The 2 nd International Conference on Phononics and Thermal Energy Science (PTES2014)

Transcription

1 The 2 nd International Conference on Phononics and Thermal Energy Science (PTES2014) Center for Phononics and Thermal Energy Science School of Physics Science and Engineering, Tongji University 26 May 31 May, 2014 SHANGHAI, CHINA

2 The 2 nd International Conference on Phononics and Thermal Energy Science (PTES2014) 26 May 31 May, 2014 TONGJI UNIVERSITY, SHANGHAI, CHINA 1

3 Table of Contents I. Sponsors, Organizers, and Committees 3 II. General Information 4 III. Maps 6 IV. Programs 7 V. Titles and Abstracts 16 VI. List of Participants 107 VII. Emergency Contacts 120 2

4 I. Sponsors, Organizers and Committees Sponsors: Tongji University National Natural Science Foundation of China Science and Technology Commission of Shanghai Municipality Sinosteel Anshan Research Institute of Thermo-Energy NovaGlobal (Singapore) Organizers: Center for Phononics and Thermal Energy Science, School of Physics Science and Engineering, Tongji University Local Organization Committee: Baowen Li (Chairman, Tongji) Yunxia Ding (Secretary, Tongji) Nianbei Li (Tongji) Yunyun Li (Tongji) Xiangfan Xu (Tongji) Yan Xu (Tongji) Jun Zhou (Tongji) 3

5 II. General Information 1. The PTES2014 will be held in Sino-French Center at Tongji University. The first half (May 26 May 28) is for the Tutorial Lectures and the second half (May 29 May 31) is for the Official Conference. 2. The time for Plenary talks is 45 minutes, for Invited talks is 30 minutes. The last 5 minutes is reserved for questions and answers. 3. Posters will be displayed throughout the conference time in the basement of the Sino-French Center. There are no codes allotted to posters. The authors can poster it on any board provided within the hall. 4. The Tutorial Reception will be held on Monday, May 26 starting from 6:30pm in the restaurant of Gan Xun Lou. 5. Cafeteria and Food: The Lunch and Dinner are provided for every participant at the restaurant of Gan Xun Lou. There are many Chinese and western restaurants in the Tongji United Square. 6. How to get to Tongji Kingswell Hotel: From Pudong International Airport By Taxi Around 170 RMB, 60 minutes. Midnight surcharge: 30% of the metered fare (11pm-6am). By Metro (available from 6am 10pm everyday) Take Metro Line 2 from Pudong International Airport to East Nanjing Road (you need to transfer at Guanglan Road by taking the metro across the aisle). Interchange to Metro Line 10 within the station of East Nanjing Road. Follow the direction board of Metro Line 10 and take the metro heading towards Xinjiangwancheng Station. Get off at Tongji University Station. Get out of the station from Exit 2 or 1. Go along the Zhangwu Road towards east for about 200 meters and the Tongji Kingswell Hotel is on the right side. The time duration is about 90 minutes. By Maglev + Metro (available from 7am 9:40pm) Take the Maglev from Pudong International Airport to the terminal Longyang Road station. The highest speed is 430km/h during 9am-10:45am and 3pm-3:45pm and 300km/h for other operating time. 4

6 The time interval is 15 minutes. The single trip costs 50 RMB and you will get a 20% discount by showing the ticket seller your boarding pass. Interchange to Metro Line 2 at Longyang Road which is next to the building of Maglev station. Take the Metro Line 2 heading towards East Xujin and get off at East Nanjing Road station. Transfer to Metro Line 10 within the same station and the following route is the same as in By Metro. The time duration is about 50 minutes. For more information about the Maglev, please refer to: From Hongqiao International Airport By Taxi Around 90 RMB, 30 minutes. Midnight surcharge is 30%. By Metro (available from 6am 10pm everyday) Take the Metro Line 10 from Hongqiao Airport Terminal 1 or Hongqiao Airport Terminal 2, heading towards Xinjiangwancheng Station and get off at Tongji University Station. Get out of the station from Exit 2 or 1. Go along the Zhangwu Road towards east for about 100 meters and the Tongji Kingswell Hotel is on the right side. The time duration is about 60 minutes. 5

7 III. Maps Map for the Sino-French Center and hotels nearby 6

8 IV. Programs 7

9 PTES2014 Program for Tutorial Lectures (Venue: Sino-French Center) Monday, May 26, :45-08:10 Registration 08:10-08:20 Opening Ceremony 08:20-09:20 David Cahill (UIUC, USA) Measurement of Thermal Transport by Time-Domain Thermoreflectance: the Fundamentals 09:20-09:40 Tea Break 09:40-10:40 Alan McGaughey (Carnegie Mellon University, USA) Predicting Thermal Conductivity from Molecular Dynamics Simulations 10:40-11:00 Tea Break 11:00-12:00 Jonathan A. Malen (Carnegie Mellon University, USA) Phonon Mean Free Path Contributions to Thermal Conductivity Measured using Frequency Domain Thermoreflectance. I 12:00-13:30 Lunch 13:30-14:30 Pramod Reddy (University of Michigan, USA) Experimental Study of Charge and Energy Transport in Molecular Junctions 14:30-14:45 Tea Break 14:45-15:45 David Cahill (UIUC, USA) Measurement of Thermal Transport by Time-Domain Thermoreflectance: Advanced Techniques 15:45-16:00 Tea Break 16:00-17:00 Yonatan Dubi (Ben Gurion University, Israel) Theoretical Approaches to Energy Transport and Thermopower in Nano-Scale Systems. I 17:00-17:15 Tea Break 17:15-18:15 Lei Wang (Renmin University of China) Normal and Anomalous Heat Conduction in Low-Dimensional Nonlinear Models 8

10 Tuesday, May 27, :20-09:20 John Thong (National University of Singapore) A Technique to Profile Nanowire Thermal Resistance with a Spatial Resolution of Nanometers 09:20-09:40 Tea Break 09:40-10:40 Alan McGaughey (Carnegie Mellon University, USA) Predicting Phonon Properties from Molecular Dynamics Simulations 10:40-11:00 Tea Break 11:00-12:00 Yonatan Dubi (Ben Gurion University, Israel) Theoretical Approaches to Energy Transport and Thermopower in Nano-Scale Systems. II 12:00-13:30 Lunch 13:30-14:30 Pramod Reddy (University of Michigan, USA) Picowatt-Resolution Calorimetry for Probing Radiative Heat Transfer 14:30-14:45 Tea Break 14:45-15:45 Jonathan A. Malen (Carnegie Mellon University, USA) Phonon Mean Free Path Contributions to Thermal Conductivity Measured using Frequency Domain Thermoreflectance. II 15:45-16:00 Tea Break 16:00-17:00 Li Shi (University of Texas at Austin, USA) Open Questions on Experimental Phonon Transport Studies of One-Dimensional and Two-Dimensional Materials 17:00-17:15 Tea Break 17:15-18:15 Renkun Chen (UCSD, USA) High-Resolution Thermometry for Heat Conduction in nanostructures. I 9

11 Wednesday, May 28, :20-09:20 Tomaz Prosen (University of Ljubljana, Slovenia) Quantum Heat Transport. I 09:20-09:40 Tea Break 09:40-10:40 Zhifeng Ren (University of Houston, USA) Nanostructure Approach for Enhancing the Thermoelectric Properties. I 10:40-11:00 Tea Break 11:00-12:00 Zhifeng Ren (University of Houston, USA) Nanostructure Approach for Enhancing the Thermoelectric Properties. II 12:00-13:30 Lunch 13:30-14:30 Tomaz Prosen (University of Ljubljana, Slovenia) Quantum Heat Transport. II 14:30-14:45 Tea Break 14:45-15:45 Renkun Chen (UCSD, USA) High-Resolution Thermometry for Heat Conduction in nanostructures. I 15:45-16:00 Tea Break 16:00-17:00 Liqiu Wang (University of Hong Kong) Constitutive Theory of Heat Transfer: Generalized Fourier Law. I 17:00-17:15 Tea Break 17:15-18:15 Liqiu Wang (University of Hong Kong) Constitutive Theory of Heat Transfer: Generalized Fourier Law. II 10

12 PTES2014 Program for Conference (Venue: Sino-French Center) Thursday, 29 May, :30-07:55 Registration 07:55-08:00 Opening Chair: Baowen Li 08:00-08:45 Plenary Talk David Cahill (UIUC, USA) Extremes and Enhancing Functionality of Thermal Transport 08:45-09:15 Dawei Tang (Institute of Engineering Thermophysics, Chinese Academy of Sciences, Beijing) Microscale Heat Transport Study by Femtosecond-Laser Pump-Probe Thermoreflectance Method 09:15-09:45 Ronggui Yang (University of Colorado at Boulder, USA) Ultrafast Lasers meet Quantum Mechanics at the Nanoscale Wonderland:Regime Maps for Nanoscale Heat Conduction and Mean Free Path Spectroscopy 09:45-10:00 Tea Break Chair: Li Shi 10:00-10:30 Jonathan Malen (Carnegie Mellon University, USA) Thermal transport in organic-inorganic hybrid materials and interfaces 10:30-11:00 Zhifeng Ren (University of Houston, USA) New High Performance Thermoelectric Materials for Power Generation and Cooling 11:00-11:30 Pramod Reddy (University of Michigan, USA) Film Thickness Dependence of Near-Field Radiative Transport 11:30-12:00 Tsuneyoshi Nakayama (Hokkaido University, Japan) Phonon-Glass Electron-Crystal Thermoelectric Clathrates: Role of Disorder Guest-Ions in Ordered Cages 12:00-13:15 Lunch;Venue: Gan Xun Lou 11

13 Chair: David Cahill 13:15-13:45 Sanjiv Sinha (UIUC, USA) Parsing the Seebeck Coefficient: the Effect of Non-Equilibrium 13:45-14:15 Yonatan Dubi (Ben Gurion University, Israel) Transport and Thermopower in Helicene-Based Molecular Junctions 14:15-14:45 Ihab El-Kady (Sandia National Labs, USA) Thermal Transport in Micro-Scale Phononic Crystals: Observation of Coherent Phonon Scattering at Room Temperature and its implications to Thermoelectrics 14:45-15:15 Junichiro Shiomi (University of Tokyo, Japan) Anharmonic Phonon Dynamics in Crystals and their Interfaces 15:15-15:45 Yabing Qi (Okinawa Institute of Science and Technology Graduate University, Japan) Renewable Energy: Low-Cost Solar Cells 15:45-16:00 Tea Break Chair: Zhifeng Ren 16:00-16:30 Fabio Marchesoni (University of Camerino, Italy) Drift in Diffusion Gradients 16:30-17:00 Xiulin Ruan (Purdue University, USA) Thermal Rectification and Thermal Non-equilibrium Phenomena in Nanoscale Heat Transfer 17:00-17:30 Jia Zhu (Nanjing University, Nanjing) Temperature Gated Thermal Rectifier for Active Heat Flow Control 17:30-18:00 Xun Shi (Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai) Abnormal Thermoelectric Properties in Copper Chalcogenides 18:00-18:30 Zhuomin Zhang (Georgia Institute of Technology, USA) Photon Tunneling Between Micro/Nanostructured Metamaterials 18:30-19:30 Dinner;Venue: Gan Xun Lou 12

14 08:00-08:45 Plenary Talk Friday, 30 May, 2014 Chair: Bangfen Zhu Xing Zhang (Tsinghua University, Beijing) Size Effects on Nanoscale Thermal Transport 08:45-09:15 Austin Minnich (Caltech, USA) Measuring and Engineering the Thermal Phonon Spectrum 09:15-09:45 Liqiu Wang (University of Hong Kong, Hongkong) Generalized Fourier Law 09:45-10:00 Tea Break Chair: Renkun Chen 10:00-10:30 Chengwei Qiu (National University of Singapore, Singapore) Thermal Metamaterials to Manipulate Heat Signatures 10:30-11:00 Sheng Shen (Carnegie Mellon University, USA) Long-Range Communication by Thermally Excited Graphene Plasmons 11:00-11:30 Yunfei Chen (Southeast University, Nanjing) Roughness Effects on Phonon Transport Across and Along the Interface between Two Materials Bonding with van der Waals Forces 11:30-12:00 Deyu Li (Vanderbilt University, USA) Contact Thermal Conductance between Individual Multi-walled Carbon Nanotubes 12:00-13:15 Lunch;Venue: Gan Xun Lou Chair: Fabio Marchesoni 13:15-14:00 Peter Hänggi (University of Augsburg, Germany) What can Statistical Physics do to understand Anomalous Heat Transport? Plenary Talk 14:00-14:30 Renkun Chen (UCSD, USA) Thermomechanical Properties of Polymer Nanofibers 14:30-15:00 Alan McGaughey (Carnegie Mellon University, USA) Phonon Transport in Periodic Silicon Nanoporous Films 15:00-15:30 Baile Zhang (Nanyang Technological University, Singapore) A simple thermal cloak with three-dimensional realization 15:30-16:00 Li Shi (University of Texas at Austin, USA) Phonons in Higher Manganese Silicide of a Complex Nowotny Chimney Ladder Structure 16:00-16:30 Tea Break and Photogragh 16:30-18:30 Poster Session (Chair of Selection Committees: Ronggui Yang) Venue: Basement of Sino-French Center 18:30-19:30 Dinner;Venue: Gan Xun Lou 13

15 Saturday, 31 May, 2014 Chair: Peter Hänggi 08:00-08:30 Tomaz Prosen (University of Ljubljana, Slovenia) Integrable Non-Equilibrium Steady State Density Operators and Exact Bounds on Ballistic Transport 08:30-09:00 Chih-Wei Chang (National Taiwan University, Taipei) Room Temperature Ballistic Thermal Conduction in SiGe Nanowires 09:00-09:30 Moran Wang (Tsinghua University, Beijing) Understanding of Non-Fourier Conduction in Nanomaterials Based on Thermomass Concept 09:30-10:00 Bei-Lok Hu (University of Maryland, USA) Nonequilibrium Transport in Open Quantum Systems: A Functional Perturbative Analysis 10:00-10:15 Tea Break Chair: Alan McGaughey 10:15-10:45 Meng Xiao (Hong Kong University of Science and Technology, Hongkong) Zak Phase and Gap Inversion in Periodic Acoustic Systems 10:45-11:15 Philippe Ben-Abdallah (Institut d Optique, CNRS, France) Toward Contactless Circuits for Thermal Light 11:15-11:45 Gengkai Hu (Beijing Institute of Technology, Beijing) Elastic chiral metamaterials based on rotational resonance 11:45-13:15 Lunch;Venue : Gan Xun Lou 14

16 Chair: Tsuneyoshi Nakayama 13:15-13:45 Minghui Lu (Nanjing University, Nanjing) Title: Sonic crystal and its exotic effects 13:45-14:15 Jie Ren (MIT, USA) Spin Seebeck Diode and Transistor: towards a Thermal-Driven Spin Computer 14:15-14:45 Yuriy Kosevich (ECP, France) Interference Phonon Mirrors in Atomic-Scale Metamaterials 14:45-15:15 Koji Miyazaki (Kyushu Institute of Technology, Japan) Thermal and Electrical Conductivities of Porous Si Thin Films 15:15-15:30 Tea Break Chair: Ronggui Yang 15:30-16:00 Andrea Cepellotti (EPFL, Switzerland) Collective Excitations in the Thermal Conductivity of Graphene 16:00-16:30 Xiangfan Xu (Tongji University, Shanghai) Phonon thermal conduction in suspended graphene using micro-fabricated devices 16:30-17:15 Plenary Talk Bangfen Zhu (Tsinghua University, Beijing) Thermo-electric effect on the surfaces or edges in topological insulators 17:15-17:30 The prize awards for best posters; Venue: Sino-French Center 17:30-18:30 Dinner;Venue: Gan Xun Lou 15

17 V. Titles and Abstracts 16

18 1. Tutorial Lectures 17

19 Measurement of thermal transport by time-domain thermoreflectance: the fundamentals David G. Cahill Department of Materials Science and Engineering and Materials Research Laboratory, University of Illinois, Urbana, Illinois Abstract: I will discuss the use of time-domain thermoreflectance for measurements of thermal transport properties of materials and material interfaces. In this first part of the two-part lecture, I will discuss the basic implementation of the method and our solution of the thermal diffusion equation as the basis of the analysis. I will describe the validation of the method, optimization of sensitivities, and the analysis of uncertainties in typical measurements. 18

20 Predicting Thermal Conductivity from Molecular Dynamics Simulations Alan McGaughey Department of Mechanical Engineering, Carnegie Mellon University, USA Abstract: The objective of this lecture is to describe how molecular dynamics simulations can be used to predict thermal conductivity. The equilibrium Green-Kubo method is first presented, with an emphasis on how to specify the converged value of the heat current autocorrelation function. The non-equilibrium direct method (an application of the Fourier law) is then presented, with an emphasis on how to handle system size effects. Case studies will demonstrate the application of these two techniques to bulk materials and nanostructures. 19

21 Phonon Mean Free Path Contributions to Thermal Conductivity Measured using Frequency Domain Thermoreflectance Jonathan A. Malen Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh PA Department of Materials Science & Engineering, Carnegie Mellon University, Pittsburgh PA Abstract: Instrumentation and interpretation of the frequency domain thermoreflectance (FDTR) technique will be presented. FDTR is an alternative to time domain thermoreflectance that can be used to measure thermal conductivity and thermal interface resistance, but has more recently been used to measure spectral contributions of phonons to thermal conductivity. FDTR uses a modulated CW laser (a.k.a. the pump) to periodically heat a sample, and an unmodulated CW laser (a.k.a. the probe) to sense the temperature response based on the sample s thermoreflectance. The amplitude and phase of the thermal response, relative to the heating, are used to determine the thermal properties of the underlying sample. Periodic modulation at high frequency f ( MHz) confines the thermal penetration depth L p =( / f) 1/2 (where is thermal diffusivity) so that it is possible to probe thin films and interfaces without being overwhelmed by the substrate properties. Recent experiments done by both TDTR and FDTR [1-3] show that when L p or the laser spot size are commensurate to the mean free paths of energy carriers, non-diffusive transport results in an apparent reduction in thermal conductivity. I will discuss analytical solutions to the Boltzmann Transport Equation that explain these results and create a pathway to study spectral contributions of phonons to thermal conductivity in non-diffusive thermoreflectance experiments. 1 Y. K. Koh and D. G. Cahill, Physical Review B 76, (2007). 2 A. J. Minnich, J. A. Johnson, A. J. Schmidt, K. Esfarjani, M. S. Dresselhaus, K. A. Nelson, and G. Chen, Physical Review Letters 107 (2011). 3 Regner, K. T., D. P. Sellan, Z. Su, C. H. Amon, A. J. H. McGaughey, and J. A. Malen, Nature Communications, 4, 1640 (2013). 20

