MEMS Seminar: Nanophononic Metamaterial - Severe Thermal Conductivity Reduction by Non-Scattering Resonance Hybridizations

Thermoelectric materials convert heat into electricity or vice versa through a solid-state process. For the conversion efficiency to be competitive with fluid-based technologies, a thermoelectric material must be a good insulator of heat while, simultaneously, exhibit good electrical properties¿a combination that is hard to find in common materials. Here we present the concept of a locally resonant nanophononic metamaterial (NPM) [1-3] to overcome this natural properties trade-off. One realization of an NPM is a freestanding silicon membrane (thin film) with a periodic array of nanoscale pillars erected on one or both free surfaces. Heat is transported along the membrane portion of this nanostructured material as a succession of propagating vibrational waves, phonons. The atoms making up the minuscule pillars on their part generate stationary vibrational waves, which we describe as vibrons. These two types of waves linearly interact causing a mode coupling for each pair which appears as an avoided crossing in the pillared membrane's phonon band structure. This in turn (1) enables the generation of new modes localized in the nanopillar portion(s) and (2) reduces the base membrane phonon group velocities around the coupling regions. Additional information can be found by visiting the MEMS Seminar website http://mems.duke.edu/about/events/seminars
Lunch will be served from 1-1:30 pm.