Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session D35: Focus Session: Thermal Transport and Thermoelectricity in Nanotubes and Graphene |
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Sponsoring Units: DMP Chair: B.C. Regan, University of California, Los Angeles Room: Baltimore Convention Center 338 |
Monday, March 13, 2006 2:30PM - 3:06PM |
D35.00001: Thermal and thermoelectric properties of individual single-walled carbon nanotubes, Bi-based and III-V nanowires Invited Speaker: Electronic and thermoelectric materials can be nanostructured to confine electrons and phonons in one or more dimensions so as to engineer the transport and interaction of charge and heat. Various classical and quantum size confinement effects on the thermal and thermoelectric properties have been suggested by theoretical calculations, but have not been experimentally verified due to the difficulty in nanoscale thermal transport measurements. We have developed MEMS (microelectromechanical systems) sensor devices for measuring the thermal and thermoelectric properties of individual one-dimensional nanostructures. Using the sensor devices, we have observed record-high thermal conductivity and ballistic phonon transport in single-walled carbon nanotubes, suppressed thermal conductivity in semiconductor nanowires, and enhanced thermoelectric figure of merit in bismuth telluride nanowires. These findings suggest an escalating self-heating problem in nanoelectronic devices and also novel uses of nanomaterials for thermal management and for efficient thermoelectric energy conversion. [Preview Abstract] |
Monday, March 13, 2006 3:06PM - 3:18PM |
D35.00002: Ballistic Phonon Thermal Transport and Thermal Properties of Carbon Nanotubes Hsin-Ying Chiu, Vikram Deshpande, Henk Postma, Chun Ning Lau, Csilla Mik\'{o}, L\'{a}szl\'{o} Forr\'{o}, Marc Bockrath We report electrical transport experiments, using the phenomenon of electrical breakdown to perform thermometry, that probe the thermal properties of individual multiwalled carbon nanotubes. Our results show that nanotubes can readily conduct heat by ballistic phonon propagation. We determine the thermal conductance quantum, the ultimate limit to thermal conductance for a single phonon channel, and find good agreement with theoretical calculations. Moreover, our results suggest a breakdown mechanism of thermally activated C-C bond breaking coupled with the electrical stress of carrying ~10$^12$ A/m$^2 $. We also demonstrate a current-driven self-heating technique to improve the conductance of nanotube devices dramatically. The results of our ongoing experiments will be reported. [Preview Abstract] |
Monday, March 13, 2006 3:18PM - 3:30PM |
D35.00003: Aspects of the Thermal Conductivity of Nanotubes Chih-Wei Chang, Adam Fennimore, Anderi Afanasiev, David Okawa, Takashi Ikuno, Henry Garcia, Alex Zettl, Deyu Li, Arun Majumdar We have measured the thermal conductivity of individual multiwalled carbon and boron nitride nanotubes using a microfabricated suspended device. The structure of the measured nanotubes also has been characterized by using a transmission electron microscope. We have found that the thermal conductivity of an isotopically pure BN nanotube is comparable to that of a carbon nanotube with the same diameter. The temperature dependence, the effect of deformation, and localized defects on the nanotubes' thermal transport will also be presented. [Preview Abstract] |
Monday, March 13, 2006 3:30PM - 3:42PM |
D35.00004: Phonon Dynamics in Carbon Nanotubes Arun Bodapati, Pawel Keblinski, Patrick Schelling Using vibrational mode analysis of pristine and defected carbon nanotubes we will demonstrate that defects cause a change in the spatial extension and polarization of phonons leading to a consequent loss of their ballistic nature. Furthermore, to gain a more detailed understanding of thermal energy flow in defected carbon nanotubes we use molecular dynamics simulation to investigate scattering of of well-defined phonon wave-packets either by structural defects or by other phonons. The dependence of scattering of longitudinal and transverse acoustic phonons on their wavelengths will be also discussed. [Preview Abstract] |
Monday, March 13, 2006 3:42PM - 3:54PM |