22 Experimental Study of Charge and Energy Transport in Molecular Junctions Pramod Reddy Department of Mechanical Engineering, University of Michigan, USA Abstract: Novel charge and energy transport phenomena arise in molecular-scale junctions. In this lecture, I will first describe the fundamentals of charge and transport in molecular scale junctions and introduce experimental techniques developed in our lab and other research groups aimed at studying these phenomena. Specifically, I will describe scanning probe techniques that have been developed to enable the study of electrical conductance and thermopower of molecular junctions. Further, I will describe other techniques that have been developed to enable active control of transport in molecular junctions. Finally, I explain in detail recent efforts in our lab to understand: a) the relationship between the electronic structure and heat dissipation characteristics of atomic and molecular junctions, and b) the relationship between the thermal conductance and the structure of atomic-scale junctions. In order to accomplish the first goal, we have nanofabricated novel scanning probes with integrated thermocouples that enable direct quantification of heat dissipation in atomic-scale junctions. We will describe, in detail, how these probes were employed to elucidate asymmetric heat dissipation characteristics of atomic-scale junctions. In order to accomplish the second goal probing heat transport at the atomic-scale it is necessary to accurately measure very small heat currents ( picowatts). To overcome this challenging experimental obstacle, we have fabricated novel scanning probes that can resolve heat currents with a resolution better than 10 pw. We will briefly discuss the design and capabilities of these probes. 21

23 Measurement of thermal transport by time-domain thermoreflectance: advanced techniques David G. Cahill Department of Materials Science and Engineering and Materials Research Laboratory, University of Illinois, Urbana, Illinois Abstract: In this second part of the lecture, I will discussion extensions and current issues in measurements by time-domain thermoreflectance: lateral heat flow, two-channel modeling of non-equilibrium effects, spot size and frequency dependence of the apparent thermal conductivity and interface thermal conductance, plasmonic sensing of interfacial heat conduction at solid-liquid/interfaces, and the use of the time-resolved magneto-optic Kerr effect as an alternative to thermoreflectance for sensing temperature changes at the surface of a sample. 22

24 Theoretical approaches to energy transport and thermopower in nano-scale systems Yonatan Dubi Ben Gurion University, Israel Abstract: In these tutorial talks we will review the available theoretical approaches to study energy transport and thermopower in nano-scale systems, focusing mainly on Molecular junctions. We will begin by reviewing the basic thermodynamic quantities of interest (that is currents and linear response coefficients). We will then review three central approaches: the (essentially classical) rate equations, the non-equilibrium Green's function approach, and the open quantum system's Lindblad approach. For each of these approaches, examples for calculations will be shown, and the advantages (and disadvantages) of each method will be discussed. 23

25 Normal and anomalous heat conduction in low-dimensional nonlinear models Lei Wang Department of Physics, Renmin University of China Abstract: We will introduce some fundamental concepts and recent studies of heat conduction in low-dimensional nonlinear models. A few classical lattice models, in which the thermal energy is mainly carried by phonons, will be presented in detail. Theoretical analyses and molecular dynamics simulations reveal the violation of Fourier's law, the empirical law of heat conduction, in some of those models. The heat conductivity is thus size-dependent and diverges to infinite in the thermodynamic limit. Such anomalous heat conduction has attracted rapidly increasing interests and is the main focus of this lecture. 24

26 A Technique to Profile Nanowire Thermal Resistance with a Spatial Resolution of Nanometers John T L Thong Department of Electrical and Computer Engineering, National University of Singapore, Singapore , Republic of Singapore Abstract: Here we present a thermal measurement technique that is capable of profiling the thermal conductance of an individual nanowire with a spatial resolution better than 20nm 1. In this technique, a focused electron beam is employed as a localized heat source to establish a temperature gradient along the nanowire. The heat fluxes from the two ends of the nanowire are measured using platinum resistance thermometers on two suspended thermally-isolated islands from which the local thermal conductivity can be derived. By using this technique, not only can the local thermal conductance of the nanowire be probed, but the thermal boundary resistance across the interface between two material segments of the nanowire can also be measured. In this lecture, we will focus on the implementation of this technique as well as some applications. 1. Liu, D., Xie, R., Yang, N., Li, B. & Thong, J.T.L. Profiling Nanowire Thermal Resistance with a Spatial Resolution of Nanometers. Nano Letters 14, (2014). 25

27 Predicting Phonon Properties from Molecular Dynamics Simulations Alan McGaughey Department of Mechanical Engineering, Carnegie Mellon University, USA Abstract: The objective of this lecture is to describe how equilibrium molecular dynamics simulations (with the help of harmonic lattice dynamics calculations) can be used to predict phonon properties using normal mode decomposition. The molecular dynamics and lattice dynamics methods are reviewed and the normal mode decomposition technique is described in detail. The application of normal mode decomposition is demonstrated through case studies on crystalline and disordered phases. 26

28 Picowatt-Resolution Calorimetry for Probing Radiative Heat Transfer Pramod Reddy Department of Mechanical Engineering, University of Michigan, USA Abstract: Precise quantification of energy transport and heat generation is key to obtaining insights into a wide range of phenomena across various disciplines including engineering, biology, physics and chemistry. This lecture will describe recent advances into heat-flow calorimetry, which enable precise measurement of energy transport at micro and nanoscales with picowatt resolution. Specifically, I will describe two classes of calorimeter devices, which are capable of achieving single digit picowatt resolution at room temperature. Each type of device incorporates two important features: A region that is isolated from the ambient via a weak thermal link with a conductance (G Th ~ 1 μw/k), and a high-resolution thermometer with temperature resolutions (ΔT res ) that are in the micro kelvin regime. This enables measurements of heat currents (q) with ultra-high resolution (q= G Th ΔTres). I will also describe how these calorimeters have been used in conjunction with a novel nanopositioning system to obtain new insights into near-filed radiative thermal transport. 27

29 Open Questions on Experimental Phonon Transport Studies of One-Dimensional and Two-Dimensional Materials Li Shi Department of Mechanical Engineering and Texas Materials Institute, the University of Texas at Austin, USA Abstract: We will review the progress made in the past decade in thermal transport measurements of one-dimensional (1D) and two-dimensional (2D) materials. The reported temperature- and sizedependent thermal conductivity data of carbon nanotubes, graphene and other 1D and 2D systems will be examined in conjunction with the experimental techniques employed to obtain these data. The objective is to identify gaps that may still exist between the available experimental data and the theoretical predictions of the unique phonon transport behaviors in 1D and 2D systems, and to suggest possible future directions. 28

30 High-resolution thermometry for heat conduction in nanostructures Renkun Chen Department of Mechanical and Aerospace Engineering University of California, San Diego Abstract: High-resolution thermometry enables the measurements of low heat flux, which is often desirable when investigating nanoscale thermal transport phenomena, such as heat conduction in nanostructures. In this tutorial, I will first review recent development in instrumentations of high-resolution thermometry/calorimetry made in our and other groups, aiming at resolving sub-picowatt heat current. Then I will show the applications of such instrumentation for measuring thermal conductivity of inorganic and polymeric nanostructures. Finally, I will present our recent progress towards measuring specific heat of individual nanofibers, which is a rarely-measured quantity at individual nanowire level but could provide some important insights. References: 1. J. Zheng*, M. C. Wingert*, E. Dechaumphai*, R. Chen Sub-picowatt/Kelvin resistive thermometry for probing nanoscale thermal transport, Rev. Sci. Instrum., 84, (2013) 2. Z. Zhong*, M. C. Wingert*, J. Strzalka, H-H Wang, T. Sun, J. Wang, R. Chen#, and Z. Jiang#, Structure-induced Enhancement of Thermal Conductivity in Electrospun Polymer Nanofibers, Nanoscale, In press, (2014) 29

31 Quantum Heat Transport The 2nd Intenational Conference on Tomaz Prosen Department of Physics, University of Ljubljana, Slovenia Abstract: In my lectures I will elaborate on non-equilibrium quantum transport in large but finite one-dimensional interacting quantum systems. After reviewing the concepts of heat, charge and magnetization transport in non-equilibrium thermodynamics and discussing fundamental linear-response relations, I will motivate and explain a simple paradigm of boundary driven quantum master equations. I will show how understanding the steady state solutions of boundary driven master equations can be useful for, both, understanding physics of closed system in the regime of linear response, and open systems far from equilibrium. I will then move to discussing efficient computational techniques, both numerical and analytical, for constructing the nonequilibrium steady state solutions of boundary driven quantum master equations. The common concept behind these techniques is the notion of a matrix product state which I will explain extensively in different examples. 30

32 Nanostructure Approach for Enhancing the Thermoelectric Properties Zhifeng Ren Department of Physics and TcSUH, University of Houston, Houston, TX Abstract: Thermoelectric materials for energy conversion are more and more promising due to the recent breakthroughs in enhancing the dimensionless thermoelectric figure-of-merit (ZT) by nanostructuring approach. I will do a detailed review on the progresses of enhancing the thermoelectric figure-of-merit of a few materials: bismuth tellurides, skutterudites, lead tellurides, lead selenides, half-heuslers, SiGe alloys, etc., and followed with a couple of examples of using these materials for applications in waste heat conversion. The main scheme is to enhance the ZT in these materials by studying the compositions and creating nanostructures to reduce the thermal conductivity and simultaneously increase the power factor. 31

33 Constitutive Theory of Heat Transfer: Generalized Fourier Law Liqiu Wang Department of Mechanical Engineering The University of Hong Kong, Hong Kong Abstract: By the second law of thermodynamics, there exists a physical quantity Q that, at a given instant, is associated with each surface in a non-isothermal body. This quantity can be interpreted as the heat flux through the surface and has two fundamental properties: behaving additively on compatible material surfaces and satisfying the first law of thermodynamics. These two properties, when rendered precise, imply the existence of the flux vector field q whose scalar product with the unit normal to the surface yields the surface density of the heat flux Q. The main aim of heat transfer studies is to predict and control q. For the heat transfer in a rigid body without macroscopic relative motion (pure heat conduction), q is proportionally related to the temperature gradient by the classical Fourier law of heat conduction, an empirical fundamental law in heat conduction. Such a relation is, however, not available for the heat transfer in a body with macroscopic relative motion such as moving fluids and solids in deformation (convective heat transfer). We develop this relation for both heat conduction and convective heat transfer by finding both the necessary and sufficient condition in a systematic, rigorous way for a heat transfer process to satisfy the principle of frame-indifference and the second law of thermodynamics. This leads to a generalized Fourier law that relates q to the temperature gradient and generalizes the classical Fourier law to the convective heat transfer. Such a study is of fundamental importance because heat transfer research aims to predict and control the rate at which the heat is transferred. Also developed are a linear theory and a decomposition theorem of motion to simplify experiments of determining three coefficients in the generalized Fourier law. 32

34 2. Planery and Invited Talks 33

35 Extremes and Enhancing Functionality of Thermal Transport David G. Cahill Department of Materials Science and Engineering and Materials Research Laboratory, University of Illinois, Urbana, Illinois Abstract: Advances in experimental and theoretical methods have dramatically broadened and accelerated research in thermal sciences in the past decade. Our field also has many examples of compelling scientific accomplishments: advances in understanding of thermal transport in nanostructures, the conductance of various types of interfaces, and effects of non-equilibrium between different populations of heat carriers to name just a few. Going forward, I argue that our field will benefit from clear statements of far-reaching problems that have the potential to produce breakthroughs in thermal science or technology. I propose two categories of such problems: i) the development of materials with extremely low thermal conductivity or extremely high thermal conductivity subjected to constraints; and ii) enhanced functionality of thermal transport, i.e., materials with abrupt changes in conductivity, materials with properties that can be modulated, or novel physics that enables new function such as the writing of magnetic information. I will give two examples of science that is motivated by these problems. Low-dimensional quantum magnets based on copper oxides demonstrate that electrons and phonons are not the only significant carriers of heat in materials; near room temperature, the magnon thermal conductivity is comparable to the electronic thermal conductivities of metal alloys. We extract the effective strength of magnon-phonon coupling from time-domain thermoreflectance data using a two temperature model. In metallic multilayers, ultrafast spin currents can be generated using fast temperature excursions and strong temperature gradients. Thermally-driven demagnetization of ferromagnetic layer produces a transient spin current and heat current passing through a ferromagnetic layer generates a spin current due to the spin-dependent Seebeck effect. 34

36 Microscale Heat Transport Study by Femtosecond-Laser Pump-Probe Thermoreflectance Method Dawei Tang and Jie Zhu Institute of Engineering Thermophysics, Chinese Academy of Sciences, Beijing , China Abstract: In this talk, I summarize the progress in the studies of the heat transport charateristics in nano-films and interfaces in the Institute of Engineering Thermophysics, CAS. This talk contains four parts: (1) ultrafast thermoreflectance technique and the analysis on simultaneous measurement of multiple thermal physical properties;(2) the measurement results of the different types of solid-liquid interfacial thermal conductance; (2) thermal conductivity temperature dependence of non-metal materials; (3) the measured thermal conductivity of ceramic materials and their interfacial thermal conductance with other materials; (4) the measured thermal conductivity of polymer thin films and their interfacial thermal conductance with other materials. 35

37 Ultrafast Lasers meet Quantum Mechanics at the Nanoscale Wonderland: Regime Maps for Nanoscale Heat Conduction and Mean Free Path Spectroscopy Ronggui Yang Department of Mechanical Engineering University of Colorado, Boulder, CO Tel: Abstract: Heat transfer at the nanoscale is fundamentally different from that at the macroscale and is determined by the distribution of the mean free paths of energy carriers in a material, the length scales of the heat sources, and the distance over which the heat is transported. Past work has shown that Fourier s law for heat conduction valid at the bulk and continuum level dramatically over-predicts the rate of heat dissipation from heat sources with dimensions smaller than the mean free path of the dominant heat-carrying phonons. In this work, we uncover a new regime of nanoscale heat conduction that dominates when the separation between nanoscale heat sources is small compared with the dominant phonon mean free paths. Surprisingly, the interplay between neighboring heat sources can facilitate efficient diffusive-like heat dissipation. This finding suggests that the thermal management problem in nanoscale integrated circuits might not be as serious as projected. Finally, we demonstrate a unique and new capability to extract mean free path distributions in materials, allowing the very first experimental validation of differential conductivity predictions from first-principles calculations. 36

38 Thermal Transport In Organic-Inorganic Hybrid Materials and Interfaces Jonathan Malen Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh PA Department of Materials Science & Engineering, Carnegie Mellon University, Pittsburgh PA Abstract: 37

39 New High Performance Thermoelectric Materials for Power Generation and Cooling Zhifeng Ren Department of Physics and TcSUH, University of Houston, Houston, TX Abstract: In this talk I am going to present our very recent discovery of a new thermoelectric material: MgAgSb with ZTs of ~0.9 at room temperature and ~1.4 at 200 C, and a heat to electricity conversion efficiency of ~9% that is much higher than that of bismuth telluride. It is well known that bismuth telluride has been the only thermoelectric material with thermoelectric figure-of-merit (ZT) of slightly above 1 in the temperature range of 20 and 150 C since its discovery in 1950s. It has been primarily used for cooling even though power generation has also been attempted for hot side of 250 C and code side of ~20 C for the efficiency of ~6%. A material that is better than bismuth telluride in the same temperature is extremely important for both cooling and power generation considering the rareness of tellurium. The materials are made by ball milling powders of elements of Mg, Ag, and Sb in a two-step process and hot pressing the powders into dense bulk samples with grains smaller than 20 nm. The small grain size together with point defects including vacancies and antisites in the structure are the main reasons for the very low thermal conductivity of ~0.7 W m -1 K -1 at room temperature. If time allows, I am also going to present another recent discovery of a high ZT material at cryogenic temperature showing a power factor more than 130 W m -1 K -2 that is 3-4 times higher than the best power factor of bismuth telluride. 38

40 Film Thickness Dependence of Near-Field Radiative Transport Pramod Reddy Department of Mechanical Engineering, University of Michigan, USA Abstract: Near-field radiative thermal transport has attracted increasing attention recently, with orders-of-magnitude heat transfer enhancement already demonstrated between bulk materials. Using a novel custom-built experimental platform, we conducted a systematic investigation of the effect of film thickness on the near-field heat transport properties. By studying thermal radiation between a hot silica microsphere and thin silica films of varying thicknesses (50 nm to 3 microns), at different gap sizes (30 nm to 10 microns), we found substantial enhancements in heat transport properties due to near-field effects, even for the thinnest films when the gaps size was comparable to the film thickness. Further, we find that at larger separations (~1 micron), the thicker films show substantially larger near-field enhancement than thinner films. These results provide the first direct evidence of a distance dependent penetration depth in thin films. 39

41 Phonon-Glass Electron-Crystal Thermoelectric Clathrates: Role of Disorder Guest-Ions in Ordered Cages Tsuneyoshi Nakayama Hokkaido University, Japan Abstract: The high performance of thermoelectricity is achieved for materials with the lowest possible thermal conductivity, the highest possible electrical conductivity and the highest possible Seebeck coefficient. These impose the conditions on efficient thermoelectric materials (TEM) so as to satisfy both of glass-like low phonon thermal conductivities and crystalline high electrical conductivities. Type-I clathrate compounds are expected as potential TEM satisfying these conditions, in which the group 1 or 2 elements in the periodic table are encaged as guest ions. It is remarkable that, though these cage-forming compounds have crystalline structure, they exhibit glass-like phonon thermal conductivity over the whole temperature range. An efficient thermoelectric effect is realized in clathrates showing these glass-like properties. The point is why these compounds without topological disorder show glass-like thermal properties. I will present, after surveying experimental data, theoretical interpretation on the emergence of glass-like phonon thermal conductivities in type-i clathrate compounds, based on our recent article 1). 1. T. Takabatake et al., Phonon-Glass Electron-Crystal Thermoelectric Clathrates: Experiments and Theory, Rev. Mod. Phys., April (2014). 40

42 Parsing the Seebeck Coefficient: the Effect of Non-Equilibrium Sanjiv Sinha Department of Mechanical Science and Engineering, UIUC, USA Abstract: The ability to reduce thermal conductivity through nanostructures has attracted interest in silicon and other materials for thermoelectric applications. In particular, the boundary scattering of phonons has been exploited to report significant enhancement in the figure of merit. It is implicitly assumed that the introduction of crystal boundaries or other defects does not affect charge transport provided there is a difference in the mean free paths of electrons and phonons. However, in a non-equilibrium picture of transport with simultaneous and self-consistent transport of electrons and phonons, phonon boundary scattering can indeed alter momentum transfer between electrons and phonons, with significant impact on the Seebeck coefficient. Here, we discuss experiments and theory to better understand the Seebeck effect from a non-equilibrium perspective. 41

