When 3:30 PM - 5:00 PM Nov 12, 2010
Where 1670 CSE
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Superlattices, Nano-dots and Hybrid Nanostructures for Advanced Thermoelectric Devices


Rama Venkatasubramanian, RTI International

Nanoscale materials – superlattices, nano dots, and bulk materials with second phases or nano-inclusions – have become the dominant approach to enhancing the figure of merit (ZT) in thermoelectric materials. The primary mechanism for ZT improvement has been the significant reduction in lattice thermal conductivity through phonon scattering processes in nanoscale materials without affecting the electron/hole transport, by so-called phonon-blocking electron-transmitting structures. At RTI, we have been working on advanced Bi2Te3-based superlattices [1] and delta-doped structures for near 300K cooling and power generation applications. Using these materials, we have developed advanced chip-cooling technologies [2], low-temperature focal plane array cooling applications with 3-stage coolers producing over 100K temperature differentials [3], energy harvesting devices [4], etc. to demonstrate the manufacturing feasibility, flexibility and reliability with thin-film thermoelectric nano-materials. To understand these superlattices further, we have recently carried out fundamental studies on the phonon-transport using femto-second optical [5] and acoustic phonon [6] property measurements, revealing the physics behind thermal conductivity reduction, as well as careful band offset measurements to study cross-plane carrier transport. Based on this “ideal” nano-system, we have pursued other superlattice concepts in PbTe/GeTe, GaSb/InAs and Si/Ge nano-dot materials. We will discuss carrier-transport modeling and measurements as well as thermal conductivity measurements in these mid-temperature and hi-temperature nano-materials. Transmission electron microscopy of the PbTe/GeTe thin-films shows novel hybrid 2-D and 1-D structures and low thermal conductivities. Beyond thin-films and their device developments at RTI, we have also started efforts in the area of bulk nano materials in collaboration with North Carolina State University and Ames Lab. Some of the early results from these collaborative efforts including device performance data from these materials will be presented.

 

1) Nature, Vol.413, pp. 597-602, October 11, (2001).

2) Nature Nanotechnology, Volume: 4   Issue: 4   Pages: 235-238 (2009).

3) Jour. of Electronic Materials Volume 38, Issue7 (2009), Page 1510.

4) Proc. SPIE Vol. 7683, 76830W (2010).

5) Appl. Phys. Lett. Vol. 93, 113114, (2008).

6) Appl. Phys. Lett. 97, 083103 (2010); doi:10.1063/1.3483767

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