Symposium Organizers
Jia Zhu, Nanjing University
Baratunde Cola, Georgia Institute of Technology
Deyu Li, Vanderbilt University
Amy Marconnet, Purdue University
ES09.01: Thermal Transport I
Session Chairs
Monday PM, November 27, 2017
Hynes, Level 3, Ballroom C
8:00 AM - *ES09.01.01
Energy Transfer in Nanoscale Gaps and Atomic Junctions
Pramod Sangi Reddy 1
1 , University of Michigan, Ann Arbor, Michigan, United States
Show AbstractUnderstanding radiative and conductive heat transfer in nanoscale gaps and devices is of considerable interest as elucidation of these transport properties is key to creating novel energy conversion and information processing devices. In this talk, I will first describe ongoing efforts in our group to experimentally elucidate nanoscale radiative heat transfer. Specifically, I will present our recent experimental work where we have addressed the following questions: Can existing theories accurately describe radiative heat transfer in single nanometer sized gaps1? Can radiative thermal conductances that are orders of magnitude larger than those between blackbodies be achieved2? In order to address these questions we have developed a variety of instrumentation including novel nanopositioning platforms and microdevices, which will also be described. In addition, I will also discuss recent experimental work3 from our group where we made first measurements of heat transport in single-atom junctions to elucidate the novel quantum transport properties that arise at the atomic scale. Finally, I will briefly outline how these technical advances can be leveraged for future investigations of nanoscale heat transport, near-field thermophotovoltaic energy conversion and near-field based solid-state refrigeration.
References:
[1] K. Kim, B. Song, V. Fernández-Hurtado, W. Lee, W. Jeong, L. Cui, D. Thompson, J. Feist, M. T. H. Reid, F. J. García-Vidal, J. C. Cuevas, E. Meyhofer and P. Reddy, “Radiative heat transfer in the extreme near-field”, Nature 528, 387-391 (2015).
[2] B. Song, D. Thompson, A. Fiorino, Y. Ganjeh, P. Reddy and E. Meyhofer, “Radiative heat conductance between dielectric and metallic parallel plates at nanoscale gaps”, Nature Nanotechnology 11, 509-514 (2016).
[3] L. Cui, W. Jeong, S. Hur, M. Matt, J. C. Klockner, F. Pauly, P. Nielaba, J. C. Cuevas, E. Meyhofer and P. Reddy, “Quantized Thermal Transport in Single-Atom Junctions”, Science 355, 1192-1195 (2017)
8:30 AM - ES09.01.02
Thermal Conductivity Enhancement of Coaxial Carbon@Boron Nitride Nanotube Arrays
Lin Jing 1 2 , Majid Samani 3 , Bo Liu 4 , Hongling Li 5 , Siu Hon Tsang 5 , Edwin Hang Tong Teo 1 5 , Alfred Tok 1 2
1 School of Materials Science and Engineering, Nanyang Technological University, Singapore Singapore, 2 Institute for Sports Research, Nanyang Technological University, Singapore Singapore, 3 Department of Microtechnology and Nanoscience, Chalmers University of Technology, Gothenburg Sweden, 4 Environmental Process Modelling Centre, Nanyang Technological University, Singapore Singapore, 5 School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore Singapore
Show AbstractVertically aligned carbon nanotube (CNT) arrays have been considered as promising thermal interface material (TIM) due to the superior thermal conductivity of the individual CNT and the absence of inter-tube phonon scattering. However, the practical heat transfer performance of most CNT arrays is restricted by the low tube volume fraction and limited quality of the individual CNT resulting from the synthesis process. Herein, for the first time, we demonstrate the enhanced thermal conductivity of the CNT arrays by introducing coaxial outer boron nitride nanotube (BNNT) with wall thickness of 0.97 nm (~3-4 walls). Impressively, a ~90% increase in thermal conductivity can be achieved for the resulting C@BNNT arrays (~29.5 W/mK) compared to bare CNT arrays (~15.5 W/mK). Furthermore, corresponding molecular dynamics simulation reveals that the outer BNNT does not impair the intrinsic thermal conductivity of the inner CNT and meanwhile serves as additional heat conducting path, which contributes to the enhanced heat transfer of the C@BNNT arrays. This work provides novel and deep insights into tailoring the thermal conductivity of arbitrary CNT arrays and will enable their broader applications as TIM.
8:45 AM - ES09.01.03
Optically-Controlled Long-Term Storage and Release of Thermal Energy in Phase-Change Materials
Grace Han 1 , Huashan Li 1 , Jeffrey Grossman 1
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractThermal energy storage offers enormous potential for a wide range of energy technologies. Phase-change materials (PCMs) such as salt hydrates or paraffins offer state-of-the-art thermal storage due to their high latent heat. However, spontaneous heat loss from thermally-charged PCMs to cooler surroundings occurs due to the absence of a significant energy barrier for the liquid–solid transition. This prevents control over the thermal storage, and developing effective methods to address this problem has remained an elusive goal. We report a combination of photo-switching dopants and organic PCMs as a way to introduce an activation energy barrier for PCM solidification and to conserve thermal energy in the materials, allowing them to be triggered optically to release their stored latent heat. This approach enables the retention of thermal energy (ca. 200 J/g) in the materials for at least 10 hours at temperatures lower than the original PCM phase transition point, unlocking opportunities for portable thermal energy storage systems.
9:00 AM - ES09.01.04
Quantized Thermal Transport in Single Atom Junctions at Room Temperature
Longji Cui 1 , Edgar Meyhofer 1 , Pramod Reddy 1
1 , University of Michigan, Ann Arbor, Michigan, United States
Show AbstractThermal transport in individual atomic junctions and chains is of great fundamental interest due to the unique quantum effects that are expected to arise in them. Here, by employing novel custom-fabricated, picowatt-resolution calorimetric scanning probes, we measure the thermal conductance of gold and platinum metallic wires all the way down to single-atom junctions [1]. Specifically, our studies reveal that the thermal conductance of gold single atom junctions is quantized even at room temperature. We also show that the Wiedemann-Franz law relating thermal and electrical conductance is satisfied even in single-atom contacts, irrespective of the metal. Furthermore, our ab initio simulations quantitatively explain all our experimental results within the Landauer picture for quantum coherent thermal transport. The experimental techniques developed in this work will enable systematic studies of thermal transport in atomic and molecular chains, which is key to investigating numerous fundamental issues that have remained inaccessible despite great interest.
[1] L. Cui et al., Science 355, 1192 (2017).
9:15 AM - ES09.01.05
Heat Dissipation and Transport in Atom-Sized Junctions
Makusu Tsutsui 1 , Takanori Morikawa 1 , Kazumichi Yokota 1 , Masateru Taniguchi 1
1 , ISIR, Ibaraki Japan
Show AbstractUnderstanding of heat dissipation and flow in current-carrying nanoscale ballistic conductors is a fundamental issue for developing energy-efficient nanoelectronics, wherein charge carriers tend to release most of the kinetic energy not in the material but outside it. Unlike isotropic energy dissipations in diffusive systems, this remote heating is known to create hot spots at a distance defined by the electron mean free path. Here, we report on, for the first time, evaluations of the remote Joule heating effects on stability of quasi-ballistic Au atom-sized junctions at room temperature. We developed a micro-fabricated break junctions consisting of a thermocouple embedded at micrometer-vicinity of a free-standing Au nanocontact. This device allowed to investigate the remote heat dissipation in the contact of variable sizes from 100 nm down to a single-atom scale through measuring the thermocouple temperature under mechanically-controlled breaking of the contact. We found larger temperature increase at the current downstream attributed to electron-hole asymmetry in the atomic contacts represented by the negative thermopower. The simultaneously-measured contact lifetime decreased with increase in the thermocouple temperature thereby suggesting a non-negligible contribution of the remote heating on the quasi-ballistic contact stability. We also provided a design concept for mitigating the contact instability by a numerical heat transfer simulations. The present finding can be used for practical design of nanoelectronic devices for heat dissipation managements.
9:30 AM - ES09.01.06
Heat Transport through Single Atoms
Nico Mosso 1 , Ute Drechsler 1 , Fabian Menges 1 , Peter Nirmalraj 1 , Siegfried Karg 1 , Heike Riel 1 , Bernd Gotsmann 1
1 , IBM Research, Zurich Switzerland
Show AbstractHeat transport and dissipation in nanoscopic contacts pose severe limitations to the scaling and performances of electronic devices. Currently available methods allow the investigation of temperature distributions in working devices with a spatial resolution of about 10 nm.
However, at smaller dimensions heat conduction mechanisms remain to be fully explored because of the lack of characterization techniques.
Here we present heat transport measurements through metallic contacts formed by single gold atoms at room temperature and analyse the dependence of the thermal conductance on the contact size. At this scale electrical and thermal conductance show quantization features owing to the availability of a finite number of transport channels. Moreover, by simultaneously measuring charge and heat transport we confirm the proportionality of electrical and thermal conductance in metallic atomic contacts. This constitutes a verification of the Wiedemann–Franz law at the atomic scale1. We anticipate that our findings will be a major advance in enabling the investigation of heat transport properties in molecular junctions, with meaningful implications towards the manipulation of heat at the nanoscale.
[1] Mosso, N., Drechsler, U., Menges, F., Nirmalraj, P., Karg, S., Riel, H., & Gotsmann, B. Heat transport through atomic contacts. Nat. Nanotech., 12, 430–433 (2017)
9:45 AM - ES09.01.07
Thermal Transport in SiGe Alloys—From First Principles to Experiment
Samuel Huberman 1 , Vazrik Chiloyan 1 , Ryan Duncan 2 , Lingping Zeng 1 , Alex Maznev 2 , Keith Nelson 2 , Gang Chen 1
1 Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractSiGe alloys have become a canonical system in the study of size effects on thermal transport because of the large contribution to thermal conductivity from long mean free path phonons. Yet, a comprehensive picture remains elusive. Here, we use first principle calculations and experimental measurements to probe size effects on thermal transport in SiGe alloys. Transient thermal grating (TTG) in the reflection geometry is used to measure the effective thermal conductivity. Under the density functional theory (DFT) framework, the virtual crystal approximation combined with impurity scattering is used to determine the phonon properties for the exact alloy composition of the measured samples. With these properties, classical size effects are calculated for the experimental geometry using the recently developed variational solution to the phonon Boltzmann transport equation under the single mode relaxation time approximation, which is verified against established Monte Carlo simulations. We find good agreement in the reduction of thermal conductivity (as much as 25% of the bulk value) across grating periods spanning one order of magnitude between theoretical prediction and experimental measurement. This work provides a foundation for the study of size effects on thermal transport in opaque materials. This work is supported by DOE EFRC (Grant No. DE-SC0001299).
10:30 AM - *ES09.01.08
Recent Experiments on High-Thermal Conductivity Materials
Li Shi 1
1 , The University of Texas at Austin, Austin, Texas, United States
Show AbstractHigh-thermal conductivity materials can both help to address various technological challenges and stimulate new fundamental studies of intriguing thermal transport phenomena. In recent years, a number of theoretical studies have suggested record-breaking ultrahigh thermal conductivity values in one-dimensional carbon nanotubes, two-dimensional hexagonal graphene, and three-dimensional cubic phase boron arsenide (BAs), unusually high thermal conductivity in molecular crystals, and breakdown of the Fourier’s law in many of these materials. While significant progresses have been made, many of these theoretical predictions have remained to be validated by experiments. Here, we review results from several recent experiments of high-thermal conductivity materials. Chemical vapor deposition (CVD), chemical vapor transport (CVT), and travelling solvent floating zone methods are employed to grow 1D and 2D hexagonal structures, continuous graphitic network structures, BAs, and spin ladder compounds with potentially high phonon or magnon thermal conductivity. New four-probe electro-thermal and elastic light scattering measurement methods are established to probe the intrinsic thermal transport property and the relaxation length scales of phonons and magnons in these and other materials with potentially high thermal conductivity. Some of these high-thermal conductivity materials are integrated with electronic and thermal storage devices to enhance the thermal performance.
11:00 AM - ES09.01.09
Simultaneous Thermal Energy Harvesting and Storage Utilizing Thermally Chargeable Supercapacitor
Jui-Hung Hsu 1 , Suk Lae Kim 1 , Choongho Yu 1
1 , Texas A&M University, College Station, Texas, United States
Show AbstractA novel concept of thermally chargeable supercapacitor (TCSC) for simultaneous energy harvest and energy storage is demonstrated. The TCSC device is all-solid-state without liquid electrolyte leakage issues, could be flexible, and is thus feasible for wearable power harvesting/storage. The TCSC is based on a three-layered structure with a solid electrolyte layer, poly(4-styrenesulfonic acid) (PSSH) sandwiched between two electrodes made of polyaniline (PANI)-coated graphene and carbon nanotube (P-G/CNT) films. Thermally driven ion diffusion, or Soret effect, in the PSSH layer was able to produce output voltage of 8 mV/K, which is much larger than the Seebeck coefficients (typically 10-100 μV/K) of conventional thermoelectric device based on electron diffusion by temperature gradient. Electrochemical reactions enabled by the thermally induced voltage lead to charging of the supercapacitor without external power supply. The highly porous P-G/CNT electrodes resulted in almost three-time higher specific capacitance (150 F/g) as compared to CNT-only electrode (52 F/g) at 0.5 A/g. The electro-deposited PANI on P-G/CNT electrodes further improved specific capacitance to 430 F/g at 0.5 A/g. With a small temperature difference of 5.3 K, which could be possibly created over wearable devices, a charged potential of 38 mV and an areal capacitance of 120 mF/cm2 were achieved. We believe the concept of utilizing thermally driven ion diffusion could open up new research possibilities about thermal energy harvesting.
11:15 AM - ES09.01.10
Effect of Simultaneous Alignment of Polymer Lamellae and Graphene Nanoplatelets on Enhancement of Thermal Conductivity
Jivtesh Garg 1 , Mortaza Saeidi-Javash 1
1 , Univ of Oklahoma, Norman, Oklahoma, United States
Show AbstractEffect of simultaneous alignment of polyethylene (PE) lamellae and graphene nanoplatelets (GnPs) on enhancement of thermal conductivity (k) is studied. Alignment is achieved by applying mechanical strain to the PE-GnP composites. Alignment of GnPs is found to have a large beneficial effect on k-increase. At 10 wt% GnP content, slope of k-increase with applied strain is found to be almost a factor of 2 higher compared to pure polymer samples. Aligned GnPs are found to be 3 times as effective in enhancing k as randomly oriented GnPs. At a draw ratio of 4 and with 10 wt% GnP, a 12-fold increase in k over the unoriented polymer is achieved. Detailed alignment measurements of both PE lamellae and GnPs are achieved through the use of wide-angle X-ray scattering (WAXS) and polarized Raman spectroscopy. These results provide avenues to develop high k polymer composites.
11:30 AM - ES09.01.11
Boron Nitride Nanotubes for Thermal Management
Mahmoud Amin 1 , David Kranbuehl 1 , Hannes Schniepp 1
1 , College of William & Mary, Williamsburg, Virginia, United States
Show AbstractWe use boron nitride nanotubes (BNNTs) prepared using the high-pressure high-temperature method to produce electrically non-conductive BNNT-polymer nanocomposites with enhanced thermal conductivity. In this work we study the chemical purification of the BNNT materials, the separation into individual nanotubes, and solvent dispersion. To monitor the progress and quality of these steps we use X-ray diffraction, atomic force microscopy, thermochemical, and spectroscopic analysis methods. Finally, these tubes are embedded into polymer matrices to enhance thermal transport. Both the polymer matrix and BNNTs are electrically insulating, which makes such materials interesting in microelectronics, where high thermal conductivities are needed, without creating short-circuits.
11:45 AM - ES09.01.12
Maximum Thermal Insulation by Nanoporous, Particulate Materials
Pia Ruckdeschel 1 , Alexandra Philipp 1 , Markus Retsch 1
1 , University of Bayreuth, Bayreuth Germany
Show AbstractEfficient thermal insulation is of high importance to decrease the overall power consumption for heating and cooling applications. Good thermal insulation materials possess typically a high degree of porosity, like foams or aerogels. This is mainly driven by the low density of such materials.
In this contribution, we use structurally well-defined hollow silica nanoparticles to elaborate the minimum thermal conductivity achievable with this sort of particulate material. The use of monodisperse hollow silica nanoparticles offers several benefits: precise adjustment of open and closed pore volume, independent variation of the density, and control over particle contact points.
By adjusting the structural properties, we find a minimum thermal conductivity to be reached at ~ 35 mWm-1K-1 in air, whereas 7 mWm-1K-1 can be achieved in vacuum. Thus, tailor-made particle ensembles based on hollow silica nanoparticles represent a dispersion processable, breathable, and non-flammable alternative to common polymer foams.
ES09.02: Thermal Transport II
Session Chairs
Monday PM, November 27, 2017
Hynes, Level 3, Ballroom C
1:30 PM - *ES09.02.01
Thermal Transport in Amorphous Si Nanostructures
Renkun Chen 1 2
1 Department of Mechanical and Aerospace Engineering, University of California, San Diego, La Jolla, California, United States, 2 Materials Science and Engineering Program, University of California, San Diego, La Jolla, California, United States
Show AbstractThermal transport in amorphous materials has been relatively less explored compared to that in crystalline materials. Amorphous materials are considered to possess the lower limit to the thermal conductivity (k), which is ~1 W/m-K for a-Si. However, recent work suggested that k of micron-thick a-Si films can be greater than 3 W/m-K, which is contributed by propagating vibrational modes, referred to as “propagons”. However, precise determination of k in a-Si has been elusive, as bulk a-Si is not available and most cross-plane measurements were influenced by interfacial thermal resistance. We used a-Si nanotubes and suspended a-Si films for precise in-plane thermal conductivity measurement within a wide thickness range of ~5 nm to 1.7 um. We showed high in-plane thermal conductivity in a-Si nanostructures, reaching ~3.0 and 5.3 W/m-K at ~100 nm and 1.7 um, respectively. Furthermore, the measured in-plane thermal conductivity is significantly higher than the cross-plane thermal conductivity on films with similar thickness. This unusually high and anisotropic thermal conductivity in the amorphous Si nanostructure manifests the broad propagon mean free path distribution, which is found to range from 10 nm to 10 um, in the disordered and atomically isotropic structure. Further, these propagon properties also lead to interesting phonon transport behaviors in amorphous Si, such as non-diffusive transport and unique temperature dependence.
2:00 PM - ES09.02.02
Thermal Transport in Quasi-1D van der Waals Crystal Nanowires
Yang Zhao 1 , Qian Zhang 1 , Lin Yang 1 , Deyu Li 1
1 , Vanderbilt University, Nashville, Tennessee, United States
Show AbstractThe recent explosive explorations of various types of two-dimensional (2D) materials stimulate strong interest in van der Waals (vdW) crystals, a class of materials composed of covalently-bonded building blocks assembled together via vdW interactions. Compared with the extensive studies of 2D vdW crystals, quasi-one-dimensional (quasi-1D) vdW materials have only attracted limited attention. However, quasi-1D materials can have unique properties for novel applications. In view of the great potential of quasi-1D vdW crystals and to understand thermal transport in quasi-1D vdW crystals, we conducted systematic measurements of the thermal conductivity of three kinds of quasi-1D vdW crystal nanowires, namely, Ta2Pd3Se8 (TPdS), NbSe3, and TaSe3 nanowires.
The thermal conductivity of these different types of nanowires demonstrates interesting dependence on the wire cross-section size and wire length. For example, the measured thermal conductivity of TPdS nanowires show strong size dependence on both wire cross-section and wire length, while the thermal conductivity of TaSe3 has a much weaker size dependence on the cross-section. We attribute these different behaviors to the different along-chain and inter-chain atomic bonding strengths in these three wires. For NbSe3 wires, we observe important effects of electron charge density wave on thermal conductivity. Separation of the electron and phonon contributions to thermal transport suggests interesting interplay between phonons and electrons as the charge density wave occurs. These studies provide new insights into thermal transport through vdW crystals, which helps to lay the foundation for applications of these novel materials in engineering applications.
2:15 PM - ES09.02.03
Electrical-Pulse Tuned Thermoelectric Properties of Germanium Telluride Nanowire
Yuxi Wang 1 , Qinghui Zheng 1 , Jia Zhu 1
1 National Laboratory of Solid State Microstructures, College of Engineering and Applied Sciences, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing China
Show AbstractPhase-change materials (PCMs), such as Ge2Sb2Te5 and GeTe, which have been proposed as the candidate for solid-state memory devices (1), can reach several different electronic states under voltage-pulse programming. Previous works have correlated the evolution of defects with that electrical properties at different states via in-suit TEM characterization in such PCMs nanowires.(2,3) Here, we observed that the structural phase-change (dislocations generation) not only induces the electrical properties (σ) transformation but also governs the seebeck coefficient(S) and thermal conductivity(ktot=kl+ke) during pulse programming from virgin state to programming states, by simultaneous thermoelectric properties measurement of GeTe nanowire on suspended micro-bridge device. The tunable seebeck coefficient and reduced thermal conductivity can be attributed to tunable fermi level position and phonon-dislocation interaction, respectively. Our results provide comprehensive understanding about the connections between structural phase-change and tunable transport properties in GeTe-system, which would be beneficial for developing new functional GeTe-based electronic devices.
1. H. S. P. Wong et al., Proceedings of the IEEE 98, 2201-2227 (2010).
2. S.-W. Nam et al., Science 336, 1561-1566 (2012).
3. P. Nukala et al., Nano Lett 14, 2201-2209 (2014).
2:30 PM - ES09.02.04
Kinks as a New Freedom to Tune Thermal Transport through Nanowires
Lin Yang 1 , Qian Zhang 1 , Yang Zhao 1 , Deyu Li 1
1 , Vanderbilt University, Nashville, Tennessee, United States
Show AbstractUnderstanding the design rules to obtain nanostructured materials that allow for tuning of thermal transport properties would aid major development in thermoelectric energy harvesting and thermal management for nanoelectronic devices. In the past two decades, the effects of several parameters, including the wire diameter, surface roughness, and acoustic softening on thermal transport through nanowires have been studied extensively. Here, we introduce how a new parameter, kinked morphology, can effectively alter the thermal transport properties of nanowires. Through systematic measurements of the thermal conductivity of boron carbide nanowires and Si nanoribbons of kinked morphologies, we reveal how kinks affect thermal transport through nanowires and can be used to tune the thermal conductivity of nanowires.
For boron carbide nanowires with a single kink, we observed thermal conductivity reduction up to 36% compared to that of straight nanowires of similar carbon concentration and diameter. This represents a remarkable kink resistance as high as 30 times that of a corresponding straight wire segment of equivalent length. Modeling based on a Monte Carlo ray-tracing scheme indicates that the pronounced kink resistance is due to back-reflection of highly focused phonons at the kink, which is supported by the observation that structural defects in the kink, instead of posing resistance, actually facilitate phonon transmission through the kink.
To further explore the kink effect, we measure the thermal conductivity of kinked Si nanoribbons of different kink period length. Because silicon is elastically much less anisotropic compared with boron carbides, a single kink poses significantly less resistance. However, we demonstrate that the thermal conductivity of silicon nanoribbons can be tuned through reducing the kink period length, and achieve a maximum thermal conductivity reduction of 12% at 300 K. Interestingly, if we further reduce the period length to a level that a straight channel opens along the heat transfer direction, the thermal conductivity starts to increase, which can eventually lead to a thermal conductivity that is ~20% higher than that of the straight counterpart.
3:30 PM - *ES09.02.06
Thermal Conductivity Tuned from Crystalline to Amorphous with Ion Irradiation
Junqiao Wu 1 , Hwan Sung Choe 1
1 , University of California, Berkeley, Berkeley, California, United States
Show AbstractThermal conductivity of amorphous materials is typically much lower than their crystalline counterparts. The wide range of thermal conductivity from crystalline to amorphous values offer a platform to explore the physics of lattice heat conduction as well as to engineer new thermal materials. We use helium ion irradiation to continuously suppress the thermal conductivity of single-crystalline Si membranes by nearly two orders of magnitude, well correlating with the gradual amorphization process of the lattice. Moreover, by tuning the spot size, energy and dose of the irradiation, we sculpture the Si membrane into arbitrary patterns that can be designed to control heat flow along the membrane, acting as a programmable nanoscale thermal metamaterial.
4:00 PM - ES09.02.07
Light-Triggered Reversible Thermal Conductivity Switching in Azobenzene Containing Polymers
Jungwoo Shin 1 , Jaeuk Sung 1 , Minjee Kang 1 , Cecilia Leal 1 , Nancy Sottos 1 , Paul Braun 1 , David Cahill 1
1 Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Show AbstractWe observe thermal conductivity switching of the azobenzene polymers by more than a factor of two associated with ultraviolet (UV) and visible light irradiation induced crystal-liquid transitions. We study the thermal and structural properties of these azobenzene polymers via in-situ time-domain thermoreflectance (TDTR) and in-situ synchrotron glancing incident X-ray scattering (GIXS). We attribute the high thermal conductivity state (0.35 W m-1 K-1) to spontaneous mesogen alignment induced by visible light photocrystallization of the azobenzene polymer. UV irradiation drives photoliquification of the azobenzene polymer, leading to a low thermal conductivity state (0.10 W m-1 K-1). The light-triggered phase transition is reversible and occurs on a time-scale of tens of seconds. We attribute the light-triggered phase transition of azobenzene polymer to cis-trans isomerization of azobezene mesogens which dramatically change the interchain cohesion strength, shifting the glass transition temperature above or below room temperature.
4:15 PM - ES09.02.08
Tuning the Temperature-Dependent Thermal Conductivity via Complex Colloidal Superstructures
Fabian Nutz 1 , Markus Retsch 1
1 , University of Bayreuth, Bayreuth Germany
Show AbstractTemperature-dependent thermal conductivity is generally driven by the monotonic increase of the specific heat capacity and by the scattering of phonons. Hence, one typically finds a maximum of the thermal conductivity for crystalline materials at low temperatures, and a negative slope of the temperature dependence at high temperatures. In amorphous materials, a monotonic increase prevails across the entire temperature range, based on the specific heat capacity. The ability to specifically tune the temperature dependence of the thermal conductivity possess an important challenge to develop and conceive future heat management devices.
In this contribution, we demonstrate the vast potential of polymer colloidal crystals to address and master these challenges. We achieve this goal based on the constriction-controlled thermal transport through well-defined colloidal crystal superstructures.[1,2,3,4] These colloidal superstructures are specifically built by tailor-made latex particles with distinct glass transition temperatures. We exploit their multiresponsive film formation at various temperatures to demonstrate an unprecedented control over thermal conductivity at temperatures between 25 °C and 200 °C. Based on the film formation process, we are able to irreversibly increase the thermal conductivity by a factor of about three. We show how to control:
i) the temperature, where the increase in thermal conductivity happens
ii) the sharpness of the thermal conductivity increase
iii) the height of the increase in thermal conductivity
iv) the incorporation of a multistep increase in thermal conductivity
[1] F. A. Nutz, P. Ruckdeschel, M. Retsch, J. Colloid Interface Sci. 2015, 457, p. 96.
[2] N. Vogel, M. Retsch, C. A. Fustin, A. Del Campo, U. Jonas, Chem. Rev. 2015, 115, p. 6265.
[3] P. Ruckdeschel, T. W. Kemnitzer, F. A. Nutz, J. Senker, M. Retsch, Nanoscale 2015, 7, p. 10059.
[4] F. A. Nutz, M. Retsch, Phys. Chem. Chem. Phys. 2017, doi: 10.1039/c7cp01994g
4:30 PM - ES09.02.09
The Role of Heterophase Boundaries in Determining Thermal Conductivity of Fe-Si-Ge Eutectic+Eutectoid Hierarchical Microstructuresβ
Wade Jensen 1 , Naiming Liu 1 , John Tomko 1 , Brian Donovan 2 , Patrick Hopkins 1 , Jerrold Floro 1
1 , University of Virginia, Charlottesville, Virginia, United States, 2 , United States Naval Academy, Annapolis, Maryland, United States
Show AbstractFe-Si-Ge alloys are being investigated for their thermoelectric properties, where Fe and Si are abundant, inexpensive and non-toxic. The β-FeSi2 phase is a semiconductor, with a modest thermoelectric figure of merit. A strategy to improve the properties, which has been recently extended upon by our group, is to exploit the eutectoid transformation, α-Fe1-xSi2 → β-FeSi2 + Si. By controlling aging conditions, arrays of embedded Si nanowires can form in the β matrix. This can be further expanded by including small amounts of Ge, of order 5 at %. The inclusion of Ge also increases phonon scattering, and reduces the bandgap of the diamond cubic (DC) phase, reducing band offsets with the silicide matrix. When alloys are made by casting, the Ge largely segregates into the diamond cubic phase, primarily in the form of eutectic lamellae. Melt spinning can greatly reduce the lamellae thickness and interlamellar spacing. Subsequent aging then produces eutectoid decomposition, so that a hierarchical eutectic+eutectoid structure is created. By controlling the casting and aging conditions, we formed a series of samples having heterointerfaces, β-FeSi2/Si1-yGey, where y varies from 0-0.3 in different samples. We have measured the thermal conductivity of the composite structures using time domain thermoreflectance. We gain insight into these measurements by comparison of analyses both as a network of thermal resistances as well as a bulk nanocomposite. In the first approach, we assume a series resistor network of thermal resistances from the bulk β and DC phases, with heterointerfaces having a thermal boundary conductance that varies with y. In the second approach, we assume that the bulk thermal conductivities themselves are modified by size effects. Our results show that alloying of the DC phase can lead to not only reductions in thermal conductivity due to mass impurity scattering, but also a stronger influence of phonon-boundary scattering on thermal conductivity. This analysis suggests that the thermal boundary conductance across alloy interfaces is influenced by the chemical composition of the alloy material comprising the interface. Support from a II-VI Foundation Block Grant is gratefully acknowledged. This material is based upon work supported by the Air Force Office of Scientific Research under award number FA9550-15-1-0079.
4:45 PM - ES09.02.10
Thermal Conductivity Maps and Interface Conductance of Die-Attached Composite Films
Miguel Goni 1 , Maciej Patelka 2 , Steve Anagnostopoulos 2 , Irma Kapoglis 2 , Terry Hartman 2 , Toshiyuki Sato 2 , Aaron Schmidt 1
1 , Boston University, Brookline, Massachusetts, United States, 2 , Namics, Byfield, Massachusetts, United States
Show AbstractDie attach applications require materials that are mechanically compliant and good conductors of heat. Composite materials offer the possibility of tailoring both the mechanical and thermal properties in order to satisfy the application requirements. In this study, we investigate several metal matrix composites with different filling configurations using a novel frequency domain thermoreflectance imaging technique to obtain high resolution thermal conductivity maps of the cross section of multiple die attach films. The thermal conductivity maps reveal matrix material migration that could not be identified in optical images. In addition, we develop a novel window etch method to directly measure the thermal interface conductance between silicon and the composite. We compare this conductance value to the thermal image results to understand how the detailed microstructure of the composite relates to the overall thermal performance of the attached die.
ES09.03: Poster Session I
Session Chairs
Tuesday AM, November 28, 2017
Hynes, Level 1, Hall B
8:00 PM - ES09.03.01
Cation and Anion Controlled Phonon Transport in Bulk, Monolayer and Short-Period Superlattice Transition Metal Dichalcodenides
Iorwerth Thomas 1 , GP Srivastava 1
1 , University of Exeter, Exeter United Kingdom
Show AbstractTransition metal dichalcodenides (TMDs) show promise as components of two-dimensional electronic devices. Experimental measurements also show that above room temperature, the lattice thermal conductivity of some TMDs in their monolayered, hexagonal form is low enough that they are suitable for use in high efficiency thermoelectric devices. Using a recently developed semi-ab-initio technique [1] based on a combination of density functional peturbation theory [2], a quasi-harmonic approximation [3], and the Boltzmann equation [3], we examine cation and anion controlled phonon transport in bulk and monolayer TMDs. We present a detailed analysis of conductivity variations in the temperature range 5 - 1700 K and sample size range 10 nm - 10 μm for bulk and monolayer CA2 TMDs where the cations C are Mo and W and the anions A are S and Te. For a sample size of 1 μm, we observe the following trends in bulk conductivity results: κin−plane(MoTe2) < κin−plane(MoS2) < κin−plane(WS2) and κcross−plane(MoTe2) < κcross−plane(WS2) < κcross−plane(MoS2). For monolayer systems we also find κ(MoTe2) < κ(MoS2) < κ(WS2), but with some differences. While κ(bulk) saturates at around sample size L = 10 μm, κ(monolayer) saturates with L at a much larger value. We present a detailed explanation of these behaviours. We also examine the results of our calculations for very short period MoS2-WS2 superlattices and find that the phonon conductivity is reduced in the cross-interface direction.
[1] I.O. Thomas and G. P. Srivastava, Submitted for publication.
[2] S. Baroni et al, Rev. Mod. Phys. 73, 515 (2001).
[3] G. P. Srivastava, The Physics of Phonons (Taylor and Francis, New York, 1990).
8:00 PM - ES09.03.02
Model for Predicting Anisotropic Lattice Thermal Conductivity
Robert McKinney 1 , Prashun Gorai 1 2 , Anuj Goyal 2 1 , Eric Toberer 1 2 , Vladan Stevanovic 1 2
1 , Colorado School of Mines, Golden, Colorado, United States, 2 , National Renewable Energy Laboratory, Golden, Colorado, United States
Show AbstractAccurately predicting the lattice thermal conductivity (κL) is crucial in the discovery of new materials for applications such as thermoelectrics and integrated circuits. We have previously developed a semi-empirical model for predicting κL under the assumption of isotropic thermal transport1. The semi-empirical, isotropic model is based on easy-to-calculate parameters from simple density functional theory (DFT) calculations such that the model can be employed for high-throughput predictions. With this model, κL is predicted within a factor of 1.5 of the experimental values across 4 orders of magnitude in κL. However, one of the limitations of the isotropic model is that it does not describe the variation in κL along the principal axes of the crystal. κL can strongly vary with direction, especially in highly anisotropic materials such as quasi-2D layered materials. In an effort to capture this variation, we have extended the isotropic model by incorporating anisotropy in the acoustic contribution to κL. The optical contribution to κL is still described in the amorphous limit such that it has no directional dependence (isotropic). In the isotropic model, the acoustic contribution is described by a Debye-Callaway approximation; the terms entering into the model are the number of atoms, the average atomic mass, the primitive cell volume, the coordination number, and the speed of sound. The isotropic speed of sound is approximated by the density and the bulk modulus. We incorporate anisotropy by replacing the isotropic speed of sound with a directionally-dependent speed of sound determined from the density and the relevant elastic tensor component calculated with DFT. Calculation of elastic tensors with DFT is fairly straightforward such that the anisotropic model of κL is still amenable to high-throughput predictions.
1Miller et al., Chem. Mater. 29, 2494 (2017)
8:00 PM - ES09.03.03
Thermal Interface Performance of Graphene at Rough Solid-Solid Interface
Chun Cheng 1 , Shiyuan Liu 1
1 , Southern University of Science and Technology of China, Shen Zhen China
Show AbstractThermal management is often discussed for ensuring the performance of electronic devices. The actual contact at solid-solid material interface consists of many voids which restricts the efficient heat dissipation from device to heat sink. Recently, graphene(Gr) is reported to be a good candidate of thermal interface materials (TIM) for improving the thermal interface transport. However, the underlying mechanism of graphene based TIM remains poorly understood and the experimental works are very inadequate. Here, we quantitatively measured the thermal contact resistance (TCR) of VO2 and Si interface (VO2/Si) with respect to contact roughness and compared with that of VO2/Gr/Si case. The experimental results show that the TCR of VO2/Si increases by 2 orders of magnitudes (from 3.75×10-6±1.14×10-6 Km2/W to 2.11×10-4±0.81×10-4 Km2/W) with the rise in contact roughness (Ra) from 0.67nm to 71.67nm. For VO2/Gr/Si, the total TCR increases slower as the contact interface becomes rougher and is about 10 times smaller than corresponding TCR of VO2/Si at a rough interface. We suggest the improvement of thermal interface transport is mainly attributed to the large area of graphene which makes the heat transport of VO2/Gr interface more dominant, isolating the effect of Si surface roughness to some extent. These results are consistent with the simulations carried out by molecular dynamics (MD).