43 Transport and Thermopower in Helicene-Based Molecular Junctions Yonatan Dubi Department of Chemistry, Ben-Gurion University, Israel Abstract: In the field of energy transport and conversion through molecular junctions (MJs), there are two outsdanding questions. The first question is: is the electronic transport in MJs coherent? There is some experimental evidence that this is indeed the case, yet these experiments compare different junctions with different molecules, and there is no control parameter which can be tuned in the same junction that will demonstrate the coherence. The second question is: can one increase the thermopower and the thermoelectric efficiency (manifestly the figure of merit) in MJs? While ideally, MJs should have a very large FOM and thermopower, in practice they turn out to be rather poor thermoelectrics. In this talk I will present a system which may help answer both these questions: a Helicene-based molecular junction. Helicenes are molecules composed of a series of connected carbon rings arranged in a Helical structure, forming a stiff spring made of carbon rings. The idea is that by pulling and pushing the electrodes, the electronic structure of the molecule can be tuned in-situ due to the spring-like structure of the bridging molecule. This will affect both conductance and thermopower of the molecular junction, but only if the transport is coherent. I will present some calculations which show that both the conductance and thermopower indeed depend dramatically on the distance between electrodes, thus providing qualitative predictions and motivation for future experiments. 42

44 Thermal Transport in Micro-Scale Phononic Crystals: Observation of Coherent Phonon Scattering at Room Temperature and its implications to Thermoelectrics Seyedhamidreza Alaie 1, Drew F. Goettler 1, Mehmet Su 1,2, Zayd C. Leseman 1,2 Charles M. Reinke 1,3 and Ihab El-Kady 1,2,3 1 Mechanical Engineering Dept., University of New Mexico, Albuquerque, NM, USA 2 Electrical and Computer Engineering Dept., University of New Mexico, Albuquerque, NM, USA 3 Dept. of Applied Photonic Microsystems, Sandia National Laboratories, Albuquerque, NM, USA, ielkady@sandia.gov Abstract: We report on the experimental observation of coherent phonon boundary scattering in micro-scale phononic crystals (PnCs) at room temperature. We show that the neglecting coherent boundary scattering leads to gross overestimation of the measured thermal conductivities of the PnC samples. We introduce a hybrid model that accounts for partial coherent and partial incoherent phonon boundary scattering. Excellent agreement with the experiment is achieved. Almost all physical processes produce heat as a byproduct making thermoelectric (TE) systems very attractive for energy scavenging applications. Energy conversion in TE devices is based on the so called Peltier effect 1. Here the temperature gradient resulting from expelled heat is used to force electronic transport resulting in an electric current. As such, heat transported via phonons represents a leakage mechanism and serves to reduce the efficiency of TE systems. Indeed the inability to suppress or eliminate the relative phonon contribution to thermal transport as compared to the electronic one has hindered the development of efficient TE devices. Recently, it has been proposed that coherent boundary scattering in micro-scale phononic crystals (PnCs) may hold the key to solving this problem by scattering phonons with minimal influence on electrons 2-4. PnCs are artificial structures with a periodic variation in mechanical impedance brought about by the introduction of holes or plugs of one material into a homogenous matrix of another 5-8. This periodic variation results in rich phonon dispersion with unusual behaviors 9. In this communication, we focus on micro-scale PnCs formed by the introduction of air holes in a Si matrix with minimum feature sizes 100nm. As a phonon population traverses such a lattice, it can undergo two types of scattering processes: simple incoherent scattering as a result of encountering a boundary; and coherent Bragg-like 7 scattering due to the periodic topology of the artificial lattice of air holes. In the first type, it is assumed that the phonons will retain no phase information after each scattering event. This implies that the phonon dispersion remains unaltered due to the introduction of the air-holes. In the second type, on the other hand, it is assumed that the phase is preserved throughout several scattering events thus enabling coherent interference to occur. Consequently, this would imply a modified phonon dispersion that is sensitive to the topology of the PnC air-hole lattice. Practically, this can have profound implications because: while incoherent boundary scattering depends only on the shape, size, and separation of the holes; coherent boundary scattering additionally depends on the symmetry and topology by which these holes are distributed. Thus, the existence of coherent scattering would allow one to further reduce the thermal conductivity of the underlying material without the need for additional boundaries (e.g. more air-holes) by simply altering the PnC topology. The claim of coherent phonon scattering in micro-scale Si/Air PnCs at room temperature has generated widespread controversy in the literature given the relatively small wavelength characteristic of the phonon population dominating the thermal transport 3, Experimentally however, the thermal conductivity (κ) of PnC samples have consistently been measured to be significantly lower than that of an unpatterned film 2,4,11,13,14. In fact far lower than what would be expected due to the combination of material removal and simple incoherent boundary scattering 2,4,13, thereby suggesting that another κ reduction mechanism, possibly coherent scattering, must be taking place. The 43

45 controversy was heightened by the discovery that ~50% of κ in Si is carried by phonons with mean free paths (MFPs) from 100nm up to 1µm15, which was recently verified experimentally 16. Since it is logical to assume that a phonon remains coherent over its MFP, we suggest here that the MFP, rather than wavelength, should be used when judging whether or not coherent scattering events can take place. In which case, a large enough fraction of the phonon population could travel sufficient distances to experience the PnC lattice periodicity and thus undergo coherent scattering. We report on the experimental observation of coherent phonon boundary scattering in micro-scale phononic crystals (PnCs) at room temperature. We investigate the existence of coherent phonon boundary scattering resulting from the periodic topology of the PnCs and its influence on the thermal in silicon. To delaminate incoherent from coherent boundary scattering, PnCs with a fixed minimum feature size, differing only in the unit cell topologies, were fabricated. A suspended island platform was used to measure the thermal conductivity. We show that the neglecting coherent boundary scattering leads to gross overestimation of the measured thermal conductivities of the PnC samples. We introduce a hybrid model that accounts for partial coherent and partial incoherent phonon boundary scattering. Excellent agreement with the experiment is achieved emphasizing the influence of coherent zone folding in PnCs. Our results yield conclusive evidence that significant room temperature coherent phonon boundary scattering does indeed take place. References 1 Slack, G. A. CRC Handbook of Thermoelectrics. (CRC Press, 1995). 2 Hopkins, P. E. et al. Reduction in the Thermal Conductivity of Single Crystalline Silicon by Phononic Crystal Patterning. Nano Lett 11, , doi:doi /Nl102918q (2011). 3 Reinke, C. M. et al. Thermal conductivity prediction of nanoscale phononic crystal slabs using a hybrid lattice dynamics-continuum mechanics technique. AIP Advances 1, (2011). 4 Yu, J.-K., Mitrovic, S., Tham, D., Varghese, J. & Heath, J. R. Reduction of thermal conductivity in phononic nanomesh structures. Nature Nanotechnology, 5, , (2010). 5 Reinke, C. M., Su, M. F., Olsson, R. H. & El-Kady, I. Realization of optimal bandgaps in solid-solid, solid-air, and hybrid solid-air-solid phononic crystal slabs. Appl Phys Lett 98, doi:artn Doi / (2011). 6 Su, M. F., Olsson, R. H., Leseman, Z. C. & El-Kady, I. Realization of a phononic crystal operating at gigahertz frequencies. Appl Phys Lett 96, ( pp.), doi: / (2010). 7 Olsson, R. H., III et al. in IEEE International Ultrasonics Symposium El-Kady, I., Olsson, R. H., III & Fleming, J. G. Phononic band-gap crystals for radio frequency communications. Appl Phys Lett 92, , doi: / (2008). 9 Kushwaha, M. S., Halevi, P., Dobrzynski, L. & Djafari-Rouhani, B. Acoustic band structure of periodic elastic composites. Physical Review Letters 71, (1993). 10 Hao, Q., Chen, G. & Jeng, M.-S. Frequency-dependent Monte Carlo simulations of phonon transport in two-dimensional porous silicon with aligned pores. Journal of Applied Physics 106, (2009). 11 Tang, J. et al. Holey Silicon as an Efficient Thermoelectric Material. Nano Lett 10, , doi: /nl102931z (2010). 12 Jain, A., Yu, Y.-J. & McGaughey, A. J. H. Phonon transport in periodic silicon nanoporous films with feature sizes greater than 100 nm. Physical Review B 87, (2013). 13 Bongsang, K. et al. in Micro Electro Mechanical Systems (MEMS), 2012 IEEE 25th International Conference on (2012). 14 El-Kady, I. et al. Phonon Manipulation with Phononic Crystals. (Sandia National Laboratories, 2012). 15 Esfarjani, K., Chen, G. & Stokes, H. T. Heat transport in silicon from first-principles calculations. Physical Review B 84, (2011). 44

46 Anharmonic Phonon Dynamics in Crystals and their Interfaces Junichiro Shiomi Department of Mechanical Engineering, The University of Tokyo, Hongo, Bunkyo, Tokyo , Japan Japan Science and Technology Agency, PRESTO, Honcho, Kawaguchi, Saitama , Japan Abstract: Perturbation theories have been successful in calculating lattice dynamics with moderate anharmonicity, which is sufficient to reproduce lattice thermal conductivity of many crystals even at high temperatures. However, there are materials and cases, where stronger anharmonicity manifests itself in the phonon dynamics, and further understanding of their nature can lead us to better design and control of lattice heat conduction. We have recently investigated anharmonic phonon dynamics in crystals and their interfaces using classical molecular dynamics simulations with interatomic force constants obtained from first principles. The molecular dynamics method allows us to simulate anharmonic lattice dynamics with atom displacements beyond the limit of the perturbation theories. With this, we have identified the origin of anomalous anharmonic lattice dynamics of lead telluride previously observed in experiments. In addition, we have clarified the contribution of the inelastic phonon transmission to the thermal boundary conductance across bonded crystal interfaces. 45

47 Renewable Energy: Low-Cost Solar Cells Yabing Qi ( 戚亚冰 ) Energy Materials and Surface Sciences Unit, Okinawa Institute of Science and Technology Graduate University (OIST), Japan Abstract: Sustainable economic development critically relies on energy. Currently there is a pressing demand for renewable energy. Solar cells have shown their potential in tackling these challenges. In this presentation, I will talk about some recent research efforts in my group related to the development of low-cost solar cells. 46

48 Drift in Diffusion Gradients The 2nd Intenational Conference on Fabio Marchesoni Department of Physics, University of Camerino, I Camerino, Italy Abstract: The longstanding problem of Brownian transport in a heterogeneous quasi one-dimensional medium with space-dependent self-diffusion coefficient is addressed in the overdamped (zero mass) limit. A satisfactory mesoscopic description is obtained in the Langevin equation formalism by introducing an appropriate drift term, which depends on the system macroscopic observables, namely the diffuser concentration and current. The drift term is related to the microscopic properties of the medium. The paradoxical existence of a finite drift at zero current suggests the possibility of designing a Maxwell demon operating between two equilibrium reservoirs at the same temperature. 47

49 Thermal Rectification and Thermal Non-equilibrium Phenomena in Nanoscale Heat Transfer Xiulin Ruan School of Mechanical Engineering, and Birck Nanotechnology Center Purdue University Abstract: Recently, thermal rectification and thermal non-equilibrium phenomena in nanoscale heat transfer have received considerable attention, and in this talk, two examples of our work will be presented: thermal rectification in asymmetric graphene nanoribbons; and thermal non-equilibrium among electrons, optical phonons, and acoustic phonons in Raman measurements of thermal conductivity of graphene. We show that thermal rectification (TR) in asymmetric graphene nanoribbons (GNRs) is originated from phonon confinement in the lateral dimension, which is a fundamentally new mechanism different from that in macroscopic heterojunctions. Our molecular dynamics simulations reveal that, though TR is significant in nanosized asymmetric GNRs, it diminishes at larger width. By solving the heat diffusion equation, we prove that TR is indeed absent in both the total heat transfer rate and local heat flux for bulk-size asymmetric single materials, regardless of the device geometry or the anisotropy of the thermal conductivity. We have performed phonon spectra analysis and shown that phonon lateral confinement can enable three possible mechanisms for TR: phonon spectra overlap, inseparable dependence of thermal conductivity on temperature and space, and phonon edge localization, which are essentially related to each other in a complicated manner. We show that other asymmetric nanostructures, such as asymmetric nanowires, thin films, and quantum dots, of a single material are potentially high-performance thermal rectifiers. We have also predicted the thermal non-equilibrium among electrons, optical phonons, and acoustic phonons in Raman spectroscopy, and investigated its impact on the thermal conductivity measurement of two-dimensional materials. Raman spectroscopy has been widely used to measure thermal conductivity (κ) of 2D materials such as graphene. In this method the temperature measured from Raman peaks is used in a Fourier model to derive the thermal conductivity κ, and a basic assumption is that different modes of phonons are in local thermal equilibrium. However, this assumption was not validated yet. In this work, we give comprehensive and predictive simulations of the intrinsic electron-phonon coupling processes and the resulting non-equilibrium in graphene, using first principles density functional theory (DFT) calculations. We calculated the electron cooling rate due to phonon scattering as a function of their corresponding temperatures (T e,t ph ), and our results clearly illustrate that optical phonons dominate the hot electron relaxation process for T e >T ph 300 K. We then used these results in conjunction with the phonon scattering rates computed using perturbation theory to develop a multi-temperature model, and resolved the spatial temperature distributions of the energy carriers. Our results show that electrons, optical phonons, and acoustic phonons are in strong non-equilibrium, with the ZA phonons showing strongest non-equilibrium mainly due to their weak coupling to other carriers in suspended graphene. We estimate that neglecting this non-equilibrium leads to under prediction of thermal conductivity in experiments by a factor of at room temperature. Such under-estimation is also expected in Raman measurements of thermal conductivity of other 2D materials. 48

50 Temperature Gated Thermal Rectifier for Active Heat Flow Control Jia Zhu College of Engineering and Applied Sciences, Nanjing University, P.R.China Abstract: Active heat flow control is essential for broad applications of heating, cooling and energy conversion. Like electronic devices developed for the control of electric power, it is very desirable to develop advanced all-thermal solid-state devices that actively control heat flow, without consuming other forms of energy. Here we demonstrate temperature-gated thermal rectification using vanadium dioxide beams, in which the environment temperature actively modulates asymmetric heat flow. In this three terminal device, there are two switchable states, which can be regulated by global heating. In the Rectifier state, we observed up to 28% thermal rectification. In the Resistor state, the thermal rectification is significantly suppressed (<1%). To the best of our knowledge, this is the first demonstration of solid-state active-thermal devices, with a large rectification in the Rectifier state. This temperature-gated rectifier can have substantial implications ranging from autonomous thermal management of heating and cooling systems to efficient thermal energy conversion and storage. 49

51 Abnormal Thermoelectric Properties in Copper Chalcogenides Xun Shi Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai , China Abstract: Solid-state thermoelectric technology uses electrons or holes as the working fluid for heat pumping and power generation and offers the prospect for novel thermal-to-electrical energy conversion technology that could lead to significant energy savings by generating electricity from waste industrial heat. The key to the development of advanced TE technologies is to find highly efficient TE materials. In current commercial materials, the zts are limited to values around unity. Recently, several novel concepts have been proposed to enhance the efficiency of TE materials and laboratory results suggest that high zt values can be realized in several families of bulk materials. In this presentation, the thermoelectric properties of bulk copper chalcogenides (Cu 2-δ X) are reported in a wide temperature range, where X could be S, Se, or Te. We will show these materials possess extremely abnormal thermoelectric properties with very low thermal conductivity and good thermoelectric figure of merit. In particularly Cu 2-δ Se is taken as an example to demonstrate the abnormal properties of the low temperature phase, the high temperature phase, and the transition states during the phase transitions. The physical mechanisms behind these abnormal thermoelectric properties will also be discussed to show the possibility of realization of ultrahigh thermoelectric figure of merit. 50

52 Photon Tunneling Between Micro/Nanostructured Metamaterials Zhuomin Zhang George W. Woodruff School of Mechanical Engineering Georgia Institute of Technology, Atlanta, GA, USA Abstract: Near-field thermal radiation holds promise for high-throughput thermophotovoltaic devices, nanomanufacturing, thermal imaging, local heat removal, and vacuum thermal rectifiers, especially when the vacuum gap separating the structures is reduced to nanometer distances. Different micro/nanostructured materials have been considered for enhancing the radiative heat flux, such as doped silicon nanowires and nanoholes, carbon nanotubes, multilayers, gratings, and graphene sheets. This presentation will summarize some of the recent theoretical studies on photon tunneling in nanostructures considering surface plasmons, hyperbolic metameterials, as well as plasmonic graphene sheets. The tunneling efficiencies will be investigated in both the frequency and wavevector spaces. 51

53 Size Effects on Nanoscale Thermal Transport Xing Zhang Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Department of Engineering Mechanics, Tsinghua University, Beijing , China , Abstract: Nanomaterials have been highlighted as promising candidates for improving traditional tissue engineering materials due to the excellent thermal, mechanical, electrical, and optical properties. Why the nanomaterials are so different from corresponding bulk? Size effect plays a key role, and hence nanomaterials are called size matters. In this keynote, size effects on thermophysical properties of nanomaterials, including metallic nanofilm, carbon nanotube, and thermoelectric nanowire, will be discussed in detail. First, size effects on metallic nanofilms. A significant size effect has been revealed for heat and charge transport in metallic nanofilms at low temperatures. Below 50 K, the normally used elastic theories fail to predict the electrical and thermal conductivities, and the Wiedemann-Franz law breaks as well. The experimental results demonstrate that a new kind of electron scattering, i.e. electron Raman scattering, exists at low temperatures. Second, size effects on carbon nanotube (CNT). Raman spectroscopy technique has been developed to study the size effects on CNT. The local temperature rise of CNT is proportional to the G-band frequency shift, providing a perfect tool for non-contact measurement of temperature. Applying this technique, the heat transfer coefficients of several single-wall carbon nanotubes have been measured. A two-layer kinetic model has been established to predict the heat transfer coefficient, covering all the free molecular, transition and continuum regimes. Meanwhile, a length-dependent thermal conductivity has been observed for multi-wall carbon nanotubes, suggesting that the heat conduction occurs in both ballistic and diffusion ways. Third, size effect on thermoelectric nanowire. A novel T-type AC heating-dc detecting method has been developed to measure the Seebeck coefficient of individual nanowires. Based on this technique, the Seebeck coefficient, thermal conductivity, and electrical conductivity of the same Bi2S3 nanowire have been comprehensively determined. A metal-insulator transition has been observed for Bi2S3 nanowire at about 225 K, and a magnetic polaron theory based on size effects has been successfully applied to describe this new phenomenon. This work was supported by the National Natural Science Foundation of China (Grant No ). 52

