Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session J12: Focus Session: Carbon Nanotubes: Thermal Transport |
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Sponsoring Units: DCMP DMP Chair: Rodrigo Capaz, UFRJ, Brazil Room: B110-B111 |
Tuesday, March 16, 2010 11:15AM - 11:27AM |
J12.00001: Direct observation of Thermal contact resistance of a Carbon Nanotube heat spreader Kamal Hussain Baloch, Norvik Voskanian, John Cumings For less than two decades the extraordinary thermal properties of carbon nanotubes (CNTs) have generated much interest in the scientific community. Even though they are a new material with one of the highest of thermal conductivities, the amount of heat CNTs can transport is limited by their thermal contact resistance. Several experiments have been performed to date to experimentally extract the thermal contact resistance of the CNTs. Thus far, all values reported in literature are extracted indirectly through models with assumptions about an uncharacterized heat source, typically Joule heating from within the nanotube itself. Values in the literature vary by more than an order of magnitude, suggesting fundamental uncertainties in the system. We report for the first time a direct in-situ observation of the thermal contact resistance of CNTs using Electron Thermal Microscopy, and we show that the strength of this thermal contact resistance can be manipulated through orders of magnitude. This study opens doors for using CNTs as effective nanoscale thermal transport devices in which the contact resistance of the CNTs could be controlled by design. Experimental results, simulations along with review of the experimental technique will be presented in this talk. [Preview Abstract] |
Tuesday, March 16, 2010 11:27AM - 11:39AM |
J12.00002: Reversible heat flow through the carbon tube junction Serhii Shafranjuk Microscopic mechanisms of the externally controlled reversible thermoelectric effect through the carbon tube junction (NJ) are examined theoretically. The theory [1] interprets earlier experiments in terms of ballistic motion the phase-correlated electrons (e) and holes (h) along the tube section T. We find that the direction and magnitude of the heat flow critically depend on the gate voltage VG and on the source-drain voltage VSD, both. The voltages adjust the electron energy $\varepsilon$ to match the quantized state and van Hove singularities inside T . Potential applications of the reversible Peltier effect are discussed.\\[4pt] [1] S. Shafraniuk, EPL, 87 (2009) 57007 [Preview Abstract] |
Tuesday, March 16, 2010 11:39AM - 11:51AM |
J12.00003: ABSTRACT WITHDRAWN |
Tuesday, March 16, 2010 11:51AM - 12:03PM |
J12.00004: ABSTRACT WITHDRAWN |
Tuesday, March 16, 2010 12:03PM - 12:15PM |
J12.00005: Molecular dynamics simulation of Carbon Nanotube-to-SiO2 heat dissipation Zhun-Yong Ong, Eric Pop Understanding the mechanism of heat dissipation from carbon nanotubes (CNTs) to their surrounding medium is essential for the operation of CNT-based electronic devices and heat sinks. At high current levels, significant Joule heating can occur in CNT devices, leading to hot phonons and energy dissipation bottlenecks which degrade electrical transport. We investigate thermal coupling between single-wall CNTs and SiO2 dielectrics by non-equilibrium classical molecular dynamics (MD) simulations. The thermal boundary conductance (TBC) is computed by setting up a temperature pulse in the CNT and monitoring its relaxation into the SiO2. The TBC is found to scale approximately linearly with CNT diameter (d $\sim$ 0.8 - 1.8 nm) and as a weak power law of temperature (T $\sim$ 200 - 600 K). We also find a linear dependence of the TBC on the strength of the CNT-SiO2 van der Waals coupling. Our simulation results are comparable to experimental data obtained from electrical breakdown thermometry of the CNT-substrate TBC. Using the power spectrum analysis technique, we also find that energy relaxation is most significant in the long wavelength, low frequency region of the phonon power spectrum. [Preview Abstract] |
Tuesday, March 16, 2010 12:15PM - 12:27PM |
J12.00006: Graphene and nanotubes on the polar insulator: Near-field thermal conductance across the interface Slava V. Rotkin, Alexey G. Petrov Our ability to apply carbon-based materials for electronic devices requires detailed knowledge of their electronic properties as well as thermal ones in the real environment (rather than in vacuum). We present a microscopic theory of the electromagnetic coupling of the charge carriers in graphene and single-wall carbon nanotube to the surface electromagnetic modes of the SiO2 substrate, which allows a new interpretation of experimental data. Such coupling changes the physics of both inelastic hot charge carrier scattering in carbon-based electronic devices and thermal conductance across the interface with the substrate. \newline Our modeling predicts that the near-field scattering by the surface modes results in (A) a dominating inelastic scattering channel (with a typical 30 nm m.f.p.) [Nano Lett 9, 1850, (2009)] and (B) the most significant interface thermal conductance mechanism (0.1 $W/m^2K$) [SPIE Proc. 7399, 7399-0F (2009)]. Both effects have to be taken into account to study the high-electric field transport and to compute the Joule losses and channel steady-state temperature. This talk focuses on the novel thermal coupling mechanism which is a QED (near-field) counterpart of the Kapitza conductance. We discuss possibilities to tweak it for graphene and nanotube materials on the polar substrates. \newline [Preview Abstract] |
