Simon R. Phillpot University of Florida
Sebastian Volz Ecole Centrale Paris, CNRS
Theodorian Borca-Tasciuc Rensselaer Polytechnic Institute
Mansoo Choi Seoul University
II1: Biological and Soft Materials, Nanofluids
Tuesday PM, April 10, 2007
Room 3020 (Moscone West)
9:00 AM - **II1.1
Heating, Movement and Visualization Challenges in the use of Iron Oxide Magnetic Nanoparticles for Biomedical Applications.
Venkat Kalambur 1 , John Bischof 1 Show Abstract
1 Mechanical Engineering, University of Minnesota, Minneapolis, Minnesota, United States
9:30 AM - **II1.2
Capillary Kinetics of Thin Polymer Films in Permeable Microcavities.
Kahp Suh 1 Show Abstract
1 School of Mechanical and Aerospace Engineering, Seoul National University, Seoul Korea (the Republic of)
10:00 AM - II1.3
Micron-scale Spatial Resolution Measurements of Thermal Conductivity and Coefficient of Thermal Expansion of a Human Tooth near the Dentin-enamel Junction.
Xuan Zheng 1 2 , David Cahill 1 2 Show Abstract
1 Department of Materials Science and Engineering, University of Illinois, Urbana, Illinois, United States, 2 Frederick-Seitz Materials Research Laboratory, University of Illinois, Urbana, Illinois, United States
The dentin-enamel junction (DEJ) in human teeth is a natural junction that successfully unites the enamel and dentin, and prevents cracks initiated in enamel from penetrating into dentin and through the whole tooth. These strong bonding and crack-arresting capabilities are suggested to originate partly from gradients in microstructure and mechanical properties near the DEJ. We measure the local thermal conductivity and linear coefficient of thermal expansion (LCTE) near the DEJ using time-domain thermoreflectance and photothermal beam deflection, respectively. During thermal measurements, the penetration depth of thermal waves is less than 100 nm and is much smaller than the 8 μm diameter of the laser spot; the lateral resolution is about 3 μm for the thermal conductivity measurement and 4 μm for the LCTE measurement. We find that the thermal conductivity of enamel (1.45 W m-1 K-1) and dentin (0.56 W m-1 K-1) is constant at different distances from the DEJ; the LCTE of enamel (18×10-6 K-1) is constant at different distances from the DEJ; the LCTE of dentin increases monotonically from 46×10-6 K-1 for bulk dentin to 58×10-6 K-1 for dentin in proximity to the DEJ over a distance of 120 μm; and both the thermal conductivity and LCTE change abruptly from enamel to dentin across the DEJ. We also find that the thermal conductivity of enamel rods (1.3 W m-1 K-1) is lower than that of interrod enamel (1.6 W m-1 K-1).
10:15 AM - II1.4
Near-Infrared Photothermal Conversion Properties and Cell Recognition of Biocompatible Germanium(0) Nanocrystals.
Timothy Lambert 1 , Nicholas Andrews 2 , Bernadette Hernandez-Sanchez 1 , Henry Gerung 3 , Timothy Boyle 1 , Paul Rotella 4 , Janet Oliver 2 , Sang Han 3 , Bridget Wilson 2 , Sanjay Krishna 4 Show Abstract
1 Advanced Materials Laboratory, Sandia National Laboratories, Albuquerque, New Mexico, United States, 2 Department of Pathology, University of New Mexico, Albuquerque, New Mexico, United States, 3 Department of Chemical and Nuclear Engineering, University of New Mexico, Albuquerque, New Mexico, United States, 4 Department of Electrical and Computer Engineering, University of New Mexico, Albuquerque, New Mexico, United States
We have previously demonstrated the controlled synthesis of Ge(0) nanocrystals and nanowires, via a thermal reduction of molecularly designed Ge(II) precursors without the need for a metal catalyst or the production of any salt byproducts. Using a molecular design approach, control over Ge(II) precursor’s reactivity was achieved by tailoring the Ge-ligand bond and the ligand steric hindrances. In general more reactive precursors yielded Ge(0) NCs while less reactive precursors yielded Ge(0) NWs. For this presentation, surfactant passivated germanium nanocrystals [Ge(0) NCs] 3-5 nm in diameter were synthesized and encapsulated with functionalized phospholipids, yielding water soluble, in vitro biocompatible Ge(0) NCs. Upon encapsulation, the nanocrystals retained their cubic crystalline phase and displayed good resistance to oxidation, as determined by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Despite numerous claims of Ge(0) NC luminescence in the literature, our functionalized Ge(0) NCs were not luminescent enough to be useful for routine live cell fluorescence microscopy. Since Ge(0) NCs are relatively inefficient emitters, likely due to non-radiative recombinations, irradiated Ge(0) NCs should generate heat via phonon vibrations. Indeed, we have found that both organic and aqueous solutions of Ge(0) NCs displayed stable photothermal behavior under repetitive and prolonged exposure to a continuous wave (CW) Ti:sapphire laser (λexc = 770nm, ~ 1.0 W/cm2). To date, such photothermal behavior and its subsequent materials and/or biological applications have been demonstrated for both noble metallic particles and with single-wall carbon nanotubes, but not with (soluble) group IV semiconductor NCs. The synthetic details and functionalization, cell signaling applications and newly discovered photothermal properties of Ge(0) NCs will be presented.This work was supported by the National Institutes of Health, through the NIH Roadmap for Medical Research (Grant #1 R21 EB005365-01) and by the United States Department of Energy. Sandia is a multi-program laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under contract DE-AC04-94AL85000.
10:30 AM - II1.5
Thermal Coupling at Biomolecule-water Interfaces.
Natalia Shenogina 1 , Pawel Keblinski 1 , Shekhar Garde 2 Show Abstract
1 Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States, 2 Chemical and Biological Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States
10:45 AM - II1.6
Electrofreezing of Water by Ion-Modified Diamond Surfaces.
Alexander Wissner-Gross 1 , Efthimios Kaxiras 1 2 Show Abstract
1 Physics, Harvard University, Cambridge, Massachusetts, United States, 2 Division of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States
Recent progress has been made toward inexpensive growth of polycrystalline diamond films, which may have important applications for corrosion-free medical implants and devices. In this work, we investigate the thermal stability of epitaxial ice Ih on a diamond (111) film, both in its natural H-terminated phase and in chemically modified phases. The most biologically interesting surface phases consist of nanostructured submonolayers of sodium ions that electrically polarize the ice layers closest to the diamond interface. We perform extensive molecular dynamics simulations employing the TIP4P/Ice water model in order to identify thermodynamic equilibria and monitor phase changes. We observe a significant elevation of the melting temperature for the interfacial ice layers, suggesting enhanced stability due to electrofreezing.
11:30 AM - **II1.7
Forced Convective Heat Transfer of Aqueous Based Dilute Suspensions of Titania Nanoparticles (Nanofluids).
Yulong Ding 1 Show Abstract
1 Institute of Particle Science & Engineering, University of Leeds, Leeds United Kingdom
12:00 PM - II1.8
Thermal Conductivity Computation of Nanofluids by Equilibrium Molecular Dynamics Simulation: Nanoparticle Loading and Temperature Effect.
Suranjan Sarkar 1 , R. Selvam 1 Show Abstract
1 Civil Engineering, University of Arkansas, Fayetteville, Arkansas, United States
Thermal management is one of the most important technical challenges for high power systems in many diverse industries and research laboratories. Nanofluids have been proposed as a route for surpassing the performance of currently available heat transfer liquids. Recent experiments on nanofluids have indicated 40%-60% increases in thermal conductivity with 0.5 to 1% of nanoparticle loading in comparison to that of the base fluid. But the extent of thermal conductivity enhancement sometimes greatly exceeds the predictions of well established classical theories like Maxwell and Hamilton Crosser theory. In addition to that, these classical theories can not explain the temperature and nanoparticle size dependency of nanofluid thermal conductivity. Recently, a few models have been proposed to predict nanofluid thermal conductivity and explain the underlying mechanisms for anomalous heat transfer seen in nanofluids. They have different level of acceptance in thermal management research community. Atomistic simulation like molecular dynamics simulation can be a very helpful tool to model the enhanced nanoscale thermal transport and predict thermal conductivities in different situations.Molecular Dynamics simulation has been successfully employed in the past to predict the thermal conductivities of solids and liquids individually. In this study a model nanofluid system of copper nanoparticles in argon base fluid is successfully modeled by Equilibrium MD simulation in NVT ensemble. The interatomic interactions between solid copper nanoparticles, base liquid argon atoms and between solid copper and liquid argon are modeled by Lennard Jones potential with appropriate parameters. Thermal conductivity of base fluid and nanofluid are computed using Green Kubo method. For different volume fractions of nanoparticle loading, the thermal conductivity is calculated. The temperature effects on thermal conductivities of nanofluids are also systematically studied. This study shows that thermal conductivity of nanofluid is much higher than that of the base fluid and also an order of magnitude higher than what is predicted by classical theories and the enhancement is similar order of magnitude found in recent experiments. The thermal conductivity of the nanofluid system also increases with increase of system temperature for a fixed volume percent of nanoparticle loading; findings which are consistent with the experimental data. This study indicates the usefulness of molecular dynamics simulation to calculate thermal conductivity of nanofluid and investigate the underlying mechanism of heat conduction in atomic level. The knowledge gained from this study will be used later to model the more realistic nanofluid system using more accurate interatomic potentials. The insight about the mechanism of thermal transport in nanofluids gained from this study might be helpful to design better nanofluids in near future.
12:15 PM - II1.9
Molecular Dynamics Studies of Thermal Relaxation in Fullerene Solutions.