54 Measuring and Engineering the Thermal Phonon Spectrum Austin J. Minnich Mechanical Engineering and Applied Physics, California Institute of Technology, USA Abstract: Recent works have demonstrated that the thermal phonons responsible for heat conduction possess a broad spectrum, yet this spectrum remains unknown for most materials and is not always accounted for in simulations due to computational cost. In this talk, I will describe our efforts to directly measure and engineer the thermal phonon spectrum using computation and experiment. Experimentally, I will describe our efforts to provide a rigorous interpretation of quasiballistic thermal transport in mean free path spectroscopy. Computationally, I will demonstrate the importance of considering the size distribution of nanostructures to achieve the minimum thermal conductivity in solids. 53

55 Generalized Fourier Law The 2nd Intenational Conference on Liqiu Wang Department of Mechanical Engineering The University of Hong Kong, Hong Kong Abstract: By the second law of thermodynamics, there exists a physical quantity Q that, at a given instant, is associated with each surface in a non-isothermal body. This quantity can be interpreted as the heat flux through the surface and has two fundamental properties: behaving additively on compatible material surfaces and satisfying the first law of thermodynamics. These two properties, when rendered precise, imply the existence of the flux vector field q whose scalar product with the unit normal to the surface yields the surface density of the heat flux Q. The main aim of heat transfer studies is to predict and control q. For the heat transfer in a rigid body without macroscopic relative motion (pure heat conduction), q is proportionally related to the temperature gradient by the classical Fourier law of heat conduction, an empirical fundamental law in heat conduction. Such a relation is, however, not available for the heat transfer in a body with macroscopic relative motion such as moving fluids and solids in deformation (convective heat transfer). We develop this relation for both heat conduction and convective heat transfer by finding both the necessary and sufficient condition in a systematic, rigorous way for a heat transfer process to satisfy the principle of frame-indifference and the second law of thermodynamics. This leads to a generalized Fourier law that relates q to the temperature gradient and generalizes the classical Fourier law to the convective heat transfer. Such a study is of fundamental importance because heat transfer research aims to predict and control the rate at which the heat is transferred. 54

56 Thermal Metamaterials to Manipulate Heat Signatures Cheng-Wei Qiu Department of Electrical & Computer Engineering, National University of Singapore Abstract: Manipulation of various physical fields, including optics, electromagnetics, acoustics, thermotics, etc. through different materials has been a long-standing dream for many researchers over the decades. Analogous to invisible cloak and wave-dynamic illusion, thermal metamaterials can potentially transform an actual perception into a pre-controlled perception, thus empowering unprecedented applications in thermal cloaking and camouflage. Here we report our recently two works about thermal cloak and thermal illusion based on simulation and experimental validation. We demonstrate a bilayer thermal cloak made of bulk isotropic materials. Our simulation work derived directly from thermal conduction equation, has been validated as an exact cloak, and we experimentally verified its ability to maintain the heat front and its heat protection capabilities. Also we propose and realize a functional thermal illusion device, which is capable of creating multiple expected images off the original object's position in heat conduction. The thermal scattering signature of the object is thus metamorphosed and perceived as multiple ghost targets with different geometries and compositions. The thermal illusion effect is experimentally confirmed in both time-dependent and temperature-dependent cases, demonstrating excellent thermotics performance. 55

57 Long-Range Communication by Thermally Excited Graphene Plasmons Sheng Shen Department of Mechanical Engineering, Carnegie Mellon University, USA Abstract: As one emerging plasmonic material, graphene can support surface plasmons at infrared and terahertz frequencies with unprecedented properties due to the strong interactions between graphene and low frequency photons. Since graphene surface plasmons exist in the infrared and terahertz regime, they can be thermally pumped (excited) by the infrared evanescent waves emitted from an object. Here, we show, for the first time, that thermal grapheme plasmons can be excited with a remarkable efficiency of about 90% and have monochromatic and tunable spectra, thus paving a way to harness thermal energy for graphene plasmonic devices. We further demonstrate that we can potentially realize "thermal information communication" via grapheme surface plasmons by effectively harnessing thermal energy from various heat sources, e.g., the waste heat dissipated from nanoelectronic devices. These findings open up a new avenue of thermal plasmonics based on graphene for different applications, ranging from infrared emission control, to information processing and communication, and to energy harvesting. 56

58 Roughness Effects on Phonon Transport Across and Along the Interface between Two Materials Bonding with van der Waals Forces Yunfei Chen School of Mechanical Engineering and Jiangsu Key Laboratory for Design and Manufacture of Micro-Nano Biomedical Instruments, Southeast University, Nanjing, , P. R. China * yunfeichen@seu.edu.cn Abstract: A non-equilibrium molecular dynamics simulation model is established to investigate the impact of vdw strength on thermal transport along the in-plane and out-plane directions in bi-layer films (BLFs). Si films and multilayer graphene sheets are both investigated. Lennard-Jones and Stillinger-Weber potential are used to describe the interaction between Si-Si atoms belong to different films and those belong to the same film. Lennard-Jones potential is used to describe the vdw interactions of the atoms belong to different thin films both for the multilayer graphene and silicon BLFs. It is demonstrated that higher strength leads to a higher possibility for phonons to pass through the vdw interface and hence larger in-plane thermal conductivities. However, interface roughness also increases with the continuous increase of the vdw strength and leads to the reduction of thermal conductivities. In our model, diffusion factors for phonon scattering on boundaries are investigated. Based on the MD model, we demonstrate a method of precisely manipulating the interfacial thermal conductance (ITC) between graphene and metal. It is demonstrated that graphene/metal interfacial thermal conductance can be tuned through adjusting the bonding strength. 57

59 Contact Thermal Conductance between Individual Multi-walled Carbon Nanotubes Deyu Li Department of Mechanical Engineering, Vanderbilt University, USA Abstract: Carbon nanotubes (CNTs) have been used as nanoscale fillers to tune the transport properties of nanocomposites. While up to seven orders of magnitude enhancement has been achieved for the electrical conductivity of CNT-polymer composites, thermal conductivity enhancement is still far below the theoretical prediction based on the particle mixing theory. This has been attributed to the contact thermal resistance between CNTs and between CNTs and various host materials such as different polymers. However, compared to the extensive studies of thermal transport through individual CNTs of different morphologies, the research on thermal transport through contacts between CNTs is still very limited. As such, a good understanding of the contact thermal conductance at CNT-CNT junctions is still lacking. Here we report on experimental measurements of contact thermal conductance between individual multi-walled CNTs. Results show that the contact thermal conductance between CNTs increases with the tube diameter with an exponent of ~2.4. The normalized contact thermal conductance per unit area linearly depends on the tube diameter, which is intriguing because it is commonly expected that the normalized conductance should be size-independent. Semi-quantitative analyses indicate that this surprising observation can be attributed to three coupled underlying mechanisms: (1) an unexpectedly long phonon mean free path along the c-axis of graphite of more than 100 nm, (2) phonon reflection from free surfaces nearby the contact, and (3) the phonon focusing effects in highly anisotropic graphitic materials. 58

60 What can Statistical Physics do to understand Anomalous Heat Transport? Peter Hänggi, Sha Liu, Nianbei Li, Baowen Li and collaborators* Dept. Physics, University of Augsburg, Natl. University of Singapore, Center for Phononics and Thermal Energy Science, Tongji University Abstract: The field of Statistical Physics provides many different tools, which are based either on microscopic approaches or on a more phenomenological level to describe the spread of heat in classical and quantum regimes in realistic and more idealized model systems of arbitrary dimensions. Typical such powerful tools are first principles Linear Response Theory for transport coefficients, yielding the celebrated Green-Kubo formulas, the stochastic theory of Random Walks, or mesoscopic approaches such as the more practical treatments in terms of kinetic transport equations. In low dimensional systems the transport of heat in form of diffusive spread or heat flux between reservoirs of differing ambient temperatures typically may exhibit anomalous features such as the violation of the Fourier Law with length-dependent heat conductivities or the diffusive spread of heat that occurs faster than normal. In this talk we discuss recent results how the dynamics of energy spread occurring in one-dimensional nonlinear lattices relates to anomalous diffusion behavior and heat conductivities. Moreover we explain how the carriers of heat, typically referred to as phonons, may be given meaning in a regime with nonlinear interaction forces beyond the ballistic behavior originating from solely present harmonic (linear) interaction forces. The underlying physical mechanism of scattering then renders corresponding mean free paths of such effective phonons finite. * This talk is based on a multinational collaboration involving members from the University of Augsburg, MPI-PKS Dresden, National University of Singapore, Tongji University and the Fudan University in Shanghai. Some pertinent own references are given below. References: [1] A.V. Zarbudaev, S. Denisov and P. Hänggi, Perturbation spreading in many-particle systems: A random walk approach, Phys. Rev. Lett. 106: (2011); ibid, Phys. Rev. Lett. 109, (2012). [2] S. Liu, P. Hänggi, N. Li, J. Ren, and B. Li, Anomalous heat diffusion, Phys. Rev. Lett. 112: (2014) [3] S. Liu, J. Liu, P. Hänggi, C. Wu, and B. Li, Triggering waves in Nonlinear Lattices: Quest for Anaharmonic Phonons and Corresponding Mean Free Paths, arxiv:

61 Thermomechanical Properties of Polymer Nanofibers Renkun Chen Department of Mechanical and Aerospace Engineering University of California, San Diego Abstract: Polymer nanofibers have recently attracted significant interests in the heat transfer community, as they have been shown to become better thermal conductors when drawn into thin nanofibers. This was believed to be caused by reduction in internal structural defects which act as phonon scattering sites, thereby effectively increasing overall fiber crystallinity. It has also been shown that mechanical properties of polymer fibers are significantly altered from their bulk forms. In most cases, the Young s modulus of nanofibers is found to be increased, while the mechanisms behind it are still elusive. Investigating the correlation between mechanical and thermal properties of polymer nanofibers would provide an opportunity to better understand both of the properties and elucidate the structure-property relationships. In this presentation, we will discuss our recent effort to experimentally characterize mechanical and thermal properties of semi-crystalline Nylon-11 nanofibers with diameter ranging from sub-100 nm to 500 nm. we will describe the instrumentations we developed that enable the characterization of these properties, including thermal conductivity, specific heat, and Young s modulus, and then discuss and interpret the measurement results. 60

62 Phonon Transport in Periodic Silicon Nanoporous Films Alan McGaughey Department of Mechanical Engineering, Carnegie Mellon University, USA Abstract: The thermal conductivities of solid silicon thin films and silicon thin films with periodic pore arrays are predicted using a Monte Carlo technique to include phonon-boundary scattering and the Boltzmann transport equation. The bulk phonon properties required as input are obtained from first principles calculations. For both solid and porous films, the in-plane thermal conductivity predictions capture the magnitudes and trends of previous experimental measurements. Because the prediction methodology treats the phonons as particles with bulk properties, the results indicate that coherent phonon modes associated with the secondary periodicity of the pores do not contribute to thermal transport in porous films with feature sizes greater than 100 nm. 61

63 A simple thermal cloak with three-dimensional realization Baile Zhang Division of Physics and Applied Physics, School of Physical & Mathematical Sciences, Nanyang Technological University, Singapore Abstract: While the majority of cloaking research in the past few years focused on various wave fields, recently diffuse-field cloaks are attracting more and more attention. A typical example is the thermal cloak that can hide objects from diffusive heat by guiding conductive thermal flux smoothly around a hidden object. Most already reported demonstrations of thermal cloaks were based on transformation thermodynamics that utilized artificial thermal metamaterials implemented mainly in the 2D geometry. A 3D thermal cloak that can hide a 3D object in a thermal environment is still difficult. Here we move one step forward to extend the 2D geometry in previous reports to three dimensions, and we demonstrate the first successful realization of a 3D thermal cloak working in the 3D space. We choose an air bubble as the object to be cloaked, since it is well known that stationary air is a poor conductor of heat which approximates to a heat insulator in many cases, and small air gaps can seriously block the channel for heat exchange and cause local overheating the main reason of thermal failure in mechanical and electronic devices. It is worth mentioning that what allows us to successfully fabricate a 3D cloak is a specially designed 3D machining process that is introduced for the first time in thermal cloaking research. Another unique aspect of our 3D cloak is its ultrathin thickness, which allows the cloak to perform satisfactorily even in transient and inhomogeneous temperature fields. 62

64 Phonons in Higher Manganese Silicide of a Complex Nowotny Chimney Ladder Structur Li Shi Department of Mechanical Engineering and Texas Materials Institute, The University of Texas at Austin, USA Abstract: Higher manganese silicide (HMS) has been studied for several decades as a p-type thermoelectric material that is made of non-toxic and earth-abundant elements. Among its attractive properties for high-temperature thermoelectric power generation, HMS is characterized with good chemical, thermal, and mechanical stability at elevated temperatures and in reactive gases. Moreover, the complex Nowontny Chimney Ladder (NCL) crystal structure of HMS gives rise to already very low and anisotropic thermal conductivity even in HMS crystals. Although the thermoelectric properties of HMS materials of different impurity doping have been obtained from past studies, there is a lack of fundamental understanding of the phonon dynamics including the phonon dispersion in the complex NCL structure, and it is unclear whether the already low lattice thermal conductivity of HMS can be suppressed much further. Here I will review the recent efforts of my co-workers in obtaining the phonon dispersion of HMS crystals from inelastic neutron scattering measurements and density functional theory calculation, and in suppressing the HMS thermal conductivity by elemental substitution and in nanostructures. These studies suggest the presence of numerous low-lying optical phonon branches in the complex NCL structure, especially a very low-lying twisting polarization of the Si ladder in the Mn chimney. The twisting polarization undergoes several avoided crossing with the three acoustic branches, and is expected to scatter the acoustic phonons. In addition, the anisotropic thermal conductivity found in HMS crystals is mainly caused by the anisotropy in the group velocity. The obtained phonon dispersion is further used to suggest that glass-like thermal conductivity can be obtained in nanostructured HMS with a grain size of about 10 nm without reducing the thermoelectric power factor. While this prediction is being examined by experiments with both individual HMS nanostructures and nanocrystalline bulk HMS, partial substitution of Mn with heavier Re has been used to obtain a thermal conductivity approaching the amorphous limit at high temperatures. 63

65 Integrable Non-Equilibrium Steady State Density Operators and Exact Bounds on Ballistic Transport Tomaz Prosen Department of Physics, University of Ljubljana, Slovenia Abstract: I will explain a fundamental connection between integrability of non-equilibrium steady states of boundary driven markovian master equations for interacting quantum chains and existence of quasi-local conserved operators which lie outside the standard quantum inverse scattering theory. I will then show how existence of quasi-local conserved operators can be implemented to yield strict lower bounds on transport coefficients, such as Drude weights or even diffusion constants. References: [1] T. Prosen, Phys. Rev. Lett. 106, (2011). [2] E. Ilievski and T. Prosen, Commun. Math. Phys. 318, 809 (2013). [3] T. Prosen and M. Znidaric, Phys. Rev. Lett. 111, (2013). [3] T. Prosen and E. Ilievski, Phys. Rev. Lett. 111, (2013). [4] T. Prosen, Phys. Rev. E 89, (2014). 64

66 Room Temperature Ballistic Thermal Conduction in SiGe Nanowires Chih-Wei Chang Center for Condensed Matter Sciences, National Taiwan University, Taipei Abstract: I will show that unexpected micron-scale ballistic thermal conduction can be found in both homogeneously alloyed SiGe nanowires and heterogeneously-interfaced SiGe nanowires exhibiting low thermal conductivities. Because of the efficient alloy scatterings that filter out most high frequency phonons, an unexpected low percentage of phonons carries out the heat conduction process in the SiGe nanowires, and that the suppressed thermal conductivity is accompanied with an elongation of phonon mean free paths over 5μm. Moreover, the ballistic thermal conduction is insensitive to twin-boundaries, defects, and local strain. The discovery will help to realize wave-engineering of phonons at room temperature and open new paradigms for heat managements in nano-devices. 65

67 Understanding of Non-Fourier Conduction in Nanomaterials Based on Thermomass Concept Moran Wang Department of Engineering Mechanics, Tsinghua University Abstract: We are revealing the mechanism of non-fourier heat conductions in materials at nanoscale using the thermon gas model, which is based on the thermomass concept by assigning effective mass to the thermal energy according to the Einstein's energy-mass equivalence. We introduce the gas dynamic equations to describe the macroscopic conduction behavior of thermal energy in materials based on similarity of microscopic statistical theories of gas molecules and thermons/phonons. By considering the "rarefied gas" effects, we are therefore able to study and reveal the mechanism of non-fourier conduction in nanoscale materials from the point of view of thermon gas model. This model has been validated for both the transient and the steady-state heat conduction in nanomaterials. For transient conduction, the unphysical temperature distribution under zero predicted by the other models does not appear in the predictions by the present model. The steady-state non-fourier heat conduction equation derived by the present model has been applied to predict the effective thermal conductivities of nanomaterials. The temperature and size dependences of effective thermal conductivities of nanofilms, nanotubes and nanowires from the present predictions agree well with the available data from experiments or MD simulations in the literature, which again proves the validity of the new heat conduction equations. Our studies suggest that (1) the non-fourier heat conduction in nanomaterials is only an external manifestation of nonlinear heat transfer at nanoscale, but not the change of intrinsic thermal conductivity of materials; (2) the inertial effect of high-rate heat and the interactions between heat/thermons and surface in confined nanostructures dominate the non-fourier heat conduction in nanoscale materials. This new model is also compatible with the existing thermodynamic laws. 66