8:00 PM - ES09.03.04
In Silico Study of a Nanoscale, CMOS-Integrable, Thermal-Guiding System for Boolean-Logic and Neural Circuits
Desmond Loke 1 , Jonathan Skelton 2 , Lunna Li 1 , Tow-Chong Chong 1 , Stephen Elliott 3
1 , Singapore University of Technology and Design, Singapore Singapore, 2 , University of Bath, Bath United Kingdom, 3 , University of Cambridge, Cambridge United Kingdom
Show AbstractThe ever-rising demand for quicker CMOS electronics, optoelectronics, and photonic devices has driven a widespread search for advanced thermal-guiding (TG) systems. TG structures, based on the controlled guiding of thermal diffusion around, as well as into, a target region of a TG matrix, are typically capable of not only steering heat away from critical nodes of integrated circuits (or silicon/ chalcogenide devices) to fabricate higher density, and smaller, transistor devices but also, more recently, able to direct heat toward key areas of silicon (or chalcogenide) systems to perform multiple, state-of-the-art circuit functions, such as Boolean-logic computations and neuromorphic computing. However, the behavior of such TG systems remain unclear, which limits our ability to understand the ultimate down-sizing and performance of this technology. Here we have harnessed a graphene-on-silica (GOS) stacked material as a model thermal-transport guide to enable thermal cloaking, as well as thermal concentration, of a CMOS-integrable, ultrathin, embedded structure, and which also demonstrates controllable and avant-garde thermal-switching operations. Utility of the simulational methodology outlined here could potentially lead to the design of superior TG systems in the future by identifying materials, for instance, that cool nanometer-scale regions for extended periods, or to much lower temperatures, and for the study of the effects of thermal guiding, for example, with chevron-like patterns.
8:00 PM - ES09.03.06
Temperature Dependences of Phosphorescence of Dy-Doped Y3Al5O12, Y2SiO5, Y2O3 and Al2O3 for Phosphor Thermometry
Eri Fujii 1 , Naohiro Ishiwada 1 , Takeshi Yokomori 1
1 , Keio University, Yokohama, Kanagawa, Japan
Show AbstractPhosphor thermometry has been paid attention as a novel alternative non-contact temperature measurement technique, because it has a potential for low-cost, simple and precise diagnostics. Most of applications of phosphor thermometry involve two type of measurements; the lifetime method and the intensity ratio method. The lifetime method is based on the decay time of phosphorescence intensity, which has strong dependence on the temperature. However, the drawback of this method is that the decay time is quite short, so highly time-resolved detection devices are desirable. By contrast, the intensity ratio method is based on the intensity ratio of two emission lines in the phosphorescence. This method has an advantage for application to two-dimensional measurements by using stereoscope imaging. However, most of the phosphors are affected by the strong thermal quenching that causes the emission intensity to vanish at relatively low temperatures, so that highly sensitive detection devices are needed.
Dysprosium is well-known dopant material for high temperature phosphor thermometry, because phosphorescence of Dy-doped phosphors survives at high temperature. However, it is still unclear that Dy-doped phosphors can be effectively applicable for which the lifetime method or the intensity ratio method. In this study, therefore, the characteristics of phosphorescence of Dy-doped phosphors were examined from the view point of temperature dependence of the lifetime and the intensity ratio. Y3Al5O12 (YAG), Y2SiO5 (YSO), Y2O3 and Al2O3 were selected as host materials in this study, since they are good candidates for Dy-doped phosphors.
The phosphor samples were made by putting phosphor powder on quartz fiber filters and it was settled in a tube furnace. Phosphors were excited by third harmonic Nd:YAG laser. Phosphorescence was measured by photomultiplier tube (PMT) for the detection of lifetime, and by spectrometer for the detection of intensity ratio of two emission lines. Phosphorescence was measured at every 50 K from room temperature to 1200 K during heating up the furnace. Temperature of phosphor sample was monitored by K-type thermocouple.
As a result, the lifetimes of all phosphors could be detected in the whole temperature range, and those of YSO:Dy, Al2O3:Dy and Y2O3:Dy showed good temperature dependence from 700 K, 1000 K, 800 K, while that of YAG:Dy did not change up to 1200 K, respectively.
In regard to the intensity ratio, they showed the temperature dependence in the relatively lower temperature range than that of lifetime. Even among them, the emission intensity of YAG:Dy was stronger and the intensity ratio was changed with the temperature more than the other phosphors. Hence, high temperature resolution was observed.
Consequently, in respect to these four phosphors, the lifetime method is appropriate only to high temperature, while the intensity ratio method is appropriate relatively low temperature especially about YAG:Dy.
8:00 PM - ES09.03.07
Laser Induced Rapid Decontamination of Aromatic Compound from Porous Soil Simulant
Wenjun Zheng 1 , Sichao Hou 1 , Ming Su 1
1 , Northeastern University, Boston, Massachusetts, United States
Show AbstractSoil contamination with organic compounds can lead to loss of farmable and habitable land, and cause long-term human and animal exposure to toxins. This paper reports a new laser based method for in situ soil decontamination at high efficiency, in which a focused excimer laser is used to remove organic contaminants from soil through burning by generating a local high temperature region. An aromatic compound, 1,1-dichloro-2,2-bis(4-chlorophenyl) ethylene (DDE) is used as an organic contaminant, and a porous silica plate is used as soil simulant. A heat transfer model is created to simulate the interaction between laser and organic compound. The lithographic mode of operation allows accurate quantitation of laser effects. The effects of power, speed, frequency and energy consumption on the efficiency of decontamination have been examined with high accuracy. The decomposition area increases with the increase of laser power, and the decreases of scan speed and frequency. Given the high energy conversion yield of high power laser, this method would be promising for large scale in situ soil decontamination.
8:00 PM - ES09.03.08
High Throughput Integrated Thermal Characterization with Non-Contact Optical Calorimetry
Sichao Hou 1 , Ruiqing Huo 1 , Ming Su 1
1 , Northeastern University, Boston, Massachusetts, United States
Show AbstractCommonly used thermal analysis tools such as calorimetry and thermal conductivity meter are separated instruments, and limited by low throughput, where only one sample is examined each time. This work reports an infrared based optical calorimetry with its theoretical foundation, which is able to provide an integrated solution to characterize thermal properties of materials with high throughput. By taking time domain temperature information of spatially distributed samples, this method allows a single device (infrared camera) to determine the thermal properties of both phase change systems (melting temperature and latent heat of fusion), and non-phase change systems (thermal conductivity and heat capacity). This method further allows these thermal properties of multiple samples to be determined rapidly, remotely and simultaneously. In this proof-of-concept experiment, the thermal properties of a pane of 16 samples including melting temperatures, latent heats of fusion, heat capacities and thermal conductivities have been determined in two minutes with high accuracy. Given the high thermal, spatial and temporal resolutions of advanced infrared camera, this method has the potential to revolutionize the thermal characterization of materials by providing an integrated solution with high throughput, high sensitivity and short analysis time.
8:00 PM - ES09.03.09
Thermal Properties of Disorderer LixMoS2—An Ab Initio Study
Teutë Bunjaku 1 , Mathieu Luisier 1
1 , ETH Zürich, Zürich Switzerland
Show AbstractMolybdenum disulfide (MoS2) is a semiconductor material, part of the transition metal dichalcogenide family. It consists of a layered structure with strong intra-layer covalent bonds and weak layer-to-layer Van der Waals forces. The large interlayer distance between the MoS2 planes offers an ideal configuration to intercalate Lithium (Li) ions, which induces significant changes to the electronic and thermal properties of this material and makes it appealing for nanoelectronics, optoelectronics, or thermoelectricity applications.
The thermal conductivity of lithiated bulk MoS2, LixMoS2 (0≤x≤1), was recently measured and it was shown that (i) it is anisotropic, (ii) the anisotropy between the in-plane κip and out-of-plane κop components strongly depends on the Li concentration, and (iii) the ratio rth=κip/κop reaches a maximum for Li0.34MoS2 [1]. Since it is not clear yet how the interplay between the intercalated Li ions and the MoS2 layers affects the thermal conductivity of this material and why this effect is more pronounced in the out-of-plane direction, we present here an ab initio study of the thermal properties of LixMoS2 to shed light on the origin of the observed anisotropy.
To do that, the dynamical matrix (DM) of the considered atomic systems is extracted from density-functional perturbation theory (DFPT) calculations, then loaded into a quantum transport simulator, and finally used to obtain the thermal current and the corresponding thermal conductance. The latter has been computed at five Li concentrations (x=0, 0.25, 0.5, 0.75, and 1 in LixMoS2). It has been found that with perfectly ordered Li ion distributions the thermal conductance ratio rth continuously decreases from 5.9 at x=0 down to 1.28 at x=1. This behavior does not coincide with the experimental results (minimum at x=0.34), but the source of the discrepancy between experiments and simulations could be traced back to the presence of disorder. In effect, the Li ions are not homogenously distributed between the MoS2 layers, but randomly. To add atomic disorder to the investigated structures we have developed a “scale up” technique. Since DFPT calculations of large crystals are computationally prohibitive, the DM of small structures can be first created and then coupled with each other to produce larger domains. By introducing disorder into the studied LixMoS2 systems, the thermal conductance anisotropy ratio drastically changed, the out-of-plane thermal conductance being more sensitive to disorder than the in-plane one. For a 25 nm long structure rth increases from 5.9 at x=0 to its maximum value of 29 at x=0.25, before decreasing to 1.28 at x=1. In other words, upon lithiation heat becomes almost five times more likely to travel in the in-plane direction than across different layers, thus suggesting that changing the Li concentration is an effective way of modulating the anisotropy of the bulk MoS2 thermal properties.
[1] G. Zhu et al., Nat. Commun. 7, 13211 (2016).
8:00 PM - ES09.03.10
Thermoresponsive Materials in Leather Making
Jaya Prakash Alla 1 , Nishad Nishter 1 , Raghava Jonnalagadda 1
1 , Central Leather Research Institute, Chennai India
Show Abstract
Stimulus is an ability to detect or react to internal or external environmental changes. Skin of a live animal can be termed as smart as it can respond to temperature, pressure and pain. After flaying, its ability to sense such stimuli is lost. In order to regain some of those smart functionalities, leather needs to be treated with stimuli responsive chemicals. Thermoresponse is one of the smart functionality which can be incorporated to leather. Leather can be made to respond to heat or cold by incorporating thermoresponsive syntans. Thermoresponsive syntans can be made by encapsulating phase changing materials (PCM) into condensate polymers. PCMs are long chain hydrocarbons that are non-toxic, inexpensive and easily available for making thermoresponsive syntans. PCMs take advantage of latent heat that can be stored or released from a material. It possesses the ability to change their state with a certain temperature range, which in turn slows down the raise in temperature by absorbing heat. Phase transitions of these materials depend on the number of carbon atoms presents in their backbone. The hydrophobicity of PCMs necessitates their encapsulation into polymeric substances as core material using condensate polymers. After application of the syntan, thermoresponsiveness of leather was analysed using infrared (IR) thermal imaging technique. We also report the synthesis and characterization of zinc oxide (ZnO) nano particles and their application on leather. ZnO nanoparticles were applied on to the leather surface to impart UV absorbing/blocking capability. The effectiveness of the treatment was assessed through IR thermal imaging camera. The dual effects of incorporating thermoresponsive syntan and nano particles were studied using fourier transformed infrared spectroscopy (FTIR), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and X-ray powder diffractometry (XRD) for understanding the nanoparticles composition, their shape, size and crystallinity. Physical strength properties of leathers were studied for understanding the strength parameters before and after application of syntan and nano ZnO material.
8:00 PM - ES09.03.11
Structural and Thermal Properties of Reaction Bonded SiC/Si Composite
Yuying Zhang 1 , Chun-yen Hsu 1 , Prashant Karandikar 1 2 , Steven Aubuchon 1 3 , Chaoying Ni 1
1 Material Science and Engineering, University of Delaware, Newark, Delaware, United States, 2 , M Cubed Technologies, Inc, Newark, Delaware, United States, 3 , TA Instruments, Newark, Delaware, United States
Show AbstractThe thermal conductivity of reaction bonded silicon carbide (RBSC) was measured as a function of SiC percentage and temperature from 25 °C to 1200 °C. The thermal conductivity increases as more SiC is incorporated in the SiC/Si composite and decreases as the temperature increases. The inclusion of Si significantly decreases the thermal conductivity and the composite thermal conductivity deviates from that predicated by the rule of mixture, suggesting considerable effects of multiphase and interface. An extensive structural characterization revealed newly formed SiC, residual Si and their growth specifics in the RBSC. As a result of high temperature growth kinetics, severe stacking faults and dislocations exist in the newly formed SiC. Interfacial features at SiC/Si and SiC/SiC were also evaluated and correlated to the thermal property of RBSC.
8:00 PM - ES09.03.12
Thermal Properties Improvement of Column Structures Formed by Ni Nanoparticles in Paraffin Wax
Che-Fu Su 1 , Junwei Su 1 , Hamed Esmaeilzadehkhosravieh 1 , Jirui Wang 1 , Edward Fratto 1 , Majid Charmchi 1 , Zhiyong Gu 1 , Hongwei Sun 1
1 , University of Massachusetts Lowell, Lowell, Massachusetts, United States
Show AbstractEnhancing the thermal conductivity of phase change material (PCM) is attracting attention for renewable energy applications such as solar, geothermal and wind energy. The use of energy storage can significantly improve the efficiency of renewable energy systems due to their intermittent nature. Latent heat thermal energy storage is a particularly attractive technique due to its high capacity and its ability to store energy at near constant temperature corresponding to the phase transition temperature of the PCM. Among the PCMs, paraffin has been widely investigated and used for latent heat thermal energy storage applications due to its high latent heat, chemical stability, less super-cooling, non-corrosive, and low vapor pressure. However, most of paraffin materials have an unacceptably low thermal conductivity (e.g. paraffin: ~0.25 W/m oC). This has severely limited the application of current PCMs for high power, transient and large scale systems and is one of the major challenges facing energy industries such as renewable energies and waste heat recovery.
The present work aims to overcome this undesirable property by embedding aligned metal fillers including nickel (Ni) nanoparticles and nanowires within the paraffin to significantly improve its thermal conductivity. The aligned filler structure in filler/paraffin composite was formed by exposing the fillers to a uniform magnetic field while the temperature of the composite was maintained above the melting temperature of paraffin and then cooling down the materials quickly. The formation of dipoles in Ni fillers and the induced moments interacting with each other leads to the formation of columns of particles/nanowires under the external magnetic field. It was found that the column structure formed depends on several parameters such as strength of magnetic field, material and geometry of particles, and viscosity of melted PCMs.
An in-house apparatus was developed to measure the thermal conductivity of the formed filler/paraffin composite. It consists of two copper plates with built-in channels to provide hot and cold thermal conditions, two polyimide heat flux sensors to measure the heat flow through the sample, two copper plates to ensure a uniform temperature across the two surfaces of the composite sample, and a polymer-polydimethylsiloxane (PDMS) chamber sandwiched by two plain glass slides for housing the composite.
It was shown that the formation of column structure and concentration of the filler materials have significant impact on the thermal conductivity of the paraffin composite. The relationship between thermal conductivity, magnetic processing parameters and filler column structures was presented in the end of the paper.
8:00 PM - ES09.03.13
Interface Thermal Resistance between Graphene and Cu Film
Jaeyoung Jeong 1 , Dongsik Kim 2 , Tae-Youl Choi 1
1 Mechanical Energy & Engineering, University of North Texas, Denton, Texas, United States, 2 , Postech, Pohang Korea (the Republic of)
Show AbstractGraphene has unique properties such as electrical, thermal, mechanical and optical properties. Among them, in-plane thermal conductivity of graphene, especially, has been reported as the highest value at room temperature. One of potential applications of graphene is thermal management of electronic devices because of such high thermal conductivity. Thermal conductance in graphene on a substrate, however, has shown to be impeded because of interacting with the substrate. In addition to in-plane thermal conductivity of supported graphene, out of plane thermal conductivity of graphene is limited by van der Waals interaction with substrates or adjacent graphene layers. Therefore, it is important to characterize not only in-plane thermal conductivity of suspended graphene but also thermal transfer in the cross-plane direction of graphene in terms of thermal management for electronic devices.
We have studied thermal transfer across interface between graphene and Cu film. Interfacial thermal resistance (ITR) has been estimated by both experiment and simulation. For experiments, the micropipette sensing technique was utilized to measure temperature profile of suspended graphene and supported graphene on Cu film which is subjected to continuous wave laser as a point source heating. Graphene has been transferred onto Cu films having 100 mm through holes and the temperature of suspended graphene has been measured by a micropipette sensor with a continuous wave laser heating. By measuring temperatures of suspended graphene, the intrinsic thermal conductivity of suspended graphene was deduced and it was used for estimating interfacial thermal resistance between graphene and Cu film. In addition, thermal conductance in supported same graphene on Cu were measured by the same technique. For simulation, a finite element method and a multiparameter-fitting technique were used for the best fitting the measured temperatures with simulated temperature profile in order to estimate interfacial thermal resistance. The simulated temperature profile was calculated by COMSOL Multiphysics with some parameters such as air gap between graphene and Cu film, laser power and in-plane and out of plane of thermal conductivities of graphene. The simulated temperature profile is compared to experiment by setting fitting parameters. For this multiparameter-fitting, the Powell’s method was used for obtaining the minimized temperature difference between the numerical and experimental temperature profiles and for best fitting those data. From based on the comparison, the interfacial thermal resistance between graphene and Cu film was estimated.
8:00 PM - ES09.03.14
Transient Hot Bridge Method (THB) for Measuring Thermal Conductivity Offers Several Advantages over Traditional Thermal Interface Material Testers (TIM) for Measuring Thermally Conductive Pads
Alexander Makitka 1
1 , Linseis Inc, Robbinsville, New Jersey, United States
Show AbstractThe Transient Hot Bridge method, which is used to measure the thermal transport properties of materials, is an enhancement of the Hot Wire or the Transient Hot Strip method (DIN EN 993-14, DIN EN 993-15). This transient, time depended measuring method was used to measure commercially available thermally conductive pads to benchmark the utility for using the THB approach for product development. Thermally conductive pads are used in the electronics industry as an interface for transferring heat from a hot body to a heat sink. They are optimized to have high thermal conductivity and yet have compliant mechanical properties to conform to non-flat surfaces.
8:00 PM - ES09.03.17
Role of Boundary, Defects and Doping on Phonon Transport Properties of Monolayer MoSe2
Zhequan Yan 1 , Mina Yoon 2 , Satish Kumar 1
1 , Georgia Institute of Technology, Atlanta, Georgia, United States, 2 Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractMoSe2 as one of the promising two-dimensional transition metal dichalcogenides (TMDCs) recently emerged as a promising alternative of graphene for nano-electronic and opto-electronic devices due to its unique transport properties. The inefficient heat removal due to the low thermal conductivity of monolayer MoSe2 can cause critical challenges for its devices, e.g., it can significantly affect the performance and reliability of these devices. Due to the imperfection of growth processes, the crystal lattice of the monolayer MoSe2 contains high density of unintentional localized defects such as vacancies, dislocations and grain boundaries. It is crucial to understand the influence of defects on phonon transport and thermal properties. Although such understanding has been comprehensively demonstrated for graphene, it remains notably elusive for the 2-D TMDs such as MoSe2. Isoelectronic doping has been shown to be an effective strategy to suppress the defect concentration. However, the mechanism of how doping process influences the thermal properties of TMDs is still not clear. To better understand the influence of boundary, defects and doping process on the phonon transport mechanism, we perform first-principles density functional theory (DFT) along with Boltzmann Transport Equations (BTE) to predict the phonon transport properties of monolayer MoSe2. The model to consider the effects of sample size, defects and Tungsten (W) doping in monolayer MoSe2 is developed. This model is built to elucidate the phonon scattering by the missing atom mass and the change of force constants between the under-coordinated atoms near the vacancies. Our results show the impact of phonon scatterings on the thermal conductivity of monolayer MoSe2 caused by the boundary, anharmonicity, Se vacancies and W doping process. Results indicate that phonon boundary scattering becomes dominant in the phonon transport process at the low temperature. The presence of 1%, 2% and 4% Se vacancies decrease the thermal conductivity of monolayer MoSe2 by 11.2%, 23.4% and 46.2% at room temperature. The W doping doesn’t have a significant influence on the thermal conductivity of pristine monolayer MoSe2. However, it amplifies the influence of defects on the thermal conductivity of monolayer MoSe2, which results in 27.0%, 51.0%, and 72.2% decrease corresponding to 1%, 2% and 4% Se vacancies. The results from this work will help in understanding the mechanism of phonon transport in 2-D materials, provide insights for the future design of MoSe2-based electronic devices, and facilitate the implementation of 2-D TMDs in these devices.
8:00 PM - ES09.03.18
Thermal Insulation by Impedance Mismatch Powder Compacts
Miriana Vadala 1 , Kevin Voges 1 , Doru Lupascu 1
1 , Univ of Duisburg-Essen, Essen Germany
Show AbstractThe concept of phonon mismatch has recently attracted much attention in the context of thermal barriers in computer chip technology where the excess of heat destroys the chips and a good impedance match is crucial. In this paper we outline a first step in the concept of using a material that contains solid components of significantly different acoustic impedance with the ultimate goal of achieving a dense material with very low thermal transport. The first step to test this concept is a powder compact of two or three materials each exhibiting largely different acoustic properties. Every interface between grains of differing neighbors will yield a large barrier to heat transport. Coal, alumina and silica are chosen as abundant cheap materials with a long term perspective in building materials. Far from being optimized from the synthesis point of view, already micron size compounds yield good thermal insulation. Thermal conductivity, scanning electron microscopy, and porosity measurements are shown and commented for the underlying physical mechanisms. Perspectives for nanosystems are delineated.
8:00 PM - ES09.03.19
Investigation into Boron Nitride Nanoparticle Effects on Thermal Properties of CaCl2.6H2O as a Phase Change Material
Nastaran Barhemmati Rajab 1 , Weihuan Zhao 1
1 , University of North Texas, Denton, Texas, United States
Show AbstractTThis paper presents thermal properties enhancement of Calcium Chloride Hexahydrate as a phase change material (PCM) by adding Boron Nitride (BN) nanoparticles leading to efficient thermal management. Boron Nitride has extremely high thermal conductivity with the value up to around 200 W/m·K. Therefore, the thermal conductivity of PCM could be remarkably enhanced by adding BN nanoparticles to improve the heat transfer performance. In this study, 0.5wt% of boron nitride nanoparticles were dispersed in the molten PCM by the sonication probe. The thermal conductivity of the BN nanoparticle dispersed CaCl2·6H2O has been characterized by the Thermocouple-laser shining method for analyzing the thermal conductivity enhancement due to adding BN nanoparticles. Moreover, the latent heat of fusion and specific heat of nano-PCM have also been investigated by the Differential Scanning Calorimetry (DSC). Depending on the thermal properties enhancement of this novel Nano-PCM, it can apply to vehicles in cold areas, thermal interface materials for efficient heat conduction, thermal managements in spacecraft for planetary missions, etc.
8:00 PM - ES09.03.20
Phonon Interface Interactions—Thermal Energy Distribution and Wave Effects in Superlattices
Kartik Kothari 1 , Martin Maldovan 1
1 , Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractUnderstanding interface scattering and thermal phonon wave effects in nanostructures such as superlattices is key in manipulating their thermal transport properties, which has applications in thermoelectrics and optoelectronics. A meticulous comprehension of phonon interface scattering mechanisms necessitates the analysis of surface conditions while incorporating different physical properties and dispersion relations of constituents across an interface. In this talk, we employ an extension of the electromagnetic wave scattering theory for rough surfaces developed by P.Beckmann and A.Spizzichino to account for thermal phonon interface scattering and predict thermal transport properties in superlattices. This is supplemented with the Fuchs-Sondheimer theory to formulate in-plane thermal transport in layered nanostructures. A rigorous analysis involving complete dispersion relations, refraction conditions, and shadowing effects is presented. We model thermal conductivity calculations for superlattices, bi-layers and sandwich-layered structures of a number of constituent materials including Si-Ge, SixGe1-x/SiyGe1-y and III-V semiconductors. For apprehension of thermal phonon wave effects, a detailed analysis of the heat spectrum is presented which allows to predict the amount of heat carried by phonons of different frequencies and mean free paths. We also present a microscopic analysis of thermal conduction including determination of phonon trajectories, examination of various surface interaction mechanisms, quantification of thermal transport across layers, and estimation of thermal flux in superlattices. The presented accurate description of phonon surface scattering and novel insights through the heat spectrum and microscopic analysis of thermal transport allow prediction of regimes for observation of wave effects in thermal transport. This would enable rational design of nano-engineered materials and devices with improved thermoelectric and optoelectronic properties.
8:00 PM - ES09.03.22
First-Principles Determination of Interconnect Thermal Resistance in Emerging Semiconductor Technologies
Oscar Restrepo 1 , Dhruv Singh 1 , Eduardo Silva 1 , Murali Kota 1
1 , GLOBALFOUNDRIES, Malta, New York, United States
Show AbstractAs the aggressive scaling of semiconductor devices continues beyond the 14nm technology, self-heating has become a critical reliability concern. Since thermal measurements at operating conditions are expensive and laborious at the device scale, modeling estimates for the thermal properties of metal/via interconnects are necessary for thermal management. A typical Back-End-Of-Line (BEOL) metal/via interconnect structure consists of a diffusion barrier (TaN) and binder (Co, Ru) thin films, both located between the Cu lines and vias. These barrier layers often dominate the overall interconnect electrical/thermal resistance and performance characteristics. In this work, we compute ab initio Lorenz number using Landauer-Buttiker transmission for a host of material system candidates for via-metal interfaces and metal-liner interfaces. This establishes a direct relation between the thermal resistance and the more accessible electrical resistance of the devices. The simulation results for all the candidate material interfaces show that the Lorenz number lies within <10% of the theoretical value. These are also in direct agreement with the experimentally measured electrical resistance. Consequently, the liners can lower the thermal conductivity by an order of magnitude compared to typical metal-via interfaces, which is the common working assumption. This methodology allows the use of well characterized electrical data in the modeling and optimization of interconnect thermal properties, which is critical to the reliability and performance of nanoscale semiconductor devices.
8:00 PM - ES09.03.23
Thermal Conductivity of SiC Thin Films*
Nitish Baradwaj 1 , Rajiv Kalia 1 , Aiichiro Nakano 1 , Priya Vashishta 1
1 , University of Southern California, Los Angeles, California, United States
Show AbstractNon-equilibrium molecular dynamics (NEMD) simulations are carried out to study thermal conductivity of SiC thin films as a function of film thickness over a wide range of temperatures between 300 and 1100 K. Film thickness is varied from three unit cells (1.308 nm) to 16 unit cells (20.2nm). We find that the thermal conductivity increases linearly with the film thickness, reaching a plateau when the film thickness is about 20 nm. To a lesser extent, the length of SiC sample has the same effect on thermal conductivity as the film thickness. Temperature has a negligible effect on thermal conductivity of SiC in the range studied.
*This work was supported as part of the Computational Materials Sciences Program funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, under Award Number DE-SC00014607.
8:00 PM - ES09.03.24
Design Principles of Thermal Metamaterials for Manipulating Local Heat Flux from Point Heat Sources
Kyung Beom Seo 1 , Sunggu Kang 1 , Howon Lee 2 , Wonjoon Choi 1
1 , Korea University, Seoul Korea (the Republic of), 2 , Rutgers, The State University of New Jersey, New brunswick, New Jersey, United States
Show AbstractThermal metamaterials are artificial materials with unusual thermal properties that do not exist in nature. Previous works in this field have explored various methods to control heat flux through thermal metamaterials, against temperature gradients between hot and cold sides. However, those functions have been limited in specific thermal energy distribution, whereas more practical problems significantly occur in local thermal energy generation in narrow space, such as wearable, portable, thin-film type devices. In this study, we present a new type of thermal metamaterials, which is a specially designed for local heat flux controls, induced by point heat sources. The assembly of thermal shifters, that could change the inclined angle of heat flux were arranged near the neighboring point heat sources, and allowed to manipulate thermal dissipation or insulation around the heat sources. Thermal simulation confirmed the design concept, and the assembly of the fabricated thermal shifters, composed of copper and PDMS performed the local controls of thermal energy distribution as thermal shield, concentrator, diffuser and rotator. In order to derive design rules, theoretical analysis and mathematical modeling were conducted to extract the optimized combination of the layered materials having different thermal conductivities, in terms of the local thermal energy confinement, originated from point heat sources. This unique design concept of thermal metastructures would contribute to the advanced thermal management of point heat sources in narrow spaces, such as electronic devices, displays, and smartphones.
8:00 PM - ES09.03.25
Analysis of High Thermal Conductivity Mechanism of 2,7-Naphthalene Benzoate Twin Mesogen Epoxy Polymer That Have Alkyl Chain Length 4
Kei Nakahira 1 , Tadatomo Kawai 1 , Yuzo Itoh 1
1 , Kogakuin University, Hachioji Japan
Show AbstractRecently, electrical machineries and apparatuses have become smaller and higher quality, and heat generated inside machineries causes overheating and various malfunctions of these. Thus it is a severe problem how the heat is radiated and cooled. As insulating materials, epoxy polymer is typically used in these kind of devices, but the thermal conductivity of the epoxy polymer is small (around 0.2 Wm-1K-1), 1 to 3 orders smaller than those of metal or ceramics in general. The addition of filler increases the thermal conductivity of epoxy polymer, but the viscosity also increases at the same time.
Therefore, the high thermal conductivity of the epoxy polymer itself is required.
The liquid crystalline epoxy polymers which include twin mesogens, the twin-mesogen epoxy polymer has shown recently to have a relatively large thermal conductivity, five times larger than those of conventional epoxy polymers and such a larger thermal conductivity of the liquid crystalline epoxy polymer has been explained qualitatively to come from its higher orderliness of liquid crystalline structure. The twin-mesogen epoxy polymers have two characteristic structures, the containing two rigid mesogens in the molecules and two mesogens are connected flexible alkyl chain. These features cause
higher-order structure and high thermal conductivities.
In this work, we synthesized twin-mesogen epoxy polymer in which there are two 2,7-naphthalene benzoate as mesogen connected by four carbons alkyl chain and investigated the effects of high-order structure changes due to the differences of alkyl chain length and mesogen group on thermal conductivities.
8:00 PM - ES09.03.26
Tunable-Responsive Thermal Metamaterials for Programmable Manipulation of Heat Dissipation and Insulation
Sunggu Kang 1 , Kyung Beom Seo 1 , Sejun Kim 1 , Howon Lee 2 , Wonjoon Choi 1
1 , Korea University, Seoul Korea (the Republic of), 2 , Rutgers, The State University of New Jersey, Newark, New Jersey, United States
Show AbstractThermal metamaterials in macroscale can act as artificial structures for local heat flux controls. For examples, they can shield or focus thermal energy in the target spot, which is surrounded by the hybrid materials, which have different thermal conductivities. However, the functions of conventional thermal metamaterials have been passive, regardless of the dynamic changes of environmental conditions, such as temperature, pressure, humidity and illumination. Herein, we present tunable thermal metamaterials for programmable manipulation of heat dissipation and insulation, according to the dynamic changes of operating temperature. The ideal structures of temperature-responsive thermal metamaterials for thermal shield at the specific spot were extracted by transformation thermodynamics, and the basic design was reconstructed by the assembly of thermal shifters, which were the simplest units for controlling the inclined angle of heat flux. In order to realize the responsive function depending on the operating temperature, thermally responsive phase change polymer from solid to liquid was embedded between copper structures, and the dramatic change of thermal conductivity of the polymer at the critical temperature of phase change enabled on/off of thermal shielding function for the targeted local spot. FEM simulation and real-time temperature measurement based on IR camera confirmed the overall performances of the developed thermal metamaterials with tunable-responsive function.
8:00 PM - ES09.03.27
Analysis of High Thermal Conductivity Mechanism of the Phenyl Benzoate Twin-Mesogen Epoxy Polymers with Alkyl Chain Length of Odd Number
Yuta Abe 1 , Tadatomo Kawai 1 , Yuzo Itoh 1
1 , Kogakuin University, Tokyo Japan
Show AbstractRecently, the electrical and electronic devices have become downsizing and high performance in the electrical equipment field. The heat increase to be generated by this progress has become to be a severe problem. The thermosetting polymers are used for the insulating material of these apparatuses, but the thermal conductivity of the thermosetting polymer is remarkably lower than the different kind of materials such as metal, ceramics and it is a big problem that the thermal conductivities of the thermosetting polymers are very low. It has been used to solve this problem that the inorganic filler of which thermal conductivities are relatively high, are added to the matrix conventional polymers of which thermal conductivities are very small. However other physical properties such as viscosity of the polymers become very bad when much inorganic filler are added to the matrix polymers in order to achieve high thermal conductivity required by the apparatus. Thus, it leads to further downsizing, and technological advance if we can make the thermal conductivity of thermosetting polymer itself high.
It was revealed that the twin-mesogen type epoxy polymers in which there are the liquid crystalline structures that could form higher order structures was effective for the improvement of the thermal conductivity. We investigated that the phenyl benzoate twin-mesogen epoxy polymers of which alkyl chain length connecting two mesogens were even numbers and found that they showed five times larger thermal conductivity than a conventional epoxy polymers.
In this work, we synthesized and analyzed the phenyl benzoate twin-mesogen epoxy polymers of which alkyl chain length connecting two mesogens were odd numbers. We considered the even-odd effect of the alkyl chain length on the thermal conductivities of the polymers, comparing those of the even and the odd twin-mesogen epoxy polymers.
8:00 PM - ES09.03.28
A MEMS Based Approach for Fabricating Conformal Nanogap Electrodes for Thermotunneling Energy Harvesting Applications
Amit Banerjee 1 , Yasuaki Mori 1 , Yoshikazu Hirai 1 , Toshiyuki Tsuchiya 1 , Osamu Tabata 1
1 , Kyoto University, Kyoto Japan
Show AbstractDeveloping efficient methods for clean energy harvesting is necessary to avert an imminent energy and environmental crisis. Thermotunneling process, exploiting quantum mechanical phenomena in nanoscale materials, is a promising futuristic method for direct conversion of wasteful heat energy to its easily consumable electrical form. A temperature bias (analogous to a voltage bias) across a nano-meter size gap is capable of inducing a tunneling current across the nanogap, resulting in the desired conversion process [1]. In spite of theoretical understanding and experimental evidences providing proof-of-principle, actual engineering applications producing significant bulk-scale effect through this process are yet not realized.
Primary obstacle in the implementation of thermotunneling energy harvesting methods lies in the difficulty of fabricating large electrode areas with uniform nanogap (~ 10 nm) size (conformal electrodes), in order to simultaneously induce tunneling processes across a large area (~ 10 µm2), necessary for achieving bulk-scale effect. Electroplating method, and precision mechanical alignment methods for achieving conformal electrode pairs were adopted in the past without an effective outcome due to thermal / thermo-mechanical instabilities.
We approach this problem by adopting a MEMS based technique [2]: an overhanging Si microbeam (~ 5 µm x 5 µm) is controllably fractured (by an integrated thermal actuator) along <111> crystalline direction, producing flat and smooth fracture surfaces that complements at corresponding points and acts as emission electrodes with a nano size (< 100 nm) controllable gap between them. Judicially placed mechanical springs on the device ensures that desired orientation of the electrodes is maintained. Beginning with a Silicon-on-insulator (SOI) wafer, silicon microfabrication techniques, such as photolithography, deep reaction ion etching, and sacrificial layer etching are sequentially employed for fabricating the proposed device, and nanogaps of controllable sizes are successfully achieved by the aforementioned process. Transport properties of the nanogaps demonstrates direct tunneling and Fowler-Nordheim type emission, indicating that they are suitable for quantum mechanical emission based applications [2]. The field enhancement factor is estimated to be low (~ 10) indicating the fracture surfaces are relatively smooth. To establish a sustainable temperature bias for uninterrupted conversion, studies pertaining to near-field effect in radiative transfer across the nanogaps are also important, and therefore, undertaken.
