Radiative Heat Transfer at the Nanoscale. Pramod Reddy University of Michigan, Ann Arbor

Transcription

1 Radiative Heat Transfer at the Nanoscale 40µm Pramod Reddy University of Michigan, Ann Arbor

2 Acknowledgements Edgar Meyhofer Juan Carlos Cuevas Francisco Garcia Vidal B. Song K. Kim V. Fernandez J. Fiest W. Lee W. Jeong L. Cui Funding: D. Thompson A. Fiorino Y. Ganjeh Homer Reid 2

3 Overview of Research Macroscopic laws of heat transfer and dissipation fail at the nanoscale Fourier s Law Stefan-Boltzmann Law Joule Heating Hot (T H ) Cold (T C ) Our research focuses on understanding the novel energy transport and conversion phenomena that arise at the micro/nanoscale and employing them for developing novel technologies www. phys. org; www. science. energy. gov 3

4 Current Research: Tools for Nanoscale Thermal Imaging Kim et al. ACS Nano. (2011); Jeong et al. Scientific Reports (2014) 4

5 Demonstration of Quantitative Measurements 5 Shi and Majumdar., J. Heat Trans., 2002

6 Topography and Thermal Fields of a 200 nm Wide Line 6

7 Thermal Imaging of Bowtie Structures 7

8 Current Research: Tools for High Resolution Calorimetry Sadat et al. Appl. Phys. Lett. (2013); Song et al. Nature Nanotechnology (2015) 8

9 40µm Nanoscale Radiative Heat Transfer

10 Fundamentals of Thermal Radiation Energy Density Intensity Cavity at Temperature T (Blackbody) Emissive Power Heat flux from the surface of a Blackbody (W/m 2 ) σ is the Stefan-Boltzmann constant Surface of a Blackbody F. Reif, Statistical and Thermal Physics 10

11 Basics of Far Field Radiative Heat Transfer Radiation power Planck spectrum of thermal radiation E(λ,T) (W m -2 nm -1 ) 2898 μm K Emissive Power Wein s law Wavelength Stefan-Boltzmann Law 11

12 Planck s Far-Field Radiation Theory 12

13 What is Near-field Thermal Radiation? Radiation power Planck spectrum of thermal radiation E(λ,T) (W m -2 nm -1 ) Wavelength λ T = μm K max Wien s law Far-field radiation d >> λ max d λ max Near-field radiation 10 µm@300k 13

14 Fluctuational Electrodynamics Formalism for Quantifying Near Field Radiation Thermal radiation Thermal fluctuation of charges Random currents Electromagnetic waves Maxwell s Equations Fluctuation-Dissipation Theorem, Source Dyadic Green s Function Method/ S-matrix Approaches Poynting Vector S. M. Rytov et al., Principles of Statistical Radio Physics K. Joulain et al., 2005, Surf. Sci. Rep. X. L. Liu, L. P. Wang et al., 2015, NMTE 14 of 15 B. Song et al., 2015, AIP Advances 14

15 Fluctuational Electrodynamics Computed Results from Fluctuational Electrodynamics Polder and van Hove, PRB P. Chapuis et al., 77, of 15 PRB Song et al., 2015, AIP Advances 15

16 Computational Predictions (Select Examples) Effect of Film Thickness Modulation of Thermal Conductance Thermal Rectification S-A. Biehs et al., Eur. Phys. J. B (2007) M. Francouer, et al., Appl. Phys. Lett. (2008) S. Basu et al., Appl. Phys. Lett. (2009) S-A. Biehs et al., 2011, Appl. Phys. Lett. P. J. van Zwol et al., 2011, Phys. Rev. B Y. Huang et al., 2014,, Appl. Phys. Lett. C. Otey et al., 2010, Phys. Rev. Lett. S. Basu et al., 2011, Appl. Phys. Lett. L. Wang et al., 2013, NMTE 16

17 Thermophotovoltaic Energy Conversion (Potential use of near-field thermal radiation) (b) (d) (c) (e) K. Chen, Appl. Phys. Lett. (201 5) Molesky et al., Phys. Rev. B, (201 5) 17