68 Nonequilibrium Transport in Open Quantum Systems: A Functional Perturbative Analysis* Jen-Tsung Hsiang ( 项人宗 ) Center for Theoretical Physics, Fudan University, China Bei-Lok Hu ( 胡悲乐 ) Maryland Center for Fundamental Physics and Joint Quantum Institute, University of Maryland, USA Abstract Existence and uniqueness of a nonequilibrium stationary state (NESS) for classical many body systems is a main theme of research by mathematical physicists in statistical mechanics for decades [1]. Answering this question for quantum many body systems poses a major challenge for the present. Research into whether closed quantum systems can come to equilibrium and thermalize has seen a spur of recent activities [2], same for transport in constrained open spin systems [3]. Our research program has a more modest goal: A) While mathematical proofs of theorems for these basic issues are of great importance it would be helpful to see how these systems evolve. For this we derive the quantum stochastic equations (master, Langevin, Fokker Planck) for prototypical quantum open systems (e.g., for two oscillators in contact with two heat baths and extension to chains and networks) so one can follow their dynamics explicitly, to examine whether NESS exist at late times, prove the energy flux relations, etc. B) The effects of nonlinearity in quantum transport, equilibration, noise and fluctuation theorems (e. g. quantum anharmonic oscillators and oscillators coupled nonlinearly, each with its own heat bath, FPU models, Fourier law, etc). In this talk we give a sketch of our methodology involving the use of coarse grained effective action for the derivation of stochastic equations the reduced density matrix, calculation of the covariance matrix and the use of functional perturbative methods for weakly nonlinear systems. *Based on 4 papers in preparation by J. T. Hsiang and B. L. H 1+4. Approach to Nonequilibrium Steady State in Open Quantum Systems: Dynamical Equations and Energy Relations I. Linear Coupling. II Nonlinear Coupling (for Annals of Physics) 2. Nonequilibrium Energy Transport in Nonlinear Quantum Systems: A Functional Prturbative Analysis (for J. Stat Mech: Theory & Expt) 3. Nonequilibrium Heat Transfer in a Quantum Anharmonic Oscillator Open System (for Phys. Rev. E) [1] E.g., Spohn, H. and J.L. Lebowitz, Comm.Math. Phys. 54, 97 (1977). Gallavotti, G. and E.G.D. Cohen, J. Stat. P hys. 80, 931 (1995). J.-P. Eckmann, Non-equilibrium steady states Beijing Lecture (2002). [2] E.g., S. Popescu, A. J. Short, and A. Winter, Nat. Phys. 2, 754 (2006). S. Goldstein, J. L. Lebowitz, R. Tumulka, and N. Zangh, Phys. Rev. Lett. 96, (2006). N. Linden, S. Popescu, A. J. Short, and A. Winter, Phys.Rev. E 79, (2009). P. Reimann, New J. Phys. 12, (2010). A. J. Short, New J. Phys. 13 (2011). Y.Subasi, C. Fleming, J. Taylor and B. L. Hu, Phys. Rev. E86, (2012) [3] E.g., D E Evans, Comm. Math. Phys. 54 (1977) 293. H Spohn, Lett. Math.Phys. 2 (1977) 33. B. Buˇca and T. Prosen, New J.Physics 14 (2012) E. Ilievski, T. Prosen, Nucl.Phys. B 882 (2014)

69 Zak Phase and Gap Inversion in Periodic Acoustic Systems Meng Xiao 1,2,, Guancong Ma 1,2, Zhiyu Yang 1, Ping Sheng 1,2, Z. Q. Zhang 1,2,, C. T. Chan 1,2,+ 1 Department of Physics, the Hong Kong University of Science and Technology Clear Water Bay, Kowloon, Hong Kong, China 2 Institute for Advanced Study, the Hong Kong University of Science and Technology Clear Water Bay, Kowloon, Hong Kong, China Abstract: Geometric phase is a useful concept in many physical systems. The Zak phase is a special kind of geometric phase that describes the topological property of an isolated band in one dimension system. In this talk, we will discuss the Zak phase of an acoustic system and its physical consequences. The Zak phase of an isolated band can assume two values only (either 0 or ) for a system with inversion symmetry, and the value of Zak phase is decided by the symmetry properties of band edge states. As the symmetry of the band edge states are also related to the reflection phase inside the band gap bounded by those band edge states, there exist a relationship between the reflection phase inside a band gap and the Zak phase of bulk Bloch bands. Thus by measuring the reflection phase at the boundary of a periodic acoustic system inside the band gap frequencies, we determine the Zak phases of bulk acoustic bands. We also find a topological transition point in a periodic acoustic band gap system where the Zak phases of bulk bands change. By turning the system parameters across this topological transition point, the analog of gap inversion in electronic topological insulators can be found in acoustic systems. The acoustic systems on different sides of this topological transition point are topologically different. When an interface is constructed between systems with different topological properties, an interface state will be formed at the boundary. We constructed such a system and verified the theoretical predictions experimentally. + phchan@ust.hk 68

70 Toward Contactless Circuits for Thermal Light Philippe Ben-Abdallah Laboratoire Charles Fabry,UMR 8501, Institut d'optique, CNRS, UniversitéParis-Sud 11, 2, Avenue Augustin Fresnel, Palaiseau Cedex, France. Abstract: The control of electric currents with diodes and transistors [1] is undoubtedly the main corner stone of modern information technologies. Such devices allow rectifying, switching, modulating and even amplifying the electric current. Astonishing, similar devices for the control of heat flow is not frequent at all in our daily life. In 2006 Baowen Li et al. [2] have proposed a thermal analog of field effect transistor to manipulate the heat flows using acoustic phonons, paving so the way to a new route for controlling heat fluxes in a similar way as electric currents. In this presentation I will introduce buiding blocks to make similar manipulations using thermal photons exchanged between contactless systems [3-4] out of thermal equilibrium. Some basic physical mechanisms such as the radiative thermal rectification [5], the photon tunneling amplification mediated by many-body interactions [6], a transistor effect [7] and bistable thermal behaviors [8] will be discussed. [1] J. Bardeen and W. H. Brattain, Phys. Rev. 74, 230 (1948). [2] B. Li, L. Wang and G. Casati, Appl. Phys. Lett. 88, , (2006). [3] P. Ben-Abdallah, R. Mesina, S. A. Biehs, M. Tschikin, K. Joulain and C. Henkel, Phys. Rev. Lett. 111, 17, (2013). [4] P. Ben-Abdallah, S.A. Biehs and K. Joulain, Phys. Rev. Lett., 107, 11, (2011). [5] P. BEN-ABDALLAH and S. A. BIEHS, Appl. Phys. Lett. 103, (2013). [6] R. Messina, M. Antezza, P. Ben-Abdallah, Phys. Rev. Lett. 109, (2012). [7] P. Ben-Abdallah and S.-A. Biehs, Near-field thermal transistor, Phys. Rev. Lett., 112, (2014). [8] V. Kubytski, S. A. Biehs and P. Ben-Abdallah, Radiative bistability and thermal memory, in preparation (2014). 69

71 Elastic chiral metamaterials based on rotational resonance Xiaoning Liu 1, Guoliang Huang 2 and Gengkai Hu 1 1School of Aerospace Engineering, Beijing Institute of Technology, Beijing Deptment of Systems Engineering, University of Arkansas at Little Rock, Little Rock, Arkansas 72204, USA hugeng@bit.edu.cn Abstract: Elastic metamaterial has a great potential in controlling low-frequency elastic waves. Negative material parameters are usually related to internal resonance of material, for example, monopole, dipole and quadruple resonances may produce negative effective bulk modulus, mass density and shear modulus. In this talk, we will explain how to realize elastic metamaterials by promoting rotational resonance with chiral microstructure, elastic metamaterials with simultaneous negative effective mass density and bulk modulus can be easily designed. We first study a mass-spring model of a chiral elastic metamaterial that exhibits simultaneously negative mass density and negative Young s modulus. Then a chiral lattice with coated inclusions are analyzed and designed to have this double negativity, the tuning of the resulting low-frequency bandgaps is discussed by adjusting microstructure parameters of the coated inclusion and lattice geometry. The capability of the proposed metacomposite beam for the low-frequency vibration suppressing is demonstrated. Finally, a novel chiral microstructure design made of single-phased solid material is suggested. The effective elastic properties of the metamaterial are numerically determined and their relations with the translational and rotational resonances are quantitatively analyzed. Transient elastic wave experiment tests in a plate structure are also conducted to successfully demonstrate the negative refraction of the proposed metamaterial at the designed frequency, which are in good agreement with predictions by the numerical simulation. 70

72 Sonic crystal and its exotic effects Minghui Lu, Xu Ni, Siyuan Yu, Liyang Zheng, Zeguo Chen and Yan-Feng Chen National Laboratory of Solid-State Microstructures and Department of Materials Science and Engineering, Nanjing University, Nanjing , China Abstract: Sonic crystal, analogous to photonic crystal, has been studied over two decades. Some of important effects, such as band-gap, dispersion relation, have been well established in it. In recent years, the abnormal phenomena, such as negative refraction, enhanced transmission of acoustic waves in sub-wavelength, and negative bulk modulus and negative mass density, etc., were founded. Much less velocity of acoustic wave than light makes it easier to directly measure its amplitude and phase of propagation, and thus provides important compensated evidence to establish basic effects shared by both photonic crystals and sonic crystals. We will describe some results we got in unidirectional propagation of acoustic waves, zero refraction index in acoustic Dirac cone, and surface acoustic wave sonic crystals operation in high frequency. These results may find new applications in the acoustic devices applications, and could be extend to heat manipulation. Reference: [1] Xue-Feng Li, Xu Ni, Liang Feng, Ming-Hui. Lu, Cheng He, Yan-Feng Chen, Tunable unidirectional sound propagation through a sonic crystal based acoustic diode. Phys. Rev. Lett. 106, (2011) [2] Ze-Guo Chen, Xu Ni, Ying Wu, Cheng He, Xiao-Chen Sun, Li-Yang Zheng, Ming-Hui Lu, and Yan-Feng Chen, Accidental degeneracy of double Dirac cones in a phononic crystal, Scientific Reports 4, 4613 (2014). [3] Xu Ni, Xiao-Ping Liu, Ze-Guo Chen, Li-Yang Zheng, Ye-Long Xu, Ming-Hui Lu and Yan-Feng Chen, Rabi splitting in an acoustic cavity embedded plate, New J. Phys. 16, (2014). [4] Li-Yang Zheng, Ying Wu, Xu Ni, Ze-Guo Chen, Ming-Hui Lu, and Yan-Feng Chen, Acoustic cloaking by a near-zero-index phononic crystal, Appl. Phys. Lett. 104, (2014). [5] Li-Yang Zheng, Ying Wu, Xiao-Liu Zhang, Xu Ni, Ze-Guo Chen, Ming-Hui Lu, and Yan-Feng Chen, A new type of artificial structure to achieve broadband omnidirectional acoustic absorption, AIP Advances 3, (2013). 71

73 Spin Seebeck Diode and Transistor: towards a Thermal-Driven Spin Computer Jie Ren MIT, USA Abstract: Energy waste is a severe bottleneck in the supply of sustainable energy to any modern economy. Besides developing new energy sources, the global energy crisis can be alleviated by re-utilizing the waste heat. In this talk, I will first introduce some background of harnessing the thermal energy by the thermoelectrics, spin caloritronics, and phononics. Then, in the second part, I would like to share with you some of my recent exciting discoveries about the rectification and negative differential spin Seebeck effects, exemplified in metal/magnetic insulator interfaces and magnon tunneling junctions. These properties lead us to the novel devices, such as thermal-driven spin diode and transistor in the absence of electric transports. I call them spin Seebeck diode and transistor. These findings imply that a spin computer driven by waste heat might not be a dream in the future, which offer us new opportunities to achieve the smart control of energy and information at nanoscale. 72

74 Interference Phonon Mirrors in Atomic-Scale Metamaterials Yuriy A. Kosevich Laboratoire d Energetique, Moleculaire, Macroscopic et Combustion, CNRS, UPR 288, Ecole Centrale Paris, France, and Semenov Institute of Chemical Physics, Russian Academy of Sciences, Moscow, Russia Abstract: In this presentation we will introduce and discuss the modeling of an atomic-scale phononic metamaterial producing two-path phonon interference antiresonances to control heat flux spectrum. We consider the interface between two solid crystals, which contains heavy isotopic impurities and/or soft-force-constant defects. If the impurities do not fill completely the interface plane, longitudinal and transverse phonons have two passes to cross such interface, through the host and through the impurity atoms bonds. Destructive interference between these passes can result in total resonance reflection of the phonon [1,2]. The zero-transmission dip in the atomic-scale phononic metamaterial is analogous to the two-photon Hong-Ou-Mandel dip in the detection probability of the output photons in the macroscopic two-path photon interferometer [3]. We perform analytical calculations of plane wave transmission and numerical molecular dynamics simulation of wave packet transmission, which give consistent with each other results. The random distribution of the defects at the interface and nonlinearity of atomic bonds do not deteriorate the reflection and transmission antiresonances. The width of antiresonance dip can provide a measure of the coherence length of the phonon wave packet. Such patterned atomic planes can be considered as high-finesse atomic-scale phononic mirrors. The antiresonances are realized in phonon transmission through a planar defect in Si crystal with segregated Ge atoms. The phonon antiresonances can be considered as interference phenomena in atomic-scale phononic metamaterials. We will discuss also some possible applications of such phononic metamaterials. [1] Yu. A. Kosevich, Prog. Surf. Sci. 55, 1 (1997). [2] Yu. A. Kosevich, Physics-Uspekhi 51, 848 (2008). [3] C.K. Hong, Z.Y. Ou and L. Mandel, Phys. Rev. Lett. 59, 2044 (1987). 73

75 Thermal and Electrical Conductivities of Porous Si Thin Films Koji Miyazaki Department of Mechanical and Control Engineering, Kyushu Institute of Technology, 1-1 Sensui-cho, Tobata-ku, Kitakyushu , JAPAN Abstract: The high thermoelectric properties were reported by using nano-structures for the reduction of thermal conductivity as well as keeping high electrical conductivity [1]. Strong phonon scattering can be expected avoiding from the electron scattering in the structured semiconductors when the phonon mean free path is longer than the electron mean free path. In this study we intend to measure both electrical conductivity and thermal conductivity simultaneously using Si thin films with periodic micro-pores. The structured Si thin films were fabricated using silicon-on-insulator wafers by standard micro-fabrication processes. The both thermal and electrical conductivities measured by a self-heating method [2] were lower in the porous membranes than in the non-porous membrane. The measured thermal conductivity was much lower than the thermal conductivities expected by classical models [3]. A significant phonon size effect was observed even in micro-sized structures, and the mean free path for phonons was very long. We concluded that phonon transport is quasi-ballistic and electron transport is diffuse in micro-porous Si structures. We also intend to make a thermal rectifier using the quasi-ballistic transport of phonons in an asymmetric structure. The thermal conductivity of Si thin films with triangle pores were measured, and the effects of the asymmetric structures on the phonon transport were discussed with numerical simulations of a phonon transport. References: [1] G.J. Snyder and E. S. Toberer, Nature mater. 7, 105 (2008). [2] X. Zhang, S. Fujiwara, and M. Fujii, Int. J. Thermophys. 21, 965 (2000). [3] A. Eucken, Forschung und Gebiete Ingenieur (Ausgabbe A) (1940). 74

76 Collective Excitations in the Thermal Conductivity of Graphene Andrea Cepellotti EPFL, Switzerland Abstract: We compute the thermal conductivity of graphene and graphite by solving the Boltzmann Transport Equation (BTE) for phonons [1], with the phonon-phonon collision rates obtained from density-functional perturbation theory. We find that the single-mode relaxation time approximation (SMRTA) cannot describe the in-plane heat transport correctly, underestimating by at least one order of magnitude the thermal conductivity and heat mean free paths. Instead, we show that the exact self-consistent solution of the BTE provides results in excellent agreement with experimental measurements [2]. The shortcomings of the SMRTA lie in the assumption that heat flow is transferred only by individual phonon excitations, whereas in layered materials the transport can only be explained in terms of collective phonon excitations. The characteristic length of these collective excitations is often comparable with that of the experimental sample - as a result, even Fourier's law become questionable, since its statistical nature makes it applicable only to systems larger than a few mean free paths. Finally, we analyze in details the effect of isotopes and strain, often deemed to be responsible for discrepancies between experiments [2]. [1] M. Omini and A. Sparavigna, Nuovo Cimento D 19, 1537 (1997) [2] A. Balandin, Nat. Mater. 10, 569 (2011) 75

77 Phonon thermal conduction in suspended graphene using micro-fabricated devices Xiangfan XU 1, Jiayi WANG 2, Baowen LI 1,2 1 Center for Phononics and Thermal Energy Science, School of Physics Science and Engineering, Tongji University, Shanghai, China 2 Department of Physicsand Centre for Computational Science and Engineering, National University of Singapore, Singapore Abstract: Although significant progress has been made for one-dimensional systems, the study of heat conduction in two-dimensional systems is still in its infancy due to the lack of proper materials and the challenge in suspending atomic-thick membrane suitable for thermal transport measurements. Here, we present the experimental studies of thermal conductivity in suspended graphene using thermal bridge method. In submicron suspended single layer graphene (SLG), at T < 100K, thermal conductance scale temperature as ~ T 1.68 and approach the ballistic limit, indicating high sample quality in the measured graphene and that the flexural acoustic phonons (ZA) dominate the thermal conduction [1]. This contribution from ZA phonons is found to be systematically suppressed by impurity atoms (Au atoms) on the surface of tri-layer suspended graphene [2]. Interestingly and in contrast to bulk materials, when temperature at 300K in SLG, thermal conductivity keeps increasing and remains logarithmic divergence with sample length even for sample lengths much larger than the average phonon mean free path [1]. This result is a consequence of the two-dimensional nature of phonons in graphene and possible mechanisms are discussed. References: [1] Xiangfan Xu et al., Nat. Commun. 5, 3689 (2014). [2] Jiayi Wang et al., Adv. Mater. 25, (2013). 76

78 Thermo-electric effect on the surfaces or edges in topological insulators Bangfen Zhu Department of Physics, Tsinghua University, Beijing , China Abstract: 77

79 3. Posters 78

80 Heat Signatures Manipulation: From Cloaking to Camouflage Xue Bai 1,2,3*, Tiancheng Han 1*, John T. L. Thong 1,3, Baowen Li 2,3,4, and Cheng-Wei Qiu 1,3 1 Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Republic of Singapore. 2 Department of Physics and Centre for Computational Science and Engineering, National University of Singapore, Singapore , Republic of Singapore 3 NUS Graduate School for Integrative Sciences and Engineering, National University of Singapore, Kent Ridge , Republic of Singapore. 4 Center for Phononics and Thermal Energy Science, School of Physical Science and Engineering, Tongji University, , Shanghai, China. Abstract: The perception and identification of an object can be realized by detecting its unique scattering signature in various physical fields, e.g., optics, electromagnetics, acoustics, thermotics, etc. cloak, is the device which can change an arbitrary object into nothing by hiding the unique signature. In contrast to cloak, illusion usually refers to the change of signatures for one object into another in a specific physical field. Based on our previous thermal cloak work, we propose and realize a functional thermal camouflage device, which is capable of creating multiple expected images of the original object s position in heat conduction. The thermal scattering signature of the object is thus metamorphosed and perceived as multiple ghost targets with different geometries and compositions. The thermal illusion effect is experimentally confirmed in both time-dependent and temperature-dependent cases, demonstrating excellent thermotics performance. References: [1] Tiancheng Han, Xue Bai, Dongliang Gao, John T. L. Thong, Baowen Li, Cheng-Wei Qiu, Experimental Demonstration of a Bilayer Thermal Cloak, Physical Review Letters, 112(2014): [2] Tiancheng Han, Xue Bai, John T.L. Thong, Baowen Li, and Cheng-Wei Qiu, Full Control and Manipulation of Heat Sig-natures: Cloaking, Camouflage and Thermal Metamaterials, Adv. Mater., DOI: /adma (2014) 79

