with narrow tip radii (about 10 nm) were synthesized using microwave plasma assisted chemical vapor deposition on platinum wire and planar graphite foils. They show enhanced field emission properties with geometrical enhancement factor as high as about 7000 and turn-on electric field as low as approximately 0.7 V/$\mu $m. The thermionic emission characteristics show work function of aproximately 4.2 eV which is considerably lower than that of aligned MWNT (4.8 eV). The reduced work function value was further confirmed using ultraviolet photoemission spectroscopy (UPS). The surface modified CCNT arrays were also studied and shown to exhibit poorer emission properties compared to pristine CCNTs. We have further coated CCNTs with diamond nanocrystals and doping of the nanocrystals is underway. [Preview Abstract] |
Thursday, March 24, 2011 10:24AM - 10:36AM |
V28.00011: Highly Efficient Field Emission from Carbon Nanotube-Nanohorn Hybrids Prepared by Chemical Vapor Deposition Ryota Yuge, Jin Miyawaki, Toshinari Ichihashi, Sadanori Kuroshima, Tsutomu Yoshitake, Tetsuya Ohkawa, Yasushi Aoki, Sumio Iijima, Masako Yudasaka It is reported that the carbon nanotube (CNT) is one of the best cold cathode emitters for field emission display (FED) and field emission lamp (FEL) due to their large aspect ratio, high mechanical strength, and high electrical conductivity. For the manufacture of highly efficient field emission (FE) devices, we synthesized single-wall carbon nanotube (SWNT) on catalyst-supported single-wall carbon nanohorn (SWNH). We incorporated Fe acetate into SWNHs, heat-treated them, and obtained Fe oxide nano-particles attached to the tips of SWNHs (Fe@NHox). Using Fe@NHox as the catalyst, SWNTs were grown by ethanol-CVD technique (NTNH). In the obtained NTNH, the SWNTs diameters were 1--1.7 nm and the bundle diameters became almost uniform, $i.e.$, less than 10 nm, since the SWNTs were separated by SWNH aggregates. We also confirmed that a large-area FE device with NTNH cathodes made by screen printing was highly and homogeneously bright, suggesting the success of the hybrid strategy. [Preview Abstract] |
Thursday, March 24, 2011 10:36AM - 10:48AM |
V28.00012: Enhanced electron field emission from simultaneously purified and nitrogen incorporated CNTs via tip opening by Novel \textit{in-situ} nitrogen ECR plasma Swathi Iyer, Paul Maguire We report a novel single step process by means of \textit{in-situ} nitrogen ECR plasma treatment with very low power and treatment time for the simultaneous metal catalyst (iron) removal via tip opening and nitrogen functionalization/incorporation of the vertically aligned multiwalled carbon nanotubes synthesised using a microwave plasma enhanced chemical vapour deposition. Microscopic (SEM) and spectroscopic (NEXAFS, XPS and Raman) studies reveal negligible remaining Fe content (0{\%}) and limited/no damage structure and alignment of the nanotubes. The incorporation of nitrogen was elucidated by the N-k edge NEXAFS spectra, where the sharp $\pi $* peak splits into three distinct peaks at energies 399, 399.5 and 401.1 eV. Increase in the at. {\%} conc. of N 1s from 0.7 to 6.9 {\%} and the disappearance of the peak at 780 eV by XPS and Raman corroborate the inclusion of nitrogen in the CNTs and the complete removal of iron metal catalyst. Metal catalyst removal and nitrogen addition by N-ECR plasma leads to enhanced field emission with very low turn on and threshold fields of 0.52 V/$\mu $m and 0.76 V/$\mu $m as compared to the recent studies of other nitrogen doped nanomaterials by plasma treatments. [Preview Abstract] |
Thursday, March 24, 2011 10:48AM - 11:00AM |
V28.00013: Spin-polarized field emission from nanotubes Joseph Driscoll, Brandon Cook, Sergiy Bubin, Kalman Varga Time-dependent density functional theory has been used to calculate the spin-polarized field emission from carbon nanotubes with and without Fe adsorbates (atoms and clusters). Using our previously-developed approach [1], the electronic wave function was propagated in real time. Complex absorbing potentials have been employed to avoid artificial reflections from the boundaries and to allow long time simulations. It was observed that various adsorbates cause the separation of density into spin-polarized regions. The calculations predict that carbon nanotubes with various adsorbates can be used as spin-polarized current sources. \\[4pt] [1] J. A. Driscoll and K. Varga, Phys. Rev. B 80, 245431 (2009). [Preview Abstract] |
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