Sergei Shenogin 1 , Pawel Keblinski 1 , Dmitry Bedrov 2 , Grant Smith 2 Show Abstract
1 Nanotechnology Center, RPI, Troy, New York, United States, 2 , University of Utah , Salt Lake City, Utah, United States
12:30 PM - **II1.10
Nanofluids for Enhanced Thermal Transport: Understanding and Controversy
Pawel Keblinski 1 Show Abstract
1 , Resselaer Polytechnic Institute, troy, New York, United States
A number of experiments on colloids of solid nanoparticles (nanofluids) have demonstrated significant thermal conductivity increases, well above those predicted by composite homogenization theories. However, other experiments showed very modest increases. In our presentation we will discuss a number of proposed mechanisms responsible for unusual thermal conductivity enhancements, including altered thermal properties of liquids at solid interfaces, Brownian motion of nanoparticles and associated hydrodynamic response of the fluid, particle clustering, and direct thermal energy exchange via dipolar interactions between proximal nanoparticles. We will present a critical examination of these mechanisms via means of theoretical analysis and molecular-level simulations and discuss possible reasons for contradictory experimental results.
Tuesday PM, April 10, 2007
Room 3020 (Moscone West)
2:30 PM - **II2.1
Solid State Thermionic Energy Conversion
Ali Shakouri 1 Show Abstract
1 , Univ. of Calif. Santa Cruz, Santa Cruz, California, United States
Energy consumption in our society is increasing rapidly. A significant amount of heat is generated in various energy conversion applications, especially in transportation and in electricity generation. It is estimated that in US more than 50% of the energy obtained from various sources is wasted. Thermoelectric effects can be used for direct conversion of heat into electricity using a solid-state device. We describe fundamental and practical limits of conventional thermoelectric power generation. Novel nanostructured materials are developed where the heat and charge transport are modified at the atomic level. At the Thermionic Energy Conversion Center, which is a consortium of research groups from seven universities, we are working to optimize thermoelectric properties of embedded metallic nanoparticles and multilayers. Hot electron filtering using heterostructure barriers is used to break the trade off between high Seebeck coefficient and high electrical conductivity. Embedded ErAs nanoparticles and metal/semiconductor multilayers are used to reduce the lattice thermal conductivity without significant effect on electrical conductivity. Cross-plane thermoelectric properties and the effective ZT of the thin film are measured using the transient Harman technique. Integrated circuit fabrication techniques are used to transfer the n- and p-type thin films on AlN substrates and make power generation modules with hundreds of thin film elements. Potential for energy conversion efficiency exceeding 20% and high power density >1W/cm2 will be discussed.
3:00 PM - **II2.2
Thermoelectric Properties of Compressed Bismuth Nanostructures.
Stephen Hostler 1 , Michael Demko 1 , Alexis Abramson 1 Show Abstract
1 , Case Western Reserve University, Cleveland, Ohio, United States
Theory predicts a substantial increase in the dimensionless figure of merit as the dimensionality and characteristic size of a thermoelectric material are decreased. We explore the use of bismuth nanoparticles and nanowires pressed into pellets as a potential increased-efficiency thermoelectric material. Moreover, this type of compression was investigated with regard to the effect that the applied pressure may have on reducing the oxide layer surrounding the nanostructures. Following an agitation period, the nanostructures were compressed uniaxially at pressures ranging from 250 to 1500 MPa using a modified hydraulic press. The effect of pellet formation via compression on thermal and electrical properties were explored. Electrical conductivity was measured using a standard four point probe technique; the pellet thermal conductivity was determined using the laser-based Mirage technique in conjunction with a differential scanning calorimeter; and a measurement of the Seebeck coefficient required the use of a standard DC technique. Additionally, x-ray photoelectron spectroscopy was employed to examine oxide formation characteristics. For comparison, a series of pellets made from commercially-available bismuth microparticles also were pressed and tested. Trends for both the microparticle and nanostructure pellets were similar. Both types of pellets showed a slight reduction in thermal conductivity relative to bulk bismuth and a Seebeck coefficient near or slightly larger in magnitude than bulk. These changes were dwarfed by a substantial decrease in the electrical conductivity as a result of the highly porous structure that formed. Though the oxide layer on the nanostructures may have also contributed to the low electrical conductivity, we determined that to some extent a reduction in oxide formation was achievable through the compression process.
3:30 PM - II2.3
Thermoelectric Transport Measurements In Lead Telluride Self Assembled Nanoparticles Thin Films Using Scanning Hot Probe Technique
Claudiu Hapenciuc 1 , Theodorian Borca-Tasciuc 1 , Arup Purkayastha 2 , Ganapathiraman Ramanath 2 Show Abstract
1 MANE, RPI, Troy, New York, United States, 2 MSE, RPI, Troy, New York, United States
A scanning hot probe technique is used for the measurement of thermoelectric properties in thin-films. In this method a resistively heated thermal probe of an Atomic Force Microscope (AFM) is brought in contact with the sample surface giving rise to a temperature gradient and a Seebeck voltage in the specimen. The average temperature rise of the probe is determined from the change in its electrical resistance. The heat transfer rate between the probe and the sample is estimated using a heat transfer model that takes into account the major heat transfer mechanisms in the system. The thermal conductivity is determined from the measured thermal resistance of the film. The Seebeck coefficient value is calculated using the measured temperature drop and the Seebeck voltage in the plane of the sample. The method is calibrated on glass and bismuth substrates. We report in this work the experminental results on lead telluride self assembled nanopartiscles thin films thermoelectric properties.
4:15 PM - **II2.4
Phase Transitions and Thermal Properties in GeSbTe (2:2:5).
John Reifenberg 1 , SangBum Kim 2 , Yuan Zhang 2 , Eric Pop 3 , H.-S. Philip Wong 2 , Kenneth Goodson 1 Show Abstract
1 Mechanical Engineering, Stanford University, Stanford, California, United States, 2 Electrical Engineering, Stanford University, Stanford, California, United States, 3 , Intel Corp., Santa Clara, California, United States
Phase change memory (PCM) offers excellent read/write characteristics, bit endurance, and long-term dimensional scaling for future high-density data storage. Though functional devices exist, reducing PCM power consumption remains a primary challenge. Optimizing device geometries for minimal write currents requires intricate knowledge of the thermal physics in the constituent thin films. Device performance is highly dependent on the spatially distributed thermal properties around the phase transition temperatures, which are not known.
Previous work has successfully captured important aspects of device operation and physics. Peng initially developed a Monte Carlo phase change model for simulations of GST thin films1. This study laid the groundwork for simulations of phase change memory devices that show the interplay between electrical and phase change phenomena2. Privitera’s measurements of the electrical resistivity lend insight into the time-temperature dependence of the amorphous to crystalline transformation3. Most recently, measurements detail the behavior of the effective thermal conductivity of GST between 20°C and 400°C4. Recent work has shown the importance of the spatial distribution of thermal properties particularly near the melting temperature of 600°C5.
In this paper, we report measurements of the thermal boundary resistance (TBR) and intrinsic thermal conductivity of thin GST films up to 600°C using the 3ω method. Measurements of the TBR and intrinsic thermal conductivity between 20°C and 600°C provide a comprehensive set of thermal property data. The thermal properties in the vicinity of the phase transition temperatures near 120°C and 150°C receive special attention. TBR data at the melting point, 600°C, offers insight into thermal transport across molten-solid interfaces. We develop a thermal transport model, which accounts for the time-dependent phase transformation kinetics in GST as a function of temperature and the temporal history of heating.
This work provides the detailed knowledge of the thermal properties of GST thin films necessary for accurate device simulations. Transient measurements of the thermal properties through phase transitions enable studies of the interplay between thermal transport and phase change kinetics. Data from 400°C to 600°C is the first taken on GST films, and offers insight into the TBR at molten/solid interfaces.
1. C. Peng, L. Cheng, and M. Mansuripur, J. Appl. Phys. 82 (1997) p. 4183.
2. A.L. Lacaita, A. Redaelli, D. Ielmini, F. Pellizzer, A. Pirovano, A. Benvenuti, and R. Bez, IEDM Tech. Dig. (2004) p.911.
3. S. Privitera, E. Rimini, C. Bongiorno, R. Zonca, A. Pirovano, and R. Bez, J. Appl. Phys. 94 (2003) p.4409.
4. H.K. Lyeo, D.G. Cahill, B.S. Lee, J.R. Abelson, M.H. Kwon, K.B. Kim, S.G. Bishop, and B.K. Cheong, Appl. Phys. Lett. 89 151904 (2006).
5. J. Reifenberg, E. Pop., A. Gibby, S. Wong, and K. Goodson, Proc. ITHERM’06 (2006) p.106.
4:45 PM - II2.5
Thermoelectric Properties of Nano-structured Thin-film Oxides.
Matthew Scullin 1 2 , Choongho Yu 2 , Renkun Chen 3 , Wei Tian 4 , V. Vaithyanathan 4 , D. Schlom 4 , Arun Majumdar 2 1 3 , R. Ramesh 1 2 Show Abstract
1 Materials Science and Engineering, University of California, Berkeley, Berkeley, California, United States, 2 Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 3 Mechanical Engineering, University of California, Berkeley, Berkeley, California, United States, 4 Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania, United States
5:00 PM - II2.6
Non-Linear Thermoelectric Properties of Silicon Nanowires
Paul von Allmen 0 , Fabiano Oyafuso 0 , Seungwon Lee 0 Show Abstract
0 , Jet Propulsion Laboratory, Pasadena, California, United States
New applications of thermoelectric materials for micro and nano-scale cooling of electronic devices and magnetic storage as well as applications for chemical sensors have renewed the need for accurate modeling of thermoelectric properties for nano-patterned materials. Thermoelectric properties are usually computed using linear response theory. This approach is appropriate in bulk materials since the change in chemical potential associated with experimentally achievable temperature gradients is small compared to the bandwidths in the electronic structure. Transport in nanowires however occurs through electronic bands that are narrower than in bulk and non-linear effects are expected in thermoelectric transport similarly to those observed in the electrical conductivity. We apply the non-equilibrium Green’s function formalism, which has been very successful at describing current-voltage characteristics in confined structures, to compute the thermal transport properties. We have calculated I-V curves with and without a temperature gradient for an infinite slab of bulk silicon using the non-equilibrium Green’s function method and a parameterized tight-binding description of the material. The voltage at zero current divided by the temperature difference between the two faces of the slab directly gives the Seebeck coefficient in excellent agreement with linear response results. Detailed results for the Seebeck coefficient will be presented for silicon nanowires and the dependence of the non-linearities on the nanowire diameter and growth direction will be discussed.
