Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session J28: Focus Session: Thermoelectricity in Semiconductor Nanostructures |
Hide Abstracts |
Sponsoring Units: DMP FIAP Chair: Li Shi, University of Texas, Austin Room: Morial Convention Center 220 |
Tuesday, March 11, 2008 11:15AM - 11:27AM |
J28.00001: Theory of enhancement of thermoelectric properties of materials with nanoinclusions. Sergey Faleev, Francois Leonard Based on the idea of Schottky potential as an energy filter for the electrons, we developed a theory that explains the enhancement of the thermoelectric properties of semiconductor materials with metallic nanoinclusions. The Boltzmann transport equation with relaxation time approximation is used for description of both electron and phonon scattering. The theory has been applied to optimize the ZT factor for n-doped PbTe with metallic nanoinclusions. We found that the contribution of electron scattering to optimized ZT is important for high electron concentration (n 3x10 cm$^{3}$), while at low concentrations (n 10 cm$^{3}$) enhancement of the ZT factor is primarily due to decrease of the phonon thermal conductivity. [Preview Abstract] |
Tuesday, March 11, 2008 11:27AM - 11:39AM |
J28.00002: Measurement of Cross-plane Thermoelectric Properties of Thin Film Structures with UHV Scanning Thermoelectric Microscopy Yong Lee, Anastassios Mavrokefalos, Michael Pettes, Li Shi In recent years various thin film structures have been under intense research in the hope for achieving increased thermoelectric figure of merit (ZT) compared to bulk materials. Accurate measurements of three quantities ($S$\ :\ Seebeck coefficient, $\sigma$\ :\ electrical conductivity, and $\kappa$:thermal conductivity) used to calculate ZT have been a challenge especially for thin film structures which may have very different values between in-plane and cross-plane directions due to the anisotropy. Here, we report our progress toward accurately measuring these thermoelectric properties of thin films along the cross-plane direction with a ultrahigh vacuum (UHV) scanning probe microscope. In particular, cross-plane Seebeck coefficient and electrical conductivity measurement of a thin film with a conductive AFM or STM probe will be discussed. [Preview Abstract] |
Tuesday, March 11, 2008 11:39AM - 11:51AM |
J28.00003: Micro- and nanomachined tools for measuring thermopower and in-plane thermal conductivity of thermoelectric thin films Azure Avery, Rubina Sultan, Greg Stiehl, Barry Zink Many of the potential next-generation thermoelectric materials being studied are either thin films or nanostructures that are expected to have anisotropic properties. Techniques such as the $3\omega$ method and picosecond thermoreflectance allow accurate measurements of $k_{\perp}$ at temperatures relevant to thermoelectrics, but measuring $k_{\parallel}$ is often difficult. In this talk we discuss our efforts to design and demonstrate accurate measurements of $k_{\parallel}$ of thin films from $77-475$ K using micro- and nanomachined thermal isolation platforms. Using thin-film structures to support the thin-film sample reduces background contributions, and careful control of the geometry keeps radiation errors small. We will discuss the optimization and micromachining of the measurement platforms and their application for studying the growth and characteristics of our first doped amorphous thin films. We will present our first tests of the devices on materials with established thermal properties. Finally, we will discuss the use of these measurement platforms to determine $k$ and $ZT$ for doped amorphous silicon thin films. [Preview Abstract] |
Tuesday, March 11, 2008 11:51AM - 12:03PM |
J28.00004: Thermopower and Electrical Conductivity of PbSe Nanocrystal Thin Films Robert Wang, Joseph Feser, Jong-Soo Lee, Dmitri Talapin, Rachel Segalman, Arun Majumdar Thin films assembled of solution-processed PbSe nanocrystals have a thermopower 2 -- 3 times greater than bulk PbSe. In addition, the thermopower and electrical conductivity both exhibit a size-dependence on nanocrystal size. As the nanocrystal diameter changes from 4 to 9 nm, the thermopower and electrical conductivity change from 850 to 650 $\mu $V/K and 10$^{-4}$ to 10$^{-2}$ S/cm, respectively. If electrical conductivity can be improved, these materials represent a new class of inexpensive and scalable thermoelectric materials. [Preview Abstract] |
