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Heat and Nanotechnologies: Focus on Thermoelectricity Sebastian Volz

Heat and Nanotechnologies: Focus on Thermoelectricity Sebastian Volz Yann Chalopin, Ali Rajabpour, Yuxiang Ni Gang Chen, Natalio Mingo, Laurent Jalabert, Michel Kazan, Ravi Prasher, Pawel Keblinski, Deepak Srivastava Laboratoire EM2C UPR CNRS 288, Ecole Centrale Paris

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Heat and Nanotechnologies: Focus on Thermoelectricity Sebastian Volz

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  1. Heat and Nanotechnologies: Focus on Thermoelectricity Sebastian Volz Yann Chalopin, Ali Rajabpour, Yuxiang Ni Gang Chen, Natalio Mingo, Laurent Jalabert, Michel Kazan, Ravi Prasher, Pawel Keblinski, Deepak Srivastava Laboratoire EM2C UPR CNRS 288, Ecole Centrale Paris Thermal Nanosciences Group - volz@em2c.ecp.fr Nanoelectronics: Concept, theory and Modeling, – Cargèse, France – October 24th 2012

  2. Heat carries in non-metals are SOUND PARTICLES or PHONONs, the quanta of lattice vibrational energy a i-1 i i+1 Fij = K.(uj- ui) w un=u.expi(kna-wt) k Periodic Boundary Conditions: k = n . 2/L Density of states

  3. Phonons form a GAS of particles to propagate heat Heat Flux: the Phonon Gas w Acoustics: Coherent Phonons Continuous limit k=>0 Knudsen Transport Applies k Phonon Wien’s Wavelength: 3nm (300K) Mean free path: 1-1000nm

  4. Kn>1: Boundary scattering predominates over diffusive scattering L p(, , pol, ) =1/3 C v 

  5. Confinement: Cavity modes appear if L< Wavelength e ikL=e ika=0 Periodicity: e ik(L+x)=e ikx un ~ expi(kna-wt)+ expi(-kna-wt) ~ cos(kna)e-iwt =1/3 C v a STEADY WAVE has ZERO group velocity

  6. The number of phonon modes depends on Dimensionnality k-space Dimension: Number of States /dk: 1D (wire) D(k) dk ~ 1 dk =1/3 C v  2D (film/SR) D(k ) dk ~ k dk 3D (bulk) D(k) dk~ k2 dk

  7. Nanostructures have exceptional thermal conductivities Carbon Nanotubes 2400-3000 W/mK@RT Silicon Nanowires 1-3 W/mK@RT

  8. WASTED HEAT RECOVERY US: 30% of the world energy consumption

  9. The Non-Dimensioned Figure of Merit ZT Qualifies TE Materials

  10. TE Applications are mostly ‘Niche’ Applications -Laser, PCR

  11. Large scale applications are still expected CAR INDUSTRY

  12. What are the Physical Mechanisms underlying TE Properties

  13. Nanostructured TE Material Concept was launched by Dresselhaus …but electron design did not yield significant ZT improvement. However, phonon thermal conductivity reduction is possible.

  14. High ZT Superlattices Ge Si Ge

  15. Boltzmann Equation Predictions Match Experimental Data G. Chen 1998 In the thin layer limit, phonon transport within each layer is ballistic, and the TBR dominates the effective thermal conductivity of superlattices.’ Gang Chen PRB, 57, 23, 1998

  16. Confinement should also contribute to the thermal conductivity decay in films Alexander Balandin 1998 ‘We show that strong modification of phonon group velocities due to spatial confinement leads to a significant increase in the phonon relaxation rates. Modification of the lattice thermal conductivity by confined phonon modes opens up a novel tuning capability of thermoelectric properties of heterostructures, and may lead to a strong increase of ZT in specially designed semiconductor nanostructures.’

  17. Strain Effects strongly affect thermal conductivity showing importance of interface scattering Experimental results - T. Borca-Tasciuc, G. Chen BOLTZMANN - G. CHEN Experiences Si/Ge superlattices SV, Saulnier, Chen, Beauchamp, Microelectronics Journal, 31, 815, 2000.

  18. According to Molecular Dynamics technique, interfacial roughness explains the experimental trend MD DATA EXPERIMENTAL DATA Daly, Maris, Imamura, Tamura, PRB, 66, 24301, 2002.