5:15 PM - II2.7
Thermoelectric Properties of La-doped and Oxygen-deficient SrTiO3 Thin-films.
Choongho Yu 1 , Matthew Scullin 2 1 , Renkun Chen 3 , Wei Tian 4 , V. Vaithyanathan 4 , D. Schlom 4 , R. Ramesh 2 1 , Arun Majumdar 1 2 3 Show Abstract
1 Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 2 Materials Science and Engineering, University of California, Berkeley, Berkeley, California, United States, 3 Dept. of Mechanical Engineering, University of California, Berkeley, Berkeley, California, United States, 4 Dept. of Materials Science and Engineering, Pennsylvania State University, University Park, Pennsylvania, United States
5:30 PM - II2.8
A Modified High-resolution TEM for Thermoelectric Properties Measurements of Nanowires and Nanotubes.
Chris Dames 1 , C. Harris 2 , S. Chen 2 , Z. Ren 3 , M. Dresselhaus 4 5 , G. Chen 2 Show Abstract
1 Mechanical Engineering, UC Riverside, Riverside, California, United States, 2 Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 Physics, Boston College, Chestnut Hill, Massachusetts, United States, 4 Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 5 Electrical Engineering & Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
5:45 PM - II2.9
Thermoelectric Properties of Carbon Nanotube Nanojunctions.
Leif Poorman 1 Show Abstract
1 Physics, UC Santa Cruz, Santa Cruz, California, United States
Simon R. Phillpot University of Florida
Sebastian Volz Ecole Centrale Paris, CNRS
Theodorian Borca-Tasciuc Rensselaer Polytechnic Institute
Mansoo Choi Seoul University
II3: Interfacial Materials
Wednesday AM, April 11, 2007
Room 3020 (Moscone West)
9:30 AM - **II3.1
Modeling Thermal Transport at Single Interfaces and in Nanostructured Materials Using Molecular Dynamics and Monte Carlo Techniques.
Robert Stevens 1 , Thomas Brown 1 Show Abstract
1 Mechanical Engineering, Rochester Institute of Technology, Rochester, New York, United States
With the growing interest in nanostructured materials, robust thermal engineering models are critical for thermal management in nanomaterials as well as the engineering of new materials with desired thermal properties. Thermal transport is often dominated by the scattering at interfaces rather than the bulk thermal conductivities of the constituent materials in structures where the characteristic length in at least one of the dimensions is on the order of tens of nanometers. There are mismatch models that have been developed to describe thermal transport at interfaces with some success. There are discrepancies between experimental measurements of thermal transport across interfaces and these models at room temperatures or higher. Recent efforts are being made to improve the modeling of nanostructured materials by using both molecular dynamics and Monte Carlo techniques. The non-equilibrium molecular dynamics (NEMD) technique, which makes no assumptions of the scattering rules, is described with applications to thermal transport at single interfaces. The impact of interface imperfections due to lattice mismatches and interface mixing is determined for a fundamental case. Simulations indicate a linear relationship between thermal boundary conductance and temperature, which points towards the possible importance of inelastic scattering processes at the interface. The NEMD is extended to examine heat transfer in real nanostructured materials such as superlattices in attempts to develop suitable engineering models for thermal transport in such structures. To complement the NEMD simulation, the Monte Carlo solution technique is applied to the Boltzmann Transport Equation. The method accounts for non-linear dispersion relationships and dual polarization. The Monte Carlo phonon transport model is used to determine the effective thermal conductivity in nanostructured materials and compared to experimental data.
10:00 AM - II3.2
Nanoscale Thermal Transport across Metal/Non-Metal Interfaces.
Nitin Shukla 1 , Scott Huxtable 1 Show Abstract
1 Mechanical Engineering, Virginia Tech, Blacksburg, Virginia, United States
Recent advances in both materials fabrication and characterization techniques have allowed for measurements of nanoscale heat transport across interfaces of dissimilar materials. Studies have been performed primarily on solid/solid interfaces, while measurements on solid/liquid interfaces have only recently become available. Therefore, we possess only a modest understanding of the physical mechanisms responsible for controlling the flow of heat across interfaces. For example, it is well known that heat transport in metals is dominated by electrons, while the flow of heat in non-metals is controlled by phonons. However, despite the ubiquity and importance of metal/non-metal interfaces, we know little about the fundamental coupling mechanisms between these two carriers at these interfaces. We do not know if the interfacial thermal conductance is controlled primarily by (a) coupling between the electrons and phonons within the metal followed by phonon-phonon coupling between the metal and non-metal, or, (b) direct anharmonic coupling between the electrons in the metal and phonons in the non-metal. We use time-domain thermoreflectance to experimentally examine thermal transport across interfaces between various solids and liquids in order to gain some insight on the role of electron-phonon coupling and metal/non-metal interfaces. Sub-picosecond optical pulses from a Ti:Sapphire mode-locked laser are used to heat a metallic surface and the thermal decay of the metallic layer is measured by examining time resolved changes in reflectivity. Using this pump-probe measurement technique we are able to determine approximate values of the thermal conductance G across either solid-solid or solid-liquid interfaces.Specifically, we measure the thermal conductance across (i) interfaces between solid metals and solid non-metals along with (ii) interfaces between liquid metals and solid non-metals. Liquid metals possess large electrical conductivity, but are essentially void of phonons due to the weak bonding between molecules in the liquid form. Therefore thermal transport across these interfaces necessarily must be via pathway (b) described previously if there is to be significant heat transfer. By examining the interface thermal conductance between solid metals and non-metals and comparing these values with measurements of liquid metals and non-metals, we are able separate out the contributions of each pathway, and to determine the relative importance of electronic and vibrational coupling at these interfaces.
10:15 AM - II3.3
Wiedemann-Franz Law and Electronic Thermal Conductivity in Tall Barrier Superlattices.
Zhixi Bian 1 , R. Singh 1 , M. Zebarjadi 1 , A. Shakouri 1 , W. Kim 2 , S. Singer 2 , A. Majumdar 2 , J. Bahk 3 , G. Zeng 3 , J. Bowers 3 , J. Zide 4 , A. Gossard 4 Show Abstract
1 Electrical Engineering Department, University of California Santa Cruz, Santa Cruz, California, United States, 2 Department of Mechanical Engineering, University of California Berkeley, Berkeley, California, United States, 3 Department of Electrical and Computer Engineering, University of California Santa Barbara, Santa Barbara, California, United States, 4 Materials Department, University of California Santa Barbara, Santa Barbara, California, United States
10:30 AM - II3.4
Carbon Nanotube/Silicon Interfacial Thermal Conductance
Jiankuai Diao 1 2 , Deepak Srivastava 1 2 Show Abstract
1 University Affiliated Research Center, , University of California, Santa Cruz, Moffett Field, California, United States, 2 Center for Nanotechnology, , NASA Ames Center, Moffett Field, , California, United States
11:15 AM - **II3.5
Exploration of Superlattice Thermal Conductivity Tensor Design Space.
Alan McGaughey 1 , Eric Landry 1 Show Abstract
1 Mechanical Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States
Given two materials with which to build a superlattice, what is the extent of the associated thermal conductivity tensor design space? To answer this question, we consider a wide range of superlattices built from simple Lennard-Jones materials that only differ by their masses with goals of (i) minimizing the cross-plane thermal conductivity and (ii) maximizing the ratio of the in-plane to cross-plane thermal conductivities.Predicting the thermal conductivity of a periodic composite material at the continuum-level is straightforward. When the length scales of the unit cell approach the nanoscale, however, continuum mixing rules cannot be applied because the phonon transport transitions from a diffusive regime to one where ballistic scattering is important. The bulk properties of the constituent species are no longer directly applicable and atomic-level simulation is required. Here, we use molecular dynamics simulations to predict the thermal conductivity of superlattices and associated bulk and alloy phases. Both the Green-Kubo and direct methods are used in a complementary manner.The superlattice thermal conductivity is bound at an upper level by structures where diffusive transport dominates (i.e., the length scales exceed the phonon mean free path). At the lower level, the thermal conductivity is bound by the alloy limit. We find that superlattices with cross-plane thermal conductivities near the alloy limit can be obtained by choosing a complex unit cell design (i.e., one where the layers of the two species do not have the same thickness and there are more than two layers per period). Such structures, which have not been systematically investigated in previous experimental or simulation work, also show larger anisotropy in their thermal conductivity tensors, and warrant further study.At a given temperature, the thermal conductivity of a superlattice is dependent on its unit-cell design. Both the layers and the interfaces make contributions to the total thermal resistance. The thermal conductivity itself does not shed direct light on how the make-up of the unit cell leads to the bulk behavior. For this reason, we also discuss the prediction of the interface thermal resistance in a superlattice from MD simulations using a new Green-Kubo method. Past molecular dynamics work has focused on isolated interfaces. The situation in a superlattice is different, in that for small enough layer thicknesses, the interfaces can “see” each other. The variation in the interface thermal resistance as the layer thickness increases is found to be consistent with a transition from ballistic to diffusive phonon transport.
