Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session A35: Focus Session: Nanoscale Thermal, Thermoelectric and Mass Transport: Measurement and Characterization |
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Sponsoring Units: DMP Chair: Heiner Linke, University of Oregon Room: Baltimore Convention Center 338 |
Monday, March 13, 2006 8:00AM - 8:36AM |
A35.00001: Nanoscale, phonon-coupled calorimetry with sub-attojoule/kelvin resolution Invited Speaker: We have developed a nanofabricated calorimeter for ultrasensitive heat capacity measurements upon externally-affixed (phonon-coupled) samples at low temperatures. For a 5s measurement at 2K, we demonstrate unprecedented resolution of C of 0.5 aJ/K (approximately 36,000 kB). This sensitivity enables, for example, possible applications such as heat capacity measurements upon zeptomole-scale samples and upon adsorbates at extremely minute coverage. We describe the configuration and operation of these devices, and demonstrate their operation by measuring an adsorbed He4 film with maximum resolution of approximately 3 x 10e-5 monolayers upon the minute device surface area, A approximately 1.2 x 10e-9 m2. [Preview Abstract] |
Monday, March 13, 2006 8:36AM - 8:48AM |
A35.00002: Thermal relaxation below 1 K by phonons and photons in metallic nanostructures Ilari Maasilta, Jenni Karvonen, Panu Koppinen, Lasse Taskinen We present experimental results on thermal energy flow (dissipation) from different metallic nanostructures below 1K, concentrating on the two possible channels: relaxation by phonon or by photon emission. We show how phonon emission can be suppressed either by lowering the dimensionality of the phonon gas (2D membranes), or by introducing impurities into the metal. As an example, we discuss Aluminum doped with Manganese, a material with significant technological importance for ultrasensitive detectors and solid-state coolers. We also discuss relaxation by photon emission in the near field, which becomes siginificant for distances in the sub-micron lengthscale at the sub-Kelvin temperature range. Theoretical understanding for most of the results obtained is still lacking. [Preview Abstract] |
Monday, March 13, 2006 8:48AM - 9:00AM |
A35.00003: Profiling the Seebeck Coefficient of III-V Superlattice Structures with nanometer resolution using Scanning Thermoelectric Microscopy (SThEM) Jianlong Li, Alexander Khajetoorians, Ho-Ki Lyeo, Colin Folta, Ali Shakouri, Li Shi, Chih-Kang Shih Recent theoretical efforts demonstrate that quantum well structures such as superlattices, nanowires, and quantum dots are good candidates for high \textit{ZT} materials. The ability to probe the thermoelectric properties of these materials on the nanometer scale requires the ability to resolve thermoelectric parameters with high spatial resolution. Recently, Scanning Thermoelectric Microscopy (SThEM) has demonstrated the ability to resolve the Seebeck coefficient and the carrier profile of GaAs $p-$n junctions with unprecedented spatial resolution (H.K. Lyeo et al \textit{Science} v.303 p816 (2004)). By applying this new technique, this work focuses on direct measurement of local thermoelectric power of GaAs/AlAs and GaAs/InGaAs superlattice structures using ultra high vacuum SThEM. We observed that the thermoelectric power in the superlattice region is greatly enhanced. Moreover, oscillations of Seebeck coefficient within the superlattice regions, with a periodicity commensurating with the superlattice structure, are also observed. [Preview Abstract] |
Monday, March 13, 2006 9:00AM - 9:12AM |