D35.00005: Heat transport and thermal management in single walled carbon nanotubes Hareem Maune, Marc Bockrath Results from our investigation of thermal transport in CVD grown Single-Walled Carbon nanotubes (SWNT) on different substrates will be reported. Chiu et al. recently showed that multi-walled carbon nanotube devices cool by ballistic phonon heat transport. To harness the remarkable thermal properties of nanotubes for thermal management, it is of interest to understand how heat energy is transported into or out of nanotubes. In this work, we investigate the breakdown power for SWNT nanotube devices using different substrate materials to determine the effect of substrate thermal conductivity on nanotube breakdown. We compare our results with those obtained with the Si/ SiO2 substrate. Our results indicate higher power dissipation on a sapphire substrate for few micron SWNTs but lower than expected dissipation for the longer length scales. We will discuss the mechanism of power dissipation and thermal transport in our devices in light of our results. [Preview Abstract] |
Monday, March 13, 2006 3:54PM - 4:06PM |
D35.00006: Interfacial Thermal Transport Between Single Wall Carbon Nanotubes Jennifer Lukes, Hongliang Zhong Due to their superior thermal conductivity, single wall carbon nanotubes have elicited great interest as potential thermal management materials, for example as fillers in polymer composites and as thermal interface materials. Recent measurements on carbon nanotube composites have revealed lower-than-expected conductivities, and thermal interfacial resistance between the nanotubes and the surrounding medium has been implicated as a key factor limiting heat flow. However, one factor that has been little-considered is the role of interfacial thermal resistance between individual nanotubes. In these composites, the nanotubes form an interconnected network and for this reason interfacial resistance at the contact points between the nanotubes is also expected to have a significant effect on thermal energy transport. Our recent modeling results indicate that a four order of magnitude reduction in nanotube-nanotube interfacial resistance is obtained as the nanotubes are brought into intimate contact. These results will be discussed in this presentation. [Preview Abstract] |
Monday, March 13, 2006 4:06PM - 4:18PM |
D35.00007: Graphene-based polymer nanocomposites: a new class of materials Dmitriy Dikin, Sasha Stankovich, Geoffrey Dommett, Kevin Kohlhaas, Eric Zimney, Richard Piner, Xinqi Chen, SonBinh Nguyen, Rodney Ruoff We have developed an approach that yields a new class of materials: the graphene-based materials. I present our `bottom up' approach to achieving highly dispersed chemically modified graphene (CMG) sheets in polymer composites. A host of novel studies of both individual CMG sheets as well as of the CMG sheet-based nancomposites, is thus now possible. An overview is given of the level of dispersion of the CMG sheets and their morphology in the composites, and of the composite thermal/electrical conductivity and thermomechanical properties. I also discuss our deposition of individual sheets and studies of them. [Preview Abstract] |
Monday, March 13, 2006 4:18PM - 4:30PM |
D35.00008: Morphology and electrical characterization of polymer nanocomposite based on chemically modified graphene sheets Dmitriy Dikin, Sasha Stankovich, Kevin Kohlhaas, Geoffrey Dommett, Eric Zimney, Rodney Ruoff, Oleksandr Chernyashevskyy, SonBinh Nguyen Graphite particles may be oxidized yielding graphene (one atom thick graphite layer) oxide sheets. Furthermore surface modification allows controllable engineering of their properties including recovery of the electrical conduction and homogeneous dispersion in different polymers. Formation of percolative network for electrical transport at very low threshold in the dielectric polymer matrix will be discussed in relation to the composite samples’ morphology, chemical modification of graphene sheets, and their topological states. DC and AC electrical measurements in combination with scanning electron microscopy (“surface” and “sub-surface” imaging) were used for composites characterization. [Preview Abstract] |
Monday, March 13, 2006 4:30PM - 4:42PM |
