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Is there a Nano Revolution in Thermal Management and Energy Conversion? Advances in Nanostructure based Thermal Interface and Thermoelectric Materials Sebastian Volz Laboratoire EM2C UPR CNRS 288, Ecole Centrale Paris Thermal Nanosciences Group - EUROTHERM 2012 – Poitiers, France – September 5th 2012

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« Nano » wire d Conduction Heat Transfer Laws at Small Scales Deviate from Classical Ones Ballistic conduction in air Kn>>1 L NEAR FIELD Radiation When L < the Predominant Photon Wavelength, coupling of Evanescent Surface Waves increases heat flux. Transition from a regime of propagative waves emitted by charges motions to a direct electrostatic interaction. STEFAN-BOLTZMANN European CNRS Network on Thermal Nanosciences and NanoEngineering Convection If Nu<1, heat conduction in air predominates. If Kn>>1 heat conduction becomes ballistic. Diffusive to Ballistic transition is well-known in gases and radiation.

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Heat carries in solids are SOUND PARTICLES or PHONONs, the quanta of lattice vibrational energy i-1ii+1 a u n =u.expi(kna- t) F ij = K.(u j- u i ) Periodic Boundary Conditions: k = n. 2 /L Density of states k

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Acoustics: Coherent Phonons Continuous limit k=>0 k Heat Flux: the Phonon Gas Phonons form a GAS of particles to propagate heat ! Knudsen Transport Applies Phonon Wiens Wavelength: 3nm (300K) Mean free path: nm Phonon Wiens Wavelength: 3nm (300K) Mean free path: nm

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p(,, pol, ) =1/3 C v =1/3 C v Kn>1: Boundary scattering predominates over diffusive scattering L

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Confinement: Cavity modes appear if L< Wavelength Periodicity: e ik(L+x) =e ikx ~ ~ cos(kna)e -i u n ~ expi(kna- t)+ expi(-kna- t) ~ cos(kna)e -i t e ikL =e ika =0 a STEADY WAVE has ZERO group velocity =1/3 C v =1/3 C v

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The number of phonon modes depends on Dimensionnality Dimension:Number of States /dk: =1/3 C v =1/3 C v k-space 1D (wire)D(k) ~ 1 2D (film/SR)D(k ) ~ k 3D (bulk)D(k) ~ k 2

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At nanoscales, thermal resistance arises from boundaries

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The KEY is to understand phonon transfer at the surface and between two systems

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Thermal Resistance is an Ambiguous Concept Relating Equilibrium and Non-Equilibrium Quantities R= (T 1 -T 2 )/Q N1N1 N 2 Q Heat Bath T 1 Heat Bath T 2 Cheating Seems Unavoidable

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Atomic Simulations involve dubious Non-Equilibrium Conditions -Thermostats Parameters -Equilibrium Temperatures: coupling with heat bath? NEMD - TRANSIENT -Thermostat Parameters (weaker) -Short time non-equilibrium -Equilibrium Temperatures at each time step? NEMD - STEADY

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Equilibrium Temperature Correlation defines Thermal Resistance τau FLUCTUATIONAL THERMODYNAMICS INTERNAL SCATTERING ACF NEGLECTED (?) JAP, 108, , 2010

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A Flux based Thermal Conductance can be equivalently derived -Interfacial Thermal Resistance only depends on Interactions between Atoms of both Sub-Systems -Temperatures involved in the definition of resistance are the Temperatures of the Interacting Atoms

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Nanostructures have exceptional thermal conductivities Carbon Nanotubes Silicon Nanowires 1-3

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Nanostructures can be used to taylor thermal conductivity Thermal Interface Materials: Increase Thermoelectricity: Decrease

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Can Carbon Nanotubes be used as Thermal Interface Materials? Use Carbon Nanotube Pellets J D L Isotropy

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Isotropic Pellet Thermal Conductivity is promising but…. Chalopin, Volz, Mingo, Journal of Applied Physics, 105, , (2009)

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…Measured Thermal Conductivity is more than disappointing Prasher, Hu, Chalopin, Mingo, Lofgreen, Volz, Cleri, Keblinski, Phys. Rev. Lett.,102, , 2009

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CNT Orientation is drastically affecting thermal conductivity Volkov and ZhigileiVolkov and Zhigilei Phys. Rev. Lett. 104, (2010) Volkov and Zhigilei

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Use of Hybrid Charges Imposes Isotropy Bozlar, He, Bai, Chalopin, Mingo and Volz, Advanced Materials, 21, 1, (2009)

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Vertically aligned CNTs appears as the optimized option CNT-Superstrate contact resistance cancels performances Applying pressure?

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Thermal Conductance is increased when applying Pressure Chalopin, Srivastava, Mingo, Volz, submitted to APL

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Transmission shows the opening of inelastic channels when increasing pressure Harmonic Green Functions Fluctuations Anharmonic Green Functions

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Introducing a polymer layer at contact reduces thermal resistance 2.5mm 2 K/W Introducing Covalent Bonds Should Increase Conductance HLK5

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CNT-HLK5 resistance is three times lower than CNT-PEMA one Ni, LeKhahn, Bai, Divay, Chalopin, Lebarny,, Volz Appl. Phys. Lett. 100, (2012)

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CONCLUSION on Thermal Interface Materials Ni, LeKhahn, Bai, Divay, Chalopin, Lebarny,, Volz Appl. Phys. Lett. 100, (2012)

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THANK YOU FOR YOUR ATTENTION Collaborators: Team: Y. Chalopin (CNRS) T. Antoni (Ass. Prof.) T. Dumitrica (Inv. Prof.) Pdocs: J. Ordonez O. Pokropivny PhDs: Y. Ni, S. Xiong, L. Tranchant W. Kassem, J. Jaramillo A.Ramière, H. Han B. Latour, J. Soussi Abroad G. Chen (MIT) H. Ban (Utah U.) C.W. Chang (National Taiwan Uniiversity) B. Kim (U Tokyo) H. Fujita (U Tokyo) H. Kawakatsu (U. Tokyo) Y. Kosevich (Semenov Inst. Moscow) M. Kazan (U Américaine de Beyrouth) A.Rajabpour (U Teheran) Y. Ciumakov (Moldova) France: N. Mingo (CEA-LITEN) E. Ollier (CEA-LITEN) A. Ziaei (Thales R&T) L. Divay (Thales R&T) P. Cortona (SPMS, Ecole Centrale Paris) H. Dammak (SPMS, Ecole Centrale Paris) J. Bai (SPMS, Ecole Centrale Paris) L. Aigouy (LPM, ESPCI) B. Palpant (LPQM, ENS Cachan) S. Merabia (LPMNC, U Lyon) P. Chantrenne (MATTEIS, U Lyon) D. Lacroix (LEMTA, U Nancy) J. Amrit (LIMSI, U Orsay) B. LePioufle (SATIE, ENS Cachan) D. Fourmy (Centre de Génétique Mol., Gif) K. Termentzidis (LEMTA, Nancy France) European CNRS Network Thermal Nanosciences and NanoEngineering

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Quantitative Micro and Nano Thermal Imaging and Analysis July 2013 Reims, France GRESPI Université de Reims-Champagne-Ardenne QMNTIA 2013

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