81 Understanding Potassium Doping in Lead Chalcogenide Thermoelectrics Dan Feng, Xudong Li, Zhao Wang Frontier Institute of Science and Technology, Xi an Jiaotong University, China Haijun Wu, Jiaqing He Department of Physics, South University of Science and Technology of China, China Abstract: We found that 2mol% potassium doped PbQ (Q = Te, Se, S) compounds have low thermal conductivity and therefore show good thermoelectric performance, especially in the PbSe+K systems. In microstructure observation by means of electron microscopy, we found a high-density nanoscale grain and precipitate distribution in the samples. Combining with numerical studies [2], we try to find the detailed correlation between the thermal transport properties and the microstructure change of the samples. References: [1]J. Q. He, L. D. Zhao, J. C. Zheng, H. J. Wu, H. Q. Wang, Y. Lee, M. G. Kanatzidis, V. P. Dravid, J. Am. Chem. Soc., (2013). [2] Wang, Z., Mingo, N. Appl. Phys. Lett. 97, (2010). 80

82 Local Angle between Heat Fluxes for Thermal Conductivity of Nanoporous Thin Film and Nanocomposite B. Fu, C. Bi and G. H. Tang* MOE Key Laboratory of Thermo-Fluid Science and Engineering, School of Energy and Power Engineering, Xi an Jiaotong University, Xi an , China Abstract: The local angle between heat fluxes is introduced for the study of thermal conductivity in nanoporous thin film and nanocomposite. The local angle is defined as the one between the directions of heat flux component q x and the local heat flux q. We show that a larger local angle leads to a lower q x and corresponding thermal conductivity. The Phonon Boltzmann Transport Equation is solved by using the Discrete Ordinates Method to numerically study the phonon thermal conductivity with the frequency-dependent model. The effect of pore shape on the thermal conductivity of the nanoporous silicon thin film is investigated. At the fixed porosity or interface area, the thermal conductivities, local angle distributions and the average angles of the thin films with square, circular, triangular and hexagonal pores are analyzed, respectively. The comparison among the angle distributions confirms that a lager average angle results in a lower thermal conductivity of the thin film. The results show that the interface area is more dominant on the thermal conductivity compared to the porosity, and the thermal conductivity decreases obviously with the increase of the interface area. Furthermore, the local angle distribution between heat fluxes is studied in the silicon-germanium nanocomposites, including the compacted nanocomposite (nanowire and nanoparticle nanocomposites) and the embedded nanocomposite (nanocomposites with aligned and staggered nanoparticles). The nanowire composite with a lower average angle presents a lager thermal conductivity than the nanoparticle composite. The thermal conductivity of the nanocomposite with aligned nanoparticle which has a lower average local angle is larger than that of the nanocomposite with staggered nanoparticle. The present study shows that the local angle between heat fluxes can be applied to optimize the arrangement of nanopore, nanoparticle and nanowire to reduce the thermal conductivity. References: [1] W. X. Tian and R. G. Yang, J. Appl. Phys. 101, (2007). [2] M. S. Jeng, R. G. Yang, D. Song, and G. Chen, J. Heat Transfer 130, (2008). [3] Q. Hao, G. Chen, and M. S. Jeng, J. Appl. Phys. 106, (2009). [4] G. H. Tang, C. Bi, and B. Fu, J. Appl. Phys. 114, (2013). [5] A. Jain, Y. J. Yu, and A. J. H. McGaughey, Phys. Rev. B 87, (2013). 81

83 Thickness-dependent Cross-plane Thermal Conductivity of Thin Graphite Flakes Qiang Fu 1, Yunfei Chen 2, Deyu Li 3, Juekuan Yang 2, and Dongyan Xu 1 1 Department of Mechanical and Automation Engineering and Shun Hing Institute of Advanced Engineering, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong, China 2 School of Mechanical Engineering and Jiangsu Key Laboratory for Design and Manufacture of Micro-Nano Biomedical Instruments, Southeast University, Nanjing, , China 3 Department of Mechanical Engineering, Vanderbilt University, Nashville, TN 37235, USA Abstract: Graphite and graphene have attracted tremendous research interests in the past decade because of their superior electrical and thermal properties. So far, extensive studies have been conducted on thermal transport properties of graphite and graphene, especially on in-plane thermal conductivity [1-3] and contact thermal resistance between graphene and other materials [4]. However, the phonon mean free path of graphite in the cross-plane direction has not been well understood yet. For example, the simplified kinetic theory predicted that the cross-plane phonon mean free path of graphite is only a few nanometers [5], but recent molecular dynamics simulations indicated that it could be as large as 2000 nm at room temperature [6]. In this work, we experimentally tackle this problem by carefully characterizing the cross-plane thermal conductivities of graphite flakes with thicknesses ranging from tens to hundreds nanometers via the three omega method. The graphite flakes are prepared on the silicon substrate by the mechanical exfoliation method. At 300 K, the measured cross-plane thermal conductivities of graphite flakes with thicknesses ranging from 20 nm to 400 nm are substantially lower than the counterpart of the bulk graphite and increase with the thickness. Our results indicate that the cross-plane phonon mean free path of graphite is above 400 nm at room temperature. References: [1] A. A. Balandin, S. Ghosh, W. Bao, I. Calizo, D. Teweldebrhan, F. Miao, and C. N. Lau, Nano Lett. 8, 902 (2008). [2] W. Jang, Z. Chen, W. Bao, C. N. Lau, and C. Dames, Nano Lett. 10, 3909 (2010). [3] W. Cai, A. L. Moore, Y. Zhu, X. Li, S. Chen, L. Shi, and R. S. Ruoff, Nano Lett. 10, 1645 (2010). [4] Z. Chen, W. Jang, W. Bao, C. N. Lau, and C. Dames, Appl. Phys. Lett. 95, (2009). [5] T. Tanaka and H. Suzuki, Carbon 10, 253 (1972). [6] Z. Wei, J. Yang, W. Chen, K. Bi, D. Li, and Y. Chen, Appl. Phys. Lett. 104, (2014). 82

84 Energy diffusion in momentum conserving one-dimensional lattice ding-a-ling model Zhibin Gao, and Nianbei Li Center for Phononics and Thermal Energy Science and School of Physical Science and Engineering, Tongji University, Shanghai, People's Republic of China Abstract: The so-called ding-a-ling model was first introduced by Dawson [1] and Casati independently introduced a modified version [2] which has an finite thermal conductivity. Subsequently, a one-dimensional system of particles which is a momentum conserving modification [3] of the famous ding-a-ling model has been confirmed to have an finite thermal conductivity independent of system length L,for L sufficiently large. In this paper,we investigate energy diffusion in momentum conserving one-dimensional lattice ding-a-ling model by measuring the correlation functions [4][5] of energy-momentum fluctuations at different times. References: [1] J.Dawson, Phys. Fluids 5 (1962) 455. [2] G.Casati, J. Ford, F. Vicaldi, W.M. Visscher, Phys. Rev. Lett. 52 (1984) 1861 [3] G. R. Lee-Dadswell,E. Turner, J. Ettinger, and M. Moy Phys. Rev. E 33, (2010). [4] Nianbei Li, Baowen Li, and Sergej Flach Phys. Rev. Lett. 105, (2010). [5] Hong Zhao, Phys. Rev. Lett. 96, (2006). 83

85 Nonequilibrium Transport in Open Quantum Systems: A Functional Perturbative Analysis* Jen-Tsung Hsiang ( 项人宗 ) Center for Theoretical Physics, Fudan University, China Bei-Lok Hu ( 胡悲乐 ) Maryland Center for Fundamental Physics and Joint Quantum Institute, University of Maryland, USA Abstract Existence and uniqueness of a nonequilibrium stationary state (NESS) for classical many body systems is a main theme of research by mathematical physicists in statistical mechanics for decades [1]. Answering this question for quantum many body systems poses a major challenge for the present. Research into whether closed quantum systems can come to equilibrium and thermalize has seen a spur of recent activities [2], same for transport in constrained open spin systems [3]. Our research program has a more modest goal: A) While mathematical proofs of theorems for these basic issues are of great importance it would be helpful to see how these systems evolve. For this we derive the quantum stochastic equations (master, Langevin, Fokker Planck) for prototypical quantum open systems (e.g., for two oscillators in contact with two heat baths and extension to chains and networks) so one can follow their dynamics explicitly, to examine whether NESS exist at late times, prove the energy flux relations, etc. B) The effects of nonlinearity in quantum transport, equilibration, noise and fluctuation theorems (e. g. quantum anharmonic oscillators and oscillators coupled nonlinearly, each with its own heat bath, FPU models, Fourier law, etc). In this talk we give a sketch of our methodology involving the use of coarse grained effective action for the derivation of stochastic equations the reduced density matrix, calculation of the covariance matrix and the use of functional perturbative methods for weakly nonlinear systems. *Based on 4 papers in preparation by J. T. Hsiang and B. L. H 1+4. Approach to Nonequilibrium Steady State in Open Quantum Systems: Dynamical Equations and Energy Relations I. Linear Coupling. II Nonlinear Coupling (for Annals of Physics) 2. Nonequilibrium Energy Transport in Nonlinear Quantum Systems: A Functional Prturbative Analysis (for J. Stat Mech: Theory & Expt) 3. Nonequilibrium Heat Transfer in a Quantum Anharmonic Oscillator Open System (for Phys. Rev. E) [1] E.g., Spohn, H. and J.L. Lebowitz, Comm.Math. Phys. 54, 97 (1977). Gallavotti, G. and E.G.D. Cohen, J. Stat. P hys. 80, 931 (1995). J.-P. Eckmann, Non-equilibrium steady states Beijing Lecture (2002). [2] E.g., S. Popescu, A. J. Short, and A. Winter, Nat. Phys. 2, 754 (2006). S. Goldstein, J. L. Lebowitz, R. Tumulka, and N. Zangh, Phys. Rev. Lett. 96, (2006). N. Linden, S. Popescu, A. J. Short, and A. Winter, Phys.Rev. E 79, (2009). P. Reimann, New J. Phys. 12, (2010). A. J. Short, New J. Phys. 13 (2011). Y.Subasi, C. Fleming, J. Taylor and B. L. Hu, Phys. Rev. E86, (2012) [3] E.g., D E Evans, Comm. Math. Phys. 54 (1977) 293. H Spohn, Lett. Math.Phys. 2 (1977) 33. B. Buˇca and T. Prosen, New J.Physics 14 (2012) E. Ilievski, T. Prosen, Nucl.Phys. B 882 (2014)

86 Anomalous effect of hydrogenation on phonon thermal conductivity in thin silicon nanowires Haipeng Li 1 and Ruiqin Zhang 2 1 Department of Physics, China University of Mining and Technology, Xuzhou, China 2 Department of Physics and Materials Science, City University of Hong Kong, Hong Kong, China haipli@cumt.edu.cn Abstract: Using equilibrium molecular-dynamics simulations, we investigate the phonon thermal conductivity of hydrogenated silicon nanowires (H-SiNWs). In contrast to the usual thermal conductivity reduction observed upon surface passivation due to the enhancement of phonon surface scattering in nanostructures[1-4], we observe increased thermal conductivity upon the surface hydrogenation of thin SiNWs as compared to pure SiNWs [5]. We show that such an anomalous effect arises mainly from the hydrogenation-induced specific changes in the lattice structures and phonon modes of surface silicon atoms. References: [1] C. W. Padgett and D. W. Brenner, Nano Lett. 4, 1051(2004). [2] Q. X. Pei, Z. D. Sha and Y. W. Zhang, Carbon 49, 4752(2011). [3] H. P. Li, A. De Sarkar and R. Q. Zhang, EPL 96, 56007(2011). [4] H. P. Li and R. Q. Zhang, Surface functionalization induced thermal conductivity attenuation in silicon nanowires, chapter in book Nanoscale Energy Transport and Harvesting: A Computational Study (edited by Gang Zhang), Pan Stan-ford Publishing, [5] H. P. Li and R. Q. Zhang, EPL 105, 56003(2014). 85

87 Thermoelectric effect in a four-terminal mesoscopic system Mengjie Li, Jun Zhou, and Baowen Li Center for Phononics and Thermal Energy Science, and School of Physics Science and Engineering, Tongji University, Shanghai , People's Republic of China Abstract: We investigate the thermoelectric effect in a four-terminal mesoscopic system using the Green s function method and the Landauer-Büttiker formula. When a temperature gradient is applied along the longitudinal direction, a transverse electric potential difference can be obtained when the symmetry along the transverse direction is broken. The transverse symmetry broken is realized by locating a triangle at the center of the system. This thermoelectric effect is analogue to the Nernst effect in which the transverse symmetry is broken by an external magnetic field. 86

88 The Modulation of Kapitza Resistance in Graphite Chenhan Liu, Zhiyong Wei, Weiyu Chen, Juekuan Yang, and Yunfei Chen Jiangsu Key Laboratory for Design and Manufacture of Micro-Nano Biomedical Instruments, Southeast University, Nanjing , P. R. China Abstract: It is demonstrated through the nonequilibrium Green s function method that the Kapitza resistance (Ω) of graphite can be modulated by loading pressure in x direction, x and y directions and all three directions respectively in this paper. For graphite without pressure, the Kapitza resistance is about m 2 K/W. The pressure in the z direction from tensile -1GPa to compressive 10GPa can reduce the Ω by one order of magnitude, which is caused by the increase in the phonon transmission possibility resulting from the increase in the interlayer interaction strength and weaker interface scattering. And the phonon transmission function has the phenomenon of blue shift in the low-frequency range during the process. The pressure in the x-y plane changes from -10GPa to 0GPa (tensile) has little effect on the phonon transmission and Kapitza resistance Ω while there has no pressure or a small pressure in the z direction. So pressure in the basal plane has little effect on the interfacial thermal conductance and phonon transmission in the graphite. Furthermore, the discrete layer in the graphite separates mutually when the pressure in the x and y directions reaches to the critical value 1~2GPa or to -2~-1GPa in the z direction. It is worth noted that low-frequency phonons have larger phonon transmission due to longer mean free path and the soft Van der Waals interaction between the neighboring layers. Our results suggest that the Kapitza resistance of graphite or few-layer graphene can be modulated in a large scope and then can be applied for both heat dissipation and insulation through the pressure engineering. 87

89 Profiling Nanowire Thermal Resistance with a Spatial Resolution of Nanometers Dan Liu 1,2,3, Rongguo Xie 1, 2, Jie Chen, Baowen Li 1,3,4, John T L Thong 2, 1 Department of Physics and Centre for Computational Science and Engineering, National University of Singapore, Singapore , Republic of Singapore 2 Department of Electrical and Computer Engineering, National University of Singapore, Singapore , Republic of Singapore 3 NUS Graduate School for Integrative Sciences and Engineering, National University of Singapore, Singapore , Republic of Singapore 4 Center for Phononics and Thermal Energy Science, School of Physics Science and Engineering, Tongji University, Shanghai, People's Republic of China Abstract: In this poster we present the electron beam heating technique a technique that is capable of profiling the thermal resistance along a single nanowire with a spatial resolution of better than 20 nm 1. The working principle and experimental set-up of this technique are presented, followed by several research findings using this technique, such as the spatially resolved thermal conductivity along a Si 0.7 Ge 0.3 /NiSi 0.7 Ge 0.3 heterostructured nanowire, and the interfacial thermal resistance (ITR) across the Si/NiSi 2 interface embedded in a Si/NiSi 2 heterostructured nanowire. In the latter part, we found that the ITR does not change even for adjacent interfaces as close as 50 atomic layers. 1. Liu, D., Xie, R., Yang, N., Li, B. & Thong, J.T.L. Profiling Nanowire Thermal Resistance with a Spatial Resolution of Nanometers. Nano Letters 14, (2014). 88

90 Anharmonic phonons in nonlinear lattices: A variational approach Junjie Liu Department of Physics, Fudan University, Shanghai Abstract: In this study, we proposed two anharmonic phonon theories for momentum conserving nonlinear lattices based on a generalized Gibbs-Bogoliubov inequality. This inequality provides a upper bound as well as a lower bound on the Gibbs free energy. Using the Gibbs free energy instead of the Helmholtz free energy enables us to investigate systems under nonzero pressure. We demonstrate the power of our theories by considering applications to one dimensional nonlinear lattices with a symmetric or asymmetric Fermi-Pasta-Ulam potential. Among two anharmonic phonon theories, we found the theory derived from the lower bound of the generalized Gibbs-bogoliubov inequality gives better theoretical predictions. Excellent agreements with molecule dynamics results bear out the superiority of our theory compared with existing quasiharmonic theories. 89

91 Triggering Waves in Nonlinear Lattices: Quest for Anharmonic Phonons and Corresponding Mean Free Paths Sha Liu Department of Physics, National University of Singapore, Singapore Abstract: Guided by a thought-experiment we develop a self-consistent anharmonic phonon concept for nonlinear lattices. The procedure simultaneously identifies the existence of the anharmonic phonon wavenumber with its corresponding mean free path and, additionally, allows for the explicit visualization of its wave propagation. The idea rests upon the application of an external driving force which excites the front particles in a nonlinear lattice slab. The method is manifest nonperturbative in the strength of nonlinearity; it thus is neither limited to low temperatures nor to small frequencies. Covering wide regimes of temperature and frequencies we apply the method to three well-known one-dimensional nonlinear lattices of current interest which either exhibit anomalous or also normal heat transport. 90