18 Solid State Cooling (Potential use of near-field thermal radiation) (a) Heat flow from a colder to a hotter body (b) (c) K. Chen, Phys. Rev. Appl. (2016) 18

19 Past Experimental Work 19 of 15

20 Parallel Plate Measurements E. G. Cravalho, G. A. Domoto, and C. L. Tien, in AIAA 3 rd Thermophysics Conference (1968) C. M. Hargreaves, Physics Letters A 30(9), (1969). 20

21 Parallel Plate Measurements Room T, gap >~ 2 µm, 2X enhancement Obstacles? Parallelism Sample surface quality R.S. Ottens et al., Physical Review Letters, Recently: Ito et al., Appl. Phys. Lett., Ijiro et al., Appl. Phys. Lett., Lim et al., Phys. Rev. B,

22 Nanoscale Measurements Room T, minimum gap ~30 nm, ~3 times enhancement in conductance S. Shen et al., 2009, Nano Letters E. Rousseau et al., 2009, Nature Photonics 22

23 Extreme Near Field Measurements Au probe-au sample 9 µw Modified Scanning Tunneling Microscope (STM) A. Kittel et al., 2005, Physical Review Letters. L. Worbes et al., 2013, Physical Review Letters. Diameter = 120 nm Au (Probe)= 25 nm Au (Substrate) =?? GNF = 9 µw/200 K = 45 nw/k Measured extreme near-field conductance ~1 000 times greater than that predicted by Fluctuational Electrodynamics 23

24 Probing Radiative Heat Transfer in the Extreme Near-Field 24 of 15

25 Fluctuational Fluctuational Electrodynamics Electrodynamics Fluctuation-Dissipation Theorem, Source Maxwell s Equations Dyadic Green s Function Method Poynting Vector Extreme near-field largely unexplored 25

26 Extreme Near Field Measurements Au probe-au sample 9 µw Modified Scanning Tunneling Microscope (STM) A. Kittel et al., 2005, Physical Review Letters. L. Worbes et al., 2013, Physical Review Letters. Diameter = 120 nm Au (Probe)= 25 nm Au (Substrate) =?? GNF = 9 µw/200 K = 45 nw/k Measured extreme near-field conductance ~1 000 times greater than that predicted by Fluctuational Electrodynamics 26

27 Our Scanning Probe Based Approach Advantage: Compatible with a wide range of materials, conductive or not. Principle: Gap control with piezo. Gap size referred to contact position, based on laser & thermal contact signal. Thermocouple on probe tip Ultra-high vacuum 27

28 Custom-Made Scanning Thermal Probe D = 200 nm DC measurement p-p noise Temperature: 50 mk, Heat flow: 20 nw 1 ) K. Kim et al., 201 2, ACS Nano, 2) W. Lee et al., 201 3, Nature. 28

29 Probe Thermal Resistance Measurement Pico-Watt Calorimeter S. Sadat et al., 2013, Applied Physics Letters. K. Kim et al., Applied Physics Letters (201 4) 29

30 SThM Probe Coated with SiO 2 30

31 How is Radiative Heat Flow Measured Q r = T p T R p a R g = T s T Q r p 31

32 Measurement of Snap-in Distance 32

33 SiO 2 -SiO 2 : Measured Probe Temperature in Extreme Near-Field & Mechanical Contact Temperature rise due to enfrht 33

34 SiO 2 -SiO 2 : Experiments Agree with Computation Local dielectric assumption Diameter = 400 nm SiO 2 (probe)= 100 nm thick SiO 2 (substrate) = 500 nm thick 34

35 Capturing Critical Experimental Details in Computational Predictions of Extreme Near-Field Radiation Boundary Element Method d R ~400 nm diameter 200 nm Roughness modeled Peak = 10 nm, Correlation = 17 nm 35

36 Experimental Data Agreement with Theory Diameter = 400 nm SiO 2 (Probe)= 100 nm SiO 2 (Substrate) = 500 nm K. Kim et al., Nature (201 5) 36

