Image courtesy of Adam Jandl and Maria Luckyanova, MIT
Recent experimental and theoretical studies of heat transport through a periodic stack of thin films known as a superlattice show that a portion of the thermal energy carriers maintain wave-like properties while traversing through the nanostructure.
Contrary to prevailing thoughts in the field of heat conduction, research demonstrated, through experiments and theoretical models, that at least some of the phonons, or lattice vibrations, that carry heat across materials travel in wavelike fashion through a superlattice (SL), or a stack of periodically alternating thin films.
This study shows that it is possible to manipulate heat conduction through the wave nature of lattice vibrations and opens up the potential to engineer the thermal conductivity of materials for many applications — low for thermoelectric energy conversion devices and high for thermal management of electronic devices.
In many materials, thermal energy is transported by vibrations of the atomic lattice known as phonons. Similar to photons of light, these lattice vibrations can be treated as waves, but in most materials the phases of the phonon waves quickly randomize after interacting among themselves, with any imperfection or with any interface between two materials. This phase randomization means that the transport of heat becomes incoherent and difficult to predict or control. In this study, heat transport through superlattices (SL) made up of periodic stacks of semiconductor thin films was studied both experimentally and theoretically with a surprising result. A novel experimental approach indicated that the wave properties of some heat-carrying phonons – and their coherence – could be maintained even with the presence of several material interfaces. Theoretical studies supported the experimental conclusions that the low frequency phonons traveled through the SL stack in coherent fashion as if the layered structure was a homogeneous material. This scientific discovery and modeling capability opens new pathways for controlling heat transfer through materials by tailoring the lattice waves at the nanostructure scale.
Director, Solid State Solar Thermal Energy Conversion (S3TEC) EFRC
DOE Office of Science, Basic Energy Sciences, Energy Frontier Research Centers (EFRC) Program.
M. N. Luckyanova, J. Garg, K. Esfarjani, A. Jandl, M. T. Bulsara, A. J. Schmidt, A. J. Minnich, S. Chen, M. S. Dresselhaus, Z. Ren, E. A. Fitzgerald, G. Chen “Coherent Phonon Heat Conduction in Superlattices” Science 338, 936 (2012); [DOI: 10.1126/science.1225549]
Solid State Solar Thermal Energy Conversion (S3TEC) EFRC