92 Thermal transport in low-dimensional nanosystems Yue-Yang Liu, Xiao-Fang Peng, Ke-Qiu Chen Department of Applied Physics, Hunan University, Changsha , China Abstract: Thermal transport in nanostructures has attracted increasing attention in recent years, and many interesting physical effects such as the universal quantized thermal conductance 1 4, thermal rectification effects 5 7, and negative differential thermal resistance 8, 9 have been found in these systems. Here, we introduce our recent works on the thermal properties of nanowires, graphene nanoribbons and quantum structures: (1) We investigated the heat flux distribution in InAs/GaAs core-shell nanowires and demonstrate that core-shell nanowire is a promising structure as nanoscale heat cables. 10 (2) A study on thermal transport in quantum structures shows that the cutoff frequency for the lowest four types of acoustic modes is zero while the cutoff frequency for optical modes is nonzero. Quantized thermal-conductance plateau which can be observed in a perfect quantum wire is broken in the structure with catenoidal contacts. 11 (3) Phonon transport and thermal conductance show the similar thermal conductance property using nonequilibrium Green s function method and elastic wave continuum model at low temperatures. However, in the higher temperature region, the thermal conductance in nonequilibrium Green s function method is bigger than that in the elastic wave continuum model. 12 (4) We studied the thermal transport properties of graphene nanoribbons with pentagon heptagon defect (PHD) by using first principles calculations in combination with non-equilibrium Green s function approach. The results show that the PHD effect on thermal conduction in armchair-oriented GNR is stronger than that in zigzag-oriented GNR. The out-of-plane acoustic mode is almost reflected by the PHD at a particular frequency. When the temperature is larger than 400 K, the thermal conduction ratio is only related to the PHD s orientation. 13 References: [1] L. G. C. Rego and G. Kirczenow, Phys. Rev. Lett. 81, 232 (1998). [2] K. Schwab, E. A. Henriksen, J. M. Worlock, and M. L. Roukes, Nature (London) 404, 974 (2000). [3] K.-Q. Chen, W.-X. Li, W. Duan, Z. Shuai, and B.-L. Gu, Phys. Rev. B 72, (2005). [4] T. Yamamoto and K. Watanabe, Phys. Rev. Lett. 96, (2006). [5] B. W. Li, L. Wang, and G. Casati, Phys. Rev. Lett. 93, (2004). [6] C. W. Chang, D. Okawa, A. Majumdar, and A. Zettl, Science 314, 1121 (2006). [7] N. Yang, G. Zhang, and B. Li, Appl. Phys. Lett. 95, (2009). [8] B. W. Li, L. Wang, and G. Casati, Appl. Phys. Lett. 88, (2006). [9] W.-R. Zhong, P. Yang, B.-Q. Ai, Z.-G. Shao, and B. Hu, Phys. Rev. E 79, (R) (2009). [10] Yue-Yang Liu, Wu-Xing Zhou, Li-Ming Tang, and Ke-Qiu Chen, Appl. Phys. Lett. 103, (2013). [11] Xiao-Fang Peng, Ke-Qiu Chen, Qing Wan, and B. S. Zou, Phys. Rev. B 81, (2010). [12] Xiao-Fang Peng, Xin-Jun Wang, Zhi-Qiang Gong, and Ke-Qiu Chen, Appl. Phys. Lett. 99, (2011). [13] Shi-Hua Tan, Li-Ming Tang, Zhong-Xiang Xie, Chang-Ning Pan, Ke-Qiu Chen, Carbon 65, (2013) 91

93 Enhancement of Thermoelectric Cooling Performance due to Inhomogeneous Thermal Conductivity Tingyu Lu, 1 Jun Zhou, i, * Nianbei Li, 1 Ronggui Yang, 2 and Baowen Li 1,3,4 1 Center for Phononics and Thermal Energy Science, and School of Physics Science and Engineering, Tongji University, Shanghai , People's Republic of China 2 Department of Mechanical Engineering, University of Colorado, Boulder, Colorado 80309, USA ii3 Department of Physics, Center for Computational Science and Engineering, and Graphene Research Center, National University of Singapore, Singapore , Republic of Singapore 4 NUS Graduate School for Integrative Sciences and Engineering, National University of Singapore, Singapore , Republic of Singapore zhoujunzhou@tongji.edu.cn Abstract: Recently, thermal rectifier with inhomogeneous thermal conductivity has been theoretically proposed and experimentally observed. We theoretically investigate the enhancement of thermoelectric cooling performance in thermoelectric devices with spatial-dependent inhomogeneous thermal conductivity. We find that the dissipation of Joule heat in such thermoelectric devices is anisotropic which differs from that in thermoelectric devices with homogeneous thermal conductivity. The anisotropic dissipation of Joule heat could enhance the heat absorption at the heat source, which leads to an significant enhancement of the maximum cooling power and the maximum cooling temperature differential. The expressions of the thermoelectric figure of merit (ZT) and the coefficient-of-performance (COP) are modified by the introduction of an inhomogeneity factor which describes the anisotropic dissipation of Joule heat. Our finding shows the potential application of thermal rectification effect on searching for thermoelectric refrigerator with high performance. 92

94 A Molecular Dynamics Study of Heat Transfer across Nanoscale Confined Thin Film Cheng Shao and Hua Bao* University of Michigan-Shanghai Jiao Tong University Joint Institute, Shanghai Jiao Tong University, Shanghai, China Abstract: The structure that a thin film confined between two materials is widely exists in microelectronic devices. Thermal resistances across the thin film include the thin film resistance and thermal boundary resistances at the two interfaces. When the thickness of the thin film is at the scale of nanometer, these three resistances are coupled with each other and the relationship is seldom discussed in literature. Using molecular dynamics simulations, we systematically investigate the net resistance across the confined thin film. The confined thin films considered in this study including crystalline, amorphous, and alloy with film thickness up to 20nm. Our results indicate that when the thin film is crystalline, the total resistance is smaller than that predicted from thermal circuit model in diffuse limit. In contrast, when the film has structure disorder (amorphous) or mass disorder, net thermal resistance is evidently larger than the prediction from thermal circuit model in diffuse limit, except the cases that the thin film is only a few atomic layers thick. For a mass mixing thin film formed at the interface of two dissimilar materials, our results indicate that when the mass mixing layer is very thin (a few atomic layers), it can reduce the thermal resistance across the interface, regardless the mixing layer is ordered or amorphous. For the cases of disorder thin film, thermal resistance is almost linearly dependent on the thickness and can still be described by the thermal circuit model if a modified thin film thermal conductivity is employed. 93

95 Sound and Noisy Light: Tuning Phonon Modes in Photo-switchable Nanostructures Sophia Sklan 1, Jeffrey Grossman2 1 Department of Physics, Massachusetts Institute of Technology, Cambridge, USA 2 Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, USA Abstract: The coupling of light to structural vibrations is well known and results in phenomena like phonon polaritons, acousto-optics (where phonons modulate optical properties), and optomechanics (where light creates or absorbs phonons). Here we consider the question of whether light could also be used to modulate the properties of phonons. We examine photo-isomers (which change their shape under exposure to light), embedded in a nanostructure designed to amplify the effects of photo-switching. To isolate the effects of photo-isomerization (jump photo-switching and shot noise), we apply a combination of analytic and computational techniques to analyze the stochastic dynamics of a toy model of this system. We observe a strong frequency-dependent control of the phonon transmission. In addition, we find that the speed of sound and phonon dispersion curve is tunable with the intensity of the illumination. Particular attention is paid to applying this model to explore the potential applications of the photo-switchable nanostructure, including a phononic filter and tunable phononic crystal. 94

96 Thermoelectric Transport in Individual Bismuth Selenide Nanoribbons Hao Tang 1, Xiaomeng Wang 1, Yucheng Xiong 1, Yan Zhang 2, Yin Zhang 2, Juekuan Yang 2, and Dongyan Xu 1 1 Department of Mechanical and Automation Engineering and Shun Hing Institute of Advanced Engineering, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong, China 2 School of Mechanical Engineering and Jiangsu Key Laboratory for Design and Manufacture of Micro-Nano Biomedical Instruments, Southeast University, Nanjing, , China Abstract: Bismuth selenide (Bi 2 Se 3 ) belongs to the (Bi, Sb) 2 (Se, Te) 3 family, which has been long known as excellent thermoelectric materials. Recently, various Bi 2 Se 3 nanostructures including nanowires and nanoribbons have been synthesized, which enable new opportunities to enhance thermoelectric efficiencies through thermal conductivity reduction. In this work, we report on thermoelectric properties characterization of individual Bi 2 Se 3 nanoribbons with the suspended-microdevice method [1]. First, the intrinsic thermal conductivities of Bi 2 Se 3 nanoribbons with different thicknesses and widths are measured through multiple measurements of the same sample with different suspended lengths to eliminate the effects of contact thermal resistance between the nanoribbon and the membranes [2]. Our results show that intrinsic thermal conductivities of Bi 2 Se 3 nanoribbons are at least 50% lower than the values of the bulk Bi 2 Se 3 in the entire temperature range from 20 K to 320 K and the temperature of the peak thermal conductivity is shifted from 10 K (for bulk Bi 2 Se 3 [3]) to ~ 50K (for Bi 2 Se 3 nanoribbons) indicating enhanced phonon-boundary scattering. On the other hand, it is shown that thermal conductivities of Bi 2 Se 3 nanoribbons depend on both the thickness and the width and thus the Casimir length has been used to interpret thermal conductivities of different nanoribbons. Moreover, thermoelectric properties of individual Bi 2 Se 3 nanoribbons have been concurrently characterized with a four-probe suspended microdevice and the maximum thermoelectric figure of merit is found to be 0.17 at 320 K. References: [1] L. Shi, D. Li, C. Yu, W. Jang, D. Kim, Z. Yao, P. Kim, and A. Majumdar, J. Heat Transf. 125, 881 (2003). [2] J. Yang, Y. Yang, S. W. Waltermire, T. Gutu, A. A. Zinn, T. T. Xu, Y. Chen, and D. Li, Small 7, 2334 (2011). [3] J. Navratil, J. Horak, T. Plechacek, S. Kamba, P. Lostak, J. S. Dyck, W. Chen, and C. Uher, J. Solid State Chem. 177, 1704 (2004). 95

97 Prediction of Thermal Conductivity of Single-layer Silicene Han Xie UM-SJTU Joint Institute, Shanghai Jiao Tong University Abstract: Silicene, a monolayer of silicon atoms arranged in honeycomb lattice, has been viewed as a new type of atomic-layered material with outstanding properties, just like graphene. Its potential applications in nanoelectronics and solar energy conversion lead it to receive exceptional attention from a wide community of scientists and engineers. However, to the best of our knowledge, the thermal conductivity of single-layer silicene has only been predicted from molecular dynamics simulations with original Tersoff potential, which is not very accurate because the original Tersoff potential cannot reproduce the buckling structure of silicene. In order to accurately predict the thermal conductivity of silicene, we optimized the Stillinger-Weber potential parameters to reproduce the low buckling structure of silicene and the full phonon dispersion curve obtained from ab initio calculations. With this optimized SW potential, the equilibrium and nonequilibrium molecular dynamics simulations, and anharmonic lattice dynamics (ALD) calculations are performed. In order to get more accurate prediction, anharmonic lattice dynamics (ALD) approach is used with interatomic force constants (IFCs) calculated from first-principles calculations. All the four methods above consistently result in very low thermal conductivity which is much smaller than that of bulk silicon. Unlike graphene, the out-of-plane vibrational modes contribute less than 10 percent of the total thermal conductivity. The difference is explained by the presence of small buckling, which breaks the reflectional symmetry of the structure. The flexural modes are thus not purely out-of-plane vibration and have strong scattering with other modes. 96

98 Phonon Softening Induced Intrinsic Thermal Resistance in Individual Single-layer Graphene Wen Xu, 1,2 Gang Zhang 2 and Baowen Li 1,3,4 1 Department of Physics and Centre for Computational Science and Engineering, National University of Singapore, Singapore , Singapore 2 Institute of High Performance Computing, A*STAR, Singapore , Singapore 3 NUS Graduate School for Integrative Sciences and Engineering, National University of Singapore, Kent Ridge , Singapore 4 Center for Phononics and Thermal Energy Science, School of Physics Science and Engineering, Tongji University, Shanghai, China Abstract: With molecular dynamics simulations, we systematically uncover a new kind of intrinsic thermal resistance that exists in two-dimensional materials under uneven external perturbation, by using partly encased graphene as a typical example. Combining with lattice dynamics analysis, we demonstrate that this intrinsic thermal resistance originates from the softening of flexural phonons partly in graphene induced by inhomogeneous external potential field or substrates which serve as perturbation. At the interface between graphene sections with and without external potential field, in-plane phonon modes can transmit well, whereas, low frequency flexural phonon modes are reflected, leading to this nontrivial intrinsic thermal resistance in the individual single-layer graphene. This intrinsic thermal resistance closely depends on coupling strength between graphene and substrates, and could be significant when the coupling is strong. Nevertheless, it is suppressed at high temperature. It is also found that this intrinsic thermal resistance depends on the size of the system to some extent, and a length independent value is extrapolated. Moreover, we demonstrate that thermal rectification can be realized by including the uneven external perturbation. Our study provides new insight to better understand thermal transport in two-dimensional materials. 97

99 Extreme Low Thermal Conductivity in Nanoscale 3D Si Phononic Crystal with Spherical Pores Lina Yang 1, Nuo Yang 2 and Baowen Li 1,2,3,4 1.Department of Physics and Centre for Computational Science and Engineering, National University of Singapore, Singapore, Singapore. 2. Center for Phononics and Thermal Energy Science, School of Physical Science and Engineering, Tongji University, Shanghai, China. 3.Graphene Research Center, National University of Singapore, Singapore , Republic of Singapore 4. NUS Graduate School for Integrative Sciences and Engineering, National University of Singapore, Singapore. Abstract: In this work, we propose a nanoscale three dimensional (3D) Si phononic crystal (PnC) with spherical pores, which can reduce the thermal conductivity of bulk Si by a factor up to 10,000 times at room temperature. Thermal conductivity of Si PnCs depends on the porosity, for example, the thermal conductivity of Si PnCs with porosity 50% is 300 times smaller than that of bulk Si. The phonon participation ratio spectra demonstrate that more phonons are localized as the porosity increases. The thermal conductivity is insensitive to the temperature changes from room temperature to 1100 K. The extreme-low thermal conductivity could lead to a larger value of ZT than unity as the periodic structure affects very little the electric conductivity. 98

100 Temperature-Dependent Thermal Conductivities of Nonlinear Klein-Gordon Lattices with Soft Potentials Linlin Yang, and Nianbei Li Center for Phononics and Thermal Energy Science and School of Physical Science and Engineering, Tongji University, Shanghai, People's Republic of China Abstract: Regarding the renormalized phonons as the energy carriers in the nonlinear lattice due to the nonlinear interaction, the scaling laws of temperature-dependent thermal conductivities of one-dimensional nonlinear lattices can be derived from the phenomenological effective phonon approach. For the 4 lattice and the Klein-Gordon (KG) lattice when the nonlinear exponent n is larger than 2, the thermal conductivities can be well explained by the current approach. For the nonlinear is larger than 2, lattice, T T T 4 2 v n T n, vn n 2, and for the nonlinear KG lattice when the nonlinear exponent n. But for the nonlinear exponent n is smaller than 2, there is no any theoretical methods to know the properties of thermal conductivities. Whether the theoretical predictions for KG lattice n>2 can be the universal theory to explain the temperature dependence behaviors both for the KG lattice n>2 and 1<n<2 is a question. In this paper, the numerical simulations are used to calculate the molecular movement situation and perfect agreements have been found which is derived based on the nonlinear exponent n>2. References: [1] K. Aoki and D. Kusnezov, Phys. Lett. A 265, 250 (2000). [2] N. Li and B. Li, AIP Advance 2, (2012). [3] N. Li, J. Ren, G. Zhang, L. Wang, P. H anggi, and B. Li, Rev. Mod. Phys. 84, 1045 (2012). [4] N. Li and B. Li, Phys. Rev. E 87, (2013). 99

101 Atomistic origin Zn4Sb3 thermal stability Xiaolong Yang, Xudong Li, Zhao Wang Frontier Institute of Science and Technology, Xi an Jiaotong University, China Abstract: Zinc antimony stands out among thermoelectrics because of its very low lattice thermal conductivity and thermal stability at moderate temperature. Recent experiments have shown that zinc antimony becomes metastable by heating and can recover its structure stability after 565K [1]. Here we study the atomistic origin of this phenomenon using molecular dynamics simulations on experimentally determined crystal structures. Our results show that the diffusion of Zn atoms to interstitial sites gradually leads to a subtle phase transition above 500K. Their movement, better explained as diffusive, is proven not to contribute to phonon conduction [2]. We find that this structural change makes Zn atoms confined at interstitial sites impeding their diffusion mobility, resulting in a more stable crystal structure of beta-zn4sb3 at high temperature [3]. References: [1] Li, X., Carrete J., Lin J., Qiao G., and Wang, Z., Appl. Phys. Lett. 103, (2013). [2] Lin J., Li X., Qiao G., Wang Z., Carrete J., Ren Y., Ma L., Fei Y., Yang B., Lei L. and Li J.,J. Am. Chem. Soc. 136, 1497 (2014). [3] Yang X., Li X., Lin J., Qiao G., Wang Z., to be published. 100

102 Molecular Dynamics Study of Thermal Transport in Amorphous Silicon Carbide Thin Film Man Li and Yanan Yue School of Power and Mechanical Engineering, Wuhan University, Wuhan, Hubei, , China Abstract: Emergence of amorphous silicon carbide (a-sic) thin film based photovoltaic applications has provoked the great interest in its physical properties. In this work, we report the first comprehensive study of thermal transport in the a-sic thin film from 10 nm to 50 nm at various conditions by using empirical molecular dynamic (MD) simulations. The thermal conductivity increases from 1.38 to 1.75 W/m K as temperature increases from 100 K to 1100 K. Similar increase of thermal conductivity from 1.4 to 2.09 W/m K is obtained with density from 2.7 to 3.24 g/cm3. Besides, a slight increase of thermal conductivity (15%) with calculation domain from 10 nm to 50 nm is observed, indicating that size dependence of thermal transport also exists in nanoscale amorphous structures. For physical interpretation of simulation results, the phonon mean free path (MFP) and the specific heat are calculated respectively, which are responsible for the temperature dependence of thermal conductivity. The phonon group velocity is the key factor for the thermal conductivity changing with density. Results also show that the phonon MFP decreases rapidly with temperature, and it is subject to the Matthiessen s rule. References: [1]. J. Tersoff, Physical Review Letters, 1986, 56, [2]. M. Ishimaru, I.-T. Bae, Y. Hirotsu, S. Matsumura and K. E. Sickafus, Physical Review Letters, 2002, 89, [3]. P. K. Schelling, S. R. Phillpot and P. Keblinski, Physical Review B, 2002, 65, [4]. D. Sellan, E. Landry, J. Turney, A. McGaughey and C. Amon, Physical Review B, 2010, 81, [5]. X.-L. Feng, Microscale Thermophysical Engineering, 2003, 7, [6]. Y. W. Yang, X. J. Liu and J. P. Yang, Molecular Simulation, 2008, 34, [7]. P. Vashishta, R. K. Kalia, A. Nakano and J. P. Rino, Journal of Applied Physics, 2007, 101, [8]. F. Finocchi, G. Galli, M. Parrinello and C. M. Bertoni, Physical Review Letters, 1992, 68, [9]. E. Kaxiras, Atomic and Electronic Structure of Solids, Cambridge University Press, [10]. J. Tersoff, Physical Review B, 1994, 49, [11]. P. C. Kelires, EPL (Europhysics Letters), 1991, 14, 43. [12]. P. Jund and R. Jullien, Physical Review B, 1999, 59, [13]. D. G. Cahill and R. O. Pohl, Physical Review B, 1987, 35, [14]. G. Chen, International Journal of Thermal Sciences, 2000, 39, [15]. S. A. Bludman and M. A. Ruderman, Physical Review, 1968, 170, [16]. C. Jianwei, Ç. Tahir and A. G. William, III, Nanotechnology, 2000, 11, 65. [17]. M.-H. Bae, Z. Li, Z. Aksamija, P. N. Martin, F. Xiong, Z.-Y. Ong, I. Knezevic and E. Pop, Nature Communications, 2013, 4, [18]. W. Jang, Z. Chen, W. Bao, C. N. Lau and C. Dames, Nano Letters, 2010, 10, [19]. J. M. Ziman, Electrons and Phonons: the Theory of Transport Phenomena In Solids, Oxford University Press, [20]. D. G. Cahill and R. O. Pohl, Annual Review of Physical Chemistry, 1988, 39,