In summary, fracture fabricated nanogap electrodes are expected to emerge as a template for futuristic clean energy harvesting processes. Simple design, well-established industrial scale fabrication method, and ease of on chip integration are additional advantages.
[1] G. Despesse et al., J. Appl. Phys. 96, 5026 (2004).
[2] A. Banerjee et al., Jpn. J. Appl. Phys. 56, 06GF06 (2017).
8:00 PM - ES09.03.29
A Highly Stable Transparent Heater Using Ni/Ag Hybrid Microgrid Electrode
Jeonghwan Park 1 , Kangmin Lee 1 , Kwanyong Seo 1
1 , UNIST, Ulsan Korea (the Republic of)
Show AbstractWe report a new strategy to fabricate a highly stable transparent heater using a Ni/Ag hybrid microgrid electrode. The microgrid-based transparent heater has a uniform heat distribution due to its electrical uniformity on an entire surface. The proposed Ni/Ag hybrid transparent heater shows outstanding optoelectronic performance (sheet resistance of 4.7 Ω/sq at transmittance of 96%). This is because the microgrid electrode not only occupies only 4% of the entire area but also has no electrical junction which may have a significant resistance. In addition, the transparent heater presents fast heating rate even at a low DC voltage by using silver (Ag) which has high thermal conductivity. Thus, our Ni/Ag hybrid transparent heater leads to high saturation temperature (up to 120 oC) at low DC voltage (5 V) compared to conventional transparent heater (ITO: 60 oC at 5V). Furthermore, nickel (Ni) layer, a corrosion-resistant material, is coated on the Ag microgrid electrode via electroplating to improve a thermal/chemical stability. As a consequence, the proposed transparent heater exhibits no degradation of sheet resistance even under harsh environments such as a high temperature of 300 oC and sulfur atmosphere, confirming a effective passivation effect against thermal oxidation and sulfurization. Therefore, the use of our designed Ni/Ag microgrid electrode presents a unique opportunity to develop a high-performance transparent heater with superior long-term stability as well as a high saturation temperature at low input voltages.
8:00 PM - ES09.03.30
The Impact of Electron-Phonon Interaction on the Lattice Thermal Conductivity in SiC
Tianshi Wang 1 , Zhigang Gui 1 , Prashant Karandikar 1 2 , Anderson Janotti 1 , Chaoying Ni 1
1 Department of Materials Science and Engineering, University of Delaware, Newark, Delaware, United States, 2 , M-Cubed Technologies, inc, Newark, Delaware, United States
Show AbstractSilicon carbide is a promising semiconductor material for applications where carrier concentration and heat conductivity are fundamental parameters in the device design. Despite the great interest, fundamental properties, such as the variation of thermal conductivity with carrier concentration, are yet to be explored. Based on density functional theory calculations, we study how the lattice thermal conductivity varies with charge carrier concentration in 3C-SiC. Here we discuss the effects of having electrons in the conduction band or holes in the valence band on the phonon transport. We find that the electron-phonon interaction strongly affects the thermal conductivity, specially in highly doped materials. For instance, in the limit of high carrier concentration of 1021 cm-3, the thermal conductivity drops by 57% for hole and 32% for electron doping. The effect is stronger for hole doped than electron doped materials, which we explain based on the features of the electronic band structure near the band edges.Our results and analysis provide an in-depth understanding of phonon transport for the design of novel SiC-based electronics.
8:00 PM - ES09.03.31
Thermal Conductivity of Ethylene Glycol Based Pure and Doped ZnO Nanofluids
Monisha Michael 1 , Aparna Zagabathuni 1 , Shyamal Kumar Pabi 1 , Sudipto Ghosh 1
1 , Indian Institute Of Technology Kharagpur, Kharapur India
Show AbstractThe thermal conductivity of metallic/intermetallic nanofluids measured and reported by different investigators are high compared to ceramic/semiconductor dispersed nanofluids. Mostly the nanofluid application involves the contact of nanofluids with metallic surfaces which are unfavourable as the charge developed on the metallic surfaces results in lower thermal conductivity. Keeping this in view ethylene glycol-based ZnO nanofluid has been chosen for the present work. The thermal conductivity of ZnO nanofluids not being as high as compared to metallic nanofluids, an attempt has been made to improve its thermal conductivity by doping ZnO nanoparticle with Tin (Sn) and Nitrogen (N). Pure and doped ZnO nanoparticles were characterized by X-ray diffraction analysis, field emission scanning electron microscopy and UV-Vis spectroscopic analysis. Doping of ZnO nanoparticles with Sn and N did not change its crystallinity. Programmed ultrasonication has been carried out for the preparation of the ethylene glycol based pure and doped ZnO nanofluids. In analysis, Nitrogen doped ZnO based nanofluid showed more better enhancement in thermal conductivity as compared to tin doped and pure ZnO based Ethylene glycol nanofluids for the same volume concentration. The thermal conductivity of pure and doped ethylene glycol based ZnO nanofluid showed an increment with increase in temperature(from room temperature to 70°C) which is in agreement with the literature.
8:00 PM - ES09.03.33
Magneto-Thermal Transport Behavior in Ferromagnetic and Semiconductor Thin Films
Paul Lou 1 , Sandeep Kumar 1
1 , University of California, Riverside, Riverside, California, United States
Show AbstractIn this work, we present an experimental study on magneto-thermal transport behavior in ferromagnetic and semiconductor materials. The measurements are carried out using in-plane self-heating three-omega method. The in-plane three-omega measurement requires a freestanding specimen. We address this challenge using micro-electro-mechanical systems (MEMS) fabrication methods. The measurements are carried out on Co/Pd multilayer thin films (perpendicular magnetic anisotropy), CoFeB/MgO multilayer (magnetic tunnel junctions) and silicon. The thermal transport measurements on these thin films are essential for the design and development of energy efficient spintronics devices.
8:00 PM - ES09.03.34
High-Capacity Thermal Energy Storage Materials—Identification by Computational Screening and Machine Learning Analysis
Steven Kiyabu 1 , Jeffrey Lowe 1 , Alauddin Ahmed 1 , Donald Siegel 1
1 , University of Michigan, Ann Arbor, Michigan, United States
Show AbstractHydration/dehydration reactions are promising methods for the storage of thermal energy due to their simplicity, cost effectiveness, and potential for reversible operation at moderate temperatures. The goal of this work is to identify thermal energy storage (TES) materials that can out-perform known compounds. High-throughput Density Functional Theory calculations were performed on essentially all plausible metal halide hydrates and metal hydroxides from the Inorganic Crystal Structure Database. In total, 265 hydration reactions were characterized with respect to their gravimetric and volumetric energy densities, and their operating temperature range. Promising reactions were identified for applications that fall in three temperature ranges: low (< 100°C), medium (100°C - 300°C), and high (> 300°C). Energy density trends amongst the salt hydrates and metal hydroxides are discussed. Additionally, machine learning techniques such as Principal Component Analysis and Decision Tree learning were used to explore correlations between fundamental material properties and thermal storage. Our study suggests new materials for TES, and identifies pathways for additional performance optimization.
8:00 PM - ES09.03.35
Charged Thermal Energy Storage Systems as a Segue from Fossil Fuel to Renewable Energy Dependent Power Plants
Laureen Meroueh 1 , Gang Chen 1
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractUnlike most other commodities, electricity produced at any given time must match the electricity being consumed or the stability of the electric grid is jeopardized. Electricity demand changes throughout the day resulting in required generation ramp-ups that strain power plants, reducing cycle efficiency and increasing CO2 emissions. This problem is exacerbated when renewable sources such as wind and solar are integrated into the grid, due to their intermittency. A change in methods of energy production globally that allows synergistic coupling of renewable and fossil fuels is needed. We present an electrically charged, large-scale energy storage system based on high temperature, high thermal conductivity phase change materials, that can couple to fossil fuel or nuclear power plants, as well as renewable energy based power plants. Although storing electricity as heat and back to electricity is thermodynamically unfavorable, we present an analysis to show that this approach can be cost competitive and provides a segue from fossil fuels to renewable energy. We discuss the design parameters and various applications the system is suitable for, and main challenges present in using high temperature phase change materials. By pacifying demands posed by both the economy and the environment with the outlined system, progress can be made in the combat against climate change.
8:00 PM - ES09.03.36
Influence of Periodicity and Interfacial Mixing on Thermal Conductivity of Reactive Metal Multilayers
Christopher Saltonstall 1 , Michael Abere 1 , David Adams 1 , Thomas Beechem 1
1 , Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractReactive metal multilayer thin films have attracted much attention for use in joining, power and ignition applications. In such applications, an external source heats a small part of the film to initiate a reaction where the two materials composing the multilayer exothermally intermix creating a self-propagating reaction until the multilayer has been fully mixed. In order to design these multilayers for a specific application, a fundamental understanding of the reaction process must be had which ultimately hinges on the propagation of thermal energy through the film. However, unlike their non-metal counterparts, thermal transport in metal multilayers and at metal interfaces has been relatively unexplored. In response, this work investigates the effects of period thickness and interfacial mixing on cross-plane thermal transport in Al/Pt and Al/Ni multilayers using time domain thermal reflectance. We find that the thickness and crystallinity of interfacial mixing strongly controls interface thermal resistance which ultimately determines if thermal transport in the films is dominated by interfaces or material layers.
8:00 PM - ES09.03.37
Anharmonic Stabilization and Renormalized Lattice Dynamics in Rutile VO2
Yi Xia 1 , Maria Chan 1
1 , Argonne National Laboratory, Lemont, Illinois, United States
Show AbstractVanadium dioxide (VO2), which undergoes a first-order metal-insulator transition (MIT) near room temperature, exhibits rich physics with coupled structural and electronic properties. Recent studies [Nature 515, 535-539 (2014) and Science 355, 371-374 (2017)] combing X-ray scattering measurements and ab initio molecular dynamics reveal that the vibrational entropy change induced by strong anharmonicity is the main driving force for MIT, and the estimated small variation of lattice thermal conductivity across the transition point suggests a breakdown of the Wiedemann-Franz law. However, a full first-principles understanding of the temperature-dependent effective phonon spectra including finite phonon lifetime induced by anharmonic scattering is still missing, mainly due to the inability to treat metallic rutile VO2 because of its metastability (imaginary phonon frequency) shown in regular phonon calculations.
In this talk, we will demonstrate our recently implemented phonon renormalization scheme based on self-consistent phonon theory on top of compressive sensing lattice dynamics (CSLD) to take into account temperature effect. After validation of the methodology against a strongly anharmonic perovskite compound (SrTiO3), we applied it to model both harmonic and anharmonic vibrational properties of rutile VO2. We performed comprehensive comparison and analysis between our computed and inelastic X-ray scattering measured phonon dispersions, further confirming the softening of low-lying transverse acoustic phonon modes in rutile VO2. Vibrational entropy change across transition point was calculated to identify the driving force for MIT in a quantitative way. We also computed lattice thermal conductivity of rutile VO2 considering three-phonon interactions and compared to the value estimated by Lee et al. [Science 355, 371-374 (2017)] through detailed analysis of mode-dependent lifetime and mean free path.
8:00 PM - ES09.03.38
Electrical and Thermal Transport in Doped Barium Plumbate
Andreza Eufrasio 2 1 , Ian Pegg 2 1 , Biprodas Dutta 2 1
2 Physics, The Catholic University of America, Washington, District of Columbia, United States, 1 , Vitreous State Laboratory, Washington, District of Columbia, United States
Show AbstractThermoelectric (TE) power is generated by utilizing a temperature differential created across a material. Such energy conversion takes place without the incorporation of any moving part and can often lead to substantial recovery of waste heat into useful electrical energy. Lately, ceramic oxides have gained attention as a new class of TE materials because of their high stability at elevated temperatures, where higher conversion efficiencies are expected. The present investigation uses lead plumbate (BaPbO3) as the starting material, the TE properties of which have been altered by reasonable cation substitutions. As BaPbO3 has high electrical conductivity, σ ~ 2.43x105 Ω-1m-1 at room temperature, its thermopower, S, is relatively low 23μV/K, as expected. With a thermal conductivity, k, of ~ 3.00 W/m.K, the figure of merit (ZT=S2σTk-1) of BaPbO3 is only ~ 0.01 at T = 300 K. Barium plumbate (BaPbO3) is a prospective TE material because it exhibits high electrical conductivity like metals. However, unlike metals, it exhibits remarkably low thermal conductivity, which renders it attractive for its TE qualities. Moreover, the open perovskite structure of BaPbO3 allows it to accommodate a large variety of dopants in relatively large concentrations. The principal objective of this work is to study the variation of TE properties of BaPbO3 as Ba ions are systematically substituted by other cations.
8:00 PM - ES09.03.39
Temperature-Dependent Thermal Transport in Oriented Crystalline Polyethylene Nanofiber
Ramesh Shrestha 1 , Maarten De Boer 1 , Sheng Shen 1
1 , Carnegie Mellon University, Pittsburgh, Pennsylvania, United States
Show AbstractOriented crystalline polyethylene nanofiber (c-PE) is of strong interest for multifunctional material because of its ultra-high thermal conductivity and strength. However, the temperature dependence of thermal transport in such ultra-drawn nanofibers, which is critical for not only elucidating the phonon transport but also developing their applications in a broad temperature range, remains unknown. Here we investigate temperature dependent thermal transport in c-PE from 20 K to 470 K. The c-PE is fabricated by locally drawing a PE microfiber heated near its melting point using a micro heater. Structural and morphological characterization using micro Raman and cryogenic TEM suggests these nanofibers are crystalline with an orthorhombic unit cell. The high strain rate fabrication method, however, leads to the presence of {310} twinning and some monoclinic component. Unlike dielectric crystals, at low temperature thermal conductivity of c-PE nanofibers increases as ~T1. Molecular dynamics simulations suggest this is due to one-dimensional phonon transport. In measurements, we find the trend is ~T1.2, which we attribute to a certain degree of local misorientation. The thermal conductivity reaches a maximum of ~90 W/mK at 130 K. At higher temperature, the thermal conductivity decreases as 1/T due to Umklapp scattering. Above 380 K, the thermal conductivity decreases at a higher rate than predicted by Umklapp scattering. We attribute this to the addition of morphology-induced phonon scattering due to segmental rotation (CH2 units) along the chain. At 440 K, c-PE undergoes an abrupt volume change. Consequently, the thermal conductivity decreases sharply by a factor of 5. This phase change is reversible upon thermal cycling and indicates that this is not a melting transition even though the temperature is higher than reported melting temperature of gel spun PE fibers in the literature (430 K). The results of this work provide insight into phonon physics of oriented crystalline polymers and point to potential application of c-PE as a heat transfer material.
8:00 PM - ES09.03.40
Doping Effect on the Thermal Conductivity of Metal-Oxide Nanofluids: Insight and Mechanistic Investigation
Anjani Nagvenkar 1 , Ilana Perelshtein 1 , Aharon Gedanken 1
1 , Bar-Ilan University, Ramat-Gan Israel
Show AbstractNanofluids which are dispersions of nanoparticles are known to exhibit anomalous heat transfer properties compared to conventional base fluids. Although many mechanisms such as Brownian motion, ballistic transport, conduction theory are attributed to this enhancement, their individual role varies with the volume fraction of the nanoparticle. The combined effect of the proposed models resulting in the enhancement in heat transfer at the two different range of concentrations is herein demonstrated. In the current study Zn2+ doping in the CuO lattice is achieved and the role of this doping on the overall thermal conductivity of the nanofluid due to the changes in the lattice of the nanoparticle is reported. The specific heat capacity (Cp) of the synthesized nanomaterials were taken into account to briefly explain the phenomenon. Interfacial resistance (Kapitza resistance) is a crucial parameter which influences the thermal flow between the particle and the liquid molecules wrapping over the particle surface (nanolayer). The nanolayer which is a thermal bridge between the nanoparticle and the base liquid plays a crucial role in enhancing the thermal conductivity. The Cp of the nanoparticle thus determines the Kapitza resistance by governing the temperature gradient in the nanolayer. In addition the effect of particle size and aggregation on the conduction mechanism of the thermal conductivity is also taken into account along with the Kapitza resistance being a primary factor for the conductive transport. A new model explicating the enhancement in the thermal transport is simulated conceiving all the parameters discussed in the study.
8:00 PM - ES09.03.41
Thermal Conductivity of Cobalt Ferrofluids—A Detailed Insight
Anjani Nagvenkar 1 , Aharon Gedanken 1
1 , Bar-Ilan University, Ramat-Gan Israel
Show AbstractFerrofluids are colloidal suspensions of magnetic nanoparticles in the non-magnetic fluid. Owing to the high stability of the ferrofluids, they are potential heat transfer fluids for practical application. The current work reports the surfactant-assisted synthesis of cobalt ferrofluid imparting it a minimum stability of 2 months. The synthesized ferrofluid undergoes self-organisation over a period of time resulting in increase in particle size from 10 nm to 1 uM. This phenomenon experimentally supported the proposed effect of particle size on the thermal conductivity. The loss of magnetization by the aged colloid is observed which is attributed to the increase of the magnetic shape anisotropy of the elongated particles. The study presented here demonstrates the effect of magnetization, viscosity, temperature and volume fraction of the nanoparticles on the thermal properties of the cobalt ferrofluid. In addition the electrical properties are also examined. Heat transfer of these material was investigated under stationary conditions, and the thermal properties are quantitated.
8:00 PM - ES09.03.42
Understanding and Accelerated Prediction of Thermal Properties through Machine Learning
Vahid Rashidi 1 , John Kieffer 2 , Kevin Pipe 1 3
1 Department of Mechanical Engineering, University of Michigan, Ann Arbor, Michigan, United States, 2 Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States, 3 Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, Michigan, United States
Show AbstractNumerous applications call for materials with engineered thermal properties. Computational methods offer a means to study or predict thermal properties without the material costs or fabrication challenges of experimental measurements, but achieving accuracy depends on knowledge of material parameters (e.g., third order force constants for density functional theory simulations) that are often time-consuming to calculate. This poses a particular challenge when exploring new materials.
In this work we present machine learning (ML) approaches we have developed to better understand and accelerate the prediction of thermal properties. These approaches utilize deep neural networks (DNNs) and state-of-the-art ML algorithms to connect combinations of basic known materials parameters (e.g., atomic mass, density, lattice structure, etc.) with macro-scale thermal properties. We find that DNNs have the capability to learn complex inter-relationships between these properties that are otherwise difficult to capture analytically. For example, after the DNN is trained using a database of material properties, we use it to predict the frequency-dependent contributions to thermal conductivity in a wide range of materials. We also use computer vision to discover complex features in phonon dispersion curves that correlate with thermal conductivity. Finally, we demonstrate the significant reduction in computational time (an order of magnitude) that can be achieved by applying ML techniques to thermal property prediction.
8:00 PM - ES09.03.43
Reversible Transition between Anisotropic and Isotropic Thermal Transport in Polyurethane Foams
Bernd Kopera 1 , Mokit Chau 2 , Markus Retsch 1 , Eugenia Kumacheva 3 , Mitch Winnik 3
1 Physical Chemistry, University of Bayreuth, Bayreuth, Bavaria, Germany, 2 Polymer Chemistry, BASF, Ludwigshafen Germany, 3 Chemistry, University of Toronto, Toronto, Ontario, Canada
Show Abstract
Polyurethane foams are well established thermal insulators and find commercial application as insulating foams. However, control over the thermal transport properties in different directions is hard to achieve with isotropic foams but imperative for future dynamic insulation materials.
Here, we demonstrate elastic polyurethane foams with anisotropic lamellar microstructure formed by freeze-casting of water based polyurethane dispersions. Freeze-casting is an emerging technology used to create freestanding foams with anisotropic structure and properties.
This anisotropy results in orientation-dependent mechanical and thermal transport properties. Most importantly, the thermal conductivity and thermal diffusivity can be reversibly transitioned between an anisotropic and an isotropic state. This transition is achieved by altering the thermal conductivity and diffusivity of the surrounding atmosphere either by changing the pressure of the gas or its composition.
Symposium Organizers
Jia Zhu, Nanjing University
Baratunde Cola, Georgia Institute of Technology
Deyu Li, Vanderbilt University
Amy Marconnet, Purdue University
ES09.04: Thermal Transport III
Session Chairs
Tuesday AM, November 28, 2017
Hynes, Level 3, Ballroom C
8:00 AM - *ES09.04.01
Engineering Thermal Conductivity of Nanoscale Materials by Defect Doping
Baowen Li 1
1 Rennie Family Endowed Professor, Department of Mechanical Engineering, University of Colorado Boulder, Boulder, Colorado, United States
Show AbstractThermal conductivity is one of the most important physical properties of materials. The ability to engineer the thermal conductivity will allow us to control the flow of heat and derive novel functionalities such as thermal rectification, thermal switching, and thermal cloaking. In macroscopic (bulk) materials, this could be achieved by making use of composites and/or transform technique (metamaterials). However, at micro or nanoscale, it is becoming very difficult and challenge. In this talk, I will demonstrate the ability of tailoring thermal conductivity of nanoscale materials by using defect doping both experimentally and theoretically.
First of all, I will shown that the local thermal conductivity along a single Si nanowire can be tuned to a desired value (between crystalline and amorphous limits) with high spatial resolution through selective helium ion irradiation with a well-controlled dose. The irradiation was carried out in a helium ion microscope, and the local thermal conductivity along the irradiated Si nanowire was measured using a recently developed electron beam heating technique (E-beam technique).
Then, I will demonstrate the modulation of the thermal conductivity of a recently widely studied 2D material - MoS2 . With controlled oxygen plasma dose, the thermal conductivity of the MoS2 can be continuously tuned to a required value from crystalline to amorphous limits with controlled plasma dose (exposed time). Numerical simulations show that the thermal conductivity reduction under diluted defects is due to the decrease of phonon transmission coefficient, resulting from phonon-defects scatterings. Beyond a threshold, a sharp drop is observed, which is believed to be a crystalline-amorphous transition in thermal conductivity.
References:
Y- S Zhao et al, Nature Comm (2017)
A Aiyiti et al, Nature xx (2017) (Submitted)
8:30 AM - *ES09.04.02
Multifunctional Nanostructured Materials for Advanced Heat Transfer
Sheng Shen 1
1 , Carnegie Mellon University, Pittsburgh, Pennsylvania, United States
Show AbstractIn this talk, I will give two examples about utilizing multifunctional nanostructured materials for developing advanced heat transfer technologies. First, I will discuss novel thermal interface materials (TIMs) for electronics cooling, based on compliant and thermally conductive nanostructures. In contrast to conventional TIMs such as solders and epoxies, large-scale ordered nanostructures, e.g., metal nanowires, can increase mechanical compliance of TIMs but maintain high thermal conductivity, thus enhancing the performance and reliability of TIMs. Second, by leveraging nanoscale effects (e.g., highly oriented polymer chains, significantly reduced defects) via polymer nanofibers, we have achieved ultra-high thermal conductivity and strength far exceeding any existing soft materials.
9:00 AM - *ES09.04.03
Exploring the Limits of Thermal Phenomena
Arun Majumdar 1
1 , Stanford University, Stanford, California, United States
Show AbstractThis talk will discuss the limits of thermal transport, conversion, and storage in the realm of conduction, radiation, phase change and chemical transformations. It will also highlight how close to these limits have we reached and explore the possibility of scientific gaps in our knowledge. Finally, it will connect the implications of these scientific explorations to engineered systems.
9:30 AM - ES09.04.04
Emergent Heat and Energy Wave Packets from Phonon Interference
Anant Raj 1 , Jacob Eapen 1
1 , North Carolina State University, Raleigh, North Carolina, United States
Show AbstractEnergy dissipation in low-dimensional systems has been of interest for over 60 years, since the seminal paper by Fermi, Pasta, and Ulam on the vibrational modes of a one-dimensional non-linear spring, popularly known as the FPU problem. Several studies have demonstrated that unlike bulk three-dimensional systems, the energy transport in low-dimensional systems does not follow Fourier’s law of heat conduction. The thermal conductivity for these systems is ill-defined and is reported to diverge, scaling with the size of the system. Such divergence is also observed in realistic polymer chains as well as in two-dimensional materials such as graphene. More recently, this anomalous behavior has been linked to the presence of cross-correlation between different phonon modes arising from collective phonon excitations.
To probe the relationship between the phonon modes and energy transport more deeply, we analyze the local energy and heat current fluctuations of a linear mono-atomic chain and relate them to the phonon modes. We demonstrate theoretically that normal modes of the displacements combine to produce energy wave packets. We further derive the condition that pairs of phonon modes interfere to produce waves of energy if and only if three-phonon scattering law is satisfied even in the absence of phonon-phonon scattering. More generally, for nth order in the interaction potential, n displacement normal modes combine to form energy waves only if (n+1)th order phonon scattering law is satisfied. Further, we show that the frequency and decay of the energy normal modes are directly associated with the collective excitation of phonon modes. Our theoretical findings link the established theory of phonon excitation modes to the normal modes of energy and heat current in crystal lattices from statistical-mechanical first principles.
9:45 AM - ES09.04.05
Nanoscale Thermal Transport away from 1D and 2D Heat Sources—Role of the Heater Size and Periodicity
Travis Frazer 1 2 , Nico Hernandez Charpak 1 2 , Joshua Knobloch 1 2 , Begona Abad Mayor 1 2 , Weilun Chao 3 , Henry Kapteyn 1 2 , Margaret Murnane 1 2
1 , JILA, Boulder, Colorado, United States, 2 Physics, University of Colorado Boulder, Boulder, Colorado, United States, 3 , Lawrence Berkeley National Laboratory, Berkeley Hills, California, United States
Show AbstractThermoelectrics, nanotherapeutics, and nanoelectronics are pushing ever deeper into the nanoscale regime, with characteristic dimensions already on the order of 10nm. Such applications require a comprehensive understanding of energy flow at the nanoscale, where deviations from bulk behavior dominate, resulting in new benefits and challenges. A complete fundamental understanding of nanoscale thermal transport is still a grand challenge due to the lack of a comprehensive theoretical description and experimental methods to probe the nanoscale. It has become clear that thermal transport over length scales comparable to the mean free paths (MFP) of heat carriers deviates significantly from the diffusive prediction, with a nontrivial dependence on nanosystem geometry.
We present experimental results on these deviations in periodic nanoscale heat sources as a function of size, periodicity, and dimensionality. Our technique directly accesses nanoscale thermal transport at the intrinsic length and time scales of the heat carrying phonons in dielectrics and semiconductors. Here, silicon, sapphire, and fused silica substrates are coated with periodic arrays of nickel nanolines (1D confined) and nanocubes (2D confined) with characteristic dimensions from 1μm down to 20nm. By pumping these nanostructures with near-infrared, ultrafast laser pulses, they serve as localized nanoscale heat sources, since the laser energy is not significantly absorbed by the substrate. The nanostructures thermally expand, then relax to their original profile as heat transfers to the substrate on picosecond to nanosecond timescales. The resulting dynamic changes to the surface profile are probed using extreme ultraviolet (EUV) high harmonic beams with 30nm wavelength [1, 2]. By measuring the change in EUV diffraction as a function of pump-probe delay time, we extract the thermal relaxation time of the nanostructure arrays and thus directly probe deviations from diffusive transport in the substrate.
In past work, we showed that although quasi-ballistic transport dominates for heater linewidths below the dominant phonon MFPs in both silicon and sapphire substrates, this effect can be counteracted if the spacing of the heaters is also comparable to the phonon MFPs in the substrate [2]. This work predicted that closely-spaced nanoscale heaters cool faster than widely-spaced ones. Here we present experimental validation of these predictions by probing the cooling dynamics of periodic arrays of nanolines on silicon and fused silica, with varying size and periodicity. We also present results on probing thermal transport from 2D confined heat sources, displaying similar size- and periodicity-dependent effects as the 1D confined study. This further validates that thermal transport over scales comparable to the MFPs of heat carriers depends nontrivially on nanosystem geometry.
[1] Rundquist, et al., Science 280, 1412 (1998).
[2] Hoogeboom-Pot, et al., Proc. Natl. Acad. Sci. 112, 4846 (2015).
10:00 AM - ES09.04.06
Controlling Coherent and Incoherent Cross-Plane Thermal Transport in Semiconductor Superlattices
Abhinav Malhotra 1 , Martin Maldovan 1
1 , Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractHeat conduction in superlattice nanostructures is of immense importance in the research effort for creating efficient thermoelectrics, manufacturing advanced electronic and optoelectronic devices and obtaining directional and spatial control over thermal flux. The modification in thermal transport properties in nanoscale semiconductor superlattices occurs due to the alteration of phononic transport mechanisms. This alteration is often broadly divided into two regimes − coherent and incoherent phononic effects. In this talk, we study the cross-plane thermal transport in semiconductor superlattices considering both coherent and incoherent effects. As coherent and incoherent effects have a common foundation as their occurrence is controlled by the interaction of phonons with interfaces, a complete understanding of these effects requires an accurate description of phonon-surface scattering. In our model, we incorporate detailed surface characteristics and phonon properties including incident phonon momentum and angle of incidence to predict the impact of the partially diffusive nature of realistic phonon-interface interactions on coherent and incoherent effects. We show that surface interactions alter the transport of phonons in a variety of ways including the ability of phonons to cross multiple interfaces, which change the thermal conduction properties significantly and determine the probability of achieving coherent effects in thermal transport. Analysis of heat spectra in the form of frequency and mean-free-path thermal conductivity accumulation functions for semiconductor superlattices will also be presented to shed light on the nature of coherent and incoherent thermal transport in these nanostructures.
10:30 AM - *ES09.04.07
Science and Engineering of Thermal Energy Materials and Devices—From Solid-State Engines to High-Energy Density Thermal Storage
Ravi Prasher 1
1 , Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractAbout 90 percent of the world’s energy use involves thermal processes of conversion, transport and storage. Examples include thermal engines to generate mechanical/electrical power; heating and cooling of buildings; and heating involved in manufacturing. For example cooling and heating of buildings alone account for 15% of primary energy used in USA. Thermal energy technologies can play even a larger role in the future by enabling cheaper energy storage for renewable power, by increasing the end-use efficiency of appliances, enabling better thermal management of automobiles and utilizing the wasted heat from various industrial sources. However to achieve these goals significant breakthroughs are needed both in thermal science and engineering. For example solid-state engines such as high temperature thermolectrics, thermionic engines and thermal photovoltaics can be potentially used for very high temperature concentrated solar plants in topping cycle mode or very high-energy density thermal storage can be used for providing air-conditioning of electric vehicles. The fundamental length scales related to flow of heat fall in the range of 1-1000 nm depending on the energy carrier type such as photons, phonons and electrons. Nanostructured materials and features of these dimensions can be used to manipulate various modes of thermal energy transport to develop next generation of thermal energy based devices.
In the first part of the seminar the speaker will briefly talk about the thermal technology programs he created during his stint as a program director at ARPA-E. In the second part of the seminar the speaker will talk about his own research and technology development work in the manipulation of thermal energy processes in nanostructured materials and devices.
11:00 AM - ES09.04.08
Reconstruction of Phonon Relaxation Times from Thermal Spectroscopy Data in Systems Containing Interfaces with Unknown Properties
Mojtaba Forghani 1 , Nicolas Hadjiconstantinou 1
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractResolution of the phonon free path and relaxation time distribution in solid materials for applications related to the development of thermoelectric materials has recently received considerable attention.
In order to convert experimentally measured temperature relaxation profiles to the free path distribution, researchers typically invoke the concept of “effective thermal conductivity” and proceed to match the experimentally measured response to solutions of the heat conduction equation with the thermal conductivity treated as an adjustable, “effective” quantity. The free path distribution is subsequently extracted by introducing additional assumptions on the relation between the effective thermal conductivity and the free path distribution. However, since, by design, the material response in the experiment is not in the Fourier regime, approaches based on fitting the material response using Fourier theory can only be understood as approximate.
In order to avoid these issues, we have developed (Forghani et al., Physical Review B 94, 155439 (2016)) a technique for reconstructing phonon relaxation times which does not assume Fourier-based heat conduction. In the proposed technique, reconstruction is posed as an optimization problem in which the relaxation time distribution is obtained as the distribution of relaxation times that minimizes the error between experimentally measured material response and the one obtained from Boltzmann transport equation solutions (numerical or analytical). This method has been validated using synthetically generated temperature profiles in the Transient Thermal Grating geometry, using both Monte Carlo (MC) and inverse fast Fourier transform algorithms, in the presence and absence of noise in the measurement, on two different sets of silicon material properties.
The current presentation addresses the more challenging problem of relaxation-time reconstruction in experiments where an interface with unknown properties between two materials is also present. We show that MC-generated synthetic relaxation profiles in the 2D-dots geometry for an Al-Si system (Hu et al., Nature Nanotechnology 10, 701 (2015)) can be reproduced with a similar optimization formulation in which the interface properties (transmission/reflection coefficients) are treated as additional unknowns. The reconstruction results suggest that the reconstruction process is not very sensitive to the interface properties, while the relaxation times/free path distribution can be obtained with reasonable accuracy.
11:15 AM - ES09.04.09
Estimation of the Minimum Lattice Thermal Conductivity from the Vibrational Density of States
Matthias Agne 1 , G. Snyder 1
1 , Northwestern University, Evanston, Illinois, United States
Show AbstractExperimental observations indicate that the lattice thermal conductivity of some thermoelectric materials falls below the Cahill-Pohl value for minimum lattice thermal conductivity, suggesting that there may be a better estimate for the minimum thermal conductivity. Unlike the approach of Kittel, Slack, and Cahill, that use a phonon picture of heat transport, we propose a phenomenological model using the diffuson picture of Allen and Feldman where diffusons are non-localized, non-propagating oscillations that can carry heat. In this context, the Einstein thermal conductivity equation is modified to estimate the minimum thermal conductivity directly from the vibrational density of states, and the mean frequency of vibration is found to be the characteristic parameter. From a large study of density of states spectra and speed of sound data, it was found heuristically that the mean frequency of the vibrational density of states is linearly correlated (R2=0.98) with the maximum Debye frequency. As a result, this estimation of minimum lattice thermal conductivity from the mean vibrational frequency, assuming diffuson-mediated transport, is consistently lower than the Cahill-Pohl value by approximately 35%.
11:30 AM - ES09.04.10
Effects of Alloying on In-Plane and Cross-Plane Phonon Transport in Transition Metal Dichalcogenide Monolayers
Zlatan Aksamija 1 , Cameron Foss 1 , Arnab Majee 1
1 , Univ of Massachusetts-Amherst, Amherst, Massachusetts, United States
Show AbstractInherently semiconducting two-dimensional (2D) materials are essential for all-2D electronic and optoelectronic devices. Transition metal dichalcogenide (TMDC) monolayers are a family of semiconducting materials with a range of band gaps and electron/hole mobilities, making them a model semiconductor family for 2D transistors and photonics. The modest thermal conductivity in some TMDCs has, in turn, spurred interest for TMDCs as thermoelectric (TE) materials for waste heat scavenging, which requires good electrical and low thermal conductivity in order to maximize the TE figure-of-merit ZT. Alloying is a method for tuning vibrational frequencies, reducing the lattice thermal conductivity, tuning the bandgap, and altering the bandgap while having minimal effects on electrical conductivity – thus alloying can effectively boost ZT. In this work, we study the effects of alloy composition on both in-plane (in the monolayer) and cross-plane (from the monolayer to substrate) phonon transport in the family of TMDC alloys Mo1-xWxS2-2ySe2y, which are typically grown by Chemical Vapor Transport (CVT) and exfoliated. We start with first principles calculations of phonon dispersion and use them in our phonon Boltzmann Transport Equation (pBTE) model, which includes all the relevant mechanisms: anharmonic three-phonon scattering, edge/boundary roughness, impurity/defect scattering, as well as alloy mass-difference scattering. Furthermore, vibrational coupling of supported TMDC sheets to the substrate results in cross-dimensional (2D-to-3D) thermal boundary conductance (TBC), which we calculate from the monolayer and substrate phonon density of states and the van der Waals (vdW) spring coupling constant between them. We find that alloy scattering substantially reduces in-plane thermal conductivity of TMDC alloys, even at modest alloy compositions. The lowest values are typically several times lower than the non-alloyed constituents, reaching a minimum of ~10 W/m-K both when transition metal is alloyed (Mo1-xWxS and Mo1-xWxSe) as well as when the chalcogenide is alloyed (MoS2-2ySe2y and MoS2-2ySe2y). Despite dominant alloy scattering, the thermal conductivity is dependent on sample size up to several microns, far exceeding the phonon mean-free-path, but the dependence is much more gradual than in non-alloyed samples, owing to contributions from long-wavelength phonons. We also show that thermal boundary conductance (TBC) in the cross-plane direction (to the substrate) depends primarily on the overlap between the vibrational densities-of-states, and thus can be tuned by the alloy composition and through the choice of substrate material. We conclude that alloy composition is a powerful way to tune the thermal properties of TMDCs and a promising avenue toward achieving low thermal conductivity and high TE figure-of-merit in energy scavenging applications. Conversely, device applications requiring better heat removal will benefit from improved TBC to the substrate.
