Bruce L. Davis, Mahmoud I. Hussein
We present the concept of a locally resonant nanophononic metamaterial for the purpose of utilization as a thermoelectric material system exhibiting a high value of the ZT energy conversion figure-of-merit. The proposed concept enables an inherent reduction in the thermal conductivity, which is desired for increasing the ZT value. Furthermore, to achieve this reduction with practically no effect on the electrical conductivity (which is also needed for attaining a high ZT value), we choose a nanophononic metamaterial configuration consisting of a thin-film with a periodic array of pillars erected on one or two of the free surfaces. This configuration qualitatively alters the base thin-film phonon spectrum due to a hybridization mechanism between the pillar local resonances and the underlying lattice dispersion. Using a full lattice dynamics-based theoretical model (or a high resolution finite-element-based model for large sizes) that utilizes experimentally determined scattering constants; we explore the performance of the proposed material system in reducing the thermal conductivity compared to a corresponding uniform thin-film. The results show that with a 50-nm thick silicon thin-film (with smooth free surfaces), a lattice spacing of 60 nm and 80-nm tall pillars introduced on a single surface, the room-temperature thermal conductivity drops to approximately 60% of the corresponding uniform thin-film value (and to approximately 50% when pillars are introduced to both free surfaces). Upon parametric optimization, selection of other base materials, as well roughening of the free surfaces, additional reductions in thermal conductivity are expected without a significant impact on the electrical conductivity. The proposed concept provides a promising new paradigm for high-performance, scalable thermoelectric materials with a configuration that is easily integrated into devices.
View original:
http://arxiv.org/abs/1304.6070
No comments:
Post a Comment