11:45 AM - II3.6
Temperature Dependent Thermal Conductivity of Carbon Nanotube/Epoxy Composites
Michael Jakubinek 1 3 , Mary White 1 2 3 , Paul Watts 4 , David Carey 4 Show Abstract
1 Department of Physics, Dalhousie University, Halifax, Nova Scotia, Canada, 3 Institute for Research in Materials, Dalhousie University, Halifax, Nova Scotia, Canada, 2 Department of Chemistry, Dalhousie University, Halifax, Nova Scotia, Canada, 4 Advanced Technology Institute, School of Electronics and Physical Sciences, University of Surrey, Guildford United Kingdom
Carbon nanotubes (CNTs) have received particular attention as fillers in polymer composites because of their exceptional properties and high aspect ratios, which suggest that significant improvements in the polymer properties might be achieved with very low CNT content. The high thermal conductivity of individual CNTs makes such composites candidates for new thermal interface materials. Advances in CNT synthesis and the availability of commercial supplies of CNTs are removing one practical obstacle to the development of these composites but the thermal conductivity enhancements achieved to date for CNT/epoxy composites are relatively poor in comparison to early expectations. It has been demonstrated that a key factor limiting the enhancement is the interfacial thermal resistance associated with the CNT/epoxy interfaces. The quality of the CNT dispersion in the epoxy matrix is also important. Here we will show results for the thermal conductivity enhancement due to CNT loading as functions of weight percent and temperature. Enhancements at 300 K are at the low end in comparison to others in the literature but the quality of the CNT dispersion limits the enhancement we observe. We show that the interfacial resistance increases at low temperature, consistent with expectations, and that the addition of CNTs can actually decrease the low-temperature thermal conductivity of the composites.
12:00 PM - II3.7
Micropatterned Adhesive Joints for Enhanced Through Thickness Thermal Conductivity
Sabyasachi Ganguli 1 , Sangwook Sihn 2 , Ajit Roy 1 , Liming Dai 3 Show Abstract
1 MLBC, AFRL, Dayton, Ohio, United States, 2 , UDRI, Dayton, Ohio, United States, 3 , University of Dayton, Dayton, Ohio, United States
Currently out of plane thermal conductivity (Kz) in adhesive joints fails to meet the needed Kz at the overall system level. In order to utilize the superior thermal conductivity of the MWNTs along the axial direction; vertically aligned MWNTs have been used in this study. Vertically aligned MWNTs has been partially infused with epoxy. Selective reactive ion etching (RIE) of the epoxy revealed the nanotube tips. In order to reduce the impedance mismatch and phonon scattering at the interface, gold is thermally evaporated on the nanotube tips. Bulk thermal conductivity measurements show marked improvement in thermal conductivity. Micropatterned aligned nanotube thermal patches would be placed at strategic locations based on thermomechanical modelling to optimize the through thickness thermal conductivity. Several nanoscale thermal conductivity measurements are being performed to investigate the thermal boundary resistances at the interfaces.
12:15 PM - II3.8
Transient States of Elemental Mixing in Reactive Multilayer Thin Films Studied with Nanosecond Electron Microscopy.
Judy Kim 1 2 , Thomas LaGrange 1 , Bryan Reed 1 , Geoffrey Campbell 1 , Nigel Browning 1 2 Show Abstract
1 Chemical & Materials Science, Lawrence Livermore National Laboratory , Livermore, California, United States, 2 Chemical Engineering & Materials Science, University of California, Davis, Davis, California, United States
Free-standing, polycrystalline Al/Ni multilayer thin films, or reactive multilayer foils (RMLF), react to form intermetallic compounds in a rapid, self-propagating reaction. Upon mixing, the exothermic formation reaction front reaches temperatures above 1120 K
and travels at a velocity of ~10m/s. Since RMLFs produce immense heat over a small surface area, they are used to fuse dissimilar materials, exposing only directly contacting surfaces to destabilizing heat.
Due to small size and fast velocity, phase change details could not be directly observed using conventional methods leaving the rate limiting mechanisms unclear, but transient states have now been observed in situ using the fast time resolution in the Dynamic TEM (DTEM). The DTEM maintains the high spatial resolution of conventional TEM and adds nanosecond time resolution capabilities. The DTEM at Lawrence Livermore National Laboratory uses high-speed ultraviolet laser pulses to induce electron photoemission, creating a fast, pulsed incident electron beam. The 125nm total thickness RMLFs are reacted in the microscope vacuum by an infrared drive laser, then the transient phases are observed with time-resolved imaging additionally showing a general temperature increase.
Because the dynamic evolution of phases occur in the narrow reaction front, a single DTEM image of this region gives significant information on metastable states, formation rate and fundamental mesoscale kinetics. Such experimental data showing a full cycle of phase transformations from discrete Al and Ni multilayers to the final intermetallic structure of Al3Ni will be presented. The cycle begins with separate Al and Ni layers, formation and depletion of transient phases, and stabilization to an Al3Ni phase. Considering that the heat from mixing travels at ~10m/s, it is intriguing to find that the entire phase transition cycle is observed to reach completion a surprisingly long time after the heat front has already passed, 13 to 20μs.
Further studies will use molecular dynamics simulations to explore this μs chasm between the thermal front and the mixing front. The RMLFs are ideal for direct experiment to simulation comparison due to the nanoscale geometry. Further DTEM analysis will focus on detection of Al melt, phase fractions, and quantification of thermal transport. This will lead to a complete picture of the dynamic process currently being observed. Direct observations of transient states in the self-propagating reaction have been made in the DTEM. This information will be used to create models completing the picture of this interesting dynamic process.
E. Ma, et al., Appl. Phys. Lett. 57, 12 (1990) 1262.
T. LaGrange, et al., Appl. Phys. Lett. 89, (2006) 044105.
This work performed under the auspices of the U.S. Dept. of Energy, Office of Basic Energy Sciences by Univ. of California Lawrence Livermore National Laboratory under contract No.W-7405-Eng-48. UCRL-ABS-225703.
12:30 PM - II3.9
Joule Heating and Current-Induced Instabilities in Magnetic Nanocontacts.
Anatoli Kadigrobov 1 2 , Sergei Kulinich 2 3 , Robert Shekhter 2 , Mats Jonson 2 , Vlad Korenivski 4 Show Abstract
1 Theoretische Physik III, Bochum Ruhr-Unuversitaet, Bochum Germany, 2 Department of Physics, Götebotg University, Götebotg Sweden, 3 , B.I.Verkin Institute for Low Temperature Physics and Engineering, Kharkov Ukraine, 4 Nanostructure Physics, Royal Institute of Technology, Stockholm Sweden
12:45 PM - II3.10
Thermal transport through Single Walled Carbon Nanotube – Benzene Junctions
Arun Bodapati 1 3 , Ki-Ho Lee 2 , Susan Sinnott 2 , Pawel Keblinski 3 Show Abstract
1 Materials Science, Harper International Corporation, Buffalo, New York, United States, 3 Materials Science, Rensselaer Polytechnic Institute, Troy, New York, United States, 2 Materials Science, University of Florida, Gainesville, Florida, United States
Transport properties of mesoscale devices involving molecular junctions with solid materials have gathered a lot of interest from both theoretical and experimental groups. In the present study, we used molecular dynamics simulations to study the flow of heat through a junction of a benzene molecule chemically bonded with carbon nanotubes, and found that the thermal conductance is quite high despite the acoustic mismatch between the molecule and the nanotube. To gain a further understanding of this phenomenon, we analyzed the vibrational modes of the junction and found that low frequency acoustic modes were delocalized over the entire junction leading to this apparent decrease in thermal resistance. The dependence of phonon transmission function of the molecular junction on it's local geometry will be explored as well.
Wednesday PM, April 11, 2007
Room 3020 (Moscone West)
2:30 PM - **II4.1
Phonon Transport Imaging up to Tera Images per Second.
S. Dilhaire 1 , J. Rampnoux 1 , S. Grauby 1 , W. Claeys 1 , C. Rossignol 2 Show Abstract
1 Centre de Physique Moleculaire Optique et Hertzienne (CPMOH), Universite Bordeaux, Talance Cedex France, 2 Laboratoire de Mecanique Physique (LMP), Universite Bordeaux, Talance Cedex France
Thermoreflectance is a powerful technique commonly used in thermal mapping and hot spot detection at micrometric scale with CW lasers. For nanomaterials, picosecond time resolution is needed to study phonon transfer at nanometric scale. This time resolution is obtained by optical sampling techniques, but the acquisition time is too important to obtain films with picosecond time resolution. The evolution of transient thermoreflecance technique will be exposed, the new performances allow mapping and imaging at 1012 image per second.New developments in phonons transport imaging will be presented. The first Tera-image per second imaging system will be described and applied to phonon transport study in nanomaterials.
3:00 PM - **II4.2
Simultaneous Imaging of Ballistic and Diffusive Phonon Transport Across Interfaces.
David Hurley 1 Show Abstract
1 Physics, Idaho National Laboratory, Idaho Falls, Idaho, United States
3:30 PM - II4.3
3D Temperature Measurement in IC Chips using Raman Spectroscopy.