11:45 AM - ES09.04.11
Short-Mean-Free Paths Limit of Suppression Function in Non-Gray, Nanostructured Materials
Giuseppe Romano 1 , Alexie Kolpak 1
1 , MIT, Cambridge, Massachusetts, United States
Show AbstractThe suppression function conveniently describes heat transport in nanostructured materials, where phonon-boundary interaction significantly decreases the thermal conductivity. Here we elucidate the short mean-free-path (MFP) regime of the suppression function in materials with broad MFP distributions. In such a region, where heat diffusion dominates over ballistic transport, the need for an accurate spatial discretization significantly increases computational effort. By developing a multiscale approach based on a modified diffusive model and Boltzmann transport equation, we were able to efficiently compute the phonon suppression function in porous Si over a wide range of MFPs. We found that the presence of ballistic phonons largely affects the diffusive regime, with the short-MFP limit of the suppression function approaching a plateau significantly smaller than that predicted by standard Fourier’s law. Finally, we apply our model to a realistic sample, finding excellent agreement with experiments. Combined with first-principle calculations, our computational approach can help design low-thermal-conductivity nanostructures with arbitrary material/geometries combinations.
ES09.05: Thermoelectric I
Session Chairs
Tuesday PM, November 28, 2017
Hynes, Level 3, Ballroom C
1:30 PM - *ES09.05.01
First-Principles Simulation of Electron and Phonon Scattering and Their Thermoelectric Transport Properties
Jiawei Zhou 1 , Te-Huan Liu 1 , Zhiwei Ding 1 , Qichen Song 1 , Qian Xu 1 , Gang Chen 1
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractThis talk will discuss our recent work to simulate electron and phonon thermoelectric properties based on the density-functional theory, including electrical conductivity, Seebeck coefficient, electronic thermal conductivity and phonon thermal conductivity. Main challenges are simulation of scattering among carriers and by impurities. For electron transport simulations, electron-phonon and electron-impurity scatterings are computed from first-principles to obtain electron relaxation times based on Fermi’s golden rule. The energy dependent relaxation times are then used in the Boltzmann transport theory to obtain the electrical conductivity, Seebeck coefficient and electronic thermal conductivity. For phonon transport, the anharmonic force constants are derived from first-principles and used to compute phonon relaxation times. The energy dependent mean free paths are computed for both electrons and phonons. After validating the simulation on well-characterized materials such as Si and GaAs (EPL, 109, 57006, 2015; PRL, 114, 115901, 2015; PNAS, 112, 14777, 2015; PRB, 95, 075206, 2017), we moved on to simulate thermoelectric materials such as half-heuslers and chalcogenides. These simulations lead to deeper understanding of thermoelectric transport in existing materials and point to new directions for improving existing materials via nanostructures, as well as for discovering new materials. This work is supported by S3TEC, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number: DE-SC0001299/DE-FG02-09ER46577.
2:00 PM - ES09.05.02
Extraordinary Thermoelectric Performance Realized in N-Type PbTe through Multi-Phase Nanostructure Engineering
Jian Zhang 1 , Di Wu 1 , Dongsheng He 1 , Jiaqing He 1
1 Department of Physics, Southern University of Science and Technology, Shenzhen China
Show AbstractLead telluride has long been realized as an idea p-type thermoelectric material at intermediate temperature range; however, its commercial applications are largely restricted by its n-type counterpart that exhibits relatively inferior thermoelectric performance. This major limitation is largely solved in this work. We present that a record high ZT value of ~1.83 can be achieved at 773 K in n-type PbTe-4%InSb composites. This significant enhancement in thermoelectric performance is attributed to the incorporation of InSb into PbTe matrix resulting in multi-phase nanostructures that can simultaneously modulate the electrical and thermal transport. On one hand, the multiphase energy barrier scattering between nanophases and matrix can boost the power factor in the entire temperature range via significant enhancement of the Seebeck coefficient and moderately reducing the carrier mobility. On the other hand, the strengthened interface scattering at the intensive phase boundaries yields an extremely low lattice thermal conductivity. This strategy of constructing multi-phase nanostructures could also be highly applicable in enhancing the performance of other state-of-the-art thermoelectric systems.
2:15 PM - ES09.05.03
Surface Chemical Tunning of Phonon and Electron Transport in Free-Standing Silicon Nanowire Arrays for Advancing Thermoelectrics
Ying Pan 2 1 , Ye Tao 1 3 , Christian Degen 3 , Dimos Poulikakos 2
2 Mechanical Engineering, ETH Zürich, Zürich Switzerland, 1 , Harvard University, Cambridge, Massachusetts, United States, 3 Department of Physics, ETH Zürich, Zürich Switzerland
Show AbstractThermoelectric energy conversion is an attractive approach to address a niche in the globally growing energy demand landscape. It is important in our quest to reduce our reliance on fossil fuels and to improve the utilization of available thermal energy.
Over the last decade, the most successful approach to inproving thermoelectric efficiency has been through device component miniaturization into the deep nm-range (101-102 nm). This approach reduces lattice conductivity without significantly altering electronic conductivity. While promising, further decrease in the diameter runs into technical barriers in fabrication and scalability, as well as fundamental limitations in material stability, quality, and the discreteness of matter.
A distinguishing characteristic common to all nanoscale devices is their increased surface-to-volume ratio. It is reasonable to postulate that, with interface atoms now constituting a substantial fraction of the total volume, their chemical state can become a principal determinant of device properties. The effect of surface chemical treatments on phonon transport, however, remains an open question. In light of the extreme sensitivity of electron transport in nanomaterials to the surface condition, a parallel, simultaneous investigation of phonon transport is clearly needed.
We explore this inadequately exploited handle for thermoelectrics. We perform temperature-dependent measurements of the electrical and thermal conductivities of silicon nanowire (SiNW) arrays after successive surface chemical functionalization treatments. This study was enabled by the batch fabrication of devices with monolithically integrated free-standing SiNWs and by the cleanliness and gentleness of gas-phase processing techniques.
We choose two prototypical modifications of the silicon surface as model procedures: hydrogen-termination following the removal of surface native oxide and n-type surface charge transfer doping. We measure an immediate increase in electrical conductivity by one order of magnitude with a concurrent decrease in thermal conductivity following vapor HF removal of surface native oxide from as-fabricated samples. Furthermore, the electrical conductivity increases by a further 2 to 4 orders of magnitude when surface charge transfer dopants are applied, in situ, via gas-phase sources to the oxide-free SiNWs. This improvement in electrical transport takes place in the absence of marked changes in thermal conductivity. These results demonstrate that surface chemical tuning is a viable pathway and also a complementary approach to size-miniaturization in the push for high-performance thermoelectric nanostructured materials.
2:30 PM - ES09.05.04
Thermoelectricity by Rational Design—New Materials and Insights from First-Principles Computations of Electron Scattering
Georgy Samsonidze 1 , Boris Kozinsky 1
1 Research and Technology Center, Robert Bosch LLC, Cambridge, Massachusetts, United States
Show AbstractAccelerated discovery of next-generation materials for thermoelectric energy conversion requires capability for efficient prediction of materials' performance from first-principles, without empirically fitted parameters. We introduce a novel simplified approach for computing electronic transport properties, which achieves good accuracy and transferability while greatly reducing complexity and computation cost compared to the existing methods. Our first-principles calculations of the electron-phonon coupling tensor demonstrate that the energy dependence of the electron relaxation time varies significantly with chemical composition and carrier concentration, suggesting that it is necessary to go beyond the commonly used approximations to screen and optimize materials' composition, carrier concentration and microstructure. We verify the new method using high accuracy computations and validate with experimental data before applying it to screen and discover promising compositions in the space of half-Heusler alloys, technologically relevant for waste heat recovery. Using the new tool we discuss the universality of the Wiedemann-Franz law and identify the effective electron mass as the single best general descriptor determining material's performance.
2:45 PM - ES09.05.05
Data-Driven Discovery and Design of Novel Thermoelectrics
Jeff Doak 1 , James Saal 1 , Greg Olson 1 2
1 , QuesTek Innovations LLC, Evanston, Illinois, United States, 2 Materials Science and Engineering, Northwestern University, Evanston, Illinois, United States
Show AbstractThe discovery of new materials to enable breakthrough technologies is one of the great challenges of the 21st century. Accelerating materials development has been identified in the White House Materials Genome Initiative as a critical ability to ensure national security and economic competitiveness. Traditional materials development followed a costly and time-consuming trial-and-error approach, where performance improvements were typically incremental. Over the past 15 years there has been a paradigm shift in this process, from development to design. The targeted design of materials is performed by conceptualizing the material as a complex hierarchy of interrelated mechanisms across numerous length and time scales, an approach called Integrated Computational Materials Engineering (ICME). This process includes concept development, parametric design, detailed measurement of properties, and qualification of materials.
The ICME approach has dramatically reduced the timeframe for structural metal alloy development, from decades to years. However, the application of ICME to less mature, yet technologically important materials systems suffers from fewer fundamental functional models and relationships. Thermoelectrics form an interesting intermediate case, where some functional property relationships and design concepts have been established but underlying chemical thermodynamics and quantitative process/structure and structure/property models have not been completely fleshed out (especially with regards to composition dependence). There is a great potential to further accelerate and revolutionize the materials design process for thermoelectrics by complementing ICME methods with data-driven machine learning techniques.
QuesTek Innovations is applying a data-driven approach to the discovery and design of novel thermoelectric materials with improved performance. In particular, we are combining disparate and heterogeneous data sources into a single homogenous database of thermoelectric transport properties upon which we are building machine learning models to identify novel materials with promising electronic structures. Simultaneously, we are synthesizing existing models of phonon scattering processes and precipitation kinetic models into an ICME framework which can optimize the microstructure of thermoelectrics for minimum lattice thermal conductivity. The goal of this two-pronged approach is the discovery of a novel thermoelectric alloy system with improved electronic transport properties and subsequent microstructure design to minimize phonon transport. In this talk we present our framework for this combined data-driven and ICME approach to thermoelectrics its application to optimizing thermoelectric microstructure to minimize lattice thermal conductivity.
3:30 PM - *ES09.05.06
Not all Grain Boundaries are the Same at Scattering Phonons
G. Snyder 1
1 , Northwestern University, Evanston, Illinois, United States
Show AbstractFor 50 years, we have commonly been using Casimir’s theory that describes the scattering of heat-carrying lattice vibrations (phonons) on the sample boundaries to also describe the reduction of thermal conductivity due to grain boundaries. In the frequency-independent Casimir model, phonons simply cannot travel across the boundaries, which is not the case in grain boundaries. This and a growing body of experimental and computational evidence shows that the modification of the Casimir model is necessary for grain boundaries. However, the precise mechanism of phonon scattering at grain boundaries is unknown. In this talk I will discuss our analysis of phonon scattering that controls the thermal conductivity of many common thermoelectric materials. We find that the grain boundary dislocation strain model can substitute for the Casimir model. More importantly, the two models can be distinguished at low temperature in fine-grained materials such that experimental evidence supports the grain boundary dislocation strain model. In this way, we suggest that grain boundaries themselves are best conceptualized as a collection of dislocations. Since strain and grain boundary structures can vary, we should be able to engineer grain boundaries or grain complexions (including extrinsic atoms) to disrupt phonon transport without harming electron transport.
[1] Hyun-Sik Kim, Stephen D. Kang, Yinglu Tang, Riley Hanus and G. J. Snyder Materials Horizons 3, 234 (2016)
4:00 PM - ES09.05.07
Design of Novel Thermoelectrics Based on Unconventional Clathrates
Kirill Kovnir 1
1 , Iowa State University, Ames, Iowa, United States
Show AbstractThe phenomenon of thermoelectricity is attributed to the interconversion of thermal and electrical forms of energy. We developed a new class of bulk thermoelectric materials based on clathrates with a three-dimensional framework comprised of oversized transition metal-phosphorus polyhedral cages that encapsulate guest cations. Transition metal-based clathrates have the following advantages over conventional Si-, Ge-, and Sn-based clathrates: i) a larger variety of framework topologies; ii) a higher tunability of the electronic properties via framework substitutions; iii) a higher thermal stability. The correlation between the crystal structure, chemical bonding, and charge and heat transport properties will be discussed.
4:15 PM - ES09.05.08
The Role of Sn Vacancies in Reducing the Thermal Conductivity of SnTe-AgSbTe2 Alloys
Riley Hanus 1 , G. Snyder 1 , Gangjian Tan 1 , Shiqiang Hao 1 , Xiaomi Zhang 1 , Trevor P. Bailey 2 , Xianli Su 1 , Ctirad Uher 2 , Vinayak Dravid 1 , Christopher Wolverton 1 , Mercouri Kanatzidis 1
1 , Northwestern University, Evanston, Illinois, United States, 2 , University of Michigan, Ann Arbor, Michigan, United States
Show AbstractAgSnmSbTe2+m has been proven to show much better thermoelectric figure of merit (zT) than its parent compound SnTe largely due to its dramatically reduced lattice thermal conductivity (klat). However, the underlying mechanism for this reduction is still ambiguous. In this study, we revisit this old but intriguing thermoelectric system by synthesizing a series of phase pure solid solutions between SnTe and AgSbTe2. It is revealed that the addition of AgSbTe2 energetically favors the formation of Sn vacancies in SnTe by pushing the system to a Sn deficient phase region. The increased vacancy concentration dramatically reduces the lattice thermal conductivity through both lattice softening and phonon-vacancy scattering to a value as low as 0.4 Wm-1K-1 at 800 K. Measurements of the sound velocity and carrier concentration were used to quantify lattice softening and the Sn vacancy concentration in a systematic Callaway-type model of klat giving quantitative validation of the proposed mechanisms. Consequently, a zT value of 0.9 is achieved at 800 K for the sample AgSn5SbTe7, which can be further improved to 1.2 by properly doping I on Te sites. This represents a 300% improvement over pristine SnTe, outperforming many other SnTe-based thermoelectric materials reported so far for the same temperature range. It is highlighted that phonon-vacancy scattering is inherently much stronger than the commonly used phonon-isotope scattering expression with DM/M=1, since this treatment neglects the change in potential energy associated with the vacancy defect. This is an important distinction in this system as well as other vacancy containing thermoelectric materials, such as AgSnmBiTe2+m and AgGemSbTe2+m.
4:30 PM - ES09.05.10
Advances in Thermomagnetic Phenomena Based on Spin Seebeck Effects in Hybrid Nanostructures
Myriam Aguirre 1 2 3 , Rafael Ramos 4 , Alberto Anadón 2 , Irene Lucas 2 , Luis Morellón 2 1 , Pedro Algarabel 5 2 , Ken-ichi Uchida 4 , Eiji Saitoh 4 , Ricardo Ibarra 1 2 3
1 , Instituto de Nanociencia de Aragón (INA), Aragón Spain, 2 Condensed Matter Physics, Universidad de Zaragoza, Aragón Spain, 3 INA, Advanced Microscopy Laboratory, Aragón Spain, 4 Institute for Materials Research, Tohoku University, Sendai 980-8577 Japan, 5 , Instituto de Ciencia de Materiales de Aragón, Zaragoza Spain
Show AbstractThermoelectric conversion efficiency is intrinsically limited by the interdependence of the thermal and electrical conductivity of the materials employed that can be partially improve with nanostructuration. Recently, a spin-based approach has been discovered and in analogy named the spin Seebeck effect (SSE)[1]. The SSE refers to the generation of spin currents [2] in a magnetic material upon application of a temperature gradient; the spin current is injected and electrically detected in a normal metal in contact with magnetic material, where spin-orbit interaction in normal metal transforms the spin current into an electric field, by means of the inverse spin Hall Effect.
The observation of the Spin Seebeck Effect (SSE) in magnetic insulators has opened the possibility to generate pure spin currents with less dissipation losses due absence of mobile charge carriers, and expand the range of possible materials for thermoelectric application due to spin mediated thermoelectric conversion. Moreover, the experimental geometry of the SSE with the thermal and electric current paths perpendicular to each other is advantageous for the implementation of thin film and flexible thermoelectric devices [3]. Since the heat and electric currents have independent paths, the properties of different materials comprising the hybrid device can be optimized independently. However, the main disadvantage for the potential application is the low magnitude of the thermoelectric output. Different possibilities are currently being explored, such as increasing the spin current detection efficiency by taking advantage of the spin Hall angle characteristics of different materials [4]. Other approaches can be directed towards increasing the thermal spin current generations, as recently shown in spin induced thermoelectric measurements in [Pt/Fe3O4] × n films multilayers, topic that will be described in this work [5,6]. A short review of advances on Spin Seebeck in oxide materials will be presented.
References:
[1] K. Uchida, S. Takahashi, K. Harii, J. Ieda, W. Koshibae, K. Ando, S. Maekawa, and E. Saitoh, Nature 455, 778 (2008).
[2] S. Maekawa, H. Adachi, K. Uchida, J. Ieda, and E. Saitoh, J.Phys. Soc. Jpn. 82, 102002 (2013).
[3] A. Kirihara, K. Uchida, Y. Kajiwara, M. Ishida, Y. Nakamura, T. Manako, E. Saitoh, and S. Yorozu, Nat. Mater. 11, 686 (2012).
[4] K. Uchida, H. Adachi, T. Kikkawa, A. Kirihara, M. Ishida, S. Yorozu, S. Maekawa, and E. Saitoh, Proceedings of the IEEE (2016).
[5] R. Ramos, T. Kikkawa, M. H. Aguirre, I. Lucas, A. Anadon, T. Oyake, K. Uchida, and H. Adachi, Phys. Rev. B 92, 220407(R) (2015).
[6] S. Daimon, R.Iguchi, T.Hioki, E.Saitoh, K.Uchida. Nat. Comm 7:13754 (2016)
ES09.06: Poster Session II
Session Chairs
Wednesday AM, November 29, 2017
Hynes, Level 1, Hall B
8:00 PM - ES09.06.01
Enhancement of Thermoelectric Properties by Using Metal/Semiconductor Bilayer with Weak Electron-Phonon Coupling
Shin Yabuuchi 1 , Yosuke Kurosaki 1 , Jun Hayakawa 1
1 Center for Exploratory Research, Hitachi Ltd., Kokubunji-shi Japan
Show AbstractThermoelectric materials have attracted much interest from a viewpoint of increasing demands for sustainable and renewable energy since wasted heat can be directly converted into electric energy by using thermoelectric modules. The efficiency of thermoelectric materials is measured by a dimensionless figure of merit, ZT =S2σT/κ, where S is Seebeck coefficient, σ is electrical conductivity, T is temperature, and κ is thermal conductivity, respectively. In order to enhance ZT, a reduction of thermal conductivity is essential. Moreover, it is necessary for realizing high ZT to have not only a low κ but also a large s and a large S. Recently, it has been reported that a nano-scaled metal/nonmetal multilayer is a potential way to reduce the thermal conductivities in spite of using metallic materials when electron-phonon coupling of the metal is weak[1,2]. In this study, we focus on meal/semiconductor bilayer. The effective Seebeck coefficients (Seff), effective electrical conductivity (σeff) and effective thermal conductivities (κeff) of the bilayer were theoretically investigated by using two-temperature model (TTM) and single parabolic band model. Our theoretical analysis reveals that a meal/semiconductor bilayer enables to enhance the σeff and remarkably reduce the κeff, which lead to large enhancement of ZT.
We evaluated the electrical conductivities, electron-phonon coupling factors and Seebeck coefficients of two layers (metal and semiconductor) at given carrier concentrations and also estimated the interfacial thermal resistance and interfacial electrical resistance of the bilayer by using diffuse mismatch model. The temperature profiles of both electron and phonon are estimated by TTM in various thicknesses. We analyzed the κeff based on TTM and Seff was evaluated by considering the electron-temperature profile. σeff was also calculated considering interfacial electrical resistance. In the case that the metal layer with small electron-phonon coupling factor has a lower lattice thermal conductivity than that of semiconductor layer, the κeff can be reduced remarkably when the thickness of both layers become thinner than a particular length defined by thermal conductivities and electron-phonon coupling factor[1]. On the other hand, the bilayer enables to enhance the power factor (S2σ) owing to large σ of the metal layer and exceed the maximum value of constituent single layer. Resultantly, the meal/semiconductor bilayer leads to a large enhancement of ZT.
This work is based on results obtained from the Future Pioneering Program “Research and Development of Thermal Management and Technology” commissioned by the New Energy and Industrial Technology Development Organization (NEDO). It is also supported by TherMAT.
[1] A. Majumdar et al., Appl. Phys. Lett., 84, 4768 (2004).
[2] J. Ordonez-Miranda et al., Appl. Phys., 109, 094310 (2011).
8:00 PM - ES09.06.02
Thermoelectric Properties and Dopant Segregation at Mg2Si Grain Boundary
Kaoru Nakamura 1 , Toshiharu Ohnuma 1
1 Materials Science laboratory, Central Research Institute of Electric Power Industry, Yokosuka Japan
Show AbstractThermoelectric conversion material has been attracted great attention, as a key technology in energy harvesting. Because the fossil power plants generate electric power by utilizing high-temperature (~900 K) steam, vast amount of thermal source is expected to be available. However, commercial thermoelectric conversion material, such as Bi2Te3, can’t be applied for the fossil power plant, mainly because the applicable temperature is room temperature. Among the thermoelectric material suitable for using at around 900 K, we have been investigated thermoelectric properties of silicide compounds from the theoretical calculation [1, 2].
In this study, we investigated the effect of dopant element on thermoelectric properties of Mg2Si and found that dopant segregation at grain boundaries significantly affect thermoelectric properties. Based on the theoretical prediction of possible dopant element by using first-principles calculation, various doped samples were synthesized by Spark Plasma Sintering (SPS), and their temperature dependence of thermoelectric properties were investigated. Beside to electron doping by Al substitution for Mg site, we found that Au can also dope electron by substitution for Si site. For the hole doping, Ag substitution for Mg site was utilized. Microstructure observation showed dopant segregation at grain boundaries and second phase was formed in the case of high dopant concentration specimen. In such case, thermoelectric properties of Mg2Si were decreased. Thus, we investigated grain boundary segregation behavior by using model Σ5 <210> grain boundary from first-principles calculation. It was found that Au and Ag show strong segregation tendency and largely modified the electronic structure of Mg2Si grain boundary. Details of dopant segregation behavior and effect on transport properties along grain boundary will be discussed at the conference.
[1] T. Kumagai, S. Yamada, T. Ohnuma and T. Ogata, proceedings of International Symposium on Atomistic Modeling for Mechanics and Multiphysics of Materials (2011).
[2] K. Nakamura, S. Yamada and T. Ohnuma, Materials Transactions, 54, 276-285 (2013).
8:00 PM - ES09.06.03
Crystal Structure and Thermoelectric Properties of P-Type Fe2TiSi1-xAlx Full Heusler Alloy
Naoto Fukatani 1 , Akinori Nishide 1 , Shin Yabuuchi 1 , Yosuke Kurosaki 1 , Jun Hayakawa 1
1 , Hitachi Ltd, Kokubunji Japan
Show AbstractEnvironmentally friendly Fe-based full Heusler alloys such as Fe2VAl have been attracting much interest as promising thermoelectric materials for low temperature use. Against the problem that the thermoelectric figure of merit (ZT) of Fe2VAl is still low, we have recently found that Fe2TiSi is a narrow gap semiconductor with large Seebeck coefficient by using first principle calculations[1]. However, single phase Fe2TiSi has been realized only in thin film by using crystallization process on a single crystal substrate because Fe2TiSi is the metastable phase[2]. Single phase Fe2TiSi bulk has not been synthesized so far. In this study, we successfully synthesized a single phase Fe2TiSi bulk through non-equilibrium process and investigated its p-type thermoelectric properties by partially substituting Si with Al.
The Fe2.04Ti0.94Si1.02-xAlx (0 ≤ x ≤ 0.15) powder alloy was fabricated by mechanical alloying (MA) method with planetary ball-milling and then sintered by spark plasma sintering method at 660°C for 30min. The composition ratio of Fe, Ti, and Si was adjusted to stabilize full Heusler phase. The crystal structure was identified by X-ray diffraction (XRD). The Seebeck coefficient and the electrical resistivity were measured by differential and 4 probe methods, respectively.
The crystal structure of the powder alloy after MA process is evaluated by XRD and confirmed to be the amorphous state which is known to be useful to synthesize metastable phase. After sintering process, (111) and (200) diffraction peaks attributed to L21 structure were clearly observed without any secondary phase. The average grain size estimated by Scherrer’s equation is about 60 nm. These results indicate that non-equilibrium process through amorphous state enables us to realize ordered full Heusler phase with nano-grains.
Next, we investigated thermoelectric properties of sintered materials. The Seebeck coefficient of 123 μV/K, which is the highest value in p-type full-Heusler alloys, was obtained at 150°C for Fe2.04Ti0.94Si1.02-xAlx (x = 0.06). As a result, the maximum power factor reaches 2.7 mW/K2m for x = 0.14, which is comparable to that of the conventional p-type full Heusler alloy of Fe2VAl[3]. We will discuss the thermal conductivity and the possible large ZT in the Fe2.04Ti0.94Si1.02-xAlx.
[1] S. Yabuuchi, M. Okamoto, A. Nishide, Y. Kurosaki, and J. Hayakawa, Appl. Phys. Expr, 6, 025504 (2013).
[2] M. Meinert, M. P. Geisler, J. Schmalhorst, U. Heinzmann, E. Arenholz, W. Hetaba, M.Stöger-Pollach, A. Hütten, and G. Reiss, Phys. Rev. B 90, 085127 (2014).
[3] Y. Nishino and Y. Tamada, J. Appl. Phys. 115, 123707 (2014).
8:00 PM - ES09.06.04
High Thermoelectric Performance through Structural Complexity in Sulphide Minerals
Anthony Powell 1 , Sebastian Long 1 , Paz Vaqueiro 1
1 , University of Reading, Reading United Kingdom
Show AbstractThermoelectric devices enable direct thermal to electrical energy conversion. The use of waste heat as the source of thermal energy provides an opportunity to achieve efficiency savings in a wide range of applications. Approximately 80% of waste heat generated in industrial processes is released as a heated gas at temperatures between 373 and 535 K. Whilst research into thermoelectric materials has led to significant performance enhancements at elevated temperatures (600 - 900 K), there remains something of a dearth of materials for energy harvesting at lower temperatures appropriate to low-grade waste heat. Much of our recent work has been directed at materials for thermal to electric energy conversion in the temperature window 373 ≤ T/K ≤ 573, where there are significant opportunities for efficiency gains in energy-intensive industries.
High thermoelectric performance requires optimisation of the Seebeck coefficient (S), electrical conductivity (σ) and thermal conductivity (κ) to maximise the figure-of-merit (ZT = S2σT/κ). Since S, σ and κ exhibit differing dependencies on charge-carrier concentration, strategies are required that achieve a degree of separation between the electrical (S2σ) and thermal (κ) components of ZT. Moreover large-scale applications require inexpensive and readily-available materials. These considerations have led us to investigate synthetic analogues of complex sulphide minerals, containing earth-abundant elements. We have focused on materials in which weakly-bound species, associated with one sub-lattice in a structure, confer a degree of ionic mobility, resulting in low lattice thermal conductivities (κL). Electrical properties can then be improved by judicious chemical substitution which maintains a low thermal conductivity.
We have successfully applied this strategy to bornite, Cu5FeS4, which adopts a complex vacancy-ordered structure at room temperature. The parent p-type semiconductor has a thermal conductivity, κ ≈ 0.4 W m-1 K-1. The power factor is enhanced through the introduction of copper vacancies in Cu5-xFeS4, due to an increased electrical conductivity, which also increases the electrical contribution to κ. However, as this is offset by a reduction in κL the overall thermal conductivity is almost invariant with copper content. Consequently the figure of merit reaches ZT = 0.6 for 0.06 ≤ x ≤ 0.12. Similar improvements have been achieved by partial substitution of iron by copper in Cu5+yFe1-yS4 which increases ithe maximum power factor by ca. 130%, and again results in a maximum figure of merit of ZT = 0.6. Combining copper substitution with the introduction of cation vacancies in materials of general formula Cu5-x+yFe1-yS4 leads to further improvements in performance. The maximum ZT = 0.8 achieved for Cu4.972Fe0.968S4 at 550 K, is amongst the highest for a sulphide in this temperature range.
8:00 PM - ES09.06.05
Control of P-Type and N-Type Conduction in Thermoelectric Mg2Si Thin Films Prepared by Sputtering Method
Mao Kurokawa 1 , Mutsuo Uehara 1 , Daichi Ichinose 1 , Takao Shimizu 1 , Kensuke Akiyama 2 , Masaaki Matsushima 1 , Hiroshi Uchida 3 , Yoshisato Kimura 1 , Atsuo Katagiri 1 , Hiroshi Funakubo 1
1 , Tokyo Institute of Technology, Yokohama Japan, 2 , Kanagawa Institute of Industrial Science and Technology, Ebina Japan, 3 , Sophia University, Tokyo Japan
Show AbstractMg2Si is a promising candidate as a thermometric material that consists of nontoxic elements. It is lighter than BiTe and PbTe, and it shows a high figure of merit at 300-600 oC. Bulk Mg2Si shows n-type conduction, which is pointed out to be due to Mg atoms occupying the interstitial site of the crystal lattice. Provided that n-type conduction is an intrinsic character of bulk Mg2Si, it is difficult to prepare p-type counterpart with an excellent figure of merit only by the doping. We grew Mg2Si films by the sputtering method. These films showed p-type conduction after the heat treatment at 500 oC in He atmosphere [1]. This is quite different from the bulk Mg2Si because p-type conduction has been hardly reported without the doping of appropriate elements. In the present study, we investigated the control method of the conduction type in Mg2Si films.
Mg2Si films after the heat treatment show the p-type conduction. However, it switched to p-type conduction after the additional heat treatment covered with Mg tape. This shows that the conduction type can be controlled by the heat treatment atmosphere. First principle calculation suggests that the interstitial Mg and Mg vacancy in Mg2Si are possible to be the origins of n-type and p-type conduction [2]. Based on this consideration, Mg2Si films after the heat treatment in He can be considered to include Mg vacancies by the evaporation of Mg from the film, which results in p-type conduction. On the other hand, these Mg vacancies were filled and additional interstitial Mg is considered to be incorporated by the heat treatment covered with Mg foil, which results in n-type conduction. These results open the possibility of the novel control method of the conduction type in Mg2Si films. [1] S.Ogawa et al., J. Electronic Mater., 43 (2014) 2269. [2] Y.Imai, J. Alloys Comp., 664 (2016) 369.
8:00 PM - ES09.06.06
Improving Thermoelectric Performance of P-Type Polycrystalline SnSe via Impurity Alloying
YongKyu Lee 1 , In Chung 1
1 , Seoul National University, Seoul Korea (the Republic of)
Show AbstractA single crystalline form of p-type SnSe has recently shown an exceptionally high thermoelectric figure of merit (ZT) of ~2.6 at 923 K along the crystallographic b-axis due to its extremely low thermal conductivity. Afterwards, polycrystalline counterparts have been intensively investigated because of their machinability and availability in large scale preparation and applications. However, obtaining a high ZT in polycrystalline SnSe materials is still challenging and their ZT remains much lower than that of the single crystals. Here we report the effects of PbSe alloying along with Na doping on thermoelectric properties of polycrystalline SnSe materials. The precise control of alloying compositions in conjunction with optimization of carrier concentration remarkably enhances electrical conductivity and consequent power factor while reduce thermal conductivity by alloy and point defect scatterings simultaneously. As a result, a markedly high ZT ~1.2 at 773 K was achieved. We also investigate nano- and microstructures of the samples at the atomic level to better understand the origin of their enhanced thermoelectric performances employing spherical-aberration corrected scanning transmission electron microscope.
8:00 PM - ES09.06.08
Evaluation of Bonding Strength in Thermoelectric Module under Various Loading Conditions
Ryo Inoue 1 , Tetsuro Takagi 1 , Tsutomu Iida 1 , Yasuo Kogo 1
1 , Tokyo University of Science, Tokyo Japan
Show AbstractThermoelectric (TE) technologies have been focused on for past decades to reduce waste heat. Mg2Si is one of the most promising candidate TE material because this material has low density and high power generation efficiency at high temperature (873K). For applying Mg2Si for TE module, development of interconnect technology between element and ceramic substrate is important. The interconnected material requires adhesion between components, low electrical resistance, and thermal stability, etc. In the present study, we developed Mg2Si uni-leg TE generators using several materials Al and Al-Si based materials. Evaluation of bonding strength was also carried out under shear loading and vibration conditions and performance of developed uni-leg TE module was examined.
The rectangular specimens were cut from the center of the sintered polycrystalline Mg2Si with a dimension of 4×4×10mm. Then, Mg2Si was bonded to Ni terminal using Al and Al-Si based interlayers at various temperatures. Evaluation of bonding strength was measured by shear test and vibration tests. After the test, fracture surface was observed by scanning electron microscopy (SEM) in order to understand fracture behavior of TE modules. Stress distribution was also simulated by finite element (FE) analysis.
Results of shear test show that crack tends to initiate at Mg2Si. Then, crack propagates toward to Mg2Si/interlayer interface. The bonding strength, which is calculated from the maximum load, measured by shear test is less than 20MPa. This result suggests that failure occurs by tensile stress generated within Mg2Si component. Shear stress distribution obtained from FE analysis suggests that shear stress generates within interlayer is 50-120MPa, however, failure initiates from Mg2Si device. The results of vibration test also show failure of TE modules do not occur even after vibration test under several conditions. These experimental results suggest that we successfully developed strong bonding between Mg2Si device and Ni terminal.
8:00 PM - ES09.06.09
Interface Effect of 2D MoS2 on Thermoelectric Properties of Bi2Te3:MoS2 and Sb2Te3:MoS2 Nanocomposites
Mujeeb Ahmad 1 , Deepak Varandani 1 , Bodh Mehta 1
1 Thin Film Laboratory, Department of Physics, Indian Institute of Technology Delhi, New Delhi, Delhi, India
Show AbstractBismuth telluride (Bi2Te3) and antimony telluride (Sb2Te3) are among the most efficient thermoelectric materials. Molybdenum disulphide (MoS2) has attracted much attention in thermoelectric application because of its high carrier mobility and its tunable electronic and thermal properties which can be tailored by controlling the number of layers. In the present study, the effect of incorporation of MoS2 nanoflakes on electronic and thermoelectric properties of Bi2Te3:MoS2 and Sb2Te3:MoS2 nanocomposite sample was studied using KPFM measurement. The Surface potential value at Bi2Te3:MoS2 interface is lower by 300 mV as compared to Bi2Te3 and in case of Sb2Te3:MoS2 surface potentials is observed to be 150 mV lower as compared to Sb2Te3. This decrement of the surface potentials value shows higher work function at the interface in comparison to the pristine sample. To further confirm the above interfaces results, KPFM analysis for measuring interface barrier between MoS2/Bi2Te3 and MoS2/Sb2Te3 bilayer samples was also carried out. This measurement is carried out by applying KPFM voltage in surface and interface mode. The interface energy barrier in Bi2Te3:MoS2 and Sb2Te3:MoS2 nanocomposite samples effectively are expected to modify electron/hole transport and phonon scattering. The value of ZT was calculated to be 0.77 and 0.48 for Bi2Te3:MoS2 and Bi2Te3 samples, respectively, at room temperature. Similarly ZT value of 0.18 and 0.28 was calculated at 427 K for Sb2Te3 and Sb2Te3:MoS2 samples, respectively. Both nanocomposite samples show higher ZT values as compared to the corresponding pristine samples. In the case of Bi2Te3:MoS2, the enhancement in ZT is due to decrease in thermal conductivity, whereas in Sb2Te3:MoS2 the enhancement is due increase in power factor. This difference is can be attributed the difference in behavior of Bi2Te3:MoS2 and Sb2Te3:MoS2 interfaces.