Tuesday, March 11, 2008 12:03PM - 12:15PM |
J28.00005: ABSTRACT WITHDRAWN |
Tuesday, March 11, 2008 12:15PM - 12:27PM |
J28.00006: First Principles Studies of Phonon Dispersion and Lattice Thermal Conductivity of Silicon Nanowires Trinh Vo, Tadashi Ogitsu, Eric Schwegler, Giulia Galli We present phonon dispersions of Si nanowires using \textit{ab initio} and linear response theory. The effects of nanowire surface structures, growth directions, and quantum confinement on phonon dispersions and phonon confinement are also discussed. The thermal conductivity of Si nanowires using the obtained full dispersion curves are also evaluated, using Boltzmann Transport Equation. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory in part under Contract W-7405-Eng-48 and in part under Contract DE-AC52-07NA27344. [Preview Abstract] |
Tuesday, March 11, 2008 12:27PM - 12:39PM |
J28.00007: Enhanced Thermoelectric Performance in Rough Silicon Nanowires Renkun Chen, Allon I. Hochbaum, Raul Diaz Delgado, Wenjie Liang, Erik C. Garnett, Mark Najarian, Arun Majumdar, Peidong Yang Due to the disparity between electron ($<$10 nm) and phonon ( $\sim $100 nm) mean free paths in silicon, nanostructured Si could effectively block phonon transport by boundary scattering while maintaining electron transport, thereby enhancing thermoelectric figure of merit, ZT. Here we report the wafer-scale electrochemical synthesis and thermoelectric characterization of rough Si nanowires with enhanced ZT, relative to the bulk material. Single nanowire measurements show that their electrical resistivity and Seebeck coefficient are similar to those of bulk Si with similar dopant concentration. Thin nanowires, however, exhibit a 100-fold reduction in thermal conductivity (k), yielding a large ZT = 0.6 at room temperature. Although bulk Si is a poor thermoelectric material, Si nanowire arrays show promise as high-performance, scalable thermoelectric materials. [Preview Abstract] |
Tuesday, March 11, 2008 12:39PM - 12:51PM |
J28.00008: Enhanced thermoelectric properties in silicon nanowires Slobodan Mitrovic, Jen-Kan Yu, Akram Boukai, Jamil Tahir-Kheli, William A. Goddard III, James R. Heath Recently, we demonstrated that silicon nanowires can be designed and fabricated to achieve an approximately 100-fold enhancement in thermoelectric efficiency compared to bulk silicon. Independent measurements of thermoelectric power, and thermal and electrical conductivities suggest that this improvement is due to phonon effects rather than quantum confinement. Here, we present the study of the scaling laws (i.e. nanowire length/width dependence) for the phonon dynamics and transport. We investigate the influence of the phonon drag, carrier mobility and doping on the thermoelectric properties, and the universality of these findings. This work is supported by the Office of Naval Research, the Department of Energy, the National Science Foundation, and the Defense Advanced Research Projects Agency. [Preview Abstract] |
Tuesday, March 11, 2008 12:51PM - 1:03PM |
J28.00009: Atomistic Modeling and Optimization of thermoelectric properties of SiGe nanowires Maria Chan, Ying Shirley Meng, Tim Mueller, Gerbrand Ceder, John Reed, Trinh Vo, Andrew Williamson, Giulia Galli Nano-structured thermoelectric materials have been shown experimentally to have superior figure of merit compared to bulk materials. To understand the origin of this superiority, it is of interest to develop physically accurate methods to compute the thermoelectric transport coefficients of nanowires. In addition, computationally inexpensive parameterization of these physical models are needed in order for efficient sampling, e.g. in atomic configuration space, so as to design systems with optimal thermoelectric properties. We consider aspects of electron and phonon transport in SiGe nanowires. For electronic transport, we work in the diffusive regime with Boltzmann transport, combining ab initio density functional theory (DFT) calculations with a perturbative treatment of electronic scattering to obtain electronic relaxation times, conductivity and thermopower. The phonon contribution to thermal conductivity is obtained from classical equilibrium molecular dynamics simulations using the Green-Kubo formalism. Cluster expansion and effective potential techniques are used to parameterize the transport coefficients for efficient sampling and optimization. [Preview Abstract] |