37 Au-Au: Unmodulated Measurements of enfrht Show No Gap-Dependence Diameter = 900 nm Au (probe) = 100 nm thick Au (substrate) = 100 nm thick noise pp ~ 500 pw/k K. Kim et al., Nature (201 5) 37

38 Au-Au: Modulated Heating of the Emitter Improves Heat Flow Resolution Challenges Emitter device fabrication Emitter surface quality Probe & emitter alignment Long-time data averaging Emitter thermal expansion Heating at 18 Hz Bandwidth = 0.8 mhz T resolution = 20 µk Q resolution = 30 pw 38 K. Kim et al., Nature (201 5)

39 Au-Au: enfrht Resolved & Analyzed Local dielectric assumption Kim*, Song*, Fernandez* et al., Nature, K. Kim et al., Nature (201 5) 39

40 Spectral & Spatial Distribution of Heat Flux SiO 2 -SiO 2 Au-Au Broadband at low frequency SPhPs Heat flux color coded Localized heat flux Distributed heat flux K. Kim et al., Nature (201 5) 40

41 Parallel Plate Nanogap Measurements: Achieving Large Radiative Enhancements 41 of 15

42 Can the Radiative Heat Conductance between Parallel Plates Increase by 1000X at the Nanoscale? Blackbody 42

43 Experimental Challenges Conductance G(d) = Q / ΔT T e? d? Q? T r? Particles Curved Rough Tilted Surface: clean, smooth, flat, stiff Alignment: angular and lateral Thermal: high-resolution in T & Q Gap: nm-size & resolution, stable Surface non-idealities limit minimum gap size! 43

44 Novel Approach Using Microfabricated Planar Emitter and Receiver Devices Song*, Thompson* et al., Nature Nanotechnology, In Press. 44

45 Thermal Characteristics of the Microdevices 45

46 Custom-Built Nanopositioner to Parallelize Planes & Form Nanoscale Gaps Motorized goniometer 6 µrad resolution Y. Ganjeh et al., RSI,

47 Experimental Platform: Eliminating Convection & Maintaining Stable nm-gaps Vacuum (< 10-6 torr) chamber where experiments are performed Microscope Temperature controlled, <10 mk drift over 10 hours Nanopositioner Optical table High flow rate ion pump Y. Ganjeh et al., RSI,

48 Approach for Parallelizing Surfaces Optical alignment, course Electrical alignment, fine Devices aligned under microscope Ganjeh et al., Rev. Sci. Instr.,

49 Quantification of Achieved Parallelization < 500 µrad angular deviation from parallelism Ganjeh et al., Rev. Sci. Instr.,

50 Experimental Procedure & Raw Data B. Song et al., Nature Nanotechnology,

51 SiO 2 -SiO 2 : Giant Heat Conductances Observed in nm-gaps Between Parallel Plates 100X enhancement Particulate contamination (30 nm) + Snap-in (20 nm) due to residual electric charges limit minimum gap size to 50 nm B. Song et al., Nature Nanotechnology,

52 Au-Au & SiO 2 -Au Experiments Au-Au SiO 2 -Au 1000X enhancement 1.3X enhancement Matching the dielectric properties of emitter and receiver is key to achieving giant conductance at the nanoscale B. Song et al., Nature Nanotechnology,

53 Summary Our studies show that existing theory is accurate in describing nanoscale radiation in gaps as small as 2-3 nm K. Kim et al., Nature, B. Song et al., Nature Nanotechnology, Radiative heat conductances increase X in nm-gaps, and exceed the blackbody limit by ~100X Provides a foundation for future explorations in the emerging field of nanoscale radiation 53

54 Future Potential Near-Field Based Energy Conversion Lithography and Novel Calorimetric Tools Nano-lithography Pendry, J. Phys. CM,

55 Acknowledgements Edgar Meyhofer Juan Carlos Cuevas Francisco Garcia Vidal B. Song K. Kim V. Fernandez J. Fiest W. Lee W. Jeong L. Cui Funding: D. Thompson A. Fiorino Y. Ganjeh Homer Reid 55

56 Thank You 56