103 Effect of coupling displacement on thermal current of Frenkel-Kontorova lattices Jianqiang Zhang, Linru Nie Science School, Kunming University of Science and Technology, Kunming , China Abstract: Heat conduction of symmetric Frenkel-Kontorova (FK) lattices with a coupling displacement was investigated in the overdamped case and underdamped case respectively. In the overdamped case, the results indicate that: (i) As the coupling displacement equals to zero, temperature oscillations of the heat baths linked with the lattices can control magnitude and direction of the thermal current; (ii) Whether there is a temperature bias or not, the thermal current oscillates periodically with the coupling displacement, whose amplitudes become greater and greater; (iii) As the coupling displacement is not equal to zero, the thermal current monotonically both increases and decreases with temperature oscillation amplitude of the heat baths, depending on values of the coupling displacement; (iv) The coupling displacement also induces non-monotonic behaviors of the thermal current with respect to spring constant of the lattice and coupling strength of the lattices; (v) These dynamical behaviors comes from the interaction of the coupling displacement with periodic potential of the FK lattices.in the underdamped case, the results indicate that: (i) As the system has less atoms and is symmetric, the coupling displacement can boost up its thermal current, and absolute value of the thermal current as a function of the coupling displacement exhibits one or two peaks, determined by period of the FK lattices. (ii) As the system has less atoms and is asymmetric, the coupling displacement affects its thermal current only in the case of either negative temperature difference or positive temperature difference, depending on asymmetry of the on-site potentials of the FK lattices. (iii) Along with an increasing atomic number of the FK lattices, the effect of the coupling displacement on the system gradually disappears. Our results have the implication that the coupling displacement between nonlinear lattices plays a crucial role in the design of thermal devices. References: [1] Linru Nie, Lilong Yu, Phys. Rev. E 87, (2013). [2]V.P.Careyet al., Nanoscale Microscale Thermophys. Eng.12,1 (2008). [3] S. Lepria, R. Livib, and A. Politib,Phys. Rep.377, 1 (2003). [4] B. Li, L. Wang, and G. Casati, Phys. Rev. Lett.93, (2004). [5] T. S. Komatsu and N. Ito,Phys. Rev. E81, (R) (2010). [6] B. Li, L. Wang, and G. Casati, Appl. Phys. Lett.88, (2006). [7] L. Wang and B. Li,Phys. Rev. Lett.99, (2007). [8] L. Wang and B. Li,Phys. Rev. Lett.101, (2008). [9] C. W. Chang, D. Okawa, A. Majumdar, and A. Zettl, Science 314, 1121 (2006). [10] J. Ren and B. Li,Phys.Rev.E81, (2010). [11] N. Li, F. Zhan, P. H anggi, and B. Li,Phys.Rev.E80, (2009). [12] N. Yang, N. Li, L. Wang, and B. Li,Phys. Rev. B76, (R)(2007). [13] J. P. Wu, L. Wang, and B. Li,Phys. Rev. E85, (2012). [14] B. Hu, L. Yang, and Y. Zhang, Phys. Rev. Lett.97,

104 Manipulation of acoustic focusing with a configurable planar metasurface transducer Jiajun Zhao Department of Physics, National University of Singapore Abstract: It has a pivotal role in medical science and in industry to concentrate the acoustic energy created with piezoelectric transducers (PTs) into a specific area. Here, a planar metasurface PT prototype is proposed to manipulate the acoustic focal pattern as well as the focal resolution freely. By using suitably optimized ring configurations of the metasurface PT, we demonstrate the manipulation of focal patterns in acoustic far fields, such as the designed focal needle and the designed multi foci. Our method is also able to manipulate and improve the cross-sectional focal resolution from subwavelength to the extreme case: deep sub-diffraction limit. Via the acoustic Rayleigh-Sommerfeld diffraction integral (RSI) cum binary particle swarm optimization (BPSO), the free manipulation of focusing properties is achieved in acoustics for the first time. 103

105 Redirection of sound waves using acoustic metasurface Jiajun Zhao Department of Physics, National University of Singapore Abstract: When acoustic waves are impinged on an impedance surface in fluids, it is challenging to alter the vibration of fluid particles since the vibrational direction of reflected waves shares the same plane of the incidence and the normal direction of the surface. We demonstrate a flat acoustic metasurface that generates an extraordinary reflection, and such metasurface can steer the vibration of the reflection out of the incident plane. Remarkably, the arbitrary direction of the extraordinary reflection can be predicted by a Green s function formulation, and our approach can completely convert the incident waves into the extraordinary reflection without parasitic ordinary reflection. 104

106 Thermoelectric transport through nanoelectromechanical system and its backaction Hangbo Zhou 1,2, Juzar Thingna 3, Jian-sheng Wang 1, Baowen Li 1,2 1 NUS graduate school for integrated science and engineering, national university of Singapore, Singapore, and 2 Department of Physics and Center for Computational Science and Engineering, National University of Singapore, Singapore Institute of Physics, University of Augsburg, Universitatsstr. 1 D Augsburg, Germany Abstract: In recent years, nanoelectromechanical systems (NEMS) have been in the limelight of intense experimental and theoretical investigation due to their potential application in quantumcontrolled devices. Most studies till date have focused on the equilibrium properties of the NEMS, but there is a dire need to systematically investigate their transport properties for future device based applications. In this work we study the theromoelectric transport through a single electron transistor (SET) coupled to the NEMS. We focus on the regime of strong SET-NEMS coupling and study its effects on the thermal/electronic current and vice versa. We observe that the strong coupling not only affects the magnitude of the electronic current but also switches the transport mechanism from an electron dominated to a hole dominated one. This in turn strongly affects the thermopower of the system, which can be tuned using a gate voltage on the SET. The passage of currents through the SET also has a backaction on the the mechanical oscillator and possible routes of heating or cooling the NEMS will be discussed. 105

107 Low Thermal Conductivity in The 2nd Intenational Conference on Ultrathin Carbon Nanotube (2, 1) Liyan Zhu 1 and Baowen Li* 1,2,3 1 Department of Physics, Centre for Computational Science and Engineering, and Graphene Research Center, National University of Singapore, Singapore , Republic of Singapore 2 NUS Graduate School for Integrative Sciences and Engineering, National University of Singapore, Singapore , Republic of Singapore 3 Center for Phononics and Thermal Energy Science, School of Physics Science and Engineering, Tongji University, Shanghai , People s Republic of China Abstract: Molecular dynamic simulations reveal that the ultrathin carbon nanotube (CNT) (2, 1) with a reconstructed structure exhibits a surprisingly low thermal conductivity, which is only ~16-30% of those in regular CNTs, e.g. CNT (2, 2) and (5, 5). Detailed lattice dynamic calculations suggest that the acoustic phonon modes greatly soften in CNT (2, 1) as compared to regular CNTs. Moreover, both phonon group velocities and phonon lifetimes strikingly decrease in CNT (2, 1), which result in the remarkable reduction of thermal conductivity. Besides, isotope doping and chemical functionalization enable the further reduction of thermal conductivity in CNT (2, 1). 106

108 Name AIT, Adil VI. List of Participants Address Center for Phononics and Thermal Energy Science School of Physics Science and Engineering Tongji University, Shanghai, China BAI, Xue National University of Singapore, Singapore BAO, Hua UM-SJTU Joint Institute, Shanghai Jiao Tong University Shanghai, China BEN-ABDALLAH, Philippe Institut d'optique, CNRS, France CAHILL, David Department of Materials Science and Engineering and Materials Research Laboratory, University of Illinois, Urbana CAO, Xiaodong Xiamen University, Xiamen CEPELLOTTI, Andrea EPFL, Switzerland CHANG, Chih-Wei Center for Condensed Matter Sciences National Taiwan University CHEN, Renkun Department of Mechanical and Aerospace Engineering UC San Diego, USA 107

109 CHEN, Weiyu School of Mechanical Engineering Southeast university, Nanjing,China CHEN, Yanfeng Nanjing University, Nanjing CHEN, Yunfei School of Mechanical Engineering Southeast University, Nanjing, China DING, Jing School of Energy and Power Engineering Xi'an Jiaotong University, Xi'an,China DONG, Lan Center for Phononics and Thermal Energy Science School of Physics Science and Engineering Tongji University, Shanghai, China DONG, Xu School of materials science and engineering, Metastable Materials Science and Technology State Key Laboratory Yanshan University, Qinghuangdao,China DUBI, Yonatan Department of Chemistry and The Ilze-Kats Institute for Nano-Scale Science and Technology Ben-Gurion University of the Negev, Beer-Sheva, Israel EL-KADY, Ihab Sandia National Labs, USA FENG, Dan Frontier Institute of Science and Technology 108

110 Xi'an Jiaotong University, Xi'an,China FU, Bo School of Energy and Power Engineering Xi an Jiaotong University, Xi an, China FU, Qiang Department of Mechanics The Chinese University of Hong Kong, HongKong, China GAO, Zhibin Center for Phononics and Thermal Energy Science School of Physics Science and Engineering Tongji University, Shanghai, China GE, Xujin Huazhong University of Science and Technologh, Wuhan HAN, Tiancheng Department of Electrical and Computer Engineering National University of Singapore, Singapore HANGGI, Peter Department of Physics University of Augsburg, Germany HSIANG, Jen-Tsung Center for Theoretical Physics Fudan University, Shanghai HU, Bei-Lok University of Maryland, USA HU, Gengkai Beijing Institute of Technology, Beijing 109

111 HU, Shiqian Center for Phononics and Thermal Energy Science School of Physics Science and Engineering Tongji University, Shanghai, China HUANG, Junxiang Xiamen University, Xiamen JIANG, Jianjun Xiamen University, Xiamen JIN, Zelin School of Energy and Power Engineering Huazhong University of Science and Technologh, Wuhan KOSEVICH, Yuriy Ecole Centrale Paris, France LI, Baowen Center for Phononics and Thermal Energy Science School of Physics Science and Engineering Tongji University, Shanghai, China LI, Deyu Vanderbilt University, USA LI, Haipeng Department of Physics China University of Mining and Technology, Xuzhou, China LI, Mengjie Center for Phononics and Thermal Energy Science School of Physics Science and Engineering Tongji University, Shanghai, China 110

112 LI, Nianbei Center for Phononics and Thermal Energy Science School of Physics Science and Engineering Tongji University, Shanghai, China LI, Rui National University of Singapore, Singapore LI, Simeng Center for Phononics and Thermal Energy Science School of Physics Science and Engineering Tongji University, Shanghai, China LI, Yunyun Center for Phononics and Thermal Energy Science School of Physics Science and Engineering Tongji University, Shanghai, China LIAO, Quanwen School of Energy and Power Engineering Huazhong University of Science and Technologh, Wuhan LIU, Chenhan School of Mechanical Engineering Southeast university, Nanjing,China LIU, Dan NUS Graduate School for Integrative Sciences and Engineering National University of Singapore, Singapore LIU, Junjie Department of Physics Fudan University, Shanghai LIU, Sha Department of Physics and Centre for Computational Science and Engineering 111

113 National University of Singapore, Singapore LIU, Yueyang Department of Physics Hunan University,Changsha LU, Tingyu Center for Phononics and Thermal Energy Science School of Physics Science and Engineering Tongji University, Shanghai, China LV, Jingtao Huazhong University of Science and Technologh, Wuhan MA, Dengke School of Energy and Power Engineering Huazhong University of Science and Technologh, Wuhan MALEN, Jonathan Carnegie Mellon University, USA MARCHESONI, Fabio Dip.to di Fisica, Universita' di Perugia, Perugia, Italy MCGAUGHEY, Alan Department of Mechanical Engineering Carnegie Mellon University, USA MINNICH, Austin Mechanical Engineering and Applied Physics California Institute of Technology, USA MIYAZAKI, Koji Kyushu Institute of Technology,Japan 112

114 NAKAYAMA,Tsuneyo shi Hokkaido University, Japan PENG, Jiebin National University of Singapore, Singapore PENG, Xiaofang Central South University of Forestry and Technology, Changsha PROSEN, Tomaz Department of Physics, University of Ljubljana, Slovenia QI, Yabing Okinawa Institute of Science and Technology Graduate University, Japan QIANG, Xin Huazhong University of Science and Technologh, Wuhan QIU, Chengwei National University of Singapore, Singapore REDDY, Pramod Department of Mechanical Engineering, University of Michigan, USA REN, Jie Massachusetts Institute Of Technology,USA REN, Mengfei Xiamen University, Xiamen 113

115 REN, Zhifeng Department of Physics and TcSUH University of Houston, USA RUAN, Xiulin Purdue University, USA SHAO, Cheng UM-SJTU Joint Institute Shanghai Jiao Tong University, Shanghai, China SHEN, Sheng Department of Mechanical Engineering Carnegie Mellon University, USA SHEN, Xiangying Department of physics Fudan University, Shanghai SHI, Li University of Texas at Austin, USA SHI, Xun Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai SHIOMI, Junichiro Department of Mechanical Engineering University of Tokyo, Japan SINHA, Sanjiv Mechanical Science & Engineering University of Illinois at Urbana-Champaign, USA SKLAN, Sophia Department of Physics, MIT, USA 114

116 SUN, Huiyuan Xiamen University, Xiamen TANG, Dawei Institute of Engineering Thermophysics Chinese Academy of Sciences, Beijing TAO, Yi School of Mechanical Engineering Southeast university, Nanjing,China WANG, Biao Center for Phononics and Thermal Energy Science School of Physics Science and Engineering Tongji University, Shanghai, China WANG, Chengru Center for Phononics and Thermal Energy Science School of Physics Science and Engineering Tongji University, Shanghai, China WANG, Jiayi National University of Singapore, Singapore WANG, Jun Beijing University of Technology, Beijing WANG, Lei Department of Physics, Renmin University of China Beijing, China WANG, Liqiu Department of Mechanical Engineering University of Hong Kong, Hongkong 115

117 WANG, Moran School of Aerosace, Tsinghua University, China WANG, Xiaomeng Department of Mechanical and Automation Engineering and Shun Hing Institute of Advanced Engineering The Chinese University of Hong Kong, Hongkong XIA, Minggang School of Science, Xi an Jiaotong University Xi an, China XIAO, Meng Department of Physics Hong Kong University of Science and Technology, Hongkong XIAO, Xianbo National University of Singapore, Singapore XIE, Han UM-SJTU Joint Institute Shanghai Jiao Tong University, Shanghai, China XIONG, Kezhao Institute of Science and Technology East China Normal University, Shanghai, China XU, Dongyan Department of Mechanical and Automation Engineering The Chinese University of Hong Kong, Hong Kong, China XU, Wen Centre for Computational Science and Engineering & 116

118 Department of Physics National University of Singapore, Singapore XU, Xiangfan Center for Phononics and Thermal Energy Science School of Physics Science and Engineering Tongji University, Shanghai, China YANG, Juekuan School of Mechanical Engineering Southeast University, Nanjing,China YANG, Lina Department of Physics and Centre for Computational Science and Engineering National University of Singapore, Singapore YANG, Linlin Center for Phononics and Thermal Energy Science School of Physics Science and Engineering Tongji University, Shanghai, China YANG, Nuo Huazhong University of Science and Technology, Wuhan YANG, Ronggui University of Colorado at Boulder, USA YANG, Xiaolong Frontier Institute of Science and Technology Xi'an Jiaotong University, Xi'an YUE, Yanan School of Power and Mechanical Engineering Wuhan University, Wuhan 117

119 ZHANG, Baile Nanyang Technological University, Singapore ZHANG,Jianbing School of Physics Science and Engineering, Tongji University, Shanghai ZHANG, Jianqiang Kunming University of Science and Technology, Kunming ZHANG,Qi School of Physics Science and Engineering Tongji University, Shanghai ZHANG, Xing Key Laboratory for Thermal Science and Power Engineering of Ministry of Education & Department of Engineering Mechanics Tsinghua University, Beijing, China ZHANG, Zhuomin Georgia Institute of Technology, USA ZHAO, Jiajun Department of Electrical and Computer Engineering National University of Singapore, Singapore ZHAO, Yunshan National University of Singapore, Singapore ZHENG,Qinghui Nanjing University,Nanjing 118

120 ZHOU, Hangbo National University of Singapore, Singapore ZHOU, Jun Center for Phononics and Thermal Energy Science School of Physics Science and Engineering Tongji University, Shanghai, China ZHOU, Ping School of Energy and Power Engineering Huazhong University of Science and Technology, Wuhan ZHU, Bangfen Tsinghua University, Beijing ZHU, Jia Nanjing University, Nanjing ZHU, Liyan Department of Physics National University of Singapore, Singapore ZHU, Weiwei Center for Phononics and Thermal Energy Science School of Physics Science and Engineering Tongji University, Shanghai, China 119

121 VII. Emergency Contacts In case of emergencies, please contact the following local organizers for help: ( 如果遇到紧急情况, 请与下面的大会组织人员联系 ) Name ( 姓名 ) Mobile ( 手机 ) Nianbei Li 李念北 Yunxia Ding 丁云霞 Jun Zhou 周俊 Yunyun Li 李云云 Xiangfan Xu 徐象繁 Center for Phononics and Thermal Energy Science School of Physics Science and Engineering Tongji University 同济大学物理科学与工程学院声子学与热能科学中心 120

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