Woodruff School of Mechanical Engineering
Modified Thermal Transport in Phononic Crystal Devices
Prof. Charles Reinke
Sandia National Laboratories
Tuesday, March 4, 2014 at 11:00:00 AM
MRDC Building, Room Room 4211
Dr. Samuel Graham
Recent work has demonstrated that phononic crystals (PnCs) formed by micro-scale patterning of thin semiconductor films can be used to significantly reduce the thermal conductivity of the semiconductor material1. Such PnCs devices can enable groundbreaking technologies such as thermal focusing and rectification, and have been demonstrated to decouple the thermal and electrical conductivities leading to high-efficiency thermoelectric devices. However, a sound understanding of the thermal transport processes at work in such devices is necessary to efficiently engineer their properties for optimal thermal performance. We present an analysis of thermal conductivity reduction in PnC devices using a method that combines the phonon dispersion of the atomic material lattice with that of the PnC lattice2. In this method, continuum mechanics is used to calculate the dispersion of the PnC and lattice dynamics is used to calculate the material dispersion based on an atomic-level system. The continuum mechanics solution was calculated using the plane-wave expansion method, and assumes constant values for the phonon velocities of the bulk material for all frequencies, i.e. the Debye model. Thus, the plane-wave calculations are augmented by lattice dynamics data for the bulk material in an effort to incorporate the dispersive behavior of the material. The phonon dispersion data from the two approaches are then used in a Callaway-Holland model to calculate the thermal transport properties of the PnC. The results of these calculations are compared with thermal conductivity measurements for corresponding PnC samples composed of air holes in silicon.
Charles M. Reinke received his B.S. in Physics from Jackson State University in 2000 and his B.S.E.E and M.S.E.E. degrees from the Georgia Institute of Technology, followed by a Ph.D. in electrical engineering in 2010. His graduate work at Georgia Tech included efficient numerical techniques for the simulation of nonlinear optical effects in photonic crystal devices and the measurement of propagation loss in photonic crystal waveguides. Charles joined Sandia National Laboratories as a postdoctoral appointee in 2009, and is currently a Senior Member of Technical Staff in the Applied Photonic Microsystems department. His research involves theoretical studies of novel photonic and phononic crystal structures with applications that include efficient solar power generation, thermal waste heat recovery, quantum computing, and nanoscale optomechanical transduction.