Atomistic Visualization of Ballistic Phonon Transport

Abstract

Heat transfer in solid materials at short time scales, short length scales, and low temperatures is governed by the transport of ballistic phonons. In anisotropic crystals, the energy carried by these phonons is strongly channeled into well-defined directions in a phenomenon known as phonon focusing. Presented here is a new molecular dynamics simulation approach for visualizing acoustic phonon focusing in anisotropic crystals. An advantage of this approach over experimental phonon imaging techniques is that it allows examination of phonon propagation at selected modes and frequencies. The spatial, mode, and frequency dependence of ballistic energy transport gained with this approach will be useful for understanding heat transfer issues in high frequency electronics and short time scale laser-material interactions.

Combined Kinetic Monte Carlo—Molecular Dynamics Approach for Modeling Phonon Transport in Quantum Dot Superlattices

“…This was verified by measuring (static) residual stresses at the start of the simulation, and verifying that they were at least an order of magnitude smaller than the stress generated by the waves traveling in the simulation. Upon approach to a scatterer, an incident phonon may experience many disturbances which could be classicaHy expressed as changes in the combinations of velocity and displacement vector fields necessary for coherent wave propagation with a single group velocity (a single mode) [64]. These local effects were captured within the MD model and quantitatively described by the effective cross-section and the scattering phase function.…”

Acoustic phonon scattering from particles embedded in an anisotropic medium: A molecular dynamics study

“…This effect will persist at all length scales within a crystal and is a dominant effect, which is infrequently discussed in the literature covering scattering of phonons. We separately used this model to simulate propagation of waves from a point source in a crystal, 34,43 and these phonon imaging results compared favorably with those of phonon focusing experiments, 44 indicating that the model properly accounts for the influence of anisotropy on group velocity. ͑2͒ The continuum theory of acoustics has mass distributed uniformly through space.…”