Tuesday, March 16, 2010 12:27PM - 12:39PM |
J12.00007: Phonon thermal conductivities of single-walled carbon nanotubes and the graphene limit L. Lindsay, D.A. Broido, N. Mingo We employ a recently developed Boltzmann transport approach to calculate the intrinsic lattice thermal conductivity of a wide range of chiral and large-diameter single-walled carbon nanotubes. This approach uses a Tersoff empirical interatomic potential [1] and exploits symmetry based selection rules for anharmonic phonon-phonon scattering [2]. We also use this Boltzmann transport approach to calculate the thermal conductivity of graphene where we find an additional selection rule that strongly limits the anharmonic phonon-phonon scattering of out-of-plane modes. The phonon dispersion curves and thermal conductivities of successively larger diameter nanotubes approach that of two-dimensional graphene. [1] J. Tersoff, Phys. Rev. Lett. 61, 2879 1988 [2] L. Lindsay, D. A. Broido, and N. Mingo, Phys. Rev. B 80, 125407 (2009). [Preview Abstract] |
Tuesday, March 16, 2010 12:39PM - 12:51PM |
J12.00008: Thermal Conductance Measurement of metal-CNT Composites using Micron-Sized Suspended Structures. Myung Rae Cho, Sung Un Cho, Young Duk Kim, Byeong Gyun O, Byung Yang Lee, Seunhun Hong, Yun Daniel Park We report on the thermal conductance measurements of metallic thin film/carbon nanotube nanolaminates by micron-sized suspended structures. Thermal conductances of low-dimensional materials are particularly difficult to measure due to various spurious environment effects. A proven method to characterize thermal properties of such samples is to thermally isolate and to incorporate measurement probes by micromachining techniques. Thermally isolating the measurement sample as well as incorporating heaters and thermometers allows for simple and direct characterization of thermal properties. As well as an absolute thermal conductivity values, their temperature dependence gives insight in the thermal transport process. Recently several studies have reported that when the thickness of metallic thin films approaches nanometer length-scales, its thermal conductivity is significantly reduced than its bulk value along with its decrease in value with temperature. Here we show that the absolute thermal conductivities of metal-CNT nanolaminates are enhanced compared to a similar metallic thin film without addition of CNT. But, the temperature dependence of the thermal conductivity is dominated by low-dimensional effects. [Preview Abstract] |
Tuesday, March 16, 2010 12:51PM - 1:03PM |
J12.00009: Thermo-Mechanical Modeling of Foil-Supported Carbon Nanotube Array Interface Materials Parisa Pour Shahid Saeed Abadi, Baratunde Cola, Samuel Graham A thin metal foil with vertically aligned carbon nanotube (CNT) arrays synthesized on both sides is a new class of thermal interface materials that has demonstrated thermal resistances less than 0.1 cm$^2$ K/W under moderate pressures. Such interface materials are able to obtain such low resistances due to their unique combination of high thermal conductivity and high conformability to surface roughness. For such structures, the contact resistances between CNT arrays and the adjacent surfaces are the major constituents of total resistance. Here we integrate a recently developed contact mechanics model for CNT arrays with a finite element code that captures the nonlinear mechanical behavior of the interface material and the effects of interface topography on the thermal performance. The developed model elucidates the relative affects of metal foil as well as CNT array deformation on the compliance of the composite structure. The results support previous experimental observations that the combination of foil and CNT array deformation significantly enhances interfacial contact and thermal conductance. [Preview Abstract] |
Tuesday, March 16, 2010 1:03PM - 1:15PM |
J12.00010: Optimal matching of thermal vibrations into carbon nanotubes: theory and simulations K.G.S.H. Gunawardana, Kieran Mullen, A.A. Moussa Carbon nanotubes (CNTs) and graphene sheets (GS) are promising candidates to improve the thermal conductivity of nano- composites and to use as a thermal interface materials. The main obstacle to these applications is the extremely high thermal boundary (Kapitza) resistance. It is possible to lower the Kapitza resistance by inserting a secondary atomic chain linking CNT or GS to the external medium. We have previously shown a theoretical approach optimizing this interface atomic chain in the continuum limit. To probe the limitations of the continuum model, an atomistic simulation was carried out. It was observed that the low frequency contribution to the thermal transport can be improved according to the continuum limit optimization. Further we have developed a theoretical tool based on R-Matrix theory to analyze the interfacial thermal transport taking phonon dispersion into account. [Preview Abstract] |
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