Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session T28: Focus Session: Thermoelectric Materials: Nanostructures |
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Sponsoring Units: FIAP DMP Chair: Donald Morelli, Michigan State University Room: 330 |
Wednesday, March 18, 2009 2:30PM - 3:06PM |
T28.00001: SiGe Nanocomposites Thermoelectrics: The Knowns and the Unknowns Invited Speaker: Silicon-germanium has been used in spacecraft for a long time to convert heat from radio isotope heat sources into electricity for deep space missions. Recently, we have reported significant improvement in the thermoelectric figure of merit of nanostructured Si$_x$Ge$_{1-x}$. The improvement in ZT comes mainly from reduced phonon thermal conductivity, while at the same time, maintaining the electron transport properties. These experimental successes, although providing strong support to the direction of using random nanostructures to improve thermoelectric performance, also call for a detailed understanding of thermoelectric transport in random bulk nanostructures. Careful examination of the spectral details of the electron and phonon transport reveals a significant deficiency in our current understanding, even for bulk materials. Different interfacial transport processes further complicate the picture. In this talk, we will discuss the current status of our understanding of thermoelectric transport in nanocomposites. In collaboration with A. Minnich, H. Lee, B. Muralidharan, and M.S. Dresselhaus, Massachusetts Institute of Technology, Cambridge, MA 02139; and X. W. Wang, G. Joshi, G. H. Zhu, Y. C. Lan, D. Z. Wang, and Z.F. Ren, Boston College, Chestnut Hills, MA 02467. [Preview Abstract] |
Wednesday, March 18, 2009 3:06PM - 3:18PM |
T28.00002: Thermoelectric Power of high concentration embedded Nano-particle Samples Mona Zebarjadi, Keivan Esfarjani, Ali Shakouri, Zhixi Bian, Je-Hyeong Bahk, Gehong Zeng, John Bowers, Hong Lu, Joshua Zide, Art Gossard High concentrations of embedded nano-particles inside thermoelectric elements are desirable because they can reduce the thermal conductivity. But they also affect the power-factor. Therefore they can enhance or suppress the figure of merit. We model the effect of such high concentrations on the power-factor using the coherent potential approximation. We optimize the power-factor versus nano-particle size, distribution and concentration. The analysis would help in designing nano-particle embedded matrices with high-performances. We characterize InGaAlAs samples with 3-10{\%} volume concentration of ErAs nano-particles and explain their properties such as the mobility and the Seebeck coefficient theoretically. [Preview Abstract] |
Wednesday, March 18, 2009 3:18PM - 3:30PM |
T28.00003: Transient Electrical and Thermal Characterization of InGaAlAs Thin Films with embedded ErAs Nanoparticles. Tela Favaloro, Rajeev Singh, James Christofferson, Younes Ezzahri, Zhixi Bian, Ali Shakouri, Gehong Zeng, Je-Hyeoung Bahk, John Bowers, Hong Lu, Arthur Gossard We developed a system for accurate high-temperature characterization of thermoelectric materials and devices. This system can be used for electrical measurements of thermoelectric properties and contains an integrated optical thermoreflectance imaging system is integrated into the thermostat for analysis of sample surface temperature profile resulting from the Peltier effect, Joule heating or external thermal excitation within the sample. Transient electrical and thermal measurements are useful to extract material diffusivity of each layer. We have performed high temperature transient analyses and thermal imaging of thin film devices optimized for direct figure of merit detection in the cross-plane direction. These devices consist of 25 micron thick samples of InGaAlAs films with embedded ErAs nanoparticles. Using the transient Harman technique, we determine the cross-plane figure of merit and electrical conductivity. Thermal imaging is used to ensure current injection uniformity across the device and to extract the Seebeck coefficient and thermal conductivity of the material. The experimental results and theoretical analysis are given. [Preview Abstract] |
Wednesday, March 18, 2009 3:30PM - 3:42PM |
T28.00004: Characterization and modeling of the randomly distributed ErAs nanoparticles in InGaAlAs semiconductors for thermoelectric power generation Je-Hyeong Bahk, Mona Zebarjadi, Zhixi Bian, Gehong Zeng, Ashok Ramu, Hong Lu, Ali Shakouri, Art Gossard, John Bowers We investigate temperature-dependent thermoelectric properties of the InGaAlAs semiconductors containing epitaxially embedded ErAs nanoparticles grown by Molecular Beam Epitaxy. Temperature-dependent Hall measurements and Seebeck coefficient measurements were performed for the materials with various Er concentrations and semiconductor compositions, and the results were analyzed using a theoretical modeling based on the ErAs nanoparticle's carrier scattering behaviors. In the analysis, the nanoparticles are modeled as charged spheres with Schottky barrier height at the interface with semiconductor, and the potential profile around a particle is used as perturbation for electron scattering. The particle scattering rate is calculated using both Born approximation and the partial wave method, respectively, and the two methods are compared to check the validity of Born approximation in various conditions. The theoretical calculation of mobility and Seebeck coefficient based on the modeling of particle scattering and other scattering mechanisms fits the measurement results, and we find that further enhancement of thermoelectric power factor is possible by optimizing the particle scattering in the materials. [Preview Abstract] |