Javad Shabani 1 , Xi Wang 1 , Ali Shakouri 1 Show Abstract
1 Jack Baskin School of Engineering, University of California, Santa Cruz, Santa Cruz, California, United States
4:00 PM - **II4.4
Phonon Engineering in Nanowires with the Acoustically Mismatched Barrier Shells: Implications for the Carrier Mobility and Thermal Management
Alexander Balandin 1 Show Abstract
1 Electrical Engineering, University of California - Riverside, Riverside, California, United States
Phonons manifest themselves practically in all electrical, thermal, optical and noise phenomena in semiconductors. Reduction of the feature size of electronic devices to the nanometer scale creates a new situation for the phonons propagation and interaction. From one side, it complicates heat removal from the downscaled electronic devices due to the increased diffuse acoustic phonon – boundary scattering. From the other side, it opens up an opportunity for the intelligent tuning of the phonon spectrum (dispersion) in nanostructures, thus achieving what has been termed as phonon engineering . In this talk I will show that while the diffuse acoustic phonon – boundary scattering is always detrimental for the electronic devices, the phonon engineering in nanoscale structures with high quality of interfaces may help to reduce the electron – phonon scattering, improve the carrier mobility and reduce heat generation in the transistor channel. I will review our recent results pertinent to the acoustic and optical phonons in nanostructures focusing on the methods of the suppression of the electron – phonon scattering in silicon nanowires with the acoustically mismatched barrier shells. The considered examples will include the silicon nanowires with the acoustically hard diamond barriers as well as the hybrid nanostructures made of silicon nanotubes assembled on biological templates . Our theoretical results show that the electron mobility in the silicon/diamond hetero-nanowires with 4-nm diameter can be made two orders of magnitude higher at 10 K and a factor of two higher at room temperature than the mobility in a free-standing silicon nanowire . The importance of this result for the downscaled architectures and possible silicon-carbon integration is augmented by an extra benefit of (polycrystalline) diamond, a superior heat conductor, for thermal management. The experimental thermal data for the electrically conducting and insulating nanodiamond films on silicon and diamond-like carbon heterostructures will also be discussed. In addition, I will present the results of the micro-Raman study of optical phonons in hybrid inorganic-biological nanostructures . This work was supported, in part, by the DARPA – SRC MARCO Center on Functional Engineered Nano Architectonics (FENA), National Science Foundation (NSF) and DARPA – DMEA funded UCR – UCLA – UCSB Center for Nanoscience Innovation for Defense (CNID).  A. Balandin and K.L. Wang, Phys. Rev. B, 58, 1544 (1998). V.A. Fonoberov and A.A. Balandin, Nano Letters, 5, 1920 (2005). V.A. Fonoberov and A.A. Balandin, “Enhancement of the carrier mobility in silicon nanowires with diamond coating,” Nano Letters, (2006). W.L. Liu, K. Alim, A.A. Balandin, et al., Appl. Phys. Lett., 86, 253108 (2005).
4:30 PM - **II4.5
Ballistic Transport of Phonons Studied by an Optical Pump and Probe Technique.
B. Perrin 1 , L. Belliard 1 , E. Perrone 1 , S. Zhang 1 Show Abstract
1 Institut des NanoSciences de Paris, Universite Pierre & Marie Curie, Paris France
5:00 PM - II4.6
Lifetimes of Si Optical Phonons by Time-Domain Raman Scattering
Jeffrey Letcher 1 2 , David Cahill 1 2 Show Abstract
1 Materials Science and Engineering, University of Illinois, Urbana, Illinois, United States, 2 Materials Research Laboratory, University of Illinois, Urbana, Illinois, United States
In high-field electronic devices, energy moves from the charge carriers through the optical phonons to the acoustic branches. The occupation number of the optical phonons, i.e. the effective temperature of the optical phonon system, is controlled by the balance between the generation of optical phonons by hot charge carriers and the decay of optical phonons by anharmonic coupling to the other vibrational modes of the crystal. The lifetimes of near-equilibrium, zone-center phonons can be measured in the frequency domain by the homogeneous Raman linewidth. In our work, using time-domain Raman scattering, we directly measure how the lifetimes of the zone-center LO phonons change as the occupation of the LO phonons is driven far from equilibrium. We use subpicosecond optical pulses at 785 nm generated by a Ti:sapphire laser oscillator in a pump-probe approach. The pump optical pulse generates hot electron-hole pairs that relax to the band edges by the excitation of optical phonons. We then measure the strength of the anti-Stokes Raman scattering of the probe optical pulse as a function of the delay time between the pump and probe. At low pump energies, we find a lifetime of 1.7 ps, in agreement with the homogeneous linewidth. At larger pump energies, when the occupation number of the zone-center optical phonons is doubled, the lifetime decreases to 1.1 ps. This reduction of the phonon lifetime with increases in the effective temperature of the optical phonons has important consequences for understanding nanoscale hot-spots and phonon-bottleneck effects in high-field devices.
5:15 PM - II4.7
Acoustic Phonon Scattering from Isolated Nanoparticles in Anisotropic Media.
Neil Zuckerman 1 , Jennifer Lukes 1 Show Abstract
1 Mechanical Engineering, University of Pennsylvania, Philadelphia , Pennsylvania, United States
5:30 PM - II4.8
Phonon Scattering and Thermal Conductivity in Doped Silicon by Molecular Dynamics Simulation.
Man Yao 1 2 , Taku Watanabe 2 , Simon Phillpot 2 , Patrick Schelling 3 , Pawel Keblinski 4 , David Cahill 5 Show Abstract
1 School of Materials Science and Engineering, Dalian University of Technology, Dalian China, 2 Department of Materials Science and Engineering, University of Florida, Gainesville, Florida, United States, 3 Department of Physics and AMPAC, University of Central Florida, Orlando, Florida, United States, 4 Department of Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States, 5 Department of Materials Science and Engineering, University of Illinois, Urbana, Illinois, United States
Simon R. Phillpot University of Florida
Sebastian Volz Ecole Centrale Paris, CNRS
Theodorian Borca-Tasciuc Rensselaer Polytechnic Institute
Mansoo Choi Seoul University
II5: Low-dimensional Systems
Thursday AM, April 12, 2007
Room 3020 (Moscone West)
9:00 AM - **II5.1
Transient Heat Transfer in Silicon Nanowire by Monte Carlo and Discrete Ordinate Methods.
Karl Joulain 1 , Damian Terris 1 , David Lacroix 2 , Denis Lemonnier 1 Show Abstract
1 LET, ENSMA, Futuroscope France, 2 LEMTA, Université Henri Poincaré, Nancy France
9:30 AM - II5.2
Thermal Conductivity of Nanocrystalline and Microcrystalline Diamond Films: Effects of the Nitrogen Doping and Boundary Scattering.
Manu Shamsa 1 , Weili Liu 1 , Irene Calizo 1 , Suchismita Ghosh 1 , Alexander Balandin 1 , Victor Ralchenko 2 , A. Popovich 2 , A. Saveliev 2 Show Abstract
1 Nano-Device Laboratory, Department of Electrical Engineering, University of California-Riverside, Riverside, California, United States, 2 , General Physics Institute of the Russian Academy of Sciences, Moscow Russian Federation
Diamond materials, owing to their extreme hardness, chemical inertness and high thermal conductivity have been used for coatings, optical windows, surface acoustic-wave devices and heat spreaders. The nanocrystalline diamond (NCD) films have recently attracted attention for potential applications in electronics. It has been demonstrated that the electrical conductivity of NCD films can be changed by nitrogen doping to form n-type material. These properties make NCD promising for the proposed carbon-based electronics, in particular, with the components made of carbon nanotubes. It may also be used in future downscaled CMOS technology . Investigation of thermal conduction in NCD films on silicon is important for their applications in electronics and coatings as well as for understanding of the properties of NCD/Si interfaces. In this talk we report the results of our experimental study of the thermal conductivity in NCD films on silicon using a variety of techniques: 3ω, laser-flash and transient hot-disk methods. The nanocrystalline nature of the samples, as opposed to the amorphous carbon films  has been rigorously checked by XRD and Raman spectroscopy. The thermal conductivity temperature dependence has been studied for the undoped and nitrogen-doped NCD films for T=80-400K and compared with that in microcrystalline diamond (MCD) films. The effects of the phonon scattering from the grain boundaries and film interfaces on the thermal conduction have been studied using three different models: Callaway-Klemens, phonon-hopping and the minimum thermal conductivity. For NCD, the room temperature thermal conductivity is 0.1-0.16W/cmK and decreases with the nitrogen doping. The temperature dependence of the thermal conductivity in NCD is different from that in MCD films and can be adequately described by the phonon-hopping model. The work at UCR was supported, in part, by MARCO center on Functional Engineered Nano Architectonics (FENA) and the National Science Foundation (NSF) award to A.A.B; the work at GPI was supported by the Russian Ministry of Science and Education.  W.L. Liu, M. Shamsa, I. Calizo, A.A. Balandin, V. Ralchenko, A. Popovich and A. Saveliev, Appl. Phys. Lett., 89, 171915 (2006). M. Shamsa, W.L. Liu, A.A. Balandin, C. Casiraghi, W.I. Milne and A.C. Ferrari, Appl. Phys. Lett., 89, 161921 (2006).
9:45 AM - II5.3
Molecular Dynamics Simulations of Diffusive-Ballistic Heat Conduction in Carbon Nanotubes.
Junichiro Shiomi 1 , Shigeo Maruyama 1 Show Abstract
1 Department of Mechanical Engineering, The University of Tokyo, Tokyo Japan
The expanding expectations for single-walled carbon nanotubes (SWNTs) include applications for various electrical and thermal devices due to their unique electrical and thermal properties. On considering the actual applications of SWNTs, one of the essential tasks is to characterize their thermal properties not only for thermal devices but also for electrical devices since they determine the affordable amount of electrical current through the system. While experimental attempts to characterize thermal properties of SWNTs encounter technical difficulties, the expectation for theories and numerical simulations is high. Here, we introduce our recent studies on SWNT heat conduction using classical molecular dynamics (MD) simulations. While detail investigations of SWNT heat conduction are strongly motivated by device applications, they also serve to provide understanding in fundamentals of heat conduction in quasi-one-dimensional systems. The phonon mean free path of an SWNT is expected to be extraordinary long due to the strong carbon bonds and quasi-one-dimensional confinement of phonons. Consequently, the ballistic phonon transport regime stretches beyond the realistic length in many applications even at room temperature. This gives rise to distinct length and diameter dependences of thermal conductivity. By using non-equilibrium MD simulations, we have calculated thermal conductivity for a range of nanotube-lengths up to a few micrometers at room temperature and characterized gradual transition from nearly pure ballistic phonon transport to diffusive-ballistic phonon transport . The diffusive-ballistic phonon transport gives rise to unique heat conduction characteristics with presence of intrinsic thermal resistances. This is demonstrated with SWNT isotope superlattice structures formed by periodically connecting 12C-SWNT and 13C-SWNT . The effective thermal conductivity was found to take a minimum value with certain critical period thickness, which reveals the key lengthscale of the diffusive-ballistic phonons. The analyses clarify the task of zone-folding and thermal boundary effects. We have also explored the non-stationary heat conduction of an SWNT . By applying a heat pulse to a pure SWNT, non-Fourier heat conduction was observed, where the dominant energy is transported in a wave-like form. The limitation and applicability of macroscopic Fourier and non-Fourier models were examined. Furthermore, modal analyses were performed to identify the phonon modes with major contribution to the non-Fourier heat conduction. References:  S. Maruyama and J. Shiomi, (To be submitted). J. Shiomi and S. Maruyama, Phys. Rev. B 74 (2006) 155401. J. Shiomi and S. Maruyama, Phys. Rev. B 73 (2006) 205420. S. Maruyama, Y. Igarashi, Y. Taniguchi and J. Shiomi, J. Therm. Sci. Tech. (in press).