  19. Superlattices have provided a Breakthrough in TE history ZT=sS2T/l

  20. Thermal Conductivity of Thermoelectric Material Superlattices is lower than Bulk ones p.597

  21. High ZT Nanoparticles? Alloying scatter high frequency phonons. How to break middle frequency phonons? DESIGNING Impurity Size OPENING Band Gaps Phonon Scatterers Thermal Phononic Crystals Phonon ‘Wave’ Phonon ‘Particle’

  22. Si/Ge Thermal Phononic Crystal Thermal Conductivity as Low as 0.2W/mK J.N. Gillet, Y. Chalopin, SV, Journal of Heat Transfer, 131, 043206 (2009)

  23. Can Middle Frequency Phonons be Scattered by 10nm Nanoparticles

  24. Thermal Conductivity below the Alloy Limit was Obtained with Nanoparticles NPs however deteriorate TE properties

  25. Impact of Nanoparticles on ZT was proven but in conventional TE compounds

  26. Can Nanowires also Improve ZT? • D,L >> Λ Diffusive regime κbulk is the bulk thermal conductivity D : diameter L : length Λ : mean free path (100nm in Si) Cv: heat capacity Vp : phonon velocity (6000 m/s) Fourier law • D ~< Λ and L>> Λ Effective MFP Ballistic regime • D < Λ and L< Λ SMOOTH SURFACES, NANOJUNCTIONS 3D: Sharvin Law 1D: Quantum of Conductance

  27. Is the 1D behaviour at low temperatures impacted by reflections at nw/substrate interface? Quantum of Conductance 1D in k-space K. Schwab, E. A. Henriksen, J. M. Worlock and M. L. Roukes, Nature 404, 974 (2000) L. G. C. Rego and G. Kirczenow, Phys Rev. Lett. 81, 232 (1998)

  28. The contact conductance includes nw and substrate contributions Qb Qw Diffuse Mismatch Model for Transmission:

  29. The contact resistance is predominant compared to the nw one

  30. The density of modes is lower in the substrate at low temperatures (k) ? TL TR 1D DOS ? Excited Modes 1D WIRE 3D SUBSTRATE T

  31. Experiments tend to confirm this trend T3 T2 T3

  32. Metal nanowires also have predominant contact resistances at higher electron density R. Venkatesh, Y. Chalopin, J. Amrit, SV, PRB 83, 115425 (2011)

  33. Is a Nanojunction a good TE system?MEMS Actuation allows forming and characterizing Nanojunctions TH G TA TA TS GS1/2 GS1/2

  34. The constriction diameter reduces with elongation

  35. Experiments agree with a Ballistic Thermal Conductance Model Jalabert, Sato, Ishida, Fujita, Chalopin, SV, Nanoletters, 12, 5213–5217, 2012 before after Experiments Theory 1 3 D=7nm D=19nm D=38nm 5 3 1 5 30nm

  36. Rough Si Nanowires are relevant candidates for improvedZT Diameter=48nm ZT=sS2T/l

  37. CONCLUSION on NANOWIRES and NANOJUNCTIONS Quantum of Conductance: At low temperatures, Heat flux in 1D Si Nanowires is dominated by CONTACT RESISTANCE . A similar but less drastic behaviour is observed in metal nws. Nanojunctions: Ballistic Heat Conduction was shown in the 400-500K range in short nanojunctions.

  38. Conclusions on ZT -Superlattices, Nanoparticles and Rough NWs present High ZT values because of enhanced Phonon Scattering. -Nanostructuraction has yielded unequalled ZT values (ZT=2-3). -Bulk TE materials can not be obtained by atomic scale fabrication techniques (MBE) and alternative routes are being explored. -Large scale applications remain quite out of reach. Restrictions on TE materials make these expectations even more difficult. -Cost effective Thermoelectric materials remains an option: ZT also depends on $ -But how to Improve electronic properties?

  39. 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 • 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) • 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 2010 2007 THANK YOU FOR YOUR ATTENTION

  40. Round Table: Thermoelectric energy conversion, insights, prospects for real applications? -Magnetic Tunnel Junctions -2D Electron: Graphene, SrTiO2… -3 or 4 terminals devices, Chaos, Fluctuations

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