Wednesday, March 18, 2009 3:42PM - 3:54PM |
T28.00005: Thermal and Thermoelectric Transport in Thin Films and Nanostructures B. L. Zink, R. Sultan, A. D. Avery Interest in increasing efficiency of energy generation continues to spur the development of new thermoelectric materials. Though bulk materials hold the most promise for large-scale energy generation, many groups continue to explore increasing the thermoelectric figure-of-merit by taking advantage of techniques for creating nanostructured materials such as multilayered thin films and nanowires. These systems could prove to have high figures-of-merit and be important for integrating energy harvesting and/or cooling with micro- or nanoscale devices ``on chip.'' Though many promising systems have been identified, measuring their fundamental thermal transport often remains a major challenge. In this talk, we briefly describe our recent advances in measuring in-plane thermal transport, thermopower and electrical conductivity on thin-films or nanolithographically patterned systems. Our technique allows great flexibility for studying the thermoelectric properties of a wide range of materials, from amorphous semiconductors to semi-metallic nanowires. [Preview Abstract] |
Wednesday, March 18, 2009 3:54PM - 4:06PM |
T28.00006: Nitride Metal-Semiconductor Superlattices for Solid State Thermionic Energy Conversion Robert Wortman, Jeremy Schroeder, Polina Burmistrova, Mona Zebarjadi, Zhixi Bian, Ali Shakouri, Timothy Sands A new class of thermoelectric materials based off of superlattices have been proposed that show a potential for enhanced thermoelectric performance$^{1,2}$. The increase of thermoelectric figure-of-merit ZT of these materials is due to both the energy filtering effect of the Schottky barriers as well as the reduced thermal conductivity that results from increased interface density. Our work has centered on the metal-semiconductor materials system of HfN-ScN. These are both high temperature materials (T$_{m} \quad >$ 2500C). They have the same rocksalt crystal structure and similar lattice constants, allowing epitaxial growth. We have grown superlattices of these materials via DC magnetron sputtering. Results from x-ray diffraction, and electrical and thermal tests will be presented. Their potential as thermoelectric energy conversion materials will be discussed. 1 G. D. Mahan et al, Phys. Rev. Lett., 80, 4016 (1998) 2 D. Vashaee et al, \textit{Phys. Rev. Lett}. 92, 106103 (2004) [Preview Abstract] |
Wednesday, March 18, 2009 4:06PM - 4:18PM |
T28.00007: ABSTRACT WITHDRAWN |
Wednesday, March 18, 2009 4:18PM - 4:30PM |
T28.00008: Thermoelectric properties of nanoporous Ge Joo-Hyoung Lee, Jeffrey Grossman Recently, silicon nanowires were shown to have a thermoelectric (TE) figure of merit ($ZT$) two orders of magnitude larger than that of bulk Si \footnote{A. I. Hochbaum {\it et al.}, Nature {\bf 451}, 163 (2009); A. I. Boukai {\it et al.}, {\it ibid.}, {\bf 451}, 168 (2009)}. In addition, recent theoretical work predicted that Si with periodically arranged nanometer-sized pores (nanoporous Si) could result in a similar increase in $ZT$\footnote{J.-H. Lee {\it et al.}, Appl. Phys. Letts. {\bf 91}, 223110 (2007); J.-H. Lee {\it et al.}, Nano Lett. {\bf 8}, 3750 (2008)}. These results open an exciting new pathway towards efficient thermoelectrics based on standard semiconductor materials. In the present work, we extend our earlier calculations on silicon to explore the TE properties of nanoporous Ge. Specifically, we calculate the thermal and electrical conductivities, Seebeck coefficient and figure of merit of nanoporous Ge for a range of configurations using a combined {\it ab initio} electronic structure calculation and Boltzmann transport approach. The results show a substantial increase in $ZT$ compared with that of bulk Ge, as in the Si nanostructures. A detailed comparison between the TE properties of nanoporous Ge and Si will be presented. [Preview Abstract] |
Wednesday, March 18, 2009 4:30PM - 4:42PM |
T28.00009: Solution processable routes to nanostructured thermoelectric materials Joseph Feser, Robert Wang, Arun Majumdar, Jeffrey Urban The previous decade of research has shown that nanostructured thermoelectric materials can have superior performance compared to their bulk counterparts.. Often, the synthesis of nanostructured materials is performed by layer-by-layer methods, which hinders their ability to be produced as thick films. Here we show a scheme by which nanocrystals embedded in a thermoelectric matrix may be produced using solution processing. Using hydrazine chemistry, we prepare soluble precursors for Bi2X3 (X=S,Se,Te). Solutions containing those precursors are spun and drop-cast onto substrates, and their electrical and thermal properties are characterized. We show ongoing research to embed colloidal nanocrystals into a matrix made from the soluble precursors. [Preview Abstract] |