10:00 AM - II5.4
Growth Mechanism & Thermal Properties of Aligned Carbon Nanotubes on Inconel Substrate.
Sunil Pal 1 , Saikat Talapatra 2 , Swastik Kar 2 , Robert Vajtai 3 , Theodorian Borca-Tasciuc 1 3 , Pulickel Ajayan 2 3 Show Abstract
1 Mechanical, Aerospace, & Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States, 2 Maerials Science & Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States, 3 Rensselaer Nanotechnology Center, Rensselaer Polytechnic Institute, Troy, New York, United States
10:15 AM - II5.5
Characterization of Heat Propagation along Single Tin Dioxide Nanobelt Using the Thermoreflectance Method
Xi Wang 1 , James Christofferson 1 , Ali Shakouri 1 , Li Shi 2 Show Abstract
1 Electrical Engineering, Univ. of California Santa Cruz, Santa Cruz, California, United States, 2 Department of Mechanical Engineering, UT Austin, Austin, Texas, United States
One-dimensional nanostructures such as nanowires and nanobelts have been studied extensively during the past few years. Compare to bulk materials, low-dimensional inorganic nanostructures benefit from quantum effects and high surface sensitivity. The modified density of electronic states and reduced electron-phonon and phonon-phonon scatterings, etc, change the bulk properties substantially. The ribbon- or belt-like SnO2 nanostructures have been synthesized using a vapor-solid method, with a thickness of 10~100nm and a width of 50~500nm. They belong to metal-oxides which are single crystalline semiconductors but without the presence of a surface insulating layer of native oxides.The micro device used for heat transfer measurements on an individual belt was fabricated by the standard IC fabrication process. It consisted of two adjacent 15µmx27µm low stress silicon nitride (SiNx) membranes suspended with five 0.5µm-thick, 420µm-long and 2µm-wide silicon nitride beams. A 30nm-thick and 300nm-wide platinum thermometer resistance (PTR) coil was deposited on each membrane. The PTR was connected to 200x200µm Pt bonding pads on the substrate via 1.8µm-wide Pt leads on the long SiNx beams. An additional Pt electrode was put on each membrane opposite to each other, providing electrical contact for the SnO2 nanobelt itself. SnO2 nanobelts were dissolved in an isopronol solution and soak in ultrasonic for 5-10s. The solution was then poured on top of the micro device, spun to dry. One nanobelt was placed across the bridge of between the two membrane heaters. Focused ion beam technique was used to achieve better electrical and thermal contact between the nanobelt and electrodes. In order to study the temperature profile along the nanobelt, we used the thermoreflectance imaging technique with blue light illumination. This non-contact optical method can produce thermal maps with <0.1C temperature and <250nm spatial resolution. The sample was put in a chamber kept in high vacuum ~ 10-4 to 10-5 torr to prevent air convection influencing the heat transfer study. Pulsed current with 20~220Hz frequency and 0~50uA magnitude were sent to one side PTR to create a temperature difference. Heat transfer along the nanobelt, temperature distribution on PTR and thermal boundary resistance between the nanobelt and the heater were studied. This is used to calculate the inherent thermal conductance of the nanobelt.
10:30 AM - II5.6
Molecular Dynamics Simulation of Thermal Conductivity of Diamondoid Crystals
Ming Hu 1 , Sergei Shenogin 1 , Pawel Keblinski 1 , Arun Majumdar 2 Show Abstract
1 Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States, 2 Departments of Mechanical Engineering and Materials Science and Engineering, University of California, Berkeley, Berkeley, California, United States
Hydrocarbon molecules with diamond structure, called diamondoids, have shown promise in a variety of fields and have been used as templates and building blocks for nanotechnology. Motivated by very large mismatch between strong, covalent intramolecular bonding with weak intermolecular bonding, we use molecular dynamics (MD) simulations to examine thermal transport of diamondoid crystals. In particular, thermal conductivity of small molecule adamantine and larger molecule pentamantane crystal is studied by non-equilibrium MD. By assessing the finite-size effects we determine thermal conductivity of these two diamondoids, and elucidate the role of the molecule size on thermal transport. In this context, we discuss a possibility of minimum thermal conductivity arising from the balance between heat transfer due to collective molecular motion and that due to motion of carbon atoms.
10:45 AM - II5.7
Thermal Conductivity of Diamond-like Carbon Films with Different Degree of Structural Disorder.
Manu Shamsa 1 , Weili Liu 1 , Alexander Balandin 1 , Cinzia Casiraghi 2 , Andrea Ferrari 2 , W. Milne 2 Show Abstract
1 Nano-Device Laboratory, Department of Electrical Engineering, University of California - Riverside, Riverside, California, United States, 2 Engineering Department, Cambridge University, Cambridge United Kingdom
Diamond-like carbons (DLC) are promising materials for protective coatings and micro-electro-mechanical systems applications. Silicon-carbon-based heterostructures are also being considered as candidates for the future “beyond CMOS” electronic circuits. Accurate values of the thermal conductivity of DLCs are important for thermal engineering of micro-devices. Understanding the specifics of heat transport through DLC/silicon interface may help in silicon-carbon integration. Thermal conductivity for different forms of carbon materials, ranging from graphite, diamond to nano-crystalline graphite and nano-diamond, has been previously reported by a number of groups. However, DLC thermal conductivity measurements were often done with different techniques and, for a given method, not for a comprehensive set of samples, resulting in a substantial discrepancy in the reported values. The effects of the thermal boundary resistance at DCL/Si interface have not been fully addressed. Here we determine the thermal conductivity for a comprehensive set of carbon films ranging polymeric hydrogenated amorphous carbons (a-C:H) to tetrahedral amorphous carbon (ta-C). All our films are directly characterized in terms of the mass density, Young’s Modulus, hydrogen content and their structure is further assessed by multi-wavelength Raman spectroscopy. The measurements for all samples have been performed using the same 3ω technique . We show that thermal conduction is governed by the amount and structural disorder of the sp3 phase. If the sp3 phase is amorphous, the thermal conductivity scales linearly with C-C sp3 content, density and the elastic constants. Polymeric and graphitic films have the lowest thermal conductivity (0.2-0.3 W/mK), hydrogenated ta-C:H has K~1W/mK; ta-C has the highest K (3.5 W/mK). If the sp3 phase orders, even in small grains such as in micro- or nano-diamond, a strong thermal conductivity increase occurs, for given density, Young’s modulus and sp3 content. M. Shamsa, W.L. Liu, A.A. Balandin, C. Casiraghi, W.I. Milne and A.C. Ferrari, Appl. Phys. Lett., 89, 161921 (2006).The work at UCR has been supported, in part, by DARPA-SRC Microelectronics Advanced Research Corporation and its Focus Center on Functional Engineered Nano Architectonics (FENA).
11:30 AM - II5.8
Frequency Dependence of the Thermal Conductivity of Semiconductor Alloys
Yee Kan Koh 1 2 , David Cahill 1 2 Show Abstract
1 Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 2 Frederick Seitz Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Low frequency phonons are relatively unaffected by point defect phonon scattering in semiconductor alloys and, therefore, it is commonly assumed that a small fraction of the phonons of a semiconductor alloy carry a large fraction of the heat. We observe a direct consequence of these lattice dynamics in the frequency dependence of the thermal conductivity of epitaxial layers of In0.49Ga0.51P, In0.53Ga0.47As and Si0.4Ge0.6. We measure the thermal conductivity by time-domain thermoreflectance and span a wide range of frequencies, 0.6 < f < 10 MHz; layer thickness 0.1 < h < 3 μm; and temperatures 88 < T < 300 K. For thick layers, the thermal conductivity measured at 10 MHz is a factor of ~2 smaller than the thermal conductivity at 0.6 MHz. Thermal conductivity measurements of single crystals (Si, GaAs, InP) and dielectrics (SiO2) over the same frequency range show no frequency dependence. A simple “two-fluid model” explains why this frequency dependence is manifested at frequencies that are much smaller than the scattering rates of the dominant heat carriers. This frequency dependence can be used as a new approach to probe the phonon distributions in semiconductor alloys.
11:45 AM - II5.9
Highly Textuted Nano-Crystalline WSe2 Thin Film- Ultra Low Thermal Conductivity Material.
Ngoc Nguyen 1 , David Johnson 1 , Catalin Chiritescu 2 , David Cahill 2 , Paul Zschack 3 , Arun Bodapati 4 , Pawel Keblinski 4 Show Abstract
1 Chemistry, University of Oregon, Eugene, Oregon, United States, 2 Materials Science Department, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 3 Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois, United States, 4 Department of Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States
Ultra low thermal conductivity of the WSe2 thin films is achieved by controlling order and disorder of two dimensional WSe2 sheets. We have prepared extremely smooth and highly textured nano-crystalline WSe2 films by modulated elemental reactant. The film structure determined from conventional and synchrotron x-ray diffractions is discussed. The film's cross plane thermal conductivity measured by time domain thermoreflectance is as low as 0.05 W/m-K at room temperature. This value is 30 times smaller than the c-axis thermal conductivity of single crystal WSe2 and a factor of 6 smaller than the predicted minimum thermal conductivity for this material. The values are confirmed by molecular dynamics simulations on model structures. Ion irradiation of the samples disrupted the layered structure and the crystallinity of the WSe2 sheets and lead to an increase thermal conductivity. We attribute the ultra-low thermal conductivity to the localization of lattice vibrations induced by the random stacking of two-dimensional crystalline WSe2 sheets.