A35.00004: A modified high-resolution TEM for thermoelectric properties measurements of nanowires and nanotubes C. Dames, C. T. Harris, S. Chen, J. Y. Huang, Z. F. Ren, M. S. Dresselhaus, G. Chen Nanowires are interesting candidates for thermoelectric applications because of their potentially low thermal conductivity and high Seebeck coefficient. However, measurements at the single-wire level are challenging and tend to lack detailed information about the atomic-level structure of the sample and contacts. We are modifying a high-resolution transmission electron microscope (HRTEM) with integrated scanning tunneling microscope (STM) for in-situ measurements of thermoelectric properties.~ A slender Wollaston wire is used to make electrical and thermal contact to the free end of a single nanowire or nanotube.~ The electrical conductance of the sample can be measured with the usual STM mode of operation.~ The Seebeck coefficient of the sample can be extracted from the transient voltage response to a step change in the joule heating of the Wollaston wire.~ These measurements are combined~with~detailed~HRTEM~observations. [Preview Abstract] |
Monday, March 13, 2006 9:12AM - 9:24AM |
A35.00005: Bi nanobelts, nanocubes and their thermoelectric properties Wenzhong Wang, Shuo Chen, Jianyu Huang, Zhifeng Ren, T. Harris, Gang Chen, M. Dresselhaus Highly crystallized Bi nanobelts and monodispersed nanocubes have been synthesized via a low-temperature organic solution approach, in which sodium bismuthate was reduced by ethylene glycol in the presence of poly(vinylpyrrolidone) (PVP). By changing some experimental conditions, Bi nanobelts and nanocubes have been prepared successfully. The as-prepared Bi nanobelts are single crystal with high crystallinity. The width of the nanobelts is in the range of 50-500 nanometers and the length is up to of several tens of micrometers. The as-synthesized Bi nanocubes are highly crystallized and monodispersed with edge length of 50-60 nm. The electrical, thermal, and Seebeck properties of the as-grown nanobelts were studied by a TEM-STM probe inside a high resolution TEM. The same studies were also carried out on bulk samples made by hot-press using the nanocubes. [Preview Abstract] |
Monday, March 13, 2006 9:24AM - 9:36AM |
A35.00006: Bismuth Nanobelts for Enhanced Thermoelectric Performance Xu Zhao, Ming Tang, Gang Chen, M. S. Dresselhaus, Zhifeng Ren Bismuth is a semimetal with high promise for thermoelectric applications if it could be made into a semiconductor by a combination of size reduction (based on quantum confinement considerations) and antimony addition. The recent experimental preparation of bismuth Nanobelts has motivated calculation of the phase diagram for the bismuth-antimony system in the regime of nanobelt cross sectional area and antimony concentration where semiconducting behavior is expected. Both direct and indirect bandgap regions are considered and regimes where the highest valence band is at the T-point, the L-point and the H-point are identified. The dependence of the semiconductor-semimetal transition on sample geometry, crystal orientation and temperature will be considered to guide in the preparation of a sample set for use in exploration of this materials system for thermoelectric applications. [Preview Abstract] |
Monday, March 13, 2006 9:36AM - 9:48AM |
A35.00007: Facet-edge fluctuations on finite volume crystallites* Masashi Degawa, William Cullen, Ellen Williams Technological demands of the fabrication of nano-structures provide renewed motivation for understanding the atomistic properties that control the morphology changes of nano-structures and nano-crystallites. Using the continuum step model of the thermodynamic correlation function of step fluctuation has proven to be very powerful in such studies. For straight isolated steps on fcc(111) metal surfaces, the principal mass transport mechanism is often found to be periphery diffusion, with time correlations $\sim $t$^{1/4}$. However with decreasing structure size, issues of finite size and shape effects become non-negligible. When considering facet-edge fluctuations, the normal assumptions of ``straight'' and ``isolated'' do not apply. ``Straight'' is changed to ``curved'' due to finite size, which results in a KPZ term in the equation of motion. ``Isolated'' is changed to ``restricted'' where the amplitude of fluctuation is restricted due to mass conservation, which alters the scaling property of the noise term. Such considerations result in a different universality class of dynamic scaling giving $\alpha $=1/3, $\beta $=1/11 and z=11/3. Here we present results of facet-edge fluctuation measurements on Pb crystallites using scanning tunneling microscopy. Results of the temporal correlation function show an exponent different from $\raise.5ex\hbox{$\scriptstyle 1$}\kern-.1em/ \kern-.15em\lower.25ex\hbox{$\scriptstyle 4$} $, of 0.15$\pm $0.02 at early times, closer to 2/11 predicted for facet-edge fluctuations. *Supported by the UMD NSF-MRSEC, with originating support from DOE-NNI. [Preview Abstract] |