8:00 PM - ES09.06.10
Influence of Grain Size and Secondary Phase on Mechanical and Thermoelectric Properties of Mg2Si
Yuya Minamida 1 , Ryo Inoue 1 , Tsutomu Iida 1 , Yasuo Kogo 1
1 Material Science and Technology, Tokyo University of Science, Tokyo Japan
Show AbstractMagnesium silicide (Mg2Si) is a promising thermoelectric material with the advantages of lightweight, abundance of its constituent elements in nature, and high power generation efficiency at about 873 K. Because above mentioned advantages, Mg2Si is expected to apply automobile applications. Strength of Mg2Si is sensitive to surface flaws and internal defects because it is brittle material. Many works reported that fracture toughness of Mg2Si is 0.7~1.0 MPa. The purpose of this study is to improve of fracture toughness of Mg2Si by refinement of Mg2Si matrix and addition of secondary phases without degradation of thermoelectric properties.
Pre-synthesized all-molten commercial polycrystalline Mg2Si-Sb 0.5 at. %- Zn 1.0 at. % was used as a starting material. Mg2Si ingots were pulverized to powder with sizes of 25-75µm (U75) and less than 25 µm (U25), respectively. In addition, the powders (U 25) were further ground into fine particles using ball-milling. Then, the powders were sintered by plasma activated sintering (PAS). We also prepared the mixture of each powders and silicon nitride particles. The volume fraction of Si3N4 was set to be 1 and 5vol%. The powder mixtures were also sintered under similar process conditions.
Young's modulus and fracture toughness of the sintered pellets were measured by ultrasonic pulse method and indentation fracture (IF) method with the indentation load of 300 and 500 gf. Electrical conductivity, Seebeck coefficient and thermal conductivity were also measured by four-terminal sensing, thermo-electromotive force method and laser flash method. Dimensionless figure of merit (ZT) was determined using those values.
In case of ball-milled specimen, Young’s modulus and fracture toughness are increased with decreasing grain size. They are reached at 138 GPa and 2.0 MPa, respectively. On the other hand, thermoelectric properties tend to decrease with decreasing grain size. Mechanical properties of Mg2Si are also improved by incorporation of Si3N4 particles. These experimental results suggest that addition of secondary phase and refinement of grain size are effective to enhance mechanical properties of Mg2Si. In this presentation, the influence of grain size of Mg2Si and second phase on the fracture toughness and thermoelectric properties will be discussed.
8:00 PM - ES09.06.11
Theoretical Investigations of Interfacial Scattering Effects on Thermoelectric Properties of Bulk Nano-Structured PbTe System
Neeleshwar Sonnathi 1 , Anjali Panwar 1 , Vikas Malik 2 , Anjana Bagga 1
1 , Guru Gobind Singh Indraprastha University, New Delhi India, 2 , Jaypee Institute of Information Technology, Noida, UP, India
Show AbstractEnhancement of thermoelectric properties at room temperature has been recently demonstrated by spark plasma sintered PbTe nanocubes as compared to the other PbTe nanostructures as well as the bulk material. The Seebeck coefficient has been reported to be 400 µV/K which is much higher than the bulk. Moreover, a moderate electrical conductivity ~8000 S/m at room temperature results in considerable higher value of power factor S2σ ~ 1.28 x 10-3 Wm-1K-2. The enhanced thermoelectric properties have been conjectured to be present due to the energy filtering effects at numerous interfaces introduced by nanostructuring. We study how the interfacial scattering affects the power factor by performing theoretical modelling based on Boltzmann transport equations. We also investigate in detail the role of various electronic structure parameters such as size, shape, mobility and effective mass etc. on interfacial scattering to optimize its effect on power factor.
8:00 PM - ES09.06.12
Microwave Assisted Synthesis of CZTS Spheres Like Particles for the Thermoelectric Applications
Neeleshwar Sonnathi 1 , Sarita Sharma 1
1 , Guru Gobind Singh Indraprastha University, New Delhi India
Show AbstractMicrowave-assisted rapid synthesis of sphere-like Copper Zinc Tin Sulphide (CZTS) particles using PVP as surfactant has been demonstrated. The physical properties of CZTS microspheres such as structural, morphological, and optical absorption are investigated by XRD, SEM, TEM, micro-Raman, and UV–Vis spectroscopy. XRD result of CZTS sample matches well with kesterite crystal structure (JCPDS card no.: 26-0575). Raman analysis confirms the formation of single phase CZTS having kesterite crystal structure with characteristics peak for CZTS at 332 cm-1. SEM and TEM studies reveal that the CZTS particles are spherical in shape with relatively uniform sizes. The particles are connected with the adjacent ones to form chain-like network. EDS analysis shows the presence of all four elements. The synthesized CZTS spheres have a direct band gap of 1.64 eV. Thermoelectric materials like CZTS with non-toxic, low cost and environmental friendly elements are highly essential for the improvement of cost effective and safe thermoelectric technology.
8:00 PM - ES09.06.13
Thermoelectric Property of Vanadium Oxide Glass-Based Materials
Akifumi Matsuda 1 , Yuki Fujimoto 1 , Satoru Kaneko 2 1 , Mamoru Yoshimoto 1
1 , Tokyo Institute of Technology, Yokohama Japan, 2 , Kanagawa Institute of Industrial Science and Technology, Ebina, Kanagawa, Japan
Show AbstractThermoelectric conversion utilizing Seebeck effect which directly convert thermal energy to electricity is of importance as an energy harvesting technology as well as solar cells. The conversion performance is commonly described as dimensionless figure-of-merit ZT = σS2T/κ; it is proportional to electric conductivity (σ) and square of Seebeck coefficient (S), while thermal conductivity (κ) has inverse effect. There have been large efforts to enhance ZT by reducing thermal conductivity owing to nanocomposites for common chalcogenide and silicide compounds as well as layered cobalt oxides. On the other hand, structures without long-range order such as amorphous and glassy materials have low-κ themselves according to short mean-free-path of phonons. Vanadium oxides, common in vanadium phosphate glasses, are known as strongly correlated materials, in which oxygen deficiency and strain cause hopping transport in this transition metal oxide according to coexistence of multiple oxidation states [1–2]. In this study, synthesis of vanadium oxide glass-based thermoelectric materials, their thermoelectric properties were investigated. The glasses had components of Bi to suppress thermal conductivity, W or Cu to improve electrical conductivity. The V2O5–Bi2O3–WO3 glasses were formed on sapphire (α-Al2O3 single crystal) or quartz glass substrates by pulsed laser deposition using a sintered ceramic target in ultra-high vacuum at room-temperature. The precursor in the process has large kinetic energy that could suppress the compositional deviation. On the other hand, V2O5–P2O5–Fe2O3–CuO glasses were printed on α-Al2O3 substrates via microparticles dispersed ink. The glass films were subsequently thermally treated in air or in reductive ambient such as vacuum or H2 gas at 200–700°C not only to form continuous film but also to control valence states. The V2O5–Bi2O3–WO3 glass film indicated n-type conduction according to the Seebeck effect and the resistivity dropped by 2–3 orders owing to treatment in reductive atmosphere. The V2O5–P2O5–Fe2O3–CuO films were treated intentionally to form glass-ceramics to improve thermoelectric properties, that conductivity and the Seebeck coefficient of the films reached 102 Ω–1cm–1 and –130 μV/K. Furthermore, it was found the strongly reductive ambient inverts the conduction type from negative to positive. The thermoelectric conversion applying the materials as well as their morphological and structural characteristics would be presented.
[1] T. Naito et al., J. Ceram. Soc. Japan 121 (2013) 452.
[2] A. Matsuda et al., J. Ceram. Soc. Japan 123 (2015) 618.
8:00 PM - ES09.06.14
Designing Optimized and Cost Effective Hybrid Thermoelectric—Photovoltaic Devices
Bruno Lorenzi 1 2 , Dario Narducci 1
1 Department of Materials Science, Univ of Milano-Bicocca, Milan Italy, 2 Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractRecently the interest around the implementation of thermoelectric generators (TEGs) to improve the performances of photovoltaics (PV) is steeply growing. Actually an increasing number of theoretical and experimental publications appeared on this topic in the last years. Although several works reported large efficiency improvements, they mostly focused on the coupling between commercial devices not optimized to work in hybrid thermoelectric – photovoltaic generators (HTEPVG) [1,2]. Actually no experimental attempt to tailor the TEG materials and design influencing the hybrid device temperature has been reported so far. Nonetheless most models neglect how the PV absorber material can impact on the amount of the recoverable power and on the temperature sensitivity of the PV part.
In this communication we report on a multi-parametric model based on previous studies [3,4] developed to find the HTEPV optimized parameters needed for a beneficial coupling between PV and TEG sections. Starting from modeling the PV part, we computed the PV and the TEG efficiencies as a function of the energy gap of the PV absorber material, the device temperature, the optical concentration, and several other parameters.
The study which has been recently supported by a first experimental evaluation showed that it is possible to achieve a TEG contribution up to 4-5% of the solar power. However this upper value can be obtained only in the case of wide energy-gap PV working at sufficiently high temperatures, limiting hybridization effectiveness to very few PV materials. This pointed out the necessity of a specific TEG design, and a proper device encapsulation (preventing radiative exchange).The main parameters ruling the hybridization effectiveness were identified, guiding the design of an optimized prototype based on Copper Gallium Selenide solar cells, an optimized TEG, and an encapsulation equipped with a heat mirror.
REFERENCES:
[1] Hsueh T-J, Shieh J-M, Yeh Y-M. Hybrid Cd-free CIGS solar cell/TEG device with ZnO nanowires. Prog Photovoltaics Res Appl 2015;23:507–12.
[2] Park K-T, Shin S-M, Tazebay AS, Um H-D, Jung J-Y, Jee S-W, et al. Lossless hybridization between photovoltaic and thermoelectric devices. Sci Rep 2013;3:422–7.
[3] Chen G. Theoretical efficiency of solar thermoelectric energy generators. J Appl Phys 2011;109.
[4] Lorenzi B, Acciarri M, Narducci D. Conditions for beneficial coupling of thermoelectric and photovoltaic devices. J Mater Res 2015;30:2663–9.
8:00 PM - ES09.06.15
Thermoelectric Properties of Single-Wall Carbon Nanotubes Investigated through Simulation, Type-Separation and Molecular Dopants
Stephen Polly 1 , Jamie Rossi 1 , Chris Schauerman 1 , Matthew Ganter 1 , Brian Landi 1 , Ryne Raffaelle 1
1 , Rochester Inst of Technology, Rochester, New York, United States
Show AbstractThermoelectric properties of single-wall carbon nanotubes (SWCNTs) were investigated both theoretically and experimentally. The density of states of over 200 different SWCNT chiralities ranging from (2,2) to (25,0) was calculated using CNT Bands, a tight-binding model available on NanoHUB.org. These simulations were used as inputs to a computer model developed to determine the overlap of the temperature dependent Fermi distribution, from a hot side to a cold side, across a given chirality as a function of energy. The resulting model describes the predicted Seebeck coefficient for each chirality, showing metallic SWCNTs may exhibit maximum Seebeck coefficients of 125 μV K-1 or less, while semiconducting SWCNTs could exhibit Seebeck coefficients approaching 5,000 μV K-1, depending on their precise doping levels. These data were further manipulated to determine the effect on expected Seebeck coefficient due to mixed distributions of SWCNT chiralities (multimodal chirality distributions are common from SWCNT production methods), as well as the expected effects of type-separation of mixed chiralities into metallic and semiconducting fractions. Experimentally, SWCNTs were synthesized using laser vaporization, and purified using acid reflux or ultracentrifuge methods. The materials were filtered into thin films or freestanding papers. Electro-thermal characterization was performed and analyzed on a custom apparatus. Purified SWCNT material (containing mixed chiralities) exhibited a Seebeck coefficient (S) of +41 μV K-1 (indicating p-type material) and a conductivity of 1.71x105 S/m, resulting in a power factor of 288 μW m-1 K-2. Further improvements to conductivity and Seebeck coefficient were investigated by separating the SWCNTs into semiconducting and metallic electronic-types using column chromatography. Semiconducting SWCNTs exhibited a larger Seebeck coefficient of as high as +110 μV K-1, while metallic SWCNTs measured lower at +25 μV K-1. While fitting the general trend of the model described above, differences in between the model prediction for these materials and the experimental results is likely tied to the efficiency of type-separation, as well as doping of these materials. Molecular dopants, known previously to maximally increase the conductivity of these materials, were used to investigate the effect on Seebeck coefficient and power factor. These materials, optimized for conductivity, typically lowered the Seebeck coefficient but remained generally net-positive, increasing the power factor of the SWCNT material. Molecular dopants were also used to n-type dope the SWCNT thin films, and functional SWCNT thermoelectric devices were produced.
8:00 PM - ES09.06.16
Thermoelectric Performance of Tetrahedrite Synthesized by a Modified Polyol Process
Daniel Weller 1 , Andrew Ochs 2 , Grace Kunkel 2 , Mary Anderson 2 , Donald Morelli 1
1 , Michigan State University, East Lansing, Michigan, United States, 2 Chemistry, Hope College, Holland, Michigan, United States
Show AbstractTetrahedrite materials demonstrate good thermoelectric properties while also being composed of earth-abundant, non-toxic elements. In this study, tetrahedrite thermoelectrics were synthesized in less than two hours by a solution-phase method, known as the modified polyol process, followed by spark plasma sintering for densification. This technique has been shown to successfully synthesize the parent copper-based compound as well as tetrahedrite doped with transition metals (Zn and Fe). Nanoparticles ranging from 50-200 nm in size were obtained from the chemical synthesis, and the nanostructuring was maintained after powder processing. Thermoelectric properties were measured for the parent and doped compounds, and the resulting figures of merit are comparable to those obtained using conventional solid-state synthesis. The nanostructured compounds demonstrated lower thermal conductivity, higher electrical resistivity, and increased thermopower compared to bulk samples. This study explores the effects of doping and nanostructuring on the thermoelectric properties of tetrahedrite synthesized by a solution-phase polyol process.
8:00 PM - ES09.06.17
Enhancing Thermoelectric Properties of N-Type SnSe
Joonil Cha 1 , In Chung 1
1 , Seoul National University, Seoul Korea (the Republic of)
Show Abstract
P-type SnSe single crystals exhibit a record-high ZT value of ~ 2.6 at 923 K because of ultralow lattice thermal conductivity. According to the first-principles calculations, even higher ZT value is expected for its n-type counterpart. However, very few experimental studies on thermoelectric properties of n-type SnSe have been reported. In fact, it is difficult to stabilize n-type SnSe systems with high thermoelectric performance is a difficult task mainly because of spontaneous formation of Sn vacancy. Its formation is thermodynamically favorable, giving rise to intrinsic p-type conduction nature. In this presentation, we report new approaches of developing high performance n-type polycrystalline SnSe systems. We investigate the effects of doping and alloying on n-type SnSe systems to improve their thermoelectric performance. We also present scanning transmission electron microscopic studies to better understand electrical and thermal transport properties of the materials developed in this work.
8:00 PM - ES09.06.18
Thermoelectric Properties of Cr-Doped Higher Manganese Silicides Prepared Using Spark Plasma Sintering
Tomoyuki Nakamura 1 2 , Kentaro Yoshioka 2 , Ryuji Arai 2 , Jun-ichi Nishioka 2 , Mikiyasu Hirakawa 1 , Kenjiro Fujimoto 3 , Ryuji Tamura 1 , Keishi Nishio 1
1 Department of Materials Science and Technology, Tokyo University of Science, Tokyo Japan, 2 Research and Development Center, SWCC SHOWA CABLE SYSTEMS CO., LTD, Sagamiharashi Japan, 3 Department of Pure and Applied Chemistry, Tokyo University of Science, Chiba Japan
Show AbstractEnergy resource depletion and global warming have become serious environmental issues. As an approach for addressing such issues, thermoelectric power generation has attracted attention because it can convert waste heat directly into electrical energy. Thermoelectric power generation can reuse wasted thermal energy, such as heat discharged from factories. Silicide-based thermoelectric materials are expected to be used because of their eco-friendliness, abundance of constituents, and relatively high performance.
Magnesium silicide (Mg2Si) is a prospective n-type thermoelectric material. As a p-type semiconductor thermoelectric material candidate, coupled with the n-type semiconductor Mg2Si, higher manganese silicides (HMSs) are promising materials. An HMS is a p-type thermoelectric material that is superior in mechanical strength and oxidation resistance; however, the thermoelectric properties of HMSs are not as high as those of Mg2Si. The power generation efficiency of Mg2Si-HMS thermoelectric p-n couples is lower than that of Mg2Si uni-leg thermoelectric modules because the electrical conductivity of an HMS is lower than that of Mg2Si.
In this study, we tried to increase the electrical conductivity of HMSs by substituting Cr for Mn at HMS sites. The HMSs were synthesized using spark plasma sintering (SPS), which can synthesize compounds in non-equilibrium states. Mechanical grinding was performed on HMSs to obtain micro-particles. For HMS bulk consisting of micro-particles, a reduction in the lattice thermal conductivity of the material should occur due to phonon scattering at the particle grain boundaries. HMSs were synthesized using SPS equipment after the mixed powder of Mn, Cr, and Si was filled into a graphite die. After the first SPS synthesis, the obtained HMS sintered bodies contained unreacted elements and impurities. However, high-purity HMSs were obtained after the second SPS synthesis using micro-particle powder, prepared by milling the first sintered body. With increased amounts of doped-Cr, the electrical resistivity of the Cr-doped HMSs decreased by up to 25at.% with Cr substitution. The electrical resistivity of 20at.% Cr-HMSs was half that of un-doped HMSs. The Seebeck coefficient of the HMSs also decreased with an increase in the amounts of doped-Cr.
8:00 PM - ES09.06.19
Energy Filtering Effect of Bi2Te3 Nanowire–PEDOT:PSS Composites
Wan Sik Kim 1 , Ji Young Jo 1
1 , Gwangju Institute of Science and Technology (GIST), Gwangju Korea (the Republic of)
Show Abstract
Thermoelectric (TE) materials, which exhibit a capability to convert heat to electricity vice versa, have received wide attention due to the world’s demand for sustainable and eco-friendly energy. It is well known that the thermoelectric efficiency can be defined as σS2T/k. Especially, organic-inorganic hybrid TE materials with high electrical conductivity σ and low thermal conductivity k have been intensively studied due to their advantages such as flexibility, light weight, low-cost, and mass production; however, there have been a critical issue for a thermoelectric efficiency arising from conflicting factors, i.e., σ and Seebeck coefficient S. Here we present that their interfaces can be facilitated to solve this problem by employing carrier energy filtering effect and phonon blocking.
In this work, we fabricated Bi2Te3 nanowires via polyol method using ethylene glycol (EG) as solvent, and then combined with poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) solution (PH 1000, Heraeus Clevios) as conducting polymer matrix. The Bi2Te3/PEDOT:PSS composite films were deposited on glass substrates through spin coating method and then annealed by solvent vapor annealing (SVA) manner using dimethyl sulfoxide (DMSO) solution.
The SVA process increases both work function and s of PEDOT:PSS by inducing formation of highly enriched PSS layer on the surface of PEDOT:PSS. Bi2Te3 nanowires facilitate that carriers can move one dimensionally by quantum confinement effect. The PEDOT:PSS matrix with a high σ provides the low k. Their interfaces play an important role as carrier energy barrier which can strongly scatter the low energy carriers by only passing high-energy carriers across interfaces, which enhances the S without significant decrease in the σ. DMSO-SVA treated composite films form different potential barrier height between PEDOT:PSS matrix and Bi2Te3 nanowire as SVA time, which cause various σ and S value due to different magnitude of energy filtering effect as potential barrier height. These interfaces also play a role of phonon glass by decreasing thermal conductivity without reduction of electrical conductivity. The highest ZT value was optimized by changing potential barrier height between PEDOT:PSS and Bi2Te3 nanowires. Our study suggests that conducting polymer matrix composites based on the nanometer-scaled nanowires are a promising structure for thermoelectric materials with high thermoelectric performance.
8:00 PM - ES09.06.20
Thermoelectric Properties of Ce-Filled P-Type Skutterudites—CexFeyCo4-ySb12
Jungmin Kim 1 , Ken Kurosaki 1 2 , Yuji Ohishi 1 , Hiroaki Muta 1 , Shinsuke Yamanaka 1 3 , Misato Takahashi 4 , Junya Tanaka 4
1 Graduate School of Engineering, Osaka University, Osaka Japan, 2 JST, PRESTO, Saitama Japan, 3 Research Institute of Nuclear Engineering, University of Fukui, Tsuruga Japan, 4 Production Engineering Laboratory, Manufacturing Technology and Engineering Division, Panasonic Corporation, Kadoma Japan
Show AbstractSkutterudite compounds such as CoSb3, showing excellent thermoelectric (TE) properties at intermediate temperature range, have been considered as a good candidate of TE materials because they mainly consist of relatively non-toxic and earth-abundant elements compared to other TE materials with high TE performances. The unique feature of the skutterudite structure is to have two cage-like voids in a unit cell which can be filled by a third atom, called as a filler. Among the filler elements, the rare-earth metals are the most powerful fillers to reduce lattice thermal conductivity and enhance figure of merit. On the other hand, generally, to make the p-type materials, the Co site of CoSb3 is substituted by Fe.1) Although, the heavily Fe-doped CoSb3 system tends to be metastable crystal structures, they can be stabilized by compensating the excess hole by the incorporation of filler elements as an electron donor. Additionally, the carrier concentration can be controlled by modifying both the Fe/Co ratio and the fraction of filler elements, which is the effective strategy to enhance the TE properties of p-type skutterudites. Furthermore, the (Fe,Co)Sb3-based p-type skutterudites generally indicate higher filling fraction than the CoSb3-based n-type ones due to the enlargement of the void sites as well as the charge compensation.2) In this study, we have developed a series of Ce-filled p-type skutterudites CexFeyCo4-ySb12 with greatly improved filling fractions and figure of merit. Polycrystalline samples of CexFeyCo4-ySb12 in the nominal compositions of x = 0.8, 0.9, 1.0 and y = 3.0, 3.5 were synthesized and the TE properties were examined from room temperature to 773 K. Effects of the Ce-filling and the Fe substitution on the TE properties were investigated.
Reference
1) Jungmin Kim, K. Kurosaki et al., Mater. Trans. in press.
2) Seongho Choi, Ken Kurosaki et al., J. Electron. Mater. 44, 1743–1749 (2015).
8:00 PM - ES09.06.21
Finite Element Simulation on Thermoelectric Properties of Tilted Rod-Ni/Mg2Si Composites
Takashi Itoh 1
1 , Nagoya University, Nagoya Japan
Show AbstractMg2Si is a promising n-type thermoelectric material for thermoelectric power generation using waste heat with temperature range of 300 to 600 oC. Construction of composites with Mg2Si and metallic material brings the anisotropic thermoelectric properties and the enhanced mechanical properties. The transverse thermoelectric force is created by giving vertical temperature difference in the tilted anisotropic material (transverse thermoelectric effect). In our previous work, we have clarified the relation between the thermoelectric properties and the structural conditions of the tilted multilayer Mg2Si/Ni composites using finite element simulation. In this study, we focused on the tilted rod-Ni/Mg2Si composite, and investigated the influence of the structural conditions on the thermoelectric performance using the finite element simulation. The simulations were carried out using the rod-Ni/Mg2Si composite element models with different tilt angle of Ni rod and different volume fraction of Ni under the same temperature conditions of 500 oC (hot side) and 100 oC (cold side). The volume fraction effect on the thermoelectric properties of the rod-Ni/Mg2Si composites with 0o and 90o of tilt angle were different from that of the Mg2Si/Ni multilayer composite due to the structural difference. The thermoelectric performance changed in the tilt angle of Ni rod and the volume fraction of Ni. There were optimum conditions of the tilt angle and the volume fraction which gave the maximum thermoelectric performance of the rod-Ni/Mg2Si composite.
8:00 PM - ES09.06.22
Experimental Study on Thermal Conductivity of Sb2Te3/Au, Sb2Te3/Ag and Sb2Te3/Cu Multilayer Thermoelectric Film Systems
Yang Gang 2 1 3 , Zhiyu Hu 2 1 3
2 , National Key Laboratory of Science and Technology on Micro/Nano Fabrication, Shanghai China, 1 , Institute of NanoMicroEnergy, Shanghai Jiao Tong University, Shanghai China, 3 , Department of Micro/Nano Electronics, Shanghai Jiao Tong University, Shanghai China
Show AbstractThermoelectric technology, harvesting electric power from heat, is a promising environmentally friendly means of energy conversion. The thermoelectric energy conversion efficiency is determined by the dimensionless figure of merit ZT, where Z is a measure of a material’s thermoelectric properties and T is absolute temperature. In order to improve the thermoelectric efficiency, various possible approaches to enhancing ZT have been proposed and developed. One of effective approach is to create nanoscale multilayer structure. Nanostructures with high interface densities can lead to significant ZT enhancement by strongly reducing phonon thermal conductivity without a deterioration of the electronic motilities. Interface scattering of phonons is the considered to be the major contributor.
In this paper, the cross-plane thermal conductivities of Sb2Te3/Au, Sb2Te3/Ag and Sb2Te3/Cu multilayer films prepared by magnetron sputtering are measured using a differential 3ω method. The heat transfer mechanisms across interface are explored by combining the experimental measurements with theoretical models. The effects of interfacial thermal resistance on thermal transport are examined. Our results indicate that the thermal conductivity of the multilayer film is significantly affected by the electron–phonon coupling at interface. The purpose of this research is providing a more insightful understanding of the thermal transport mechanism of the multilayer film system.
8:00 PM - ES09.06.23
Thin-Film Thermoelectric Peltier Unit with a 2D Horizontal Structure for On-Chip Cooling
Hong Bum Park 1 , Min-Woo Jeong 1 , Haishan Shen 2 , Hoo-Jeong Lee 2 , Young-chang Joo 1
1 , Seoul National University, Seoul Korea (the Republic of), 2 , Sungkyunkwan University Advanced Institute of NanoTechnology, Suwon Korea (the Republic of)
Show AbstractRecently, operation problem occurs with heating at electronics microprocessor which has been shrunk the line width. The conventional thermoelectric cooler cannot be applied to portable electronics such as smartphone due to its limited dimension. Therefore, 2D horizontal thermoelectric cooling method is a potential candidate for stabling temperature with decreasing noise and increasing speed. 2D horizontal thin-film thermoelectric microcooler should be useful and alternative plan by optimizing and improving the system efficiency. We demonstrated the 2D horizontal thin-film thermoelectric Peltier unit which consist of n-type Bi2Te3, p-type Sb2Te3 one pair, and Cu electrode, respectively. The films were deposited by ultra high vacuum radio-frequency sputtering at room temperature and thermal evaporation using shadow metal mask. The thickness of films deposited from 250nm to 10um. The deposition recipe was optimized for high Seebeck coefficient and electrical conductivity. Cu electrode can easily diffused into bismuth and antimony tellurides, a diffusion barrier layer employed at interface between electrode and thermoelements. Ta, Au were selected for diffusion barrier material which has good anti-diffusion properties with metal based electrode from the consideration of thermodynamic stability. After the film deposition, we evaluated the microstructure of the films using FE-SEM, and measured the electrical properties. The cross-sectional image showed that the interface didn’t react with each other, and contact resistance was highly decreased after post annealing. Furthermore, we measured temperature difference of hot and cold junctions by infrared thermal microscopy. The temperature difference of hot and cold junction was obtained due to decreasing the contact resistance which means contact resistance significantly affected the junction temperature. The cooling performance is proportional to the number of Peltier pair. It will be discussed that higher temperature difference can be obtained by connecting p-, n- pair unit in series.
8:00 PM - ES09.06.24
Preparation of NiSi2 and Application to Thermoelectric Silicide Elements Used as Electrodes
Kentaro Yamamoto 1 , Tomoyuki Nakamura 1 2 , Kenjiro Fujimoto 3 , Ryuji Tamura 1 , Keishi Nishio 1
1 Department of Materials Science and Technology, Tokyo University of Science, Katsusika-ku Japan, 2 , SWCC SHOWA CABLE SYSTEMS CO., Kanagawa Japan, 3 Department of Pure and Applied Chemistry, Tokyo University of Science, Chiba Japan
Show AbstractThermoelectric power generation is a method that converts the waste heat from various sources, e.g., cars and factories, into electrical energy by using the Seebeck effect. Silicide-based thermoelectric materials have high performance in the temperature range from 573 to 873 K. Magnesium silicide (Mg2Si) and higher-manganese silicides (HMSs) are used as n-type and p-type semiconductor materials, respectively. In π-structure modules, consisting of Mg2Si as an n-type semiconductor and HMSs as a p-type, the thermal expansion coefficient of Mg2Si is approximately 1.5 to 2.0 times larger than that of HMSs, which is one of the factors that impairs durability of the module. It is important to reduce the difference in the thermal expansion coefficient between the electrode material and the two thermoelectric materials. Many researchers have used Ni as an electrode for Mg2Si because the thermal expansion coefficient of Ni is close to that of Mg2Si. Previous studies have shown that fractures occur due to the formation of MgO and a Ni-Si compound, which form because of the inter-diffusion of Si on the interface of Mg2Si and Ni. They have also shown that fractures occur in HMSs due to the large difference in the thermal expansion coefficient between Ni and HMSs. In this study, we applied NiSi2 as an electrode for thermoelectric modules because NiSi2 has higher electric conductivity and is expected to suppress the inter-diffusion of Si from MgSi2 and HMSs.
The thermal expansion coefficient of NiSi2 is close to that of Mg2Si; however, the thermal expansion coefficient of NiSi2 differs from that of HMSs. Therefore, to reduce thermal stress, we tried to insert gradients consisting of HMS and NiSi2 for the interface between the HMS sintering body and the NiSi2 electrode. The NiSi2 was prepared using spark plasma sintering (SPS) equipment. To obtain NiSi2 fine powder, NiSi2 sintered bodies were crushed, milled, and pulverized into a powder of 75 μm or less. After putting NiSi2 and the NiSi2/HMS powder mixture on top of sintered HMSs in a graphite die, NiSi2 electrodes and gradients were formed and connected with the HMS by SPS treatment.
Crack-free bonding was achieved by inserting gradients consisting of HMSs and NiSi2.
8:00 PM - ES09.06.25
Synthesis of Higher Manganese Silicide by Spark Plasma Sintering and Planetary Ball Milling and Thermoelectric Performance Evaluation
Mikiyasu Hirakawa 1 , Tomoyuki Nakamura 1 2 , Kenjiro Fujimoto 3 , Ryuji Tamura 1 , Keishi Nishio 1
1 Department of Materials Science and Technology, Tokyo University of Science, Tokyo Japan, 2 , SWCC SHOWA CABLE SYSTEMS CO, Kanagawa Japan, 3 Department of Pure and Applied Chemistry, Tokyo University of Science, Chiba Japan
Show AbstractThermoelectric power generators are solid-state devices that generate electricity from temperature differences. For a given temperature difference, the conversion efficiency of thermoelectric materials depends on the dimensionless figure of merit ZT = S2 sT/k, where S, s, T, and k are the Seebeck coefficient, electrical conductivity, absolute temperature, and total thermal conductivity, which includes both lattice thermal conductivity (kph) and electronic thermal conductivity kel contributions. An ideal thermoelectric material would possess a large S, high s, and low k. Higher manganese silicide (HMS) has recently attracted much attention as a p-type thermoelectric material owing to its eco-friendliness, lower toxicity, and constituent abundance compared with other thermoelectric materials. However, the melting method commonly used for HMS materials generates an impurity—MnSi, which has high electrical and thermal conductivities and a lower Seebeck coefficient. The presence of MnSi reduces the thermoelectric properties of HMS, making it difficult to obtain high purity HMS.
In this study, we investigated the use of spark plasma sintering (SPS), which can synthesize a compound in a non-equilibrium state, combined with mechanical grinding, which produces micro particles, to synthesize HMS. Our objective was to suppress the MnSi phase. For HMS bulk consisting of micro particles, the lattice thermal conductivity of the material should be reduced due to phonon scattering at the grain boundaries.
A powder mixture of Mn and Si was filled in a graphite die, and HMS bulk samples were synthesized using SPS. The Si ratio of the MnSix was varied from 1.75 to 1.90. High purity HMS samples with reduced amounts of MnSi and Si were obtained by performing the SPS twice. The samples were milled using a planetary ball mill to obtain micro particles. The milled particles were again heat-treated using SPS to obtain sintered samples. X-ray diffraction and thermoelectric performance analyses of the samples showed that the electric conductivity decreased and the Seebeck coefficient increased with an increase in the Si ratio. The maximum ZT was 0.43 at 750 K when x = 1.75.
8:00 PM - ES09.06.26
Thermoelectric Bi2Te3 Nanowires—Diameter Reduction Effect
Olga Caballero-Calero 1 , Dieter Platzek 3 , Alejandra Ruiz de Calvijo 1 , Maria Cristina Vicente Manzano 1 2 , Marisol Martin-Gonzalez 1
1 , IMM-CSIC, Madrid Spain, 3 , PANCO, Mulheim Germany, 2 , Empa–Swiss Federal Laboratories for Materials Science and Technology, Thun Switzerland
Show AbstractThermoelectric materials can convert a gradient of temperature in a difference of voltage, providing a quite appealing way of recovering wasted heat in the form of usable electricity, and thus, a sustainable source of energy. Those materials should have a good electrical conductivity, high Seebeck coefficient, along with low thermal conductivity. One of the most used materials for room temperature applications is bismuth telluride, but its thermoelectric efficiency is not enough to make it competitive with other ways of energy recovering. In order to enhance the thermoelectric efficiency of given materials for actual applications, one of the most studied routes is the reduction in the dimensionality, via nanowire fabrication, for instance.
Bi2Te3 nanowires via electrochemical deposition inside alumina matrices of different diameters with the same stoichiometry and crystal orientation have been measured in previous works, showing a reduction of the thermal conductivity of the material with the decrease of the nanowire diameter. This has been explained as a consequence of the phonon dispersion in the surface of the nanowires [1], which increases with the increase of the surface to volume ratio. As far as electrical conductivity is concerned, the measurement as function of the nanowire diameter also showed an increase with the diameter reduction, due to a different surface conduction [2]. In order to fully characterize the thermoelectric efficiency of those nanowires, we present the measurement of their Seebeck coefficient along the direction of the nanowire growth as a function of the nanowire diameter with a Potential Seebeck Microprobe [3]. This measurement involves the study of the measurement conditions on the effect of the absolute value of the measurement, along with a round robin with different samples to fully calibrate the system.