12:00 PM - II5.10
Nanoscale Thermal Property of Amorphous SiC: A Molecular Dynamics Study.
Weiqiang Wang 1 , Aiichiro Nakano 3 , Rajiv Kalia 2 , Priya Vashishta 1 Show Abstract
1 Materials Science, Univ. of Southern California, Los Angeles, California, United States, 3 computer sciences, Univ. of Southern California, Los Angeles, California, United States, 2 Physics, Univ. of Southern California, Los Angeles, California, United States
12:15 PM - II5.11
Size and Temperature Dependence of the Thermal Response of ZnO Nanowires.
Ambarish Kulkarni 1 , Min Zhou 1 Show Abstract
1 GWW School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
The thermal conductivity of zinc oxide (ZnO) nanowires with lateral dimensions between 18-41 Å and the [01-10] growth direction over the temperature range of 500-1500 K is characterized through molecular dynamics (MD) simulations which use the Green-Kubo approach. Values obtained are approximately one order of magnitude lower than that for the corresponding bulk ZnO single crystal. Surface scattering of phonons and the high surface-to-volume ratios of the nanowires are primarily responsible for the significantly lower thermal conductivity at the nanosize scale which is found to be size-dependent over the range of lateral dimensions considered. Specifically, over 500-1500 K, the conductivity of the 21.22×18.95 Å belt is approximately 8-0.5% lower than that of the 31.02×29.42 Å belt and the conductivity of the 31.02×29.42 Å belt is approximately 6-5% lower than that of the 40.81×39.89 Å belt. Significant temperature dependence is also observed. The conductivity is seen to decrease by 52% as the temperature is increased from 500 K to 1500 K. This effect is attributed to thermal softening of the material, three- and four-phonon processes, and optical phonon interactions.
12:30 PM - II5.12
Experimental Observation of Heat Transport in Silicon Nanowires
Helena Silva 1 , Nathan Henry 2 , Ali Gokirmak 1 Show Abstract
1 Electrical and Computer Engineering , University of Connecticut, Storrs, Connecticut, United States, 2 Electrical Engineering, Michigan Technological University, Houghton, Michigan, United States
Thursday, April 12New Presenter Time and Paper NumberII5.13 @ 11:45 to II5.12 to 11:30Experimental Observation of Heat Transport in Silicon Nanowires. Helena Silva
II6: Experimental Methodologies
Thursday PM, April 12, 2007
Room 3020 (Moscone West)
3:00 PM - **II6.1
Laser-Assisted Nanoprocessing via Near Field Optics
Costas Grigoropoulos 1 , David Hwang 1 Show Abstract
1 Department of Mechanical Engineering, Laser Thermal Laboratory, University of California, Berkeley, Berkeley, California, United States
Research results on laser-assisted nanomachining, nanolithography and nanodeposition will be presented. Ultra-fast and nanosecond pulsed lasers have been coupled to near-field-scanning optical microscopes (NSOMs) through fiber probes as well as with atomic force microscope (AFM) tips in apertureless configurations. Experiments have been conducted on the surface modification of metals, polymers and semiconductor materials. By combining nanoscale ablative material removal with subsequent chemical etching steps, ablation nanolithography and patterning of fused silica and crystalline silicon wafers has been demonstrated. Confinement of laser-induced crystallization to nanometric scales has also been shown. Nucleation and growth of semiconductor materials has been achieved by Laser Chemical Vapor Deposition (LCVD) at the nanoscale level. Time resolved emission measurements indicate potential application in the context of nanoscale chemical analysis. Work on laser-assisted current measurement in nanosctructures using scanning probes is presented.
3:30 PM - **II6.2
High Resolution Thermal Imaging of Integrated Circuits.
Gilles Tessier 1 , Mathieu Bardoux 1 , Celine Filloy 1 , Daniele Fournier 1 Show Abstract
1 , UPR A005 CNRS / ESPCI, Paris France
4:30 PM - II6.3
Parallel Measurement of Thermal Conductivity in Sub-100 nm Thin Film Copper
Patrick McCluskey 1 , Jae-Hyun Kim 1 , Joost Vlassak 1 Show Abstract
1 DEAS, Harvard University, Cambridge, Massachusetts, United States
The parallel nano-differential scanning calorimeter (PnDSC) is a new device that employs an array of chip nanocalorimeters to allow high throughput materials thermal analysis. Each calorimetric cell consists of a thin (~80 nm) SiNx membrane and thin (~125 nm) W Joule heater/thermistor patterned in a 4-point resistance measurement scheme; these calorimetric cells are supported by a relatively massive Si frame. Addendum heat capacities are on the order 100 nJ/K, with even smaller sample heat capacities. These small heat capacities make the device very sensitive to heat loss, which facilitates thermal conductivity measurements at reduced length scales.Since measurements using the PnDSC are performed in vacuum, convection losses are negligible and the primary modes of heat transfer are radiation and conduction through the SiNx and W. These significant modes of heat transfer have been considered using analytical, numerical and finite element analysis (FEA). In some cases (length scale of radiation-mitigated diffusion < width of the membrane) the 1D nonlinear-radiation diffusion equation can be used to model the steady-state heat loss in the SiNx. Numerical methods extend this analysis into the W metallization and the transient regime. FEA and experimental results verify the analytical and numerical solutions. The PnDSC uses these models to measure the transverse thermal conductivity of thin (< 100 nm) films. The nonlinear analyses enable thermal conductivity to be measured over a large temperature range. Optimization of metallization pattern geometry produces an approximately uniform temperature along the length of the sensor. The parallel nature of the PnDSC allows many samples of unique composition, film thickness, grain size, etc. to be prepared and measured in parallel, substantially reducing the analysis times for such measurements. The capability of this new measurement device/ technique is demonstrated by determining the transverse thermal conductivity of thin (< 100 nm) film copper as a function of film thickness.
4:45 PM - II6.4
Thermal Characterization of Micro/Nanoscale One-dimensional Structures Using Transient Electro-thermal Technique
Xinwei Wang 1 , Jiaqi Guo 1 , Tao Wang 1 Show Abstract
1 Mechanical Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska, United States
In this paper, a transient technique is developed to characterize the thermophysical properties of one-dimensional conductive and non-conductive micro/nanoscale wires/tubes. In this technique, the thin wire/tube to be measured is suspended between two electrodes. When feeding a DC current to the sample, its temperature will increase and take a certain time to reach the steady state. This temperature evolution is probed by measuring the variation of voltage over the wire, which is directly related to resistance/temperature change. The temperature evolution history of the sample can be used to determine its thermal diffusivity. A 25.4-um thick platinum wire is used as the reference sample to verify this technique. Sound agreement is obtained between the measured thermal diffusivity and the reference value. Applying this transient electro-thermal technique, the thermal diffusivities of single-wall carbon nanotube bundles and polyester fibers are measured successfully.
5:00 PM - II6.5
Ratio Function Approach for 3ω Data Reduction.
T. Tong 1 , Arun Majumdar 1 Show Abstract
1 Mechanical Engineering, UC Berkeley, Berkeley, California, United States
5:15 PM - II6.6
Thermal Processing of Composite Nanoparticles
Mansoo Choi 1 Show Abstract
1 Mechanical and Aerospace Engineering, Seoul National University, Seoul Korea (the Republic of)
We present thermal processing of composite nanoparticles and their unique properties. The topic includes the synthesis of well mixed composite nanoparticles, crystallite embedded nanoparticles, doped nanoparticles, and coated nanoparticles. The methodology utilizes flame aerosol technique and the materials include various oxides and carbon nanoparticles.We will also present possible application area such as nanofluids, field emission, nanooptical device, and magnetic devices.
5:30 PM - II6.7
Thermal Conductivity Measurement of Thin Metallic Films using Radiation Heat Exchange Method.
Sang Ryu 1 , Seungwhan Ma 1 , Youngman Kim 1 , Woonam Juhng 2 Show Abstract
1 Dept. of Materials Science & Engineering, Chonnam National University, Gwangju Korea (the Republic of), 2 Dept. of Mechanical Engineering, Chonnam National University, Gwangju Korea (the Republic of)
5:45 PM - II6.8
Measurement of Thermal Properties of Thin Films Using the Photothermal Deflection and Phototermal Displacement Methods.
Chang Han Park 1 , Hyongmoo Rhee 1 , Chang-Koo Kim 1 , Hyunjung Kim 2 , Jaisuk Yoo 2 Show Abstract
1 Chemical Engineering, Division of Energy Systems Research, Ajou University, Suwon Korea (the Republic of), 2 Mechanical Engineering, Ajou University, Suwon Korea (the Republic of)
Understanding of thermal properties, such as thermal conductivity and thermal diffusivity, of thin films becomes very important for the fabrication of various devices including microelectronic devices, photonic devices, microelectromechanical system (MEMS) devices, and so on. In the course of the use of thin films for the fabrication of the above-mentioned devices, the heat generated must be rapidly dissipated in order to protect the thin films from thermal shock. In addition, it is known that the thermal conductivity of thin films may be different from the bulk values due to differences in the phonon transport mechanisms between thin films and the bulk material. Therefore, the precise measurement of thermal conductivity and thermal diffusivity of thin films is of primary concern to the fabrication of many devices. The measurement technique of thermal properties can be classified into a contact and non-contact method. The contact method has a limitation for a precise measurement of the thermal property because it includes a large unavoidable error due to thermal contact resistance. For this reason, the non-contact method is currently preferred to the contact method. In this study, we have developed an experimental system and a methodology to measure thermal properties of various thin films. Non-contact methods such as the photothermal displacement method and the phtothermal deflection method were used to measure thermal conductivity and diffusivity of metal and non-metal thin films with single or multiple layers. It was found that thermal properties of thins films depended on the thickness of the films in the range of 0.01 – 1 μm. This behavior could be explained by the micro-scale heat transfer mechanism.