Monday, March 13, 2006 9:48AM - 10:00AM |
A35.00008: Pb-based Nanomaterials for Thermoelectric Application Bed Poudel, Dezhi Wang, Lili Chen, Wenzhong Wang, Yi Ma, Zhifeng Ren, Qing Hao, Hohyun Lee, Gang Chen, Mildred S. Dresselhaus PbTe, PbSe, PbSeTe, and PbSnTe nanocrystals having sizes in the range of $\sim $5-50 nm have been synthesized using a simple hydrothermal method. As-prepared nanopowder was processed using P$^{2}$C device, and samples with almost 100 percent density and small grain sizes were achieved. The thermoelectric properties of such samples have been investigated. Lower values of thermal conductivity were obtained from the samples prepared from nanomaterials. For further enhancement of the thermoelectric properties, the nanocrystals were doped with different elements, for example Ag, Cu, Eu, Bi, Sb, etc., and their thermoelectric properties have been studied. [Preview Abstract] |
Monday, March 13, 2006 10:00AM - 10:12AM |
A35.00009: Nanoscale clusters in the thermoelectric AgPb$_{m}$SbTe$_{m+2}$ and Ag$_{n}$Sn$_{m}$Sb$_{n}$Te$_{m+2n}$ materials He Lin, Emil Bozin, Khang Hoang, S.D. Mahanti, Simon Billinge, Eric Quarez, John Androula, Mercouri Kanatzidis The local structure of the AgPb$_{m}$SbTe$_{m+2}$ series of high performance thermoelectric materials has been studied using the atomic pair distribution function (PDF) method. The dimensionless thermoelectric figure of merit, $ZT$, of the $m\sim 18$ composition material was found to reach 1.7 at 700 kelvin, compared to the highest observed $ZT$ of only 0.84 for PbTe at 648 kelvin in n-doped material. This is asurprisingly large enhancement in $ZT$ for the addition of just 10\%per formula-unit of silver and antimony ions. It is clearly of the greatest importance to trace the origin of the $ZT$ enhancement. Three candidate-models were attempted for thestructure of this class of materials using either a one-phase or a two-phase modeling procedure. Combining modeling the PDF with HRTEM data we show that AgPb$_{m}$SbTe$_{m+2}$ contains nanoscale inclusions with composition close to AgPb$_{3}$SbTe$_{5}$ randomly embedded in a PbTe matrix. We extended the local structural PDF study to Ag$_{n}$Sn$_ {m}$Sb$_{n}$Te$_{m+2n}$, preliminary results of which suggest the presence of nanoscale inclusions in this system as well. [Preview Abstract] |
Monday, March 13, 2006 10:12AM - 10:24AM |
A35.00010: Thermal conductivity of nanoparticle suspensions David Cahill, Shawn Putnam We present our experimental study on the thermal conductivity of nanofluids loaded with small volume fractions of C$_{60}$-C$_ {70}$ fullerenes and alkanethiolate-protected Au nanoparticles. We use an optical beam deflection technique that measures the thermal diffusivity of fluid mixtures and suspensions of nanoparticles with a precision of better than 1\%. Our approach is tested using the thermal conductivity of ethanol-water mixtures; in nearly pure ethanol, the increase in thermal conductivity with water concentration is a factor of two larger than predicted by effective medium theory. The solutions of the C$_{60}$-C$_{70}$ fullerenes and the alkanethiolate-protected Au nanoparticles were measured to maximum volume fractions of 0.6\% and 0.35 vol\%, respectively. We do not observe anomalous enhancements of the thermal conductivity that have been reported in previous studies of nanofluids; the largest increase in thermal conductivity we have observed is $1.3 \pm 0.8$\% for 4 nm diameter Au particles suspended in ethanol. However, within the context of effective medium theory, these findings are expected: effective medium theory predicts that the largest possible increase in the thermal conductivity of a fluid loaded by a volume fraction $\phi \ll 1$ of spherical particles will be $3\phi \Lambda_0$, where $\Lambda_0$ is the thermal conductivity of the carrier fluid. [Preview Abstract] |