Tuesday, March 11, 2008 1:03PM - 1:15PM |
J28.00010: Strain-superlattice nanowires via SiGe epitaxy on ultrathin Si ribbons C. Ritz, Yu Zhang, Decai Yu, D. Savage, C.-H. Lee, Feng Liu, M. Lagally We demonstrate a method to create a system of precisely positioned strain superlattice nanowires. These are similar to superlattice nanowires, which are traditionally created by VLS growth techniques and are of great interest for thermoelectric applications. We pattern the top layer of thin Si-on-insulator (SOI) into nanoribbons and undercut them, leaving freestanding bridges that are directly integrated into microfabricated devices. The thin freestanding Si is used as a substrate for the Stranski-Krastanov growth of coherent 3D Ge islands, where the thinness of the Si allows for island-island interactions through the ribbon thickness. This elastic interaction causes lateral order in island positions, forming a strain superlattice. A periodic bandgap modulation can result from the periodic island-induced strain. The combination of strain and bandgap modulation should act to improve the thermoelectric figure of merit of these structures. Thermal conductivity measurements of such structures will be discussed. [Preview Abstract] |
Tuesday, March 11, 2008 1:15PM - 1:27PM |
J28.00011: Thermoelectric Properties of Semiconducting Silicide Nanowires Song Jin, Jeannine Sczech, Jeremy Higgins, Feng Zhou, Li Shi Semiconducting silicides are promising thermoelectric materials. In addition to their respectable thermoelectric figure-of-merit (\textit{ZT} up to 0.8), silicides have the advantages of low cost, excellent thermal stability and mechanical strength, and outstanding oxidation resistance, making them suitable for high temperature applications. We have developed general synthetic approaches to single crystal nanowires of silicides to investigate the enhancement of thermoelectric properties due to the reduced nanoscale dimension and to explore their applications in thermoelectrics. We will discuss the synthesis and structural characterization of nanowires of chromium disilicide (CrSi$_{2})$ prepared via a chemical vapor transport (CVT) method and chemical vapor deposition (CVD) of organometallic precursors to synthesize the Novontony Chimney ladder phase MnSi$_{1.75}$. The Seebeck coefficient, electrical conductivity, and thermal conductivity of individual CrSi$_{2}$ nanowires were characterized using a suspended microdevice and correlated with the structural information obtained by microscopy on the same nanowires. This combined Seebeck coefficient and electrical conductivity measurements also provide an effective approach to probing the Fermi level, carrier concentration and mobility in nanowires. We will also discuss our progress in using individual nanostructures combined well-defined structural characterization to conclusively investigate the complex thermoelectric behaviors of silicide materials. [Preview Abstract] |
Tuesday, March 11, 2008 1:27PM - 1:39PM |
J28.00012: Investigation of Thermoelectric Transport in Individual Bismuth Nanowires Arden Moore, Michael Pettes, Anastassios Mavrokefalos, Li Shi Bismuth is a material of special interest for studying nanoscale transport behavior. Its extremely small effective mass and long electron mean free path suggest that quantum and classical confinement effects might be observed at realistic dimensions and higher temperatures than in other material systems. In addition, the predicted enhancement of the thermoelectric figure of merit \textit{ZT} due to quantum confinement effects has only served to increase the desire to measure the transport properties of individual bismuth nanowires. However, efforts to measure the thermoelectric properties of bismuth nanowires have been hindered thus far by the presence of a highly stable surface oxide layer, making reliable ohmic contact to individual nanowires problematic. In this work, we present the synthesis and measurement methods used by our group to make electrical contact with individual nanowires in order to measure the thermal conductivity, thermopower, and electrical conductivity of individual bismuth nanowires of varying diameter. The obtained data is presented with comparison to bulk values and analysis of the transport behavior. [Preview Abstract] |
