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Innovative Simulation Techniques
for Probing Phonon Transport in Materials

(Funding: National Science Foundation CAREER Award )

A key research goal of our group is to create innovative molecular dynamics simulation methods capable of probing fundamental thermal transport processes at length and time scales difficult or impossible to interrogate with existing theory and/or experiment. Work in this area includes the following projects:

 
Scattering Phase Functions for Phonons
 

We have developed a new simulation technique to probe phonon-nanoparticle scattering in anisotropic materials. This technique enables, for the first time, direct observation of the effects of mode conversion, lattice mismatch strain, elastic anisotropy, and atomistic granularity on the spectral-directional scattering of phonons from nanoparticles. The technique will be useful for the design of novel nanoparticle-based thermal insulating materials for thermoelectric energy conversion.

 
 
Phonon Focusing "Experiments" using Molecular Dynamics
 

We have created the first molecular dynamics approach capable of studying phonon focusing. This approach, which generates multidimensional acoustic phonon wavepackets and visualizes their arrival at an image plane "detector," provides new capabilities for identifying regions where thermal energy is preferentially channeled and offers an alternative to existing experimental techniques. Additionally, it enables direct observation of phonon frequency redistribution as the wave packet propagates.

 

Compare simulation movie above to experimental movie from Wolfe group

 
 
 
Thermal Expansion and Impurity Effects on Lattice Thermal Conductivity
 

We have used molecular dynamics simulations to probe how thermal expansion and impurities affect the thermal conductivity of materials with point defects. We found that strain induced by the defect (and not mass difference between the defect and its surroundings) is the dominant mechanism contributing to the thermal conductivity reduction occurring in such materials. Also we have found that inclusion of temperature dependent lattice constants is essential to recover the correct thermal conductivity temperature dependence. Finally, we have found that molecular dynamics is a viable alternative to phonon scattering theory for obtaining phonon scattering parameters for use in thermal conductivity models such as the Callaway model. This discovery provides a step toward expedient calculation of thermal conductivity in materials with defects.

 
 
 
Relevant Publications
 
N. Zuckerman and J. R. Lukes, 2008, Acoustic Phonon Scattering from Particles Embedded in an Anisotropic Medium, to appear in Physical Review B.
 
N. Zuckerman and J. R. Lukes, 2007, Dependent Scattering of Acoustic Phonons from Particles Embedded in an Anisotropic Medium, Proceedings of the 2007 International Mechanical Engineering Congress and Exposition, Seattle, Washington, IMECE2007-41850.
 
N. Zuckerman and J. R. Lukes, 2008, Atomistic Visualization of Anisotropic Wave Propagation in Crystals, to appear in Journal of Heat Transfer.
 
N. Zuckerman and J. R. Lukes, 2007, Atomistic Visualization of Ballistic Phonon Transport, Proceedings of the 2007 ASME-JSME Thermal Engineering Summer Heat Transfer Conference, July 8-12, 2007, Vancouver, Canada, HT2007-32674.
 
Y. Chen, J. R. Lukes, D. Li, J. Yang, and Y. Wu, 2004, Thermal Expansion and Impurity Effects on Lattice Thermal Conductivity of Solid Argon, Journal of Chemical Physics, Vol. 120, pp. 3841-3846.
 
Y. Chen, G. Wang, D. Li, and J. R. Lukes, 2006, Thermal Expansion and Isotopic Composition Effects on Lattice Thermal Conductivity of Crystalline Silicon, Proceedings of the 2006 International Mechanical Engineering Congress and Exposition, November 5-10, 2006, Chicago, Illinois, IMECE2006-13870.
 
                   

© Nanoscale Engineering Laboratory Lukes Research Group