[1] M. Muñoz Rojo, B. Abad, C.V. Manzano, P. Torres, X. Cartoixa, F.X. Álvarez, Nanoscale, 9 (2017) 6741
[2] M. Muñoz Rojo, Y. Zhang, C.V. Manzano, R. Álvaro, J. Gooth, M. Salmeron, M. Martín-González, Scientific Reports 6 (2016) 19414
[3] D. Platzek, G. Karpinski; C. Stiewe, P. Ziolkowski, M. Stordeur, B. Engers, and E. Müller; Spatial Resolution of the Seebeck Coefficient Measured on Thermoelectric Thin Films; Proceedings of the 3rd European Conference on Thermoelectrics, Nancy (2005)
8:00 PM - ES09.06.27
Examination of Thermal Stability and Deterioration at Grain Boundary of N-Type Mg2Si for Better Endurance
Mako Tokumura 1 , Tsutomu Iida 1 , Hiroto Hanba 1 , Daishi Shiojiri 1
1 , Tokyo University of Science, Katsusika Japan
Show AbstractMagnesium silicide (Mg2Si) has been identified as a promising advanced thermoelectric material and it has some important attributes in that it is lightweight, there is a worldwide abundance of its constituent elements, and it is non-toxic. Moreover, since it has good power generation performance in the mid-temperature (~900K) range, it is expected that it can be applied in the automotive industry or in industrial furnaces. The current status for Mg2Si is
aimed toward TE module fabrication and appropriate system integration techniques for automotive applications. For the industrialization, thermal stability under the practical operation temperatures is needed to ensure the power generation durability. It has been brought out that the oxidation of Mg, a constituent element instrument of Mg2Si matrix, is a dominant degradation occasion in air circumstance at elevated temperature. The instrument of oxidation of Mg is seen to be closely associated with a contamination of MgO which is located at grain boundary. This MgO is initiated from the native oxides surrounding the Mg2Si power pulverized for compaction and outgrowth during sintering process. Typically, degradation of the sintered Mg2Si thermoelectric power generation tips begin at grain boundaries and proliferate to the periphery. Thus, we are interested in a contribution of MgO at grain boundary in term of degradation at elevated temperature of Mg2Si.
In this report, we examined thermal behavior of grain boundary containing MgO, which is formed by the plasma activated sintering process. Besides, polycrystalline Mg2Si by all-molten synthesis using Bridgman method is performed to obtain a sample possessing a thermodynamically stable grain boundary with less process contaminant. The used Mg2Si specimens were with donor impurities of Sb and isoelectric impurity of Zn with concentration range of 0.1 to 0.64 at%. Variation of grain boundaries for the sintered and melt grown specimens were examined during heat treatment at 873K in air for several ten of hours, and were analyzed using in situ surface morphology monitoring apparatus, high-resolution filed-emission scanning electron microscope (FE-SEM). Formation of MgO and related substances were studied using FE-SEM-EDX and X-ray diffraction. Experimental information on degradation of Mg2Si which is associated with MgO will be shared in this report, and variation in thermoelectric properties correlated to deterioration will also be discussed.
8:00 PM - ES09.06.28
Thermoelectric Power Factor Enhancement in Thin-Film Bilayered Structures of Undoped Germanium (001) and PEDOT:PSS
Dongwook Lee 1 , Jiawei Zhou 1 , Gang Chen 1 , Yang Shao-Horn 1
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractModulation doping is one of the strategies to improve thermoelectric power factors of nano-composites and thin film bilayered structures. In this work, we report thin film of heavily doped p-type organic conducting polymer, Poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) acting as the modulation-dopant that donates holes into the adjacent 21 nm-thick undoped Ge (001) layer. The maximum power factor and Seebeck coefficient of the bilayered structures are 78 μW/m.K2 and 325 μV/K, respectively, corresponding to a 13 fold and 25 fold increase compared to those of PEDOT:PSS and 64 fold increase compared to power factor of undoped Ge. The enhancement in power factor and Seebeck coefficient is explained by the charge transfer through our simulation by considering the band alignment at the interface. We reveal that the valence band offset between PEDOT:PSS and Ge crucially affects the Seebeck coefficient and the electrical conductivity of the thin film bilayered structure. This work suggests the modulation doping as an effective method for enhancing thermoelectric power factors in nanoscale composites and thin film multilayered structures, via tuning the band offset between adjacent compositions. This work is supported by DOE EFRC (Grant No. DE-SC0001299) and Samsung Scholarship.
8:00 PM - ES09.06.29
Thermoelectric Properties of Molybdenum Disulfide (MoS2) with Noble Metal Doping
Gilbert Kogo 1 , Sangram Pradhan 1
1 , Norfolk State University, Norfolk, Virginia, United States
Show AbstractTwo-dimension transition metal dichalcogenides like Molybdenum disulfide (MoS2) has recently been a subject of intensive research because of its excellent electrical, optical properties, and its applications in rechargeable batteries, sensors, transistors and integrated circuits. Due to its low thermal conductivity, high electrical conductivity, and high Seebeck coefficient, MoS2 is a promising candidate for thermoelectric applications. Its room temperature figure of merit (zT=S2σT/Ktot) exceeds the performance of most laboratories reported thus far. We report on the thermoelectric performance of MoS2 thin films grown by PLD on Silicon and Sapphire substrates. Its resistivity displays semiconductor behavior, electrical conductivity increases with temperature. The Power factor (PF=S2σ) increases with temperature until it reaches a value of 3.86x10-4Wm-1K-2 at 300 K and 4.5x10-4Wm-1K-2 at 320 K. The thermal conductivity of 5.16E-02 W/mK was achieved at 300 K. The figure of merit (zT) increases to about 2.24 at 300 K. Our results show that Molybdenum disulfide (MoS2) efficiency is slightly higher than other promising thermoelectric conventional materials with lower thermal conductivity and higher Seebeck coefficient at room temperature. Detailed studies with doping of noble metals will also be reported.
This work is supported by NSF-CREST-CREAM.
8:00 PM - ES09.06.30
Enhancing Thermoelectric Performance in Single-Crystal-Like Semiconducting Films by Tuning the Carrier Scattering Mechanism
Shivkant Singh 1 , Pavel Dutta 2 3 4 , Monika Rathi 2 3 4 , Yao Yao 1 3 4 , Ying Gao 1 3 4 , Sicong Sun 1 3 4 , Devendra Khatiwada 1 3 4 , Venkat Selvamanickam 2 3 4 , Anastassios Mavrokefalos 2
1 Material Science and Engineering, University of Houston, Houston, Texas, United States, 2 Mechanical Engineering, University of Houston, Houston, Texas, United States, 3 , Advanced Manufacturing Institute, Houston, Texas, United States, 4 , Texas Center for Superconductivity, Houston, Texas, United States
Show AbstractThe past two decades, the onset of nano-engineering of materials has ushered a tremendous research interest in tuning the thermoelectric properties of semiconducting materials. Generally, there are two approaches to design thermoelectric materials: reducing the lattice thermal conductivity and enhancing the power factor (PF=S2s, where S is Seebeck coefficient and s is electrical conductivity). The majority of the research done so far has been on reducing the thermal conductivity because enhancing the power factor is more challenging due to the interdependence of S and s. Here we show a new approach to overcome this PF limitation by utilizing a new class of single-crystal-like biaxially-textured thin films with low angle grain boundary misalignment.
These new class of single-crystal-like semiconducting films are comprised of grains with extremely small angle misorientation (<1°) over long range (meters). These single-crystal-like semiconductor films are grown on randomly-aligned polycrystalline or amorphous metal and glass substrates employing the ion-beam assisted deposition (IBAD) technique. Compared to polycrystalline films, which exhibit grain-to-grain misorientation of over 10 degrees, these single-crystal-like semiconducting films consist of grains with very low angle misorientation (< 1 degree) [1].
The unique structure of these films gives rise to new charge transport properties. Specifically, it is found that in GaAs thin films, the carrier mobility paradoxically increases up to values of 1200 cm2/Vs with carrier concentration. This trend is opposite to what has been reported for their single crystal counterpart where mobility decreases with increasing carrier concentration due to ionization scattering of the carriers. We may attribute this to the modification of the charge carrier scattering mechanisms, which leads to either a band modification or an energy filtering effect as it is evident from the Pisarenko plots. This leads to a profound effect in the Seebeck coefficient where we observed an almost two-fold enhancement. So, even though the electrical conductivity is somewhat lower in these films, the Seebeck enhancement leads to a 20-30% increase in PF at high doping concentrations. Here we will present the temperature-dependent experimental PF, mobility, and carrier concentration data coupled with the theoretical models to elucidate the charge transport characteristics of this new class of films. Moreover, these unique charge transport characteristics are material growth dependent, and thus, such novel thermoelectric properties are expected in different materials systems.
[1] Dutta, P., M. Rathi, N. Zheng, Y. Gao, Y. Yao, J. Martinez, P. Ahrenkiel, and V. Selvamanickam. "High mobility single-crystalline-like GaAs thin films on inexpensive flexible metal substrates by metal-organic chemical vapor deposition." Applied Physics Letters 105, no. 9 (2014): 092104.
8:00 PM - ES09.06.31
Thermoelectric Model of High ZT Silicon Nanocomposite for High Temperature Applications
Seyed Aria Hosseini 1 , Jackson Harter 2 , Devin Coleman 1 , Todd Palmer 2 , Lorenzo Mangolini 1 , Alex Greaney 1
1 , University of California, Riverside, Riverside, California, United States, 2 Nuclear Engineering, Oregon State University, Corvallis, Oregon, United States
Show AbstractResearchers have recently developed processes for synthesizing monolithic Si with large thermoelectric figure-of-merit ZT. These materials hold fantastic promise for realizing large scale waste heat recovery using materials that are inexpensive, abundant and environmentally benign. These materials obtain large ZT through a fine dispersion of nanoscale carbide particles. In this work we elucidate the role these particles play in two processes to increase ZT: (1) scattering of phonons to reduce thermal conductivity, and (2) energy selective scattering of electrons to increase the seebeck coefficient. To address the former problem we use a multiscale approach using molecular dynamics simulations to quantify the effect of impurities on scattering cross section for phonon wavepackets with different wavelengths. This information is used as the starting point for Boltzmann transport simulations to predict the collective effect of the particle dispersion close to the Knudsen regime. We also investigate the effect of phonon-inclusion coupling for different inclusion sizes and misorientations. To address electron energy filtering phenomenon, we use semiclassical Boltzmann transport model of Seebeck coefficient. Density functional theory has been used to feed parameters in Seebeck coefficient formula. By increasing inclusion volume fraction, Seebeck coefficient increases but the electrical conductivity decreases in like manner, which shows the importance of finding optimum value of inclusion density. In this research, the effect of inclusion density and size are evaluated at different temperatures. Developing high ZT Si based thermoelectrics will have technological impact through devices which increase the efficiency of many heat engine cycles and make possible affordable solar thermal energy cycles.
8:00 PM - ES09.06.32
Optical and Electro-Thermal Characterization of the Spin-Hall and Spin-Peltier Effect in Pt/YIG
Sean Sullivan 1 , Annie Weathers 2 , Li Shi 1 2
1 Materials Science and Engineering Program, The University of Texas at Austin, Austin, Texas, United States, 2 Mechanical Engineering Department, The University of Texas at Austin, Austin, Texas, United States
Show AbstractThe spin analogue of the Peltier effect – i.e, spin current induced heating and cooling of a material – has recently been measured at the interface between platinum and the insulating ferromagnet yttrium iron garnet (YIG) (Flipse et al. PRL 2014). Using a combination of electro-thermal and micro-Brillouin light scattering (BLS), we probe the heating and cooling of local magnons in the YIG directly underneath and adjacent to a Pt transducer. Using a modulated heating/cooling approach, we significantly improve the sensitivity of the BLS measurements to changes in the thermal magnon population induced by the spin Hall and spin Peltier effects. In conjunction, electro-thermal measurements of the Pt/YIG are used to probe the heating of the YIG phonons. The two measurements allow us to directly examine the magnon-phonon coupling, the spin-flip diffusion length, and the interface spin mixing conductance in the structure.
8:00 PM - ES09.06.33
Experimental Thermal Characterization of a Hybrid Solar Thermoelectric (HSTE) System
Paulina Escobar 1 , Andrea Arias 1 , Antonia Vargas 1 , Jorge Acuna 1 , Amador Guzman 1
1 , Pontificia Universidad Catolica de Chile, Santiago Chile
Show AbstractTemperature, heat flux and electrical power are measured in an experimental concept of a Hybrid Solar Thermoelectric (HSTE) system with the purpose of evaluating its technical feasibility and performance. The simulated HSTE system was proposed by Nenad Miljkovic and Evelyn Wang as a solar energy conversion system that can produce both electricity and process heat by an optical concentrator, a thermoelectric module (TE), and a thermosyphon.
In this work, we developed a relatively low temperature HSTE experimental concept that is composed by a tube that contains a heater that generates heat that is axially transported to a subsystem with three zones (evaporator, adiabatic region, and condensator) to mimic a thermosyphon. Once the heat passes through the TE, electricity is generated by the Seebeck effect, and it reaches the evaporator region of the thermosyphon until is transported later to the condenser region. Thermocouples and sensors for measuring the temperature profile, voltage and current were positioned in the evaporator region, the heater section, and the TE module, respectively. In addition, temperature measurements were carried out in the condenser section for measuring the condensation temperature for each applied heat flux. Evaluations of the electrical power and efficiency were performed and compared to the theoretical predictions for this HSTE system.
8:00 PM - ES09.06.34
Experimental and Numerical Investigation and Development of a Thermoelectric Generation (TEG) System with a Cold Plate Based Cooling System
Francisco Montero 1 , Paulina Escobar 1 , Daming Chen 1 , Natalia Osorio 1 , Amador Guzman 1
1 , Pontificia Universidad Catolica de Chile, Santiago Chile
Show AbstractA thermoelectric generator (TEG) system composed of a heat concentrator system, a bismuth-telluride thermoelectric module, and a cold plate-based cooling system was developed and tested, in order to measure the efficiency of electric generation of a commercial TE module under controlled temperatures. The heat concentrator system is composed of an array of electrical resistances that allows a constant temperature of 200 °C to be reached, which is coupled to the hot side of the thermoelectric system that consists of a high temperature commercially available thermoelectric module.
The cold plate water-based cooling system consists maintains a temperature of 50 °C on the cold side of the thermoelectric system. An experimental setup that includes the systems described above and allows us to the measure the temperature on the hot and cold sides, and the difference of electric potential and current generated by the thermoelectric system, was developed and tested. A TEG efficiency of around 5% was achieved when a temperature difference between the hot and cold sides of the commercial TE modules of 150 °C was maintained.
In order to get a better understanding of the efficiency experimentally achieved, we carried out two additional analytical-numerical analyses: the first one numerically simulates the TEG system using Comsol software; whereas, in the second one, we perform a numerical analysis using the Hogan and Shih model that uses the thermoelectric properties exposed by Chen et al. The numerical results show a good agreement with the experimentally obtained efficiency.
8:00 PM - ES09.06.35
Ab Initio Study of the Effect of the Grain Boundary on Electron Transport in Thermoelectric Materials
Qichen Song 1 , Jiawei Zhou 1 , Te-Huan Liu 1 , Gang Chen 1
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractLast two decades have seen the significant enhancement of figure of merit in thermoelectric materials via nanostructuring. The large discrepancies between electron and phonon mean free paths in many thermoelectric materials lead to the nanostructures with sizes in between preferentially scattering phonons while not affecting electrons. The understanding of the electron transport in nanostructures is further deepened due to the recent progress in first-principles calculation on electron transport mode by mode. However, the calculation is mainly on the bulk electron transport properties and how electron transport is influenced by the interface at the grain boundary is barely studied in detail. It is known that the energy barrier formed at the interface plays a key role in determining the electron transmission across the interface. Here, we present the first-principles calculation of energy barrier across the interface at the grain boundary and the corresponding effect on the electron transport. Our study helps the understanding on the electron transport in realistic thermoelectric nanocomposites. This work is funded by the DARPA MATRIX program under Grant HR0011-162-0041.
8:00 PM - ES09.06.36
Fabrication and Evaluation Modeling of Unconventional Unileg Structure Power Generator Using N-Type Mg2Si
Takeaki Harada 1 , Tsutomu Iida 1 , Tatsuya Yamashita 1 , Daishi Shiojiri 1 , Keishi Nishio 1 , Yasuo Kogo 1
1 , Tokyo University of Science, Katsushika Japan
Show AbstractFor automotive applications, lighter and tougher thermoelectric power generators are advantageous; however, these applications are sometimes demanding on the devices. Magnesium silicide (Mg2Si) has emerged as one of the most promising thermoelectric (TE) materials for automotive applications. An important aspect of Mg2Si is its capability for being doped to modify its electrical conductivity, thermal conductivity and durability at elevated operating temperatures. A functional value for the TE figure-of-merit of Mg2Si has been obtained after the incorporation of donor impurities. Basically, the p-type conductivity of Mg2Si is possible but the thermoelectric properties of p-type material are not equivalent to that those of n-type Mg2Si one. Therefore, a so-called “unileg” device structure, incorporating only an n-type Mg2Si TE leg, is one possible solution to realizing practical Mg2Si TEGs. In order to design an appropriate unileg TE module, we need to coordinate (i) the dimensions of the TE chip (cross-section and height), (ii) the thermal contacts at the heat source and the drain thermal interface material, and (iii) the peculiar heat flow associated with a unileg module structure to achieve system integration for TEG applications such as automobile combustion engines and industrial furnaces. We are currently tuning the TE chip power generation ability by modifying the type of dopant and the contents of the matrix and the TE chip dimensions. The elemental n-type Mg2Si TE chip, which is co-doped by donor /isoelectric impurities of Sb+Zn with dimension of 5x5x5 mm3, exhibits power generation density of 2.9 W/cm2 over a temperature difference at between 873 K and 373 K (DT= 500 K). Using this TE chip, a prospective unileg structure TE module consisting of the arrangement of 6 TE chips in a line as a basic TEG structure. The results of the power curve measurements of the basic unileg TEG, and of TEGs consisting of between 2 to and 6 TE chips will be demonstrated in terms of possible maximum output power and thermal loss peculiar to the unileg configuration. The thermal distribution and power generation characteristics for the fabricated unileg TEG was analyzed using finite element modeling using the ANSYS code, and heat transfer analysis to understand the thermal impedance characteristics using the Flow Designer code. A making a consistency between the calculation parameters of the ANSYS and the Flow Designer and the fabricated TEG, precise measurements of the temperature, heat flow, and power generation at various probe points on the module were made.
8:00 PM - ES09.06.37
Origin of Exceptionally Large Power Factors in Half-Heusler System
Jiawei Zhou 1 , Hangtian Zhu 2 , Te-Huan Liu 1 , Qichen Song 1 , Ran He 2 , Jun Mao 2 , Bolin Liao 3 , David Singh 4 , Zhifeng Ren 2 , Gang Chen 1
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 , University of Houston, Houston, Texas, United States, 3 , California Institute of Technology, Pasadena, California, United States, 4 , University of Missouri, Columbia, Missouri, United States
Show AbstractAdvancements for thermoelectric materials benefit from understandings of the underlying charge transport mechanism. One example is given by the “band engineering” approach, which seeks to enhance the power factor by tuning the electron density of states. Despite tremendous work that shows enhanced electrical properties via this strategy, the large power factors often possessed by the half-Heusler system – with a highest value ever reported for semiconductors at room temperature (>100 μW/cm-K2 in Ti-doped NbFeSb) – remains unclear. Using first principles electron transport calculation, we reveal that such high power factor results from a distinct transport regime where the electron scattering by acoustic phonons is strongly suppressed, making half-Heusler a unique system that contrasts traditional III-V semiconductors where acoustic phonons limit the charge transport. We pinpoint the reason for the observed weak electron-phonon interaction based on chemical bonding concepts. Large room temperature power factors well above 100 μW/cm-K2 are predicted for several compositions. We believe the results will stimulate future work into discovering new thermoelectric materials with exceptional power factors. This work is supported partially by DOE EFRC (Grant No. DE-SC0001299, for fundamental theory on thermoelectrics), and partially by DARPA MATRIX program (Grant No. HR0011-162-0041 for supporting its thermoelectrics programs).
8:00 PM - ES09.06.38
Dual-Beam Pulsed Laser Deposition of Sb2Se3/Cu Nanocomposite Films
Po-Hung Chen 1 , Yi-Syuan Chen 1 , Chun-Hua Chen 1
1 Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu Taiwan
Show AbstractHeterocomposites comprising a variety of functional components for respectively improving specific thermoelectric properties such as the Seebeck coefficient, electrical conductivity, and thermal conductivity have become a promising branch of thermoelectric materials in these years and are expected to tackle the energy issue of the future. In this study, we combined Antimony selenide (Sb2Se3) which typically exhibits a very high Seebeck coefficient (~1800 μVK-1) and a low thermal conductivity (~2.7 Wm-1k-1) and metallic copper, one of the most conductive materials as the heterogeneous dopant, and have successfully fabricated a series of novel Sb2Se3/Cu hetero-nanocomposite films using a dual-beam pulsed laser deposition system. Despite the obtained Seebeck coefficient of ~625 μVK-1 is only one third of intrinsic Sb2Se3 bulk, the electrical conductivity are several orders of magnitude increased. As a consequence, the power factor achieved ~30 µW/cmK2 which is 105–106 times higher than that for Sb2Se3 bulk.
8:00 PM - ES09.06.39
Thermoelectric BixSb2-xTe3/Diamond-Like Carbon Nanocomposite Films
Po-Hung Chen 1 , Tsung-Han Chen 1 , Chun-Hua Chen 1
1 Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu Taiwan
Show AbstractHeterogeneous nanostructuring has been considered to be one of the most effectively strategy to obtain high thermoelectric figure of merits, ZTs, defined as S2σTK-1, where S is the Seebeck coefficient, σ the electrical conductivity, k the thermal conductivity, and T the absolute temperature. In this work, from the view point of lowering the thermal conductivity, diamond-like carbon (DLC) was specially introduced as the heterogeneous component to cooperate with BixSb2-xTe3(BST) to form a series of novel BST/DLC hybrid films via pulse laser deposition. The strong correlation between the formed nanostructures and the significantly enhanced power factor as well as the decreased thermal conductivity will be discussed.
8:00 PM - ES09.06.40
Combined Experimental and Theoretical Investigation of the Thermoelectric Coefficient of NaxCoO2
Yoyo Hinuma 1 2 , Yuya Fukuzumi 3 , Wataru Kobayashi 3 4 5 , Yutaka Moritomo 3 4 5
1 Center for Frontier Science, Chiba University, Chiba, Chiba, Japan, 2 Center for Materials Research by Information Integration (CMI2), Research and Services Division of Materials Data and Integrated System, National Institute for Materials Science, Tsukuba, Ibaraki, Japan, 3 Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki, Japan, 4 Division of Physics, Faculty of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki, Japan, 5 Tsukuba Research Center for Interdisciplinary Materials Science (TIMS), University of Tsukuba, Tsukuba, Ibaraki, Japan
Show AbstractHeat-to-electricity conversion can be accomplished by battery-type thermocells (1), where the configuration is the same as that of lithium-ion/sodium-ion secondary batteries with the exception that the anode and cathode is the same system. Thermocells can utilize existing battery technologies, therefore fast time-to-market is anticipated once suitable electrodes are identified. An indicator of performance in conventional thermoelectric devices is the Seebeck coefficient S= ΔV /ΔT, which is voltage difference ΔV divided by the temperature difference ΔT between the hot and cold electrodes. On the other hand, the corresponding quantity in a thermocell is the electrochemical thermoelectric coefficient SEC= ∂V /∂T, where V and T are the redox potential and temperature, respectively. Both positive and negative SEC has been measured in transition metal hexacyanoferrates (M-HCF), LixM[Fe(CN)6]y, where M is a transition metal (2). SEC is, by definition, equivalent to the difference in heat capacities of the redox couple.
We will present the thermoelectric coefficient of NaxCoO2, which is a well-known sodium ion battery cathode material. Experimental measurements will be compared with first-principles heat capacity calculations for known ordered phases (3). Theoretical prediction of the thermoelectric coefficient is expected to speed up the search for high-performance thermocells, a new player in the field of thermal energy utilization.
(1) W. Kobayashi, A. Kinoshita, and Y. Moritomo, Appl. Phys. Lett. 107, 073906 (2015).
(2) R. L. Magnússon, W. Kobayashi, M. Takachi, and Y. Moritomo. AIP Advances 7, 045002 (2017)
(3) Y. Hinuma, Y. S. Meng, and G. Ceder. Phys. Rev. B 77, 224111 (2008).
8:00 PM - ES09.06.41
Giant Temperature Coefficient of Resistivity and Cryogenic Sensitivity in Silicon with Galvanically Displaced Gold Nanoparticles in Freeze-Out Region
Seung-Hoon Lee 1 , Seongpil Hwang 2 , Jae-Won Jang 1
1 Physics, Pukyong National University, Busan Korea (the Republic of), 2 Advanced Materials Chemistry, Korea University, Busan Korea (the Republic of)
Show AbstractThe temperature coefficient of resistivity (TCR) and cryogenic sensitivity (Sv) of p-type silicon (p-Si) in the low-temperature region (10−30 K) are remarkably improved by increasing the coverage of galvanically displaced Au nanoparticles (NPs). By increase of the galvanic displacement time from 10 to 30 s, the average surface roughness (Ra) of the samples increases from 0.31 to 2.31 nm and the coverage rate of Au NPs increases from 3.1% to 21.9%. In the freeze-out region of the sample, an up to 103% increase of TCR and
dramatically improved Sv of p-Si (∼5813%) are observed with Au coverage of 21.9% compared to p-Si without galvanically displaced Au NPs. By means of a finite element method (FEM) simulation study, it was found that the increase of surface roughness and a number of Au NPs on p-Si results in a higher temperature gradient and thermoelectric power to cause the unusual TCR and Sv values in the samples
8:00 PM - ES09.06.42
Spin Mediated Thermal Transport in p-Si
Paul Lou 1 , Sandeep Kumar 1
1 , University of California, Riverside, Riverside, California, United States
Show AbstractThe observation of the spin-Seebeck effect has opened a new direction to spin current generation and manipulation. This alternative thermal approach of spin injection is believed to be energy-efficient. The spin-Seebeck effect is attributed to phonon-driven spin redistribution. This has led to significant interest in spin-mediated thermal transport and spin-phonon interactions in non-magnetic semiconductors. The spin-phonon interactions can be understood by studying the spin-mediated thermal transport behavior. In silicon, electron-phonon scattering (Elliot-Yafet mechanism) is believed to be the primary spin relaxation mechanism at room temperature. We hypothesized that spin relaxation due to phonon absorption or emission may change phononic thermal transport behavior. In this work, we measured the spin mediated thermal transport behavior using self-heating 3 omega method for in-plane thermal conductivity. The spin polarization is achieved using spin-Seebeck tunneling from ferromagnetic spin source. We observe a magnetic field dependent thermal conductivity from 300 K - 50 K.
Symposium Organizers
Jia Zhu, Nanjing University
Baratunde Cola, Georgia Institute of Technology
Deyu Li, Vanderbilt University
Amy Marconnet, Purdue University
ES09.07: Thermoelectric II
Session Chairs
Wednesday AM, November 29, 2017
Hynes, Level 3, Ballroom C
8:00 AM - *ES09.07.01
High Thermoelectric Performance of New Zintl Materials
Zhifeng Ren 1
1 , University of Houston, Houston, Texas, United States
Show AbstractZintl materials have been studied as thermoelectric materials for many years, but the materials are almost all p-type with thermoelectric figure-of-merit (ZT) just about 1. Recently we have extensively studied this class of materials and achieved ZT above 1.3 in p-type by improving the power factor and also decrease the thermal conductivity. In addition to the p-type, we have also surprisingly achieved ZT as high as 1.8 in the newly discovered n-type Mg3Sb2-based Zintls by doping transition metals to tune the electron scattering mechanism and also understand the defect physics.
8:30 AM - ES09.07.07
Inhomogeneity in Spark Plasma Sintered Bismuth Antimony Telluride Nanoplate Composite
Enzheng Shi 1 , Yue Wu 1
1 Department of Chemical and Biological Engineering, Iowa State University, Ames, Iowa, United States
Show AbstractMost of thermoelectric studies are focused on improving the figure of merit and exploring more alternatives comprised of earth-abundant elements. To precisely estimate the performance of thermoelectric materials, anisotropy and inhomogeneity must be considered in thermoelectric measurement and zT calculation. The anisotropy has been reported and studied in many literatures. However, the inhomogeneity didn’t draw much attention so far. Herein, we systematically studied the inhomogeneity in spark plasma sintered bismuth antimony telluride (BiSbTe) nanoplate composite. A substantial reduction of electrical conductivity was observed on a BiSbTe sample after it was diced from a BiSbTe disk to a bar in the same direction, which directly led to a significant reduction in power factor. The thermal conductivity of the bar is measured by 3ω method. And the zT peak for the bar can reach 1.18, while it will be overestimated to be 1.88 for the disk if inhomogeneity is not considered. Electron backscatter diffraction, energy dispersive spectroscopy, Seebeck coefficient and thermal conductivity mapping are performed to investigate the inhomogeneity. This finding can be applied to estimate the performance of thermoelectric materials more precisely and can also shed light on the optimization of thermoelectric materials designing.
8:45 AM - ES09.07.08
Synthesis and Thermoelectric Properties of Nanodiamond/Bi-Te-Se Composites with Point-Defects Clustered Zones
Kyung Tae Kim 1 , Injoon Son 2
1 , Korea Institute of Science and Technology, Changwon Korea (the Republic of), 2 , Kyungpook National University, Daegu Korea (the Republic of)
Show AbstractImprovement in thermoelectric performance of n-type Bi2Te3 materials should be significantly considered for practical applications of thermoelectric devices. In this study, nanodiamond-dispersed Bi2Te2.7Se0.3 (ND/BTS) matrix composites were fabricated in order to investigate changes of TE properties utilizing point-defects. The fabricated ND/BTS composites show the characteristic microstructure where ND particles with 5nm in diameter are homogeneously dispersed in the BTS matrix. The HAADF-STEM results clearly show that atomically disordered-lattice structures are concentrated on the newly formed ND/BTS interfaces. The interfacial zone artificially formed by addition of ND particles has weak strain fields visualized by LAADF-STEM images and it is analyzed as atomic-scale defects zone. Consequently, electric conductivities of the ND/BTS composites show significantly increased values compared to that of pure BTS in the temperature range from 298K to 473K. However, total thermal conductivity of the composites indicates higher values than the BTS due to increased electric conductivity in spite of active lattice phonon scattering at the ND/BTS interfaces. The maximum ZT, 0.97 was obtained from 0.5vol% ND/BTS composite at 473K and enhancement in ZT values was clearly revealed above 348K. Thus, it is analyzed that these variations in thermoelectric properties are originated from dispersion of defect-zone acting as a carrier supplier in n-type BTS matrix.
9:00 AM - ES09.07.03
High Efficiency Thin-Film Superlattice Thermoelectric Cooler Modules Enabled by Low Resistivity Contacts
Yuping He 1 , Francois Leonard 1 , Douglas Medlin 1 , Nicholas Baldasaro 2 , Dorota Temple 2 , Philip Barletta 3 , Catalin Spataru 1
1 , Sandia National Laboratories, Livermore, California, United States, 2 , RTI International, Research Triangle Park, North Carolina, United States, 3 , Micross Components, Research Triangle Park, North Carolina, United States
Show AbstractV-telluride superlattice thin films have shown promising performance for on-chip cooling devices. Recent experimental studies have indicated that device performance is limited by the metal/semiconductor electrical contacts. For example, a contact resistivity of ~10-8 Wcm2 is desired for a cooler module with the thickness of the V-telluride thin film smaller than 2 mm. One challenge in realizing such low resistivity contacts is the limited fundamental knowledge of the physical and chemical properties of interfaces between metal and V-telluride materials. Here we present a combination of experimental and theoretical efforts to understand, design and harness low resistivity contacts. We carried out a series of ab initio calculations of metal (i.e. Cr) and V-telluride (i.e. Sb2Te3) interfacial structure, band bending, and chemical dipole, aimed to understand the effect of chemical and physical properties on the contact resistivity on the atomic level. We then used macroscopic models to estimate the limit of low contact resistivity using input from the ab initio calculations. We found (a) significant atomic disorder and large chemical dipole of Sb2Te3 within 1 nm of the interface, but a well ordered structure for Cr; (b) heavily n-type doped Sb2Te3 within 3 nm of the interface. We predict a fundamental limit of contact resistivity for planar interfaces of ~10-8 Wcm2 at high doping. Based on this knowledge, we developed a new approach to fabricate low resistivity contacts to V-telluride thin film superlattice, achieving a 100-fold reduction compared to previous work [1]. Interfacial characterization and analysis using both scanning transmission electron microscopy (STEM) and energy-dispersive x-ray spectroscopy (EDS) show the unusual interfacial morphology and the potential for further improvement in contact resistivity. Importantly, we harness these new contacts to demonstrate thin film coolers with improved performance. [1] Nat. Commun. 7, 10302 (2016)
9:15 AM - ES09.07.04
Development of N-Type Metal Nanowire/Polymer Thermoelectric Nanocomposites with Large Power Factor
Yani Chen 1 , Minhong He 1 , Guillermo Bazan 3 , Jun Zhou 2 , Ziqi Liang 1
1 , Fudan University, Shanghai China, 3 , University of California, Santa Barbara, Santa Barbara, California, United States, 2 , Tongji University, Shanghai China
Show AbstractOrganic/inorganic hybrids have become the central focus of developing the next-generation thermoelectric (TE) materials owing to a combination of their unique properties of individual components. However, most organic-inorganic thermoelectric nanocomposites (TENCs) contain a mixture of carbon-based nanomaterials and inorganic semiconductors. Major obstacles limiting applications of TENCs include low power factors (PFs) and the general absence of n-type TE materials. Despite their intrinsic high electrical conductivity and low cost, metals have been seldom reported as the inorganic component.
In this contribution, we will report the solution fabrication of flexible n-type TENCs comprising metallic Ni nanowires (NWs) embedded in an insulating polyvinylidene fluoride (PVDF) matrix. The electrical conductivity and Seebeck coefficient of these TENCs are decoupled and both increase with Ni content. The nanocomposites also exhibit typical temperature dependences of magnetic metals, such as Ni, namely, negative in electrical conductivity, while positive in absolute Seebeck coefficient. The resulting PF is progressively enhanced over temperature. Moreover, a remarkably low thermal conductivity of 0.55 W m−1 K−1 is found in these TENCs. As a result, the maximum PF of 220 μW m−1 K−2 and the best ZT of 0.15 are obtained at 380 K with 80 wt% Ni NWs. Recently, we further fabricated Co NWs/PVDF TENCs via self-assembly of Co NWs in solution, which remarkably improve PF up to 520 μW m−1 K−2. This value is among the highest achieved for n-type TENCs. Intriguingly, these TENCs are highly bendable and hard to deform, suggesting its relevance for flexible and portable TE modules.
This work offers the first demonstration that a combination of an insulating polymer and an inorganic metal, each of which is a poor TE material, can be brought together to form a nanocomposite with unexpectedly outstanding TE properties.
Reference
Y. Chen, M. He, B. Liu, G. C. Bazan, J. Zhou, Z. Liang, Bendable n-Type Metallic Nanocomposites with Large Thermoelectric Power Factor. Adv. Mater. 2017, 29, 1604752.
9:30 AM - ES09.07.05
High Performance Shape Engineerable Thermoelectric Materials
Jae Sung Son 1 , Seungki Jo 1 , Fredrick Kim 1
1 , Ulsan National Institute of Science and Technology, Ulsan Korea (the Republic of)
Show AbstractOutput power of thermoelectric generators depends on device engineering minimizing heat loss as well as inherent material properties. However, the device engineering has been largely neglected due to the limited flat or angular shape of devices. Considering that the surface of most heat sources where these planar devices are attached is curved, a considerable amount of heat loss is inevitable. To address this issue, here, we present the shape-engineerable thermoelectric painting and 3D printing, geometrically compatible to surfaces of any shape. We prepared Bi2Te3-based inorganic inks using the molecular Sb2Te3 chalcogenidometallate as a sintering aid for thermoelectric particles, with ZT values of 0.5~0.7 for n-type and 1.0~1.2 for p-type materials that compete the bulk values. Devices directly brush-painted onto curved surfaces produced several tens of μW. Also, the shapes of 3D blocks printed by dispensing process were controllably varied to cube, circle, and half ring. Half-ring shaped thermoelectric 3D blocks were used to fabricate the cylindrical power generating module with three n-type and p-type pairs, which exhibited mW-level power under the temperature difference of 30~40 oC. These approaches paves the way to designing materials and devices that can be easily transferred to other applications.