D35.00009: Transmission Electron Microscopy of a Graphene-based Polymer Nanocomposite Kevin Kohlhaas, Dmitriy Dikin, Sasha Stankovich, Rodney Ruoff, Eric Stach A Polystyrene/CMG (chemically modified graphene) composite has been made by a solution-based processing technique followed by hot pressing or injection molding to form continuous specimens. Microtomed samples were prepared for study by transmission (TEM) and scanning (SEM) electron microscopy. The electron diffraction patterns and the resulting d-spacings, as well as high-resolution bright field TEM images, suggest that the platelets are individual graphene sheets randomly dispersed in the polymer matrix. Scanning electron microscopy observation indicates that the sheets are in a wrinkled conformation; this wrinkling has also been observed in TEM, in the form of ~10 nm “domains” exhibiting lattice fringes of varying orientations. We gratefully acknowledge the NASA University Research, Engineering and Technology Institute on Bio Inspired Materials (BIMat; No. NCC-1-02037) and the National Science Foundation (No. DMR-0526959). [Preview Abstract] |
Monday, March 13, 2006 4:42PM - 4:54PM |
D35.00010: Electrical Properties of a Graphene-based Polymer Nanocomposite. Geoffrey Dommett, Dmitriy Dikin, Eric Zimney, Sasha Stankovich, Rodney Ruoff A polymer/CMG (chemically modified graphene) composite has been prepared by a solution-based processing technique followed by hot pressing or injection molding to prepare continuous sample specimens. The electrical properties of these composites have been measured by 2- and 4-probe techniques, as a function of temperature and concentration to investigate the mechanisms by which electrical transport occurs in a composite with single graphene sheet filler material, and the percolation threshold at which conduction occurs. We gratefully acknowledge the \textit{NASA University Research, Engineering and Technology Institute on Bio Inspired Materials (BIMat)} under award No. NCC-1-02037. [Preview Abstract] |
Monday, March 13, 2006 4:54PM - 5:06PM |
D35.00011: Correction Factors for 4-probe Electrical Transport Measurements with Finite Size Electrodes: Analytical and Finite Element Analysis E.J. Zimney, G. Dommett, D.A. Dikin, R.S. Ruoff In most real specimens the current density is non-uniform through the thickness between the sense (potential) probes. Non-uniformities in the current density can result from many effects including the geometry of the specimen, the finite size of the electrodes, anisotropic behavior of the material, etc. Thus great care must be taken in extracting the correct bulk resistivity from the measured resistance. We have developed a method, based on finite element analysis, to accurately determine the bulk in-plane resistivity from collinear 4-probe resistance measurements on isotropic and anisotropic materials. The effect of boundary conditions on the measured resistivity is explored. Our finite element approach can be universally applied to 4-probe measurements on complex specimen geometries with arbitrary electrode arrangements. [Preview Abstract] |
Monday, March 13, 2006 5:06PM - 5:18PM |
D35.00012: Development of optical approaches for identifying individual graphene-based sheets on surfaces Inhwa Jung, Richard Piner, Dmitriy Dikin, Sasha Stankovich, Rodney S. Ruoff, Martina Hausner We are developing a light microscope-based method for identifying thin graphene-based sheets on silicon wafers with a thin dielectric layer (SiO2 or Si3N4). Different thicknesses of this dielectric layer have been tested. Optics, and experiments with these thin dielectric layers, enabled us to optimize the thickness that yields the best contrast; SiO2 is useful for discerning multiple stacked sheets and Si3N4 for identifying individual sheets. Both multiple or single wavelength sources can be used effectively. By comparing the optical images with data obtained by AFM and SEM, it has been possible to prove that our method can detect the presence of individual graphene- based sheets. [Preview Abstract] |
Monday, March 13, 2006 5:18PM - 5:30PM |
D35.00013: Possibilities for graphene for field emission: Modeling studies using the boundary element method Supinda Watcharotone, Rodney S. Ruoff, Frank H. Read Field emission from a graphene sheet has been modeled with the boundary element method. A modeled flat thin sheet is used. The local electric field and hence the field enhancement factor have been obtained, and the relative magnitude of the field enhancement factors at the corners and the edges has been established. A comparison with field emission from carbon nanotubes will be presented. [Preview Abstract] |
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