Monday, March 13, 2006 10:24AM - 10:36AM |
A35.00011: Thermal Conductance of metal-metal interfaces Bryan Gundrum, David Cahill, Robert Averback The first quantitative measurement of a metal-metal interface thermal conductance has been carried out using time-domain transient reflectivity in the temperature rage 78 $<$ T $<$ 278 K. The thermal conductance, at room temperature, for the as deposited Al-Cu interface was measured to be 4 GW m$^{-2}$ K$^{-1}$. This is an order of magnitude larger than the largest phonon-mediated interface transport measured to date. It is shown that an extension of the diffusive mismatch model to electrons reproduces the magnitude and temperature dependence accurately. The chemical abruptness of the Al-Cu interface is systematically varied by ion-beam mixing using 1 MeV Kr ions. These results combined with the interface form of the Wiedemann-Franz law could provide a powerful tool for investigating the thermal and electrical transport across metal interfaces. [Preview Abstract] |
Monday, March 13, 2006 10:36AM - 10:48AM |
A35.00012: Thermal conductance of hydrophilic and hydrophobic interfaces Zhenbin Ge, Paul Braun, David Cahill Interfaces between water and hydrophilic or hydrophobic surfaces are of great importance for many biological and engineering systems. Using time-domain thermoreflectance, we have measured the transport of thermally-excited vibrational energy across planar interfaces between water and solids that have been chemically functionalized using self-assembled monolayer. The thermal conductance per unit area of the interface G for hydrophobic Al or Au surface in water is determined to be 37 to 55 MW m$^{-2}$ K$^{-1}$. G for hydrophilic Al or Au surface in water is 150 to 300 MW m$^{-2}$ K$^{-1}$. Our new work on thermal transport complements the extensive research literature on momentum transport at aqueous interfaces: the Kapitza length---i.e., the thermal conductivity of water divided by the thermal conductance per unit area of the interface---is analogous to the ``slip-length'' for water flowing tangentially past a solid surface. We find that the Kapitza length at hydrophobic interfaces (11-16 nm) is a factor of 3-8 larger than the Kapitza length at hydrophilic interfaces (2-4 nm); a change of terminal group from methyl to hydroxyl increases the Kapitza length by approximately 10 nm. [Preview Abstract] |
Monday, March 13, 2006 10:48AM - 11:00AM |
A35.00013: Interfacial thermal transport at Liquid-Liquid and Biomolecular Interfaces Pawel Keblinski, Natalia Shenogina, Harshit Patel, Shekhar Garde Systems with nanoscopic features contain a high density of interfaces. Thermal transport in such systems can be governed by the resistance to heat transfer of the interface. Although soft interfaces, such as those between immiscible liquids or between a biomolecule and solvent, are ubiquitous, few studies of thermal transport at such interfaces have been reported. Here we characterize the interfacial conductance, i.e., the inverse of the interfacial resistance, of soft interfaces as a function of molecular architecture, chemistry, and the strength of cross-interfacial intermolecular interactions through detailed molecular dynamics simulations. The conductance of various interfaces studied here, for example, water-organic liquid, water-surfactant, surfactant-organic liquid, is relatively high (in the range of 65-370 MW/m2/ K) compared to that for solid-liquid interfaces ( 10 MW/m2/ K). Interestingly, the dependence of interfacial conductance on the chemistry and molecular architecture cannot be explained solely in terms of either bulk property mismatch or the strength of intermolecular attraction between the two phases. We will also discuss vibrational mode dependent thermal coupling at biomolecule-water interfaces. [Preview Abstract] |
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