Wednesday, March 18, 2009 4:42PM - 4:54PM |
T28.00010: Self-supporting (Bi$_{0.11}$Sb$_{0.29 })$(Te$_{0.25}$,Se$_{0.41})$ nanowire arrays for thermoelectric microdevices Hatem El Matbouly, Timothy Sands, Kalapi Biswas Nanostructuring of thermoelectric material can lead to improved performance through suppression of the lattice contribution to thermal conductivity and enhancement of the power factor by quantum confinement or thermionic energy filtering. To take advantage of these effects in a Peltier microcooler or Seebeck generator, it is necessary to prepare nanostructure materials with leg lengths ranging from tens of microns to millimeters. We have developed a process for fabrication of thick, self-supporting (Bi$_{0.11}$,Sb$_{0.29})$(Te$_{0.25}$,Se$_{0.41})$ nanowire arrays using a novel branched porous anodic alumina template that can be removed completely by selective etching following electrodeposition of the thermoelectric material, resulting in 100-micron-thick nanostructured thermoelectric material without the parasitic thermal shunt that is associated with the template. The electrodeposition process allows composition modulation and grading, effects that are difficult to achieve by bulk synthesis. Bandgaps of the electrodeposited material range from 0.13 eV for Bi$_{2}$Te$_{3}$ to an optical gap of 0.52 eV measured for a (Bi,Sb)$_{2}$(Te,Se)$_{3}$ alloy, suggesting an operating tempurature range from below room temperature to $\sim $300\r{ }C. [Preview Abstract] |
Wednesday, March 18, 2009 4:54PM - 5:06PM |
T28.00011: Thermoelectric Properties of Nanostructured n-type Yb$_{x}$Co$_{4}$Sb$_{12 }$Bulk Jian Yang, Hui Wang, Yucheng Lan, Xiao Yan, Bo Yu, Xiaowei Wang, Gaohua Zhu, Dezhi Wang, Zhifeng Ren, Qing Hao, Gang Chen, Qinyu He, Mildred S. Dresselhaus Nanostructured single phase of Yb filled skutterudites CoSb$_{3}$ with a nominal composition of Yb$_{x}$Co$_{4}$Sb$_{12 }$(X = 0.3, 0.35, 0.4, and 0.5) have been synthesized by ball milling and direct current induced hot press. Thermoelectric properties including electrical conductivity, Seebeck coefficient, and thermal conductivity from room temperature to 550${^\circ}$ were measured and discussed. It was found that Yb$_{0.35}$Co$_{4}$Sb$_{12}$ has the optimal dimensionless figure of merit of 1.2 at 550${^\circ}$. [Preview Abstract] |
Wednesday, March 18, 2009 5:06PM - 5:18PM |
T28.00012: Thermoelectricity in Arrays of Thiolate Coated Au Nanoparticles E. Covington, F. Bohrer, E.T. Zellers, C. Kurdak We have developed a new technique to measure the thermopower of highly resistive films of thiolate coated Au nanoparticles. Using e-beam lithography, we fabricate two long parallel gold wires, spaced by 500 nm, on an insulating substrate and subsequently coat with a thin film of nanoparticles. The wires are used as electrodes for electronic conduction and heaters for thermopower measurements. We characterize the Joule heating in the wires using noise thermometry. To characterize the thermopower of the film, we excite one wire by an ac current with frequency $f$. Due to Joule heating, we establish a temperature difference between the two wires modulated with frequency 2$f$. We extract the thermopower by measuring the 2$f$ voltage signal between the wires using lock-in techniques.~We used this method on Au nanoparticles with 1-octanethiol (C8) ligands where the thermopower was less than 10 $\mu $V/K at room temperature. From the sign of the thermopower, we determined transport was mainly due to tunneling of electrons through the lowest unoccupied molecular orbital of the C8 molecule. [Preview Abstract] |
Wednesday, March 18, 2009 5:18PM - 5:30PM |
T28.00013: Molding Phonon Flow with Symmetry: Rational Design of Hypersonic Phononic Crystals Cheong Yang Koh, Edwin L. Thomas Phononic crystals structured at appropriate length scales allow control over the flow of phonons, leading to new possibilities in applications such as heat-management, sound isolation and even energy transfer and conversion. Symmetry provides a unified framework for the interpretation 1D to 3D phononic band structures, allowing utilization of a common set of principles for designing band structures of phononic crystals as well as actual purposeful defects such as waveguide location and boundary termination in finite devices. In this work, we explore the band structure properties of phononic crystals with non-symmorphic space groups, as well as those having quasi-crystalline approximants. We demonstrate gap opening abilities from both anti-crossing and Bragg scattering, as well as unique features like ``sticking'' bands. Symmetry concepts are also powerful means to tune the density of states of the structures. Importantly, we fabricate various theoretical designs and measure their experimental dispersion diagrams for comparison with theoretical calculation. This affords an elegant approach toward a design blueprint for fabricating phononic structures for applications such as opto-acoustic coupling. [Preview Abstract] |
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