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Unformatted text preview: INVESTIGATION OF LOW-DIMENSIONAL THERMOELECTRICS M. S. Dresselhaus, 1 , 2 Y. M. Lin, 2 S. B. Cronin, 1 M. R. Black, 2 O. Rabin, 3 and G. Dresselhaus 4 ABSTRACT After 30 years of slow progress, thermoelectric materials research experienced a recent resurgence, inspired by the developments of new concepts and the- ories to engineer electron and phonon transport in both nanostructures and bulk materials. In nanostructures, quantum and classical size effects provide opportunities to tailor the electron and phonon transport through structural engineering. Quantum wells, superlattices, quantum wires, and quantum dots have been employed to change the band structure, energy levels, and density of states of electrons, and offer new promise for the development of new materi- als of interest for thermal transport applications. Interface reflection and the scattering of phonons in these nanostructures have been utilized to reduce heat conduction. Increases in the thermoelectric figure-of-merit have been demon- strated for a few model 2D systems, and predictions of enhanced thermoelectric performance have been made for other low dimensional systems. 1. INTRODUCTION Thermal transport in low dimensional systems has recently become a subject of considerable interest, especially due to the development of devices of nano length scales. The interest is drawn to new thermal transport science, that is operative at these small length scales and where quantum mechanical phenomena become 1 Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139 2 Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA 02139 3 Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139 4 Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139 important. At small length scales, the number of atoms or the number of elec- trons in the system becomes small, so that continuum mechanics and elastic continuum models have to be replaced by models that take account of the dis- crete nature of the electronic and vibrational states and their distribution in energy. In this realm, we can expect devices to be much smaller and faster, but to exhibit new unexpected phenomena of scientific interest and technological importance. Research in thermal nanoscience is thus becoming a popular new research direction because of the needs of thermal management at the nanoscale and the new technical challenges raised by the design and fabrication of thermal devices below 100 nm, where the electronics, communications, and data storage industries are now heading. For this reason, the study of thermal transport phenomena in nanoscale structures is becoming very active in university research and for advanced de- velopment for industrial applications. Two interesting limits of the thermal conductivity in nano-systems can be considered. In the high thermal conductiv- ity limit, one might consider a single wall carbon nanotube, with a cylindrical...
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This note was uploaded on 05/21/2010 for the course MS Thermoelec taught by Professor Snyder during the Spring '10 term at Caltech.
- Spring '10