Tuesday, March 11, 2008 1:39PM - 1:51PM |
J28.00013: Thermopower Measurements of Pure and Sn (Te) Doped Bismuth Nanowires Tito Huber, A. Adeyeye, A. Nikolaeva, L. Konopko, R. Johnson, M.J. Graf Theoretical work based on one-dimensional (1D) models indicates that Bi wires with diameter smaller than 50 nm can exhibit superior thermoelectric properties since the density of states at the Fermi level of a 1D system can be tuned to very high values. Also, recently, angle-resolved photoemission spectroscopy (ARPES) studies of Bi thin films have shown that Bi nanowires support Rashba spin-orbit surface states, with high carrier densities of around$5\times 10^{12}cm^{-2}$, that are hybridized with ``bulklike'' electrons and holes, a phenomenon that has not been considered in current models of Bi nanowires. We carried out an experimental study of the transport properties and thermopower of bismuth nanowire arrays (NWA) with wire diameters ranging between 60 nm and 13 nm at temperatures ranging between 4 K and 300 K, for magnetic fields of up to 1 T. Both pure bismuth and doped Bi were studied. The results are interpreted in a multicarrier diffusion thermopower model. [Preview Abstract] |
Tuesday, March 11, 2008 1:51PM - 2:03PM |
J28.00014: Tuning the Thermoelectric Properties of Metal-Molecule-Metal Junctions K. Baheti, J.A. Malen, P. Doak, T.D. Tilley, A. Majumdar, R. Segalman Thermoelectric materials have application in power generation and refrigeration, with several advantages over conventional power cycles including lack of moving parts, silent operation, miniaturization, and CO2 free conversion of heat to electricity. Nonetheless, low thermodynamic efficiency has limited their applicability. Here we examine a new class of inexpensive thermoelectric materials composed of organic-inorganic heterostructures. Thermopower measurements of 1,4-Benzenedithiol (BDT) molecule between Au electrodes, using a modified scanning tunneling microscope (STM), have been previously reported. This method is used to interrogate junctions where, the BDT molecule has been doped by the addition of substituent groups on the benzene ring. Our measurements show that we can tune the thermoelectric properties of such junctions in a controllable way by the addition of substituents. This in conjunction with a calculated transmission function imply a simultaneous increase in the thermopower and conductance, which has hitherto been impossible to attain in simple materials. We observe an increase of $\sim $50{\%} in the power factor, defined as S$^{2}\sigma$, of the junction upon substitution of electron donating groups in benzenedithiol. Hence, a ground up approach to building thermoelectric materials, from an endless array of possible organic-inorganic heterostructures, evokes hope for efficient thermoelectric energy conversion. [Preview Abstract] |
Tuesday, March 11, 2008 2:03PM - 2:15PM |
J28.00015: Transport properties and the thermoelectric figure-of-merit of single molecule systems. Padraig Murphy, Subroto Mukerjee, Joel Moore The thermoelectric properties of molecules are both of fundamental interest and of interest for the construction of energy conversion devices. These transport properties are sensitive to interactions within the molecule, the hybridization energy between the molecular energy levels and the leads, and to the temperature. We present numerical and theoretical results on the conductance and thermopower, and discuss the parameter values for which the figure-of-merit, which parametrizes the efficiency of energy conversion devices, is optimal. The numerical results for the thermopower can be obtained at fixed particle number for finite systems using an appropriate generalization of the approach of Gogolin and Prokof'ev to electrical conductance. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700