Report on 7th US-Japan Joint Seminar on Nanoscale Transport Phenomena

– Science and Engineering –

December 11-14, 2011, Shima, Japan

co-chairs:

Shigeo Maruyama, Kazuyoshi Fushinobu, Jennifer Lukes, Li Shi

Sponsors:

Japan Society for the Promotion of Science National Science Foundation, U.S.A.

Office of Naval Research, U.S.A.

Participants

35 Japanese participants

31 US participants (including 5 assistant professors, 2 post-docs, and 3 grad students)

Technical Sections • Interfacial Thermal Transport

• Thermophysical Measurements of Nanostructures

• Optical Characterization of Transport Processes

• Molecular Dynamics Simulation

• Phonon Transport Modeling

• Energy Conversion and Storage

• Novel Thermoelectric and Thermal Management Materials

• Nanocarbon Materials and Devices

• Nanoscale Fluidic and Phase Change Phenomena

• Transport in Biological and Organic Systems

• Opening Plenary

• Expert Panel

• Posters

• Culture Excursion

• Closing Summary

Focused Topics on Fundamental Phonon Transport

Thermal Transport Across Interfaces

Phonon-Interface Scattering in Nanostructures

Heat Conduction Outside Nanostructures

Coupled Electron and Phonon Transport in Devices

Phonon Recycling

Thermal Transport in Soft Matters

Science Systems

Whatever you do, ask yourself:

How is this going to make a positive impact on the world?

Society

Haber Bosch

Arun Majumdar: Opening Plenary-Global Energy Challenge and Oportunities

Experimental, Computational, and Theoretical Investigation of Thermal Boundary Conductance

Pamela M. Norris U. Va. Nanoscale Energy Transport Lab December 13, 2011

Thermal Transport at Solid-Solid Interfaces

6

• As device features approach the mean-free-path of pertinent energy carriers (~10-100 nm at room temperature), scattering at interfaces is the dominant factor limiting conductance

< 50 nm < 500 μm < 100 mm < 5 cm

G. Chen. Nanoscale Energy Transport and Conversion, Oxford Press, 2005

A typical resistance of 10-9-10-7 m2K/W

is equivalent to ~ 0.15-15 mm Si

•hBD at various interfaces •Highest known conductance is at good metal interfaces (Al/Cu) where electrons dominate transport

•Lowest is between materials with highly mismatched phonon modes and Debye temperatures (such as Bi/H-diamond)

•hBD between ~10-100 MW/m2K at room temperature

Pop, Nano Res, 3, 147-169, 2010 “We now have powerful tools (experiment and computation).”

Progress & Achievement

1.E+07

1.E+08

1.E+09

1.E+10

10 100 1000

New: Anisotropic

DMM

1010

109

108

107

100 1000 10

Temperature, T [K]

Bo

un

dar

y C

on

du

ctan

ce, G

[W

/m2-K

] Effect of Phonon Focusing on Thermal Transport

Traditional: Isotropic DMM

graphite

Al

• Increase vab reduce transport in c.

• Anisotropic DMM agrees much better with experiments. (No free parameters in either model.)

Experiments [Schmidt et al., JAP (2010)]

Iso-DMM

isov

isov

Aniso- DMM

cv

abv

Chris Dames

Experimental, Computational, and Theoretical Investigation of Thermal Boundary Conductance

Pamela M. Norris U. Va. Nanoscale Energy Transport Lab December 13, 2011

Interfacial Thermal Transport

• Inelastic Scattering Processes

• Role of Optical Phonons

• Role of Electrons

• Physical Aspects of the Interface

• Bonding Effects at the Interface

9

Issues:

Experimental, Computational, and Theoretical Investigation of Thermal Boundary Conductance

Pamela M. Norris U. Va. Nanoscale Energy Transport Lab December 13, 2011

Interfacial Thermal Transport

“Nanoscale Thermal Transport” by Cahill, Ford, Goodson, Mahan, Majumdar, Maris, Merlin, and Phillpot, Journal of Applied Physics, 93, 703-818, 2003.

“the interactions of phonons with a single interface still offers significant challenges to both experiments and theory/simulation”

“spectral methods, involving phonons of well-defined frequencies and wave vectors, offer the promise of providing insignts into thermal transport not accessible by more traditional experiments”

“a need for simulations of the interaction of individual phonons with interfaces”

10

Future Directions

Interface Scattering of Phonons in Graphene and Nanotubes

• Relevance: nanotubes and graphene are supported on a substrate or embedded in a medium in most foreseeable applications.

• Issues: Roughness scattering or phonon leakage?

• Directions: Engineer interface interaction to enhance thermal transport in nanostructures?

• Seol,…, Shi, Science 328, 313 (2010) • Ong…, Shiomi, Phys. Rev. B 84, 165418 (2011)

Enhanced and Switchable Nanoscale Thermal Conduction Due to van der Waals Interfaces

• Potential approach to engineering thermal transport in nanostructure assembly

The thermal conductivity of double

ribbons could be 45-75% higher than that

of single ribbons and tuned by wetting

the interface between two ribbons with

different solutions.

J. Yang, …, D. Li, Nature Nanotech 7,91 (2012)

Surface Scattering of Phonons in Nanowires and Casimir’s Limit

Symbols:

D. Li, et al., Appl. Phys. Lett. 83, 2934 (2003).

A. I. Hochbaum, et al., Nature 451,163 (2008).

A. I. Boukai, et al., Nature 451, 168 (2008).

K. Hippalgaonkar, et al., Nano Letters 10, 4341 (2010).

Lines: Casimir’s limit of diffuse boundary scattering.

• Relevant to heat dissipation in nanoelectronic devices

Issues and Directions:

• Surface roughness scattering or bulk defects?

• Multiscale simulation of larger structures?

Issue: Ballistic effects

Quantitative Nanoscale Imaging of Temperature Fields

Line Scan Direction Measured and Modeled Temperature Profiles of a 200 nm Wide Line

Topographical Image of Temperature Profiles Pramod Reddy

Phonon Recycling

Massoud Kaviany

• Phonon recycling as a possible path to enhanced efficiency of lasers and

photovoltaic devices

Tahu Ohara: Closing Summary- The Middle Way: Thermal Transport in Soft Matter

Direction:

Tahu Ohara: Closing Summary- The Middle Way: Thermal Transport in Soft Matter

Gang Chen: Closing Summary-Two Decades of Micro/Nanoscale Thermophysics and Heat Transfer

Gang Chen: Closing Summary-Two Decades of Micro/Nanoscale Thermophysics and Heat Transfer