Simon R. Phillpot University of Florida
Sebastian Volz Ecole Centrale Paris, CNRS
Theodorian Borca-Tasciuc Rensselaer Polytechnic Institute
Mansoo Choi Seoul University
II7: Modelling and Simulation: Methods and Applications
Friday AM, April 13, 2007
Room 3020 (Moscone West)
9:30 AM - **II7.1
Quantum Mechanical Description of Phonon Transport Through Atomically Defined Systems.
Natalio Mingo 1 2 3 Show Abstract
1 , CEA-Grenoble, Grenoble France, 2 , University of California at Santa Cruz, Santa Cruz, California, United States, 3 , UARC/NASA-Ames, Moffett Field, California, United States
Many different theoretical approaches have been developed to model lattice thermal transport through nano-sized solid structures. At the smallest level, atomistic calculations provide the route towards fully understanding the phonon transport process across nanomaterials and interfaces. Within the atomistic descriptions, there are several categories: 1-“classical”, such as molecular dynamics, 2-“semi-classical”, such as the Boltzmann-Peierls equation, and 3-“quantum-mechanical”, such as Green’s functions techniques. In this talk we will focus on quantum mechanical effects on nanoscale thermal transport, with specific examples in nanowires, nanotubes, and molecular junctions. Thus, we will discuss specific theoretical techniques from categories 2 and 3 above.We will start from the simplest of these approaches , which gives a good account of experimental measurements in semiconductor nanowires. Then we will discuss the more complex problem of thermal conduction in single walled carbon nanotubes, graphene, and graphite. We will see how the character of the 3-phonon scattering processes in these systems results in long phonon mean free paths and in large thermal conductivities . Subsequent experimental results have confirmed findings from the theoretical study .Then, we will discuss a newer technique, based on non-equilibrium Green’s functions, developed to study the quantum mechanical many-body problem of interacting phonons flowing through generic, atomically described, anharmonic structures . This technique is applied to investigate a simple model molecular junction. We will show some strictly quantum mechanical effects that take place in the anharmonic scattering process. Finally, we will present new results on first-principles calculations of phonon conduction across nitrogen impurities in carbon nanotubes . N. Mingo, Phys. Rev. B 68, 113308 (2003); N. Mingo and D. A. Broido, Phys. Rev. Lett. 93, 246106 (2004). N. Mingo and D. A. Broido, Nano Letters 5, 1221-1225 (2005); N. Mingo and D. A. Broido, Phys. Rev. Lett. 95, 096105 (2005).  C. Yu, L. Shi, Z. Yao, D. Li, A. Majumdar, Nano. Lett., Vol. 5, 1842-1846 (2005); E. Pop, D. Mann, Q. Wang, K. E. Goodson and H. Dai, Nano Letters, 6, 96 (2006). N. Mingo, Phys. Rev. B, 74, 125402 (2006). N. Mingo, D. A. Stewart, D. A. Broido, and D. Srivastava, Nanoscale phonon transport from First-Principles (to be published).
10:00 AM - II7.2
Atomic-Scale Modeling of Phonon-Mediated Thermal Transport in Microsystems
Chris Kimmer 1 , Sylvie Aubry 1 , Patrick Schelling 1 , Ashton Skye 1 Show Abstract
1 Mechanics of Materials, Sandia National Laboratories, Livermore, California, United States
An atomistic model of phonon-mediated thermal transport for subgrid physicsinput to microsystems device design modeling, generating a robust, multiscaledescription of thermal transport is presented. Pre-existing and novelmolecular dynamics techniques are used to perform simulations explicitlyexamining phonon-microstructure interactions for a range of defects and grainboundaries, providing a detailed characterization of phonon transport at theatomic scale. In particular we will demonstrate that this model is able todetermine thermal conductivities at the macroscopic level and Kapitzaconductances at the nanoscale level for different grain boundaries and defectsin polycrystalline silicon.The simulation results are analyzed to produce subgrid models of phonontransport for use in our mesoscale models which, in turn, provide input todevice-scale models. Comparison against existing experimental data and furthermeasurements of thermal conductivity over a broader range of temperatures inwell-characterized polycrystalline samples are used to validate the new model. This work was supported by the Office of Basic Energy Sciences, the U.S.DOE under contract no. DE-AC04-94AL85000.
10:15 AM - II7.3
Thermal Transport in Nanocrystalline Ceramics by Atomic-Level Simulation.
Taku Watanabe 1 , Priyank Shukla 1 , Susan Sinnott 1 , Juan Nino 1 , Simon Phillpot 1 , James Tulenko 2 , Robin Grimes 3 Show Abstract
1 Department of Materials Science and Engineering, University of Florida, Gainesville, Florida, United States, 2 Department of Nuclear and Radiological Engineering, University of Florida, Gainesville, Florida, United States, 3 Department of Materials, Imperial College, London United Kingdom
In ceramic insulators, heat is carried by phonons, and their dynamics dictate the thermal conductivity of the material. While in coarse-grained materials phonon-phonon interactions dominate, in nano-size materials phonon-interface interactions can dominate the thermal conductivity of the material. We have performed large scale molecular dynamics (MD) simulations to calculate the thermal conductivity of three polycrystalline ceramics of differing crystal structures (UO2, MgO, and Nd2Zr2O7) as a function of temperature and grain size. The thermal conductivities of the polycrystalline materials are analyzed in detail to extract the effects of the interfaces. It is found that the interface conductance increases with temperature. This is understood as arising from anharmonic interactions associated with interface modes that enhance the coupling of phonon modes on the two sides of an interface.
This work was funded by DOE-NERI Awards DE-FC07-05ID14649 and DE-FC07-05ID14647.
10:30 AM - II7.4
Phonon Rarefaction and Diffraction Effects in Nanoconstrictions.
Sebastian Volz 1 , Olivier Chapuis 1 Show Abstract
1 EM2C, Ecole Centrale Paris, Chatenay Malabry France
10:45 AM - II7.5
Thermal Conduction at the Nanoscale in Al and Ni/Al by MD.
Ya Zhou 1 , Benjamin Anglin 1 , Alejandro Strachan 1 Show Abstract
1 School of Materials Engineering, Purdue University, West Lafayette, Indiana, United States
11:30 AM - **II7.6
Thermal Radiative Transport in Nanostrctures and its Application in Energy Technology.
Gang Chen 1 , Lu Hu 1 , Dye-Zone Chen 1 , Arvind Narayanaswamy 1 , Xiaoyuan Chen 1 Show Abstract
1 , MIT, Cambridge, Massachusetts, United States
12:00 PM - II7.7
Heat Transfer in Disordered Layered Crystals
Lin Hu 1 , Arun Bodapati 1 , Pawel Keblinski 1 , David Cahill 2 Show Abstract
1 Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States, 2 Department of Materials Science and Engineering, Frederick Seitz Materials Research Laboratory, University of Illinois, Urbana, Illinois, United States
Recent experiments demonstrated that the cross-plane thermal conductivity of WSe2 thin films is as small as 0.05 W/m-K at room temperature, 30 times smaller than the c-axis thermal conductivity of single-crystal WSe2 and a factor of 6 smaller than the predicted minimum thermal conductivity for this material. It was hypothesized that the ultra-low thermal conductivity of these layered crystals is due to the localization of lattice vibrations induced by the random stacking of two-dimensional crystalline WSe2 sheets. We use a combination of equilibrium and non-equilibrium molecular dynamics (MD) simulations as well as phonon localization analysis to examine this hypothesis. In particular simulation of fully ordered and disordered layered crystals at a range of temperatures allow evaluation of thermal phonon-phonon scattering and structural disorder induced thermal conductivity reduction. Preliminary results of non-equilibrium MD simulations indicate that stacking disorder is very effective in thermal conductivity reduction at room temperature, while ordered structures show higher and size dependent thermal conductivity values.
12:15 PM - II7.8
Non-Local Near Field Heat Transfer between Metallic Bodies
Olivier Chapuis 1 , Sebastian Volz 1 , Marine Laroche 1 , Jean-Jacques Greffet 1 Show Abstract
1 EM2C, Ecole Centrale Paris, Chatenay Malabry France
Heat transfer between closely spaced bodies does not involve emission and absorption of photons but mainly electrostatic interactions. This Near-Field heat transfer can be enhanced when surface waves such as Plasmons-Polariton are involved. Calculations indeed proved a six orders of magnitude increase of the heat transfer coefficient. However, the analytical solution diverges at very small scales because no physical cut-off is involved. Besides, experimental works proved a one to two orders of magnitude increase between bodies of bulk gold but a saturation is observed when the separation distance becomes smaller than 10nm.The physical solution to remove the divergence is to include non-local effects: the dielectric constant depends on frequency and wave-vector.We present the calculation of the non-local contributions in Near-Field heat transfer between metals when the separation distance between two bodies becomes very small. We show that non-locality does not affect radiation between metals due to the very small cut-off distances. Heat flux is enhanced due to S-polarized waves. We explain why this fact implies the observed saturation in the experimental signals and also means that plasmon waves are ineffective in the case of metals.
12:30 PM - II7.9
Thermal Conductivity of Diamond-Silicon from First-principles.
Keivan Esfarjani 1 , Joseph Feldman 2 , Harold Stokes 3 Show Abstract
1 Physics, University of California, Santa Cruz, California, United States, 2 , Naval Research Labs, Washington, District of Columbia, United States, 3 Physics, Brigham Young University, Provo, Utah, United States