9:45 AM - ES09.07.06
Silver Alloyed PbTe—A Promising Compound for Mid-Temperature Thermoelectric Energy Conversion
Yaron Amouyal 1
1 Materials Science and Engineering, Technion, Haifa Israel
Show AbstractA promising way for electric power generating from waste heat flux is utilizing the thermoelectric (TE) effect. Application of TE generators in daily life strongly depends on their thermodynamic conversion efficiency, which is determined by the dimensionless TE figure-of-merit, ZT. Good TE materials possess high ZT-values, which are obtained by combination of high electrical conductivity and low thermal conductivity, at the same time with high Seebeck coefficient. Besides TE performance, knowledge of the microstructure evolution of these materials under service conditions is of utmost technological importance.
Herein, we investigate the microstructure evolution of Ag-alloyed PbTe compounds with or without 0.04 at. % Bi additions. We control the nucleation and temporal evolution of Ag2Te-precipitates in the PbTe-matrix, aiming to achieve homogeneous dispersion of precipitates with high number density values, hypothesizing that they act as phonon scattering centers, thereby reducing lattice thermal conductivity. We measure the temperature dependence of the Seebeck coefficient and electrical and thermal conductivities, and correlate them with the microstructure.
We manage to reduce thermal conductivity of PbTe by controlled nucleation of Ag2Te-precipitates, and obtain a number density value as high as 2 1020 m-3 after 6 h aging at 380 °C. This yields ZT value of ca. 1.4 at 450 °C, which is one on the largest values reported for n-type PbTe compounds. Subsequent aging leads to precipitate coarsening and deterioration of TE performance. Interestingly, we find that doping with Bi atoms, besides their role as electron donors, improve the alloys’ thermal stability by suppressing microstructure evolution; thereby maintaining high TE performance with no degradation at elevated service temperatures.
10:30 AM - *ES09.07.02
Approaching Efficient Thermoelectrics—From Materials to Modules
Lidong Chen 1
1 , Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai China
Show AbstractThe continuous enhancement of the figure of merit zT of thermoelectric (TE) materials is an important enabling step that bodes well for widespread practical applications of thermoelectric conversion technology. Nevertheless, the TE device technology has progressed less rapidly. Especially, the conversion efficiency of fabricated TE modules falls far below the theoretical efficiency based on the performance of TE materials themselves. The pivotal reason for this is the lack of notable breakthroughs regarding the optimized design of topology and integration technology with minimized energy loss. Recently, we have demonstrated the effectiveness of full-parameter numerical analysis for approaching maximized conversion efficiency of a TE module. Combined with the developed bonding schemes and assembly techniques, the segmented modules consisting of Bi2Te3-based alloys and CoSb3-based filled skutterudites were successfully fabricated with a record-high efficiency of up to 12% when operating under a temperature difference of 541 °C reaching up to 96.9% of the theoretical efficiency based on the thermoelectric materials’ properties. In this talk, the recent progresses on both the thermoelectric materials and device technology will be overviewed.
11:00 AM - ES09.07.09
High Thermoelectric Performance in N-Doped Silicon-Based Chalcogenide Si2Te3
Rinkle Juneja 1 , Tribhuwan Pandey 1 , Abhishek Singh 1
1 , Indian Institute of Science, Bangalore India
Show AbstractAchieving large thermoelectric figure of merit in a low-cost material, having an appreciable degree of compatibility with the modern technology is required to convert waste heat into electrical energy efficiently. Since silicon forms backbone of electronic industry, getting a silicon-based thermoelectric material would be of great significance and would have more chances of integration into on-chip electronic devices. Bulk silicon is not a good thermoelectric material due to its very high thermal conductivity, which limits its thermoelectric efficiency. In the past few decades, much efforts have been devoted to enhance figure of merit (ZT) of silicon and silicon-based materials via nanostructuring or alloying. Although, these techniques are partially successful in reducing the lattice thermal conductivity, the complex synthesis techniques involved in such processes make them very costly, thereby limiting the large-scale production of such materials for commercial-scale thermoelectric applications. Recently, a silicon-based chalcogenide Si2Te3 has been experimentally synthesized. Si2Te3 exhibits layered structure, in which Te atoms form hexagonal sub-lattice and Si atoms can occupy any of the octahedral voids. Due to uncertainty in Si positions, previously unknown ground state structure of Si2Te3 was obtained using the Wyckoff positions of space group P-31c. The minimum energy configuration exhibits combination of desirable electronic and transport properties for an efficient thermoelectric material, which result in very high figure of merit. In particular, n-doped Si2Te3 has unprecedented ZT of 1.86 at 1000 K, which is comparable to some of the best state-of-the-art thermoelectric materials. So n-doped Si2Te3 can be a long sought silicon-based thermoelectric material having exceptionally good energy conversion efficiency and which could be integrated to the existing electronic devices.
Reference:
1. R. Juneja, T. Pandey, and A. K. Singh, High Thermoelectric Performance in n-doped Silicon-Based Chalcogenide Si2Te3 Chem. Mater. 29, 3723-3730, 2017
11:15 AM - ES09.07.10
Turning up the Heat on Energy Harvesting—Flexible Printed Thermoelectric Nanogenerators
Canlin Ou 1 , Abhijeet Sangle 1 , Michael Smith 1 , Anuja Datta 1 , Sohini Kar-Narayan 1
1 , University of Cambridge, Cambridge United Kingdom
Show AbstractCompared with traditional energy sources, harvesting waste heat from the environment into usable electricity by means of the thermoelectric generator is predicted as one of the most promising renewable energy solutions in the future. Thermoelectric generator can also be easily scaled down to charge ‘small power’ applications such as wireless electronics and wearable devices.
In this work, a flexible and robust thermoelectric nanogenerator (ThENG) based on a novel hybrid organic-inorganic nanocomposite structure for thermoelectric energy harvesting applications has been successfully fabricated via a cost-effective, scalable and low-temperature aerosol jet printing (AJP) technique with the combination of our in-house nanocrystal fabrication methods. The flexible thermoelectric nanocomposite and nanogenerator fabrication processes developed in this project include the nanocrystal synthesis, nano-ink processing, AJP of thermoelectric nanocomposite, and final thermoelectric nanogenerator fabrication.
Nanostructured and micro-sized Bi2Te3 and Sb2Te3 were firstly prepared by various fabrication methods e.g. hand grinding, ball milling, and solvothermal synthesis. Then, these thermoelectric nanocrystals were dispersed into different water or organic-based solvents to prepare printable inks for the subsequent AJP process. By integrating high Seebeck coefficient and high electrical conductivity Bi2Te3 and Sb2Te3 with low thermal conductivity organic polymers, the resulting figure of merit could be optimised. Different loading weight percentage of Bi2Te3 and Sb2Te3 in the polymer matrix and different thicknesses of thermoelectric nanocomposites were printed onto a flexible polyimide sheet via AJP method. Their morphological, microstructural, and thermoelectric properties were investigated in order to optimise their ink formulation and printing conditions, thereby maximising their final thermoelectric performance.
The as-printed organic-inorganic thermoelectric nanocomposites on a flexible substrate can be directly integrated into a ThENG with minimal post-possessing treatment, and the resulting ThENG can be particularly flexible and robust with stable energy harvesting performance. Thermoelectric properties measurements are on-going to determine their thermoelectric performance. The improvement of flexibility enables potential applications in wearable electronic devices.
11:30 AM - ES09.07.11
Using the 18-Electron Rule To Understand the Nominal 19-Electron Half-Heusler NbCoSb with Nb Vacancies
Shashwat Anand 1 , Wolfgang Zeier 2 , Christopher Wolverton 1 , G. Snyder 1
1 , Northwestern University, Evanston, Illinois, United States, 2 Physikalisch-Chemisches Institut, Justus-Liebig-Universität Giessen, Giessen Germany
Show AbstractThe 18-electron rule is a widely used criterion in the
search for new half-Heusler thermoelectric materials. However, several
19-electron compounds such as NbCoSb have been found to be stable
and exhibit thermoelectric properties rivaling state-of-the art materials.
Using synchrotron X-ray diffraction and density functional theory
calculations, we show that samples with nominal (19-electron)
composition NbCoSb actually contain a half-Heusler phase with
composition Nb 0.84 CoSb. The large amount of stable Nb vacancies
reduces the overall electron count, which brings the stoichiometry of the
compound close to an 18-electron count, and stabilizes the material.
Excess electrons beyond 18 electrons provide heavy doping needed to make these good thermoelectric materials. This work
demonstrates that considering possible defect chemistry and allowing small variation of electron counting leads to extra degrees
of freedom for tailoring thermoelectric properties and exploring new compounds. Here we discuss the 18-electron rule as a guide
to find defect-free half-Heusler semiconductors. Other electron counts such as 19-electron NbCoSb can also be expected to be
stable as n-type metals, perhaps with cation vacancy defects to reduce the electron count.
11:45 AM - ES09.07.12
Coexisting Phonon Quasiparticles and Stochastic Diffusion in Superionic CuCrSe2
Jennifer Niedziela 1 , Dipanshu Bansal 1 , Andrew May 1 , Jingxuan Ding 2 , Georg Ehlers 3 , Douglas Abernathy 3 , Said Ayman H. 4 , Olivier Delaire 1 2
1 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Department of Mechanical Engineering and Materials Science, Duke University, Durham, North Carolina, United States, 3 Quantum Condensed Matter Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 4 Advanced Light Source, Argonne National Laboratory, Lemont, Illinois, United States
Show AbstractSuperionic conductors, crystalline solids that exhibit liquid-like diffusivity of some of their ions, are of considerable interest as solid-state electrolytes for applications in batteries and fuel cells, and more recently in thermoelectrics as potential realizations of the ``phonon liquid - electron crystal'' (PLEC) concept . Since thermoelectric conversion efficiency is maximized by suppressing the lattice thermal conductivity, while maintaining appropriate electronic transport, extensive efforts have sought to devise effective phonon scattering strategies to reduce the lattice contribution. Despite the strong interest in superionic conductors to realize the PLEC state, the underlying atomistic mechanisms and possible connection between low thermal conductivity and superionicity remain unsettled. It is thought that the anharmonicity of lattice vibrations (phonons) plays a key role in enabling unusual dynamics. Yet, the precise connection between anharmonicity, sublattice melting, and phonon scattering remains to be established. Critically, the behavior of acoustic modes across the superionic transition remains unclear.
In this work, we investigated the evolution of the atomic dynamics in CuCrSe2 across the superionic transition, including on single-crystals. We used inelastic neutron scattering (INS) and inelastic x-ray scattering (IXS) to unravel the phonon scattering processes, and clarify the relation between the phonon picture of atomic vibrations and superionic diffusive behavior. The INS measurements revealed the striking behavior of the phonon density of states (DOS) and quasi-elastic neutron scattering (QENS), providing quantitative information into Cu superionic diffusion. Our complementary momentum-resolved IXS measurements on crystals provided a definite determination of phonon dispersions, polarization vectors, and mode-specific linewidths, and unequivocally show that acoustic modes remain well defined in the superionic phase. Further, we compare our experimental results with density functional theory (DFT) calculations of the phonons and finite temperature ab-initio molecular dynamics (AIMD) simulations. Our results reveal a dramatic evolution of the dynamics of the Cu sublattice across the superionic transition, resulting in liquid-like copper layers, while a robust framework of CrSe6 octahedra persists and sustends solid-like acoustic excitations. We discuss the role of strong anharmonicity in enabling both ultralow thermal conductivity and superionic behavior in CuCrSe2 and we highlight similarities with related compounds MCrX2 and Cu2-xSe.
ES09.08: Thermoelectric III
Session Chairs
Wednesday PM, November 29, 2017
Hynes, Level 3, Ballroom C
1:30 PM - *ES09.08.01
Enhancing Condensation Heat Transfer with Scalable Micromesh-Covered Superhydrophobic Surfaces
Ronggui Yang 1 2
1 Department of Mechanical Engineering, University of Colorado, Boulder, Colorado, United States, 2 Materials Science and Engineering Program, University of Colorado Boulder, Boulder, Colorado, United States
Show AbstractCondensation is a ubiquitous phase-change phenomenon and has been widely used in energy-intensive industrial applications. By promoting rapid droplet removal, the micro/nanostructured materials offer an avenue to potentially improve the condensation heat transfer performance. However, these approaches suffer from the nucleation within the structures and the flooded mode for high heat flux that make it difficult to thoroughly exceed the state-of-the-art dropwise condensation heat transfer. Here, we report the development of a micromesh-covered superhydrophobic surface via a simple yet scalable fabrication method that allows for highly efficient jumping condensation at small surface subcooling and continuous droplet suction-enhanced condensation at large surface subcooling. We show that the unique surface morphology can lead to unprecedented condensation heat transfer enhancement compared to the plain hydrophobic surface. The new insights about the cost-effective surface fabrication and the novel condensation mechanism we discovered in this work can guide the development of new technology for a wide range of phase-change heat transfer applications.
2:00 PM - ES09.08.02
Scalable, ‘Dip-and-Dry’ Fabrication of a Plasmonic, Wide-Angle Selective Absorber for High-Efficiency Solar-Thermal Energy Conversion
Jyotirmoy Mandal 1 , Yuan Yang 1
1 , Columbia University, New York, New York, United States
Show AbstractSolar-thermal energy conversion is a highly promising way to harness the energy available in sunlight due to its high efficiency, and has seen increasing use around the world in recent years. Different architectures to achieve selective solar absorption have been reported in literature - with designs like cermet solar absorbers, metal-dielectric multilayer-broadband absorbers, semiconductor-metal tandems and photonic crystals all showing the required high solar absorptance and low thermal emittance for high-efficiency selective solar absorption. [1-2] However, such designs are often expensive, environmentally hazardous and complicated to make, and usually suffer from low solar absorptance at high incidence angles, which limits their use in real settings.
Here, we present a simple, inexpensive, ‘dip-and-dry’ technique for fabricating selectively solar absorbing plasmonic nanostructure-coated foils (PNFs). The process, which is based on galvanic-displacement reactions, allows for easy tuning of the PNFs' spectral reflectance to suit different radiative and thermal environments, and imparts excellent, wide-angle solar absorptance (0.96 at 15°, to 0.97 at 35°, to 0.79 at 80°) and low hemispherical thermal emittance (< 0.10) without the aid of antireflection coatings. The thermal emittance is comparable to those of notable selective solar absorbers (SSAs) in the literature, while the wide-angle solar absorptance surpasses those of previously reported SSAs with comparable optical selectivities. Furthermore, the PNFs show promising mechanical and thermal stabilities at temperatures of up to 200°C. Given this performance of the PNFs, the simplicity, inexpensiveness and environment-friendliness of the ‘dip-and-dry’ technique makes it an appealing alternative to current methods for fabricating selective solar absorbers.
[1] F. Cao, K. McEnaney, G. Chen, Z. F. Ren, Energy & Environmental Science 2014, 7, 1615.
[2] C. E. Kennedy, Review of Mid- to High-Temperature Solar Selective Absorber Materials, National Renewable Energy Laboratory Golden, CO 2002
2:15 PM - ES09.08.03
Silicon Carbide Nanoinclusions for Improved Thermoelectrics
Devin Coleman 1 2 , Lorenzo Mangolini 1 , Sabah Bux 2
1 , University of California, Riverside, Riverside, California, United States, 2 Advanced Thermoelectric Materials Research Group, Jet Propulsion Laboratory, Pasadena, California, United States
Show AbstractOur measurements on solid inclusions suggest small volume fractions (<10%) of silicon carbide nanoparticles in nanostructured bulk silicon have a beneficial effect on thermoelectric performance, with improvements of up to 80% in peak zT compared to a control with no nanoinclusions. The thermal and electrical conductivities are both slightly depressed to due electron and phonon scattering as well as carrier loss. However there is a large increase in the magnitude of the Seebeck coefficient, resulting in a significant improvement in performance.
The synthesis of beta-phase silicon carbide nanoparticles is demonstrated by means of a 2 stage non-thermal plasma reactor. First, silane gas is diluted in argon and flown into the primary plasma reactor, where it is converted to crystalline silicon nanoparticles. These particles then enter a secondary plasma reactor containing methane, where full carbonization into silicon carbide occurs. This in-flight process yields beta-phase silicon carbide nanoparticles with narrow particle size distributions (<20nm). The morphology can be tuned via the power supplied to the secondary reactor to be hollow shells with a ~10nm void, or solid particles. This process and the mechanisms of the different morphologies will be discussed in detail.
These particles are investigated as nanoinclusions in bulk nanostructured silicon for thermoelectrics applications. The plasma produced silicon carbide nanoparticles are mixed with silicon nanopowders produced by high energy ball milling, and sintered via hot pressing. While the silicon nanoparticles exhibit grain growth during the densification process, the isolated silicon carbide nanoparticles retain their initial size in the bulk material. The result is a nanograined bulk silicon matrix decorated with silicon carbide nanoinclusions. Moreover, the unique ability to pre-engineer a perfect void presents the opportunity to introduce nanoporosity with an unprecedented level of control, and elucidate its effects on electron and phonon transport in bulk semiconductors. Mechanisms to control the dispersion and mitigate aggregation will be presented.
3:30 PM - ES09.08.04
Ballistic Thermophoresis on a 2D Suspended Sheet—A Gold Cluster on Graphene
Erio Tosatti 2 , Emanuele Panizon 1 , Roberto Guerra 3 1
2 , SISSA & ICTP, Trieste Italy, 1 , SISSA, Trieste Italy, 3 , University of Milan, Milano Italy
Show AbstractThe textbook thermophoretic force which acts on a body in a fluid is proportional to the local temperature gradient. The same is expected to hold for the macroscopic drift behavior of a diffusive cluster or molecule physisorbed on a solid surface. The question we explore here is whether that is still valid on a 2D membrane such as graphene at short sheet length.
By means of a non-equilibrium molecular dynamics study of a test system – a gold nanocluster adsorbed on free-standing graphene clamped between two temperatures DeltaT apart – we find a phoretic force which for submicron sheet lengths is proportional to Delta T, but independent of sheet length and thus of the local temperature gradient. This identifies a thermophoretic regime that is ballistic rather than diffusive, persisting up to and beyond a hundred nanometer sheet length.
Analysis shows that the phoretic force is due to the flexural phonons, whose flow is known to be ballistic and distance-independent up to relatively long mean-free paths. Yet, ordinary harmonic phonons should only carry crystal momentum and, while impinging on the cluster, should not be able to impress real momentum. We show that graphene, and other membrane-like layers, support a specific anharmonic connection between the flexural corrugation and longitudinal phonons. The fast escape of the latter leaves behind a 2D-projected mass density larger than its rest value, endowing the flexural phonons, as they move with their group velocity, with real momentum, part of which is transmitted to the adsorbate through scattering.
The resulting distance-independent ballistic thermophoretic force is likely to possess practical applications in nanomanipulation and transport of matter using temperature imbalances .
3:45 PM - ES09.08.05
Competing Dopants Grain Boundary Segregation and Resultant Seebeck Coefficient and Power Factor Enhancement of Thermoelectric Calcium Cobaltite Ceramics
Cullen Boyle 1 , Liang Liang 1 , Yun Chen 1 , Jacky Prucz 1 , Ercan Cakmak 2 , Thomas Watkins 2 , Edgar Lara-Curzio 2 , Xueyan Song 1
1 , West Virginia Univ, Morgantown, West Virginia, United States, 2 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractThis work demonstrates the feasibility of increasing the values of Seebeck coefficient S and power factor of calcium cobaltite Ca3Co4O9 ceramics through competing dopant grain boundary segregation. The nominal chemistry of the polycrystalline material system investigated is Ca3-xBixBayCo4O9 with simultaneous stoichiometric substitution of Bi for Ca and non-stoichiometric addition of minute amounts of Ba. There is continuous increase of S due to Bi substitution and Ba addition. The electrical resistivity also changes upon doping. Overall, the power factor of best performing Bi and Ba co-doped sample is about 0.93 mW m-1K-2, which is one of the highest power factor values ever reported for Ca3Co4O9, and corresponds to a factor of 3 increase compared to that of the baseline composition Ca3Co4O9. Systematic nanostructure and chemistry characterization was performed on the samples with different nominal compositions. When Bi is the only dopant in Ca3Co4O9, it can be found at both the grain interior and the grain boundaries GBs as a result of segregation. When Bi and Ba are added simultaneously as dopants, competing processes lead to the segregation of Ba and depletion of Bi at the GBs, with Bi present only in the grain interior. Bi substitution in the lattice increases the S at both the low and high temperature regimes, while the segregation of Ba at the GBs dramatically increase the S at low temperature regime.
4:00 PM - ES09.08.06
Phonon Diffraction and Dimensionality Crossover in Phonon-Interface Scattering
Riley Hanus 1 , Anupam Garg 1 , G. Snyder 1
1 , Northwestern University, Evanston, Illinois, United States
Show AbstractThis theoretical work provides several mechanistic understandings of phonon-interface scattering. Unlike the current standard models for describing phonon-interface interactions, which define the interface as a discrete planar defect, the treatment provided here defines the interface as an array of linear defects. This is the basis on which prevailing models for describing the structure and energy of interfaces is grounded, and we propose that a theory for phonon-interface scattering should be grounded in this definition as well. We apply the analytical expression derived here to phonon-interfacial strain field scattering from a symmetric tilt grain boundary and a semi-coherent phase boundary. It is shown that phonon diffraction conditions arise from the periodic nature of these defect arrays as can be expected from the wave-like nature of phonons. Furthermore, for diffuse heat conduction, a dimensionality crossover is observed in the frequency (ω ) dependence of the scattering rate. Phonons with a wavelength longer than the linear defect spacing scatter as if the defect were planar, meaning they scatter into the 1D phonon density of states (pDOS) contributing no ω -dependence to the scattering rate. Phonons with a wavelength shorter than the defect spacing will scatter as if the defect were linear, in that they scatter in the 2D pDOS which contributes one factor of to the scattering rate. This crossover in defect dimensionality provides a mechanistic understanding for ω -dependent phonon-interface scattering, as well as the ω -dependence of interface specularity. This crossover in the ω -dependence of the scattering rate is then used to explain the temperature dependence that is commonly observed in the low- lattice thermal conductivity of polycrystalline and nanocrystalline materials.
4:15 PM - ES09.08.07
Chemical Potential Gradient-Induced Extraordinary High Peak Voltage of Thermopower Waves
Swati Singh 1 , Hyeona Mun 1 , Sanghoon Lee 1 , Sung Wng Kim 1 2 , Seunghyun Baik 2 3
1 Department of Energy Science, Sungkyunkwan University, Suwon Korea (the Republic of), 2 Center for Integrated Nanostructure Physics, Institute for Basic Science (IBS), Suwon Korea (the Republic of), 3 School of Mechanical Engineering, Sungkyunkwan University, Suwon Korea (the Republic of)
Show AbstractThermopower wave, where chemical energy is directly converted into electricity, has received considerable attention recently.[1,2] Higher Seebeck coefficient materials have been actively investigated in the past to achieve higher peak voltage and specific power.[1] However, here we employed the chemical potential gradient as a key mechanism to improve thermal to electrical conversion performance [2]. Unprecedented high peak voltage (maximum: 8 V, average: 2.3 V) and volume-specific power (maximum: 0.11 W mm-3, average: 0.04 W mm-3) were achieved using n-type single-crystalline Bi2Te3 substrates.[2] A large down-shift in Fermi energy (~5.09 eV) of the substrate by p-doping of fuel (nitrocellulose + sodium azide) was experimentally observed by ultraviolet photoelectron spectroscopy.[2] The electrical potential generated by the Seebeck effect was only 2.5% (~200 mV) of the maximum peak voltage. In contrast, an order of magnitude greater chemical potential shift (~5.09 eV) could be achieved by the right combination of substrate, fuel doping, and anisotropic substrate geometry. The effect of crystallinity (single vs. poly-crystal) on the thermopower wave form will also be discussed together with the mathematical wave model.[2] [1] Energy Storage Materials, 3, 55 (2016) [2] Advanced Materials, In press (10.1002/adma.201701988, 2017)
4:30 PM - ES09.08.08
Enhanced Thermoelectric Figure of Merit by Different Micro-Nanostructure Inclusions in PbTe Bulk Nanostructures
Neeleshwar Sonnathi 1 , Bayikadi Khasimsaheb 1 , Rajeshkumar Mohanraman 2 , Husam Alshareef 2 , Sivaiah Bathula 5 , Sriparna Bhattacharya 3 , Y Y Chen 4 , AM Rao 6
1 , Guru Gobind Singh Indraprastha University, New Delhi India, 2 Materials Science and Engineering, King Abdullah University of Science and Technology (KAUST), Thuwal Saudi Arabia, 5 , National Physical Laboratory, New Delhi India, 3 , Clemson University , Clemson, South Carolina, United States, 4 Institute of Physics, Academia Sinica, Taipei Taiwan, 6 , Clemson University , Clemson, South Carolina, United States
Show AbstractNovel Strategies for high power factor are of great interest in a thermoelectric energy conversion. A simple experimental strategy for enhancing the figure-of-merit (ZT) of PbTe nanocubes is proposed in which different heterogeneous structures are incorporated in the host materials. This incorporation of micro-nanostructures results in increase in the electrical conductivity. However, micro-nanostructures interfaces do not considerably affect Seebeck coefficient which eventually results in increase of the Power Factor. Hence incorporation of micro-nanostrucres have a decoupling effect on the inter dependence of Seebeck coefficient and electrical conductivity. Furthermore a significant shift in the bipolar effects towards higher temperatures is observed, due to which high values of the figure of merit are obtained for wider range of temperature. In view of this, fabricating a material with the coexistence of heterogeneous structures (micro and nanostructures) can be considered as an effective way to obtain an enhanced figure of merit for a wider range of temperature.
ES09.09: Poster Session III
Session Chairs
Thursday AM, November 30, 2017
Hynes, Level 1, Hall B
8:00 PM - ES09.09.01
Nanoporous Thermal Filters for High-Performance Sub-Ambient Radiative Cooling
Hannah Kim 1 , Regina Garcia-Mendez 2 , Travis Thompson 3 , Jeff Sakamoto 3 , Andrej Lenert 1
1 Chemical Engineering, University of Michigan–Ann Arbor, Ann Arbor, Michigan, United States, 2 Materials Science and Engineering, University of Michigan–Ann Arbor, Ann Arbor, Michigan, United States, 3 Mechanical Engineering, University of Michigan–Ann Arbor, Ann Arbor, Michigan, United States
Show AbstractMaterials that reject heat into Space by selectively radiating through the atmospheric 8-13 um transparency band show promise in passive cooling applications such as reduction of peak air-conditioning loads and dry cooling. Being able to strongly emit in the 8-13 um “atmospheric window” while simultaneously preventing solar radiation from reaching the cold emitter is crucial to the performance of the device. We investigate an approach where porosity is introduced in an 8-13 um transparent material to block solar and atmospheric heat. We conduct a systematic study of the effect of size and density of the pores on the optical and thermal properties of the material. By tailoring the porosity and molecular absorption of the structure we define regions for short-wavelength scattering and long-wavelength absorption. The combination of low thermal conductivity and controlled transport of radiation enable thermal filtering. Ultimately, this thermal filter is expected to enhance cooling power (>70 W/m2) and temperature drop (>20 K) of passive cooling systems that reject heat to Space.
8:00 PM - ES09.09.02
High Emissivity Coating for Energy Saving in Industrial Furnaces
Jaturong Jitputti 1 , Koichi Fukuda 1 , Noppakun Sanpo 1
1 , SCG Chemicals Company Limited, Bangkok Thailand
Show AbstractThe furnace wall in industrial furnaces are lined with refractory, brick and fiber materials possessing a relative low emissivity. By applying a "High Emissivity Coating" on the fire-side surface, it increases the emissivity and thereby improve the thermal efficiency of the furnace box significantly. It was found that applying high-emissivity coating on the furnace wall of industrial furnaces, e.g. naphtha steam cracker, steel reheating furnace, improves the thermal efficiency of the furnace, which resulted in fuel savings(∼3-6%), increased production and improved quality in firing and heat treating furnaces. These differences are small, but considering the industrial importance and scale of the furnace, it significant. In addition, other benefits, such as increased life of refractory, less NOx emission, etc., are obtained by applying emissivity coating material onto the furnace wall. Recently, high emissivity coating has been applied in several steam crackers with satisfactory results. Moreover, high emissivity coating was also applied to other industrial furnaces, such as steel reheating furnaces, and the results will be presented.
8:00 PM - ES09.09.03
Development of ‘Thermoelectric Power Generating Threads’ Based on Carbon-Nanotube-Composite Threads
Ryota Arakaki 1 , Kazuki Kawata 1 , Hayato Kitamura 1 , Hiroyuki Shimizu 2 , Katsuaki Ishii 2 , Takahide Oya 1
1 , Yokohama National University, Yokohama Japan, 2 , Textile Research Institute of Gunma, Kiryu Japan
Show AbstractWe propose a unique and flexible thermoelectric power generating element, i.e., a “thermoelectric power generating thread,” based on carbon-nanotube (CNT)-composite threads (CNTCTs). The CNTCT is a composite material based on the CNT and the ordinary thread. Therefore, it shows various properties based on the CNT despite of a thread.
Nowadays, as one of environmental problems, it is focused that much consumed energy is wasted as heat. Therefore, to realize a “low-carbon society, ” the way to utilize the wasted heat is required. As one of candidates for solution of this problem, the thermoelectric power generating technologies are focused. However, existing thermoelectric conversion elements are made from rare metal that has a limit to mine.
In this study, we are aiming to develop thermoelectric conversion element by using CNTs. Recently, it has been reported that the CNT shows a giant Seebeck effect (about 170 μV/K, an important property for the thermoelectric conversion) and is expected to be new elements instead of the rare metal. However, the CNT is difficult to handle because general form of it is like powder. In addition, for efficient thermoelectric power generation, “high electrical conductivity” and “low thermal conductivity” are requested for the element. However, the general CNTs show high electrical and thermal conductivities. To solve these problems, we have proposed the use of our CNTCTs. They are expected to have the requested above two properties because the thread fibers that are contained in the CNTCTs are expected to prevent the heat spreading, i.e., our CNTCT is expected to have “high electrical conductivity” and “low thermal conductivity.”
To develop our “thermoelectric power generating thread,” we prepare a CNTCTs by using a dyeing method based on a traditional technique. In concrete, we prepare the CNT dispersion by mixing 25 mg of multi-wall CNTs, 25 mg of sodium dodecyl sulfate as dispersant in 25 ml of pure water and ultrasonication for them, firstly. After that, we dye 9 cm of an ordinary cotton thread by using the CNT dispersion, and dry it. Finally, we can obtain our “thermoelectric power generating thread.” For demonstration and evaluation, we add temperature differences (about 60 °C) to both ends of our sample (its distance is 5.5 cm), and measure electromotive force (E.M.F.) between both ends of it. As a result, we could obtain 0.1 mV of E.M.F., i.e., 1.6 μV/K of the Seebeck coefficient, from our sample. This result indicates our sample is expected to be the aiming “thermoelectric power generating thread.” As a next step of this study, we aim to improve the Seebeck coefficient by using semiconducting-(S-)CNTs because the S-CNT generally shows a larger Seebeck effect. We believe our threads will be used as flexible thermoelectric power generating elements or thermal sensors in our daily life.
Acknowledgement: This work was partly supported by JSPS KAKENHI Grant No. 25110015.
8:00 PM - ES09.09.04
Direct Thermal Probing of Quenched Radiation of Polar Dielectric Thin Ribbons
Sunmi Shin 1 , Renkun Chen 1
1 , University of California, San Diego, La Jolla, California, United States
Show AbstractPolar dielectric materials support surface phonon polariton (SPhP) and exhibit interesting optical properties in the infrared (IR) regime, which can be utilized for promising heat management applications, such as radiative cooling and solar thermal energy harvesting. It is well known that the IR optical properties of polar dielectric nanostructures would be significantly altered from their bulk counterparts, as the sizes are smaller than the dominant thermal wavelength (~ 10 micron at 300K) and the skin depth (hundreds of nanometer). For example, it was predicted by Golyk et al. (Phys. Rev. E 85, 046603 (2012)) that the radiation of polar dielectric nanostructures is significantly quenched. However, the common optical methods to measure the IR properties, such as spectral absorptance and the emittance measurements, would be challenging due to the transparency and the small size (smaller than the diffraction limit) of the nanostructures. Therefore, there is a growing need to develop precise and direct measurements of infrared thermal properties of polar dielectric nanostructures for in-depth study of their interaction with light and the properties of SPhP.
Here we demonstrate a direct thermal approach to measure the emissivity of low-dimensional polar dielectric materials in the IR regime. By measuring the length dependent thermal transport properties in thin ribbons, we can readily extract the radiation heat transfer coefficient through a fin model. To eliminate the potential impact of thermal contact resistance, the nanostructures are monolithically integrated with the thermal reservoirs by employing a microfabrication process. We have demonstrated this technique on SiO2 ribbons with ~100 nm thickness, and shown that the effective emissivity of the ribbons is significantly lower than that of bulk SiO2 (~0.9 at 300 K). We will also discuss the effects of the ribbon geometry and the temperature on the IR emission properties.
8:00 PM - ES09.09.05
Enhancing Passive Radiative Cooling Performance with Impedance Matching
Muhammed Kecebas 1 , Ibrahim Sendur 1
1 , Sabanci University, Istanbul Turkey
Show AbstractPassive radiative cooling is a promising cooling technique which can reach 100 W/m2 of cooling performance under direct sunlight without energy consumption. There are two requirements that affect the cooling performance: a high reflectivity in the visible and near-infrared spectrums and a high emissivity in the 8-13 µm spectrum. Increasing emissivity in 8-13 µm spectrum enhances the rate of heat transfer between the object and sky. For this purpose, we utilize an impedance matching technique, a two-section transformer, which is widely used in microwave applications. We modified the traditional method such that the compensation of destructive effects of the adjacent layers on reflectivity at the front surface can be achieved. With this modification a perfect match between air and the substrate, even in the presence of several layers in between, is achieved. When applied to a radiative cooling system we observed that average emission in 8-13 µm spectrum can be increased, thus cooling performance of the system is enhanced.
8:00 PM - ES09.09.06
Design of High-Temperature Solar Receiver Integrated with a Short-Term Thermal Storage System for Solar MGTs
Muhammad Bashir 1
1 , University degli studi RomaTre, Rome Italy
Show AbstractThe technological progress carried out in the development of high-temperature materials has led to the design of new Concentrated Solar Power plants, like Dish-Micro gas turbines (Dish-MGTs). Such systems could show several advantages in terms of costs, reliability and availability if compared with Dish-Stirling plants and better performance than Solar Organic Rankine Cycles. In such plants, natural solar radiation fluctuations can reduce system performance and damage seriously the Micro Gas Turbine. To stabilize the system operation, the solar receiver has to assure a proper thermal inertia. Therefore, a solar receiver integrated with a short term storage system based on high-temperature phase-change materials is proposed in the present paper. A tubular cavity receiver has been proposed having phase-change material inside its volume. The preliminary design process has taken into consideration a receiver shape optimization to improve heat transfer inside the component volume and to reduce maximum temperatures on the irradiated surface, making them compatible with material operating maximum values. Furthermore, aim of this work has been the reduction of temperature gradients inside the Phase-Change Material contained in the receiver structure to maximize the effectiveness of the thermal storage system. In order to evaluate the detailed thermo-fluid dynamic component behavior in steady-state and transient conditions, CFD analyses have been performed for different receiver geometric parameters. The detailed simulation results has been discussed and presented.
8:00 PM - ES09.09.07
Passive Directional Daytime Radiative Cooling
Bikram Bhatia 1 , Arny Leroy 1 , Yichen Shen 1 , Lin Zhao 1 , Marin Soljacic 1 , Evelyn Wang 1
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractPassive approaches exploiting high atmospheric transmittance at mid-infrared wavelengths (8-13 µm) are promising for cooling terrestrial objects by radiating heat to the low-temperature upper atmosphere. One of the primary challenges preventing widespread adoption of passive radiative cooling is its ineffectiveness during the day due to the high solar intensity. Some recent studies have demonstrated the possibility of achieving sub-ambient cooling during the day using nanophotonic structures that are highly reflecting in the solar spectrum and have strong emission in mid-infrared wavelengths. In this work, we demonstrate an alternate approach that exploits the directional nature of solar flux and is capable of achieving cooling powers up to 100 W/m2 and minimum temperatures of 17 °C below ambient during daytime. Unlike previous work on daytime radiative cooling that rely on complex photonic structures, we used a polished aluminum reflector, physically separated from a simple blackbody emitter, to reflect the direct solar radiation. In addition, we incorporated a nanoporous polyethylene convection cover which reflects ~80% isotropic diffuse solar radiation. The proof-of-concept radiative cooler was able to achieve a minimum emitter temperature of 2.4 °C at peak solar irradiation and a sub-cooling of >2 °C below the ambient air temperature. We further analyzed the performance of the radiative cooler by quantifying the relative contributions of different heat transfer pathways – incoming and outgoing atmospheric radiation, incoming direct and diffuse solar irradiation, and conduction and convection losses to the surroundings. We show the possibility of achieving sub-ambient cooling by using a simple geometric optics-based approach which could lead to low-cost, high-performance passive air conditioning and refrigeration solutions.
8:00 PM - ES09.09.08
Exploring and Improving Thermoradiative Cells for Energy Generation from Terrestrial Sources
Svetlana Boriskina 1 , Marcus Abate 1 , Thomas Cooper 1 , Yi Huang 1 , Gerald Mahan 1 , Gang Chen 1
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractAlthough sun provides an abundant source of renewable energy in the daytime, solar harvesting technologies face serious challenges due to intermittent nature of sunlight. Solar-generated energy storage either comes at high price (for electrical storage) or requires high capital investments and large scale facilities (for thermal storage). Although counter-intuitive, "reverse solar cell" systems can also generate electric power by emitting rather than absorbing photons. Such systems – known as thermoradiative (TR) cells – generate voltage and electric power via non-equilibrium thermal radiation of infrared photons. TR cells offer an opportunity to generate clean energy from largely untapped terrestrial thermal sources, are portable, and can potentially be designed to operate more efficiently at nightime. However, the reported efficiencies of TR cells need to be significantly improved before they can be considered a practical energy source. We will report on our theoretical studies and experimental exploration of TR cells aimed at understanding the fundamental physics of TR cells and improving their performance. Our theory predicts that when low frequency photons dominate the TR cell emission spectrum, its efficiency is increased and, in an ideal case, can approach the Carnot limit, which significantly exceeds the limiting efficiency of an ideal solar PV cell made of the same material. However, sub-bandgap absorption and non-radiative losses significantly degrade the cell performance. We will report on our modeling of the efficiencies of the TR cells under different emission scenarios, and will discuss opportunities for their performance enhancement via the use of selective filters, far- and near-field photon extractors, and electron bandstructure engineering. Harvesting the energy of terrestrial heat sources via TR cells can provide small-scale sustainable power solutions for remote locations and for disaster-relief effort, potentally making possible nighttime operation when solar energy is not available.
This work was supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Science and Engineering Award No. DE-FG02-02ER45977 (for the thermal emission manipulation) and by the ‘Solid State Solar-Thermal Energy Conversion Center (S3TEC)’, funded by the US Department of Energy, Office of Science, and Office of Basic Energy, Award No. DE-SC0001299/DE-FG02-09ER46577 (for solid-state energy conversion applications). M.A. was supported by the MIT Summer UROP program.
8:00 PM - ES09.09.09
Experimental and Numerical Characterization of CPV Microchannel Based Cooling Systems
Natalia Osorio 1 , Mario Di Capua 1 , Amador Guzman 1
1 , Pontifica Universidad Catolica de Chile, Santiago Chile
Show AbstractNumerical and experimental thermal analyses are carried out to evaluate microchannel based cooling devices for concentrated photovoltaic (CPV) systems. In CPVs, lenses and mirrors are used to concentrate the direct solar irradiance (DNI) onto a small area occupied by a high efficient III-V multi-junction solar cell. Sunlight used in high CPV systems is highly concentrated between 300 to 1000 times, which combined with the high efficiency of the multi-junction solar cell reduces the required area to generate a specific power. A high concentration factor onto a dense solar package cell with a size equivalent to 1 cm2 or higher however, requires an effective cooling system to avoid overheating since only a fraction of the incoming irradiance is absorbed by the solar cell and converted into electrical energy, with the highest reported power conversion efficiency of 40%. The remaining energy will be converted into thermal energy, which leads to an increase in the solar cell temperature, to a decrease in the conversion efficiency, and even degradation of the solar cell. This work report flow and heat transfer numerical simulations in microchannels, which is used as an effective cooling alternative for multi-junction solar cells corresponds. We carry out the numerical simulations using COMSOL-5.1, with two type of computational domains. The first domain corresponds to flat rectangular microchannels, whereas, the second domain corresponds to a microchannel with vortex generator elements (VGE) installed on the inner sidewalls. We use water in single-phase conditions as a coolant and a Reynolds number range of 100 to 500. The thermal boundary conditions are a given heat flux on the upper face of the microchannel, which is equal to the total heat producer by the solar cell under different efficiency conversion values, and insulated walls elsewhere. For the entrance we use a constant temperature of T=20°C and outflow condition for the outlet. The results generated by the simulations show that VGE enhances the heat transfer performance of the microchannel, because the created vortices increase the heat transfer convection, however, flat microchannel can be successful for low concentration level of sunlight. Additionally an experimental study is designed to teste microchannel devices. We initially start with a minichannel configuration of the cooling systems to validate the numerical results. The experiment is designed thermally by using heat source that generates the equivalent to the fraction of the solar radiation concentrated that the PV cells that not convert into electricity for its efficiency, and in consequence is converted to heat. The devices is cooled by a minichannel cooling system to keep the surface temperature lower that 110°C, over three different concentration ratio (CR), low, medium and high CRs. Heat flux and surface temperature over the cells are investigated and compared to numerical results.
8:00 PM - ES09.09.10
Ice Mitigation Using Photothermal Effect
Susmita Dash 1 , Jolet de Ruiter 1 , Kripa Varanasi 1
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractIce buildup can lead to reduction in energy efficiency and safety issues in power lines, wind turbines, and residential buildings. Current methods for ice removal, including chemical, thermal and mechanical approaches, are costly and energy intensive. Here, we investigate a passive technique for deicing using a multi-layer surface design that can efficiently absorb and convert the incident solar radiation to heat. The corresponding increase in substrate temperature leads to the formation of an interfacial melt layer that allows for easy removal of the accumulated ice from the surface. We demonstrate the applicability of the designed surface to remove ice structures such as frost and patches of snow.
8:00 PM - ES09.09.11
Opportunities, Obstacles, and Recent Developments for Concentrating Solar Power Receiver Technologies Operating above 700°C
Matthew Bauer 1
1 Contracted to the US Department of Energy's Solar Office, ManTech International, Washington, District of Columbia, United States
Show AbstractA concentrating solar power (CSP) thermal receiver converts solar radiation to heat. For CSP to be a cost competitive electricity source this solar heat exchanger must be efficient and operate at a high temperature to support advanced power cycles (governed by Carnot’s theorem). The US Department of Energy’s SunShot Initiative targets receiver efficiencies of 90% operating at temperatures above 700°C. This aligns with other technoeconomic metrics to create a solution space for CSP that is economically viable. Compared to current commercial CSP receivers operating at 565°C, critical challenges arise in this elevated temperature regime: black body radiation increases drastically, traditional solar selective materials become unstable and degrade, and the maximum allowable thermal stress in alloys rapidly decreases.
These obstacles must be addressed while accounting for new coupling challenges induced by the needs of other emerging subsystems being developed for a next generation (elevated temperature) CSP plant. Viable advanced power cycles (particularly the supercritical CO2 Brayton cycle) will likely dictate a reduced temperature change within the heat transfer fluid across the receiver. The maximum solar concentration ratio achievable from cost effective heliostats has not been demonstrated (directly influencing receiver efficiency). Additionally, the current state of the art heat transfer fluid (HTF), Solar Salt, decomposes above 600°C. Recent investigations suggest the viability of a high temperature receiver coupling with one of three unique heat transfer media applicable to CSP: chloride based molten salts, supercritical CO2, and ceramic falling particles.[1] This work presents the effects and constraints of manipulating the solar selective properties, the influence of material properties at the solar-to-HTF interface, and the impact of adjacent subsystems on the receiver performance and the CSP application. Critical research challenges gating development of this high temperature embodiment of CSP are also highlighted.
[1]Mehos, Mark, et al. Concentrating Solar Power Gen3 Demonstration Roadmap. No. NREL/TP-5500-67464. National Renewable Energy Laboratory, Golden, CO, United States, 2017.
8:00 PM - ES09.09.12
Tuneable Sputtered Films by Doping for Wearable and Flexible Thermoelectrics
Katrina Morgan 1 , Andrea Ravagli 1 , Chris Craig 1 , Ioannis Zeimpekis 1 , Jin Yao 2 , Ghada Alzaidy 1 , Daniel Hewak 1
1 Optoelectronics Research Centre, University of Southampton, Southampton United Kingdom, 2 Chemistry, University of Southampton, Southampton United Kingdom
Show AbstractAn efficient, flexible power supply is in demand for the billion dollar wearable market. Thermoelectrics (TE) are the ideal choice, utilising body heat to produce green, uninterrupted energy.
Screen-printing, a complicated process requiring synthesis, is the common fabrication method for flexible TEs but suffers from limited material choices and low-throughput [1]. Sputtering, however, is able to deposit a large array of materials, is already used in fabrication lines and is easily incorporated into roll-to-roll manufacturing; a flexible device mass-production technique.
The limited efficiency of TE cells remains to be the main challenge and is related to material properties. Previous investigations into sputtered materials for flexible TE cells is sparse. This work will provide a comprehensive study of sputtered materials and doping effects, for efficient flexible TE cells.
An optimal bandgap for a TE material is dependent on the hot side of the application Th, given by Eg = 4kTh [2]. For body temperature regimes, BiTe, SnTe and GeTe exhibit energy gaps close to this optimum and were therefore chosen for this work.
BiTe, GeTe and SnTe were singly and co-sputtered with Ge, Si and Zn. Soda lime and polyimide substrates were used, with the latter demonstrating wearable applications. The Seebeck coefficient and electrical resistivity were measured.
For BiTe films, pure BiTe exhibited the lowest resistivity of 5 mOhm-cm and was found to be n-type. As both n- and p-types are required for TE cells, and as chalcogenides are naturally p-type, it is beneficial to have identified a high performance n-type material. Doping BiTe with Zn changed it from n-type to p-type but at the compromise of slightly increased resistivity. BiTe-Ge had the highest seebeck coefficient for BiTe films, S=-65.1uV/K.
Pure SnTe exhibited the lowest resistivity of 2 mOhm-cm for the SnTe films, whilst SnTe-Ge had the highest seebeck coefficient, S=50.8uV/K. Doping with Zn however reduced the Seebeck coefficient considerably to S=1.4uV/K.
Only pure GeTe and GeTe-Si were found to be TE compatible, with p-type behaviour and low resistivities ~ 3 mOhm-cm. Doping with Ge resulted in a resistivity increase of 8 orders of magnitude, whilst GeTe-Zn was beyond the measurement limit. This is a surprising as doping SnTe and BiTe with Zn and Ge had no such effect.
The most efficient TE material was identified by the power factor. BiTe had the highest power factor for n-type whilst GeTe had the highest for p-type, with 0.81 and 1.4 mW/mK^2 respectively. Whilst BiTe has been relied on previously for TE cells, GeTe exhibited a much larger power factor, demonstrating its potential for use as a highly efficient TE material in the future. Further work will be conducted into the effects of doping seen in this work, whilst a flexible TE cell using BiTe and GeTe will be demonstrated.
[1] Raihan. A, et al., Ren. & Sus. Energy Rev., 73, 730-744 (2017)
[2] Wood. C, Rep. on Prog. In Phys. 51, 459-539 (1988)
8:00 PM - ES09.09.13
The Planer Sodium Exposure Test to Evaluate Na-TEC Electrodes
Jong Min Ha 1 , Shannon Yee 1 , Seung Woo Lee 1
1 , Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractThe sodium thermal electrochemical converter (Na-TEC) is a thermal engine which generates electrical power through the redox reaction of the sodium vapor. Due to the challenges in building an electrochemical cell for a high temperature and high vacuum environment, few studies have been conducted to test the optimization of the electrodes within the Na-TEC. We develop a planar sodium exposure test cell to evaluate the electrochemical properties of high exchange-current density electrodes (Mo, TiB2, and LaB6). This testing cell is capable of measuring important electrode parameters that elucidate the kinetic and mass transfer polarizations within the electrode. Our design allows for measurements of uniform, well-defined electrodes by eliminating the angle effects of depositions on tubular electrolytes. A mechanical spring is implemented within the cell to remove the need for additional welding or brazing, both of which can contaminate the samples, on the electrical wiring. Sputtered electrode properties are measured and then optimized by tuning the sputtering conditions (i.e., varying argon pressure from 3.75 to 15 mTorr). The porosity and the structure of the electrodes are examined with SEM, while EDX measurements are required to verify the composition of boride electrodes. As the argon pressure increases the films begin to form a columnar structure which increases the porosity of these electrodes. The current distribution within the solid electrolyte used in this testing cell is also modeled to identify the proper location for the reference electrode. It is shown that placing the working and counter electrodes on the same surface simplifies the design and reduces the measurement uncertainty caused by the location of the reference electrode.
8:00 PM - ES09.09.14
3D Imaging and Modeling of Porous Composite Phase Change Materials for Thermal Energy Storage
Xin Wang 1 , Yongjie Ma 1 , Ye Xu 2 , Danyong Li 3 , Chaohua Guo 4 , Zhonghai Zhou 1
1 , Institute of Oceanographic Instrumentation, Shandong Academy of Sciences, Qingdao City China, 2 , Beihang University, Beijing China, 3 , Oleumtech Co.,Ltd., Beijing China, 4 , China University of Geosciences, Wuhan China
Show AbstractPhase change materials (PCMs) are key components in many energy storage solutions, particularly those involving energy from renewable resources such as solar and wind. To overcome the limit of low thermal conductivity in most pure PCMs, composite structures consisting of PCMs and conducting materials network have been developed. The thermal conductivity of those composites depends strongly on their microscopic structures. In this work, we combine three dimensional (3D) imaging and simulation to understand the effect of pore structures on the thermal behaviors of composite PCMs. We first fabricate composite PCMs consisting of sodium nitrate, potassium nitrate, and expanded graphite (EG) using the vacuum impregnation method. We then reconstruct a 3D pore-scale model using X-ray CT and extract key pore structure parameters such as pore size distribution, connectivity function curve, and tortuosity factor. With the 3D model, we numerically investigate the motion of salt/air interface and the evolution of solid/liquid interface during the melting process using VOF and enthalpy-porosity coupled model. A 3D model considering thermal non-equilibrium between the salt and EG is established to describe the heat transfer characteristics and two-temperature energy equations are used in the laminar flow of liquid molten salt in the porous structure. Our findings will shed light on how pore structure affects the thermal behaviors and can be used to guide the design of better composites PCMs.
8:00 PM - ES09.09.15
Enhanced Solar-Thermal Conversion Efficiency in Ultrathin Plasmonic Metamaterial Absorbers
Yang Li 1 , Dezhao Li 1 , Baoling Huang 1
1 , Hong Kong University of Science and Technology, Hong Kong Hong Kong
Show AbstractApart from the well-known photovoltaic (PV) cells, another promising approach to harnessing solar energy is solar thermal technology, which enables a much higher solar-electricity energy conversion efficiency up to 85%. To reach such a high conversion efficiency, the key component of a solar thermal system, i.e., solar absorber, must show spectrally selective absorption: it can perfectly absorb all the short-wavelength sunlight, while shows no emission above a cut-off wavelength to avoid thermal re-radiation in the infrared range. Besides, an ideal solar absorber must withstand high operating temperatures (i.e., >973 K) where a high thermal-electricity conversion efficiency can be achieved. Moreover, an ideal solar absorber is expected to be as thin as possible to reduce its heat loss, and to have as few as possible interfaces to ensure its thermal stability. Selective absorbers with various structures have recently been extensively studied to realize ideal solar absorbers. However, despite significant advances, the energy conversion efficiency, thermal stability, and structural complexity of all state-of-the-art selective absorbers still fall short of the standard of ideal solar absorbers at elevated temperatures. In this study, we develop a 240-nm-thick plasmonic metamaterial absorber (PMA) displaying a high solar-thermal conversion efficiency of >90% and an excellent thermal stability at 1000 K. Specifically, we take advantage of triangular meta-atoms made of high-loss materials (e.g., Ti) to address the imperfect absorption caused by significant impedance mismatch in the visible range. Consequently, broadband near-perfect (>98% in average) absorption below the cut-off wavelength of 1.35 μm is achieved due to the combination of hybrid strategies: structure-based, material-based and shape-based strategies. Moreover, a refractory metal (i.e., Ta) is employed as the bottom reflector to address the high IR emittance of PMAs made of high-loss materials, obtaining a low emittance of only 24% at 1000 K. Additionally, the ultrathin PMA can be easily heated up to high temperatures due to the large surface-to-volume ratio. In addition, this new class of selective solar absorbers based on metal-insulator-metal structures is almost independent on the planar pattern alignment, showing great potential for large-scale production when combined with chemically synthesized nanoparticles. These advantages make the PMA a promising candidate for solar thermal conversion at elevated temperatures.
8:00 PM - ES09.09.16
A Silicon Nanowire as an Inherent Heater and Thermometer for Thermoelectrics
Xingyan Zhao 1 , Yaping Dan 1
1 , Shanghai Jiao Tong University, Shanghai China
Show AbstractWith the global crisis of energy resource shortage, high performance thermoelectric material is in urgent need to convert the thermal energy to electric energy. The thermoelectric figure of merit, ZT has been improved to up to 1 on nanomaterials in recent years1-4. The measurement of ZT factor include the independent measurements of seebeck factor,electrical conductivity and thermal conductivity. Thermal condcutivity measurement of nanoscale materials is usually conducted on a micorfaricated structure consists of two suspended SiNx membranes1-4. Each SiNx membrane has a thin platium resistance coil patterned on it. The nanomaterial to be measured are placed between the two SiNx membranes. The Pt resistance coil serves as a heater to increase the temperature and a thermometer to measure the temperature of the nanomaterial at each end. But there are some drawbacks with this method. First, a large thermal contact resistance may exists and results in a large error in the measured thermal conductivity. Secondly, it’s hard to precisely place the nanomaterial to the two suspendend membranes. One way is to pick up the nanomaterial with a sharp probe and then manipulate the probe with a probe station under high resolution microscope. This is a tedious process and can’t be used for large scale fabrication. But for nanoscale materials, the thermal conductivity is usually size dependent. Characterization of a large number of devices is often required. Thirdly, the Pt resistance coil as a thermometer has a low sensitivity under low temperature. Here we demonstrate a new method to measure the thermal conductivity of SiNW using silicon as an inherent heater and thermometer. The SiNW to be measured and the SiNW heater and thermometer are patterned out of the same device layer of a silicon-on-insulator (SOI) wafer. The thermal contact resistance is zero in theory. SiNW as a thermometer has a high sensitivity under low temperature, as a result the thermal conductance can be accurately measured. The whole structure is easy to fabricate. It is easy to measure an array of SiNWs with different size, doping level and surface roughness. This method can be applied to other semiconducting materials and is useful in searching for high performance thermoelectric materials.
References
[1] D. Li, Y. Wu, et al, Appl. Phys. Lett. 83, 2934 (2003).
[2] D. Li, Y. Wu, et al, Appl. Phys. Lett. 83, 3186 (2003).
[3] J. Lim, K. Hippalgaonkar, et al, Nano Lett. 12, 2475 (2012).
[4] T. Zhang, S.-L. Wu, et al, Nanotechnology 24, 505718 (2013)
8:00 PM - ES09.09.17
Thermal Capacitive Electrochemical Cycle for Converting Low-Grade Heat to Electricity
Xun Wang 1 , Shien Ping Feng 1
1 , The University of Hong Kong, Hong Kong Hong Kong
Show AbstractLow-grade thermal energy is abundantly available in industry, power plant, combustion engines, solar and geothermal heat. However, it is still a great challenge to convert low grade heat into electric energy in an efficient way. Here we explores the temperature-dependence electrostatic potential (non-faradic) in electric double layer (EDL) to construct a thermal capacitive electrochemical cycle (TCEC) using electrochemical capacitor, where the connection to only the hot or cold reservoir alternates in a cyclic charging-heating-discharging-cooling mode to convert low-grade heat into electricity. In this work, TCEC was investigated by molecular dynamic simulations in the supercapacitor consisted of parallel graphene electrodes and organic electrolyte (tetraethylammoinum tetrafluoroborate in acetonitrile). The change of temperature influences the distribution of ions and dipoles near graphene electrode. A temperature rise increases the ion thermal motion and thus the ions move farther into solution, leading to capacitive double layer expansion (CDLE). The cell can be then discharged at higher potential. The cycle is completed by cooling at open circuit, compressing the EDL. The theoretical model shows that the conversion efficiency of TCEC is higher than that of thermoelectric generators at a low temperature range. The model demonstrates efficiency of 1.08% using an electrochemical cell when cycling between 0oC and 80oC. The finding shows a potential to use an electrochemical heat engine for low-grade heat recovery.
8:00 PM - ES09.09.18
White-Light-Activated Photothermal Effect of Fe3O4 Nanoparticles for Energy-Efficient Windows
Yuan Zhao 1 , Donglu Shi 1
1 , University of Cincinnati, Cincinnati, Ohio, United States
Show AbstractA significant energy loss results from the poor thermal insulations of the commercial and public buildings, especially from windows. Natural solar light can induce the photothermal effect in Fe3O4 nanoparticles, that can be applied to single-pane windows for reduced heat loss without relying on insulating materials. The insulation efficiency is quantified through the so-called U-factor, defined as the ratio of the heat flux per unit area through the pane to the interior and exterior temperature difference (ΔT). Upon solar irradiation, single-panes can “self-heat” via the photothermal effect from the nanoparticle coatings. This can effectively reduce ΔT for enhanced thermal insulation. In this study, the photothermal effect of Fe3O4 nanoparticles, irradiated by solar light, was investigated for energy–efficient windows. The Fe3O4 nanoparticles were surface-functionalized with different polymers to modulate colloidal stability. The photothermal heating efficiencies of Fe3O4 with different surface coatings were found to be much greater under the white-light irradiation than NIR in both aqueous suspension and as thin films. The mechanism for the photothermal effect of Fe3O4 was identified in terms of its band structure. Both Urbach energy and band gap were obtained based on absorption spectra of various Fe3O4 nanoparticles. The Urbach “tail” was found consistent with nanoparticle surface defect structures, while the band gap (~3.1 eV) corresponded to the electronic transitions in the octahedral site of Fe3O4. We also discuss the absorption mechanism that is responsible for enhanced photothermal heating by white-light.
8:00 PM - ES09.09.19
Absorptive Spectral Control for High Efficiency Thin-Film Thermophotovoltaics
Tobias Burger 1 , Dejiu Fan 2 , Yulei Zhang 1 , Kyusang Lee 3 , Stephen Forrest 2 , Andrej Lenert 1
1 Department of Chemical Engineering, University of Michigan, Ann Arbor, Michigan, United States, 2 Department of Electrical Engineering, University of Michigan, Ann Arbor, Michigan, United States, 3 Department of Electrical & Computer Engineering and Materials Science & Engineering, University of Virginia, Charlottesville, Virginia, United States
Show AbstractThermophotovolatics (TPVs) are a promising energy conversion technology for application in concentrated solar power and distributed combined heat and power. TPV devices boast a solid-state design that enables scalable implementation for a variety of high-temperature heat sources. To achieve high conversion efficiency in the presence of realistic losses, it is critical to suppress net transport of sub-bandgap radiation between the emitter and cell. Here, we investigate the utilization of absorptive spectral control for recycling sub-bandgap radiation in high performance TPV devices. A computational study was performed in order to characterize radiative transport and energy conversion processes in a parallel plate TPV system, and subsequently predict device performance. Fabrication and characterization of a thin film InGaAs cell with back-surface reflector has served to validate our model’s predictions and diagnose sources of device inefficiency.
8:00 PM - ES09.09.20
Multi-Layered Photothermal Actuator Based on Conjugated Polymer for a Wireless Light Switching
Lim Hanwhuy 1 , Eunkyoung Kim 1 , Byeonggwan Kim 1
1 , Yonsei University, Seoul Korea (the Republic of)
Show Abstract
The photothermally induced heat from conducting polymer can be converted into other type of energy such as electrical, mechanical, or chemical energy. Especially, photothermal energy conversion into mechanical energy gives a unique method for reversible change of multi-layered actuator from 2-dimensional to 3-dimensional structure by thermal expansion coefficient mismatch among the layers. A thin conjugated polymer film was transferred onto a soft polymeric film to prepare a bimorph. Then the conjugated polymer surface of the bimorph was coated by a thin metallic film to prepare multi-layered photothermal actuator (MLPTA) with enhanced mechanical strength. The actuation of the MLPTA was remotely controlled by near-infrared light stimuli to afford an ON/OFF switch for an electrical circuit. A wireless light driven switch could be demonstrated with the MLPTA reversibly. Herein we present the effect of layer composition on the photothermal actuation and application of the MLPTA as a wireless light driven switch for a display.
8:00 PM - ES09.09.21
Photothermal Effect of Fe3O4@Cu2-xS Nanoparticles for Energy-Efficient Window Coatings
Jou Lin 1 , Yuan Zhao 1 , Donglu Shi 1
1 Mechanical and Materials Engineering, University of Cincinnati, Cincinnati, Ohio, United States
Show AbstractThe energy loss in buildings is mainly through poor thermal insulations, especially from windows. Upon solar irradiation, single-pane energy-efficient windows can “self-heat” via the photothermal effect from the nanoparticle coatings. The photothermal coatings can effectively reduce the temperature differences between the window and room interior, resulting in reduced heat loss through window. For an ideal window, the photothermal coating should exhibit high transparency in the visible region but large UV and IR absorbances that can be converted to heat. The photothermal effects of Fe3O4@Cu2-xS nanoparticles were investigated for developing energy-efficient windows with unique optical and thermal properties. Sufficient photothermal effect was found in the Fe3O4@Cu2-xS nanoparticles, while maintaining high transparency. Strong IR absorbance was also found, responsible for effectively raising the substrate temperature. Also reported are the nanoparticle synthesis and thin film deposition methods on glass substrates.
8:00 PM - ES09.09.22
Photonic Crystal Emitter for High Temperature Thermophotovoltaic Cell
Youngseok Kim 1 , Boyoung Park 1 , KeumHwan Park 1
1 , KETI, Seongnam-si Korea (the Republic of)
Show AbstractThermophotovoltaic (TPV) system has been much attention for creating electric resource from radiation caused by heat. TPV cell aims specific range of wavelength as conversion target. In this field, emitter serves as selective wavelength filter, which does significant role. And emitter should minimize rest heat from reflection of needless wavelength and be stable at high temperature over 1000 degree celcius in TPV system. In terms of heat resistance, ceramic has its own advantage. More over specific kind of ceramic and rare earth show sharp absorption spectrum near the infrared range compared to normal black body which absorbs almost over range of light. There were several experiments to apply those matters into TPV cell emitter, however, the efficiency was limited by intrinsic nature of materials. Photonic crystal was also widely considered as emitter because it can selectively reflect the specific light using photonic bandgap risen from periodic nanopattern of dielectric refractive material although oxidation at high temperature.
In this study, we devised collaboration of ceramic material and photonic crystal. At specific infrared range, ceramic has refractive index(n) and extinction coefficient(k) so it can be designed into periodic nanopattern to show the photonic crystal property. We used magnesium oxide (MgO) and nickel oxide (NiO) as ceramic material and designed the process for photonic crystal patterning. Photonic properties such as absorption/reflection spectrum were compared with various ceramic or metallic emitter. The results showed improved efficiency at specified spectrum for GaSb cell with good thermal stability. This experiment has important sense at increasing total conversion efficiency of TPV cell by combining two kinds of photonic advantage.
8:00 PM - ES09.09.23
Effect of Cooling Rates on Atomic Structure of Al-Based Metallic Glasses
Sung Hyuk Lee 1 , Jeon Taik Lim 1 , Taewon Yuk 1 , Gyutae Jeon 1 , Suk Jun Kim 1
1 , Koreatech, Cheonan-si Korea (the Republic of)
Show AbstractThe cooling rates (CR) can controlled mechanical properties of Al-based metallic glasses(MGs) with their atomic structure was studied. Enthalpy transition for vaporization (ΔHvap) and stress in atomic level related to cooling rates though all of fabricated Al-MGs appeared amorphous structure and glass transition temperatures (Tg) while heating. Al84.5Y10Ni5.5 showed no apparent changes both of the ΔHvap and the stress in atomic level regardless of cooling rates. At lower cooling rates, however, Al85Y8Ni5Co2 exhibited higher ΔHvap and compressive stress and Al86Y4.5Ni6Co2La1.5 indicated lower ΔHvap and tensile stress. It was strongly predicted that the coordination number (NC) was altered as RC changed. The change of Al concentration in Al85Y8Ni5Co2 supported the dependent on ΔHvap and the stress in atomic level on NC.
8:00 PM - ES09.09.24
High Resolution Calorimetry for Biological Applications
Sahngki Hong 1 , Edward Dechaumphai 1 , Renkun Chen 1
1 , University of California, San Diego, La Jolla, California, United States
Show AbstractHeat generation/transfer and the associated temperature change are directly linked with many biological phenomena such as metabolism of cells and ligand-protein bindings. Calorimetry is an excellent method for directly measuring heat generation from biological materials. For example, calorimetry can be used to monitor metabolic behavior of cells which is an excellent indicator of health conditions including diabetes, obesity and cancer. Likewise, measurements of thermodynamic properties of ligand-protein bindings are critical in drug discovery, and high-resolution calorimeters could lead to saving in cost and time. Thus, improving performance of a calorimeter will have an impact on a broad range of biomedical applications. However, biomedical use of calorimetry is still largely unexplored and hindered by the resolution limit.
The key design of the high-resolution calorimetry lies in the integration of a microfluidic platform for handling biological samples and a highly sensitive calorimetry scheme. The high resolution can be attained by using a sensitive thermometer and minimizing the thermal conductance between the measuring chamber and the thermal reservoir. In addition to the sensitivity, another challenge is the ability to a small amount of biological samples in fluids . In this presentation, we will describe our work on the development of a high-resolution chip calorimeter for bio-applications. Our chip calorimeter integrates three key components: i) microfluidic system for handling biological samples, ii) low parasitic heat loss design, and iii) a temperature controller with long-term temperature stability. By implementing these new designs, we demonstrate calorimetry with substantially improved measurement resolution compared to the state-of-the-art.
8:00 PM - ES09.09.25
Thermo-Electrochemical Cells for Waste Heat Harvesting
Madeleine Dupont 1 , Douglas MacFarlane 2 , Jennifer Pringle 1
1 ARC Centre of Excellence for Electromaterials Science, Institute for Frontier Materials, Deakin University, Melbourne, Victoria, Australia, 2 ARC Centre of Excellence for Electromaterials Science, School of Chemistry, Monash University, Melbourne, Victoria, Australia
Show AbstractIt is becoming increasingly necessary to generate energy from renewable and sustainable resources. Waste heat, such as that produced via industrial processes, vehicles or the human body, represents a large source of potential sustainable energy. Thermo-electrochemical cells (thermocells) are electrochemical devices which can harvest this thermal energy and continuously convert it into electrical energy which can be used in a range of applications.
A thermocell consists of two identical electrodes separated by an electrolyte containing two halves of a redox couple. When a temperature gradient is applied to the cell, the temperature dependence of the redox reaction generates a potential difference between the two electrodes, causing oxidation to occur at one electrode and reduction at the other. This generates a continuous flow of electricity because the species oxidised at the anode are then transported across the cell (via convection, migration and diffusion) where they are reduced at the cathode, and vice versa.
The power output of a thermocell is determined by a range of factors, relating to both fundamental properties and cell design. Properties of the redox couple, the electrolyte and the electrode all play a significant role in determining the performance of a cell. There has been considerable focus on developing redox couples that give rise to large cell potentials, and therefore, large power output, such as cobalt-based complexes which have exhibited some of the largest potential differences of any redox couples [1].
Additionally, non-aqueous electrolytes, such as ionic liquids, have recently been utilised due to their many advantageous properties including high boiling points, which allows increased cell operating temperature, high ionic conductivity and low thermal conductivity [2]. Further work into the development of electrode materials has also been shown to improve the power output of thermocells, particularly the use of high surface area carbon materials [3] due to its large electrode surface area and, in many systems, improved charge transfer kinetics.
In this work, the effects of fundamental properties, such as the redox couple, electrolyte and electrode material on the power output of thermocells has been investigated. Additionally, new redox couples and electrolyte combinations have been developed in order to optimise the performance of thermocell devices.
References
1. M. F. Dupont, et al, Chemical Communications, 2017, 53, 6288-6302
2. Abraham, T.J, et al, Energy and Environmental Science, 2013, 6, 2639
3. L. Zhang, et al, Advanced Materials, 2017, 29(12), 1605652
8:00 PM - ES09.09.26
Phonon Transport Properties of Thermoelectric MnxGe1-x Compounds with Various Mn/Ge Compositions from First-Principles Calculations
Yang Han 1 , Laurent Chaput 1 , Konstantinos Termentzidis 1 , David Lacroix 1
1 , University de Lorraine, Nancy France
Show AbstractTo fulfill a sustainable energy future is a vast challenge for material science both in elaboration and measurement/prediction level. It is worth noting that approximately 40% of the primary energy produced world-wide is lost as waste heat, so the recovery of even a fraction of this heat by converting it to useful electric power would have a dramatic impact on energy efficiency and sustainability. Mn/Ge compounds have many outstanding properties such as broad structural and stoichiometry variety and usage as scattering inclusions in bulk Ge matrix etc. which make them one of the excellent candidates for engineering thermal transport properties of thermoelectric (TE) materials and devices. Nanocomposite samples of this material have been grown as nanocolumns as well as quantum dots experimentally[1,2]. Electronic, magnetic and stability properties for some specific compositions have been studied in the past[3,4]. However, a systematical study of phonon transport properties of these synthesized Mn/Ge compounds is still lacking.
In this work, electronic band structures and lattice thermal transport properties of MnxGe1-x compounds with different Mn/Ge compositions (0xGe1-x compounds with different Mn/Ge compositions (Mn2Ge [F_43m], Mn3Ge [Fm_3m] and Mn3Ge [Pm_3m]), the electronic properties calculations show that they are all metallic with low lattice thermal conductivities, which are in good agreement with experimental measurements[5]. We find that the structure of Mn3Ge [Pm_3m] has the lowest thermal conductivity of the three compounds investigated. By comparing the key factors of thermal conductivity at the phonon mode level, it is found that the three aforementioned structures have almost similar phonon group velocities. However, the structure of Mn3Ge [Pm_3m] has the lowest volumetric heat capacity and phonon lifetime among them all in the whole frequency region, thus causing its lowest thermal conductivity.
Based on analysis of frequency accumulated thermal conductivities, it is reported that for the structure of Mn2Ge, only phonons in the lower frequency region contribute more to the total thermal conductivity, in contrary to Mn3Ge with different space groups for which all phonons in the whole frequency range contribute with the similar weight to the total thermal conductivity. Our results can provide clear theoretical supports for experimental investigations and are helpful for further explorations on Mn/Ge compounds for future thermoelectrics.
References
[1] M. Jamet et al., Nature Materials 5, 653 (2006).
[2] A. Jain et al., Journal of Applied Physics 109, 013911 (2011).
[3] S. Picozzi et al., Physical Review B 70, 235205 (2004).
[4] E. Arras, et al., Physical Review B 83, 174103 (2011).
[5] Y. Liu, Universite Joseph Fourier; Centre National de la Recherche Scientifique, 2015.
Symposium Organizers
Jia Zhu, Nanjing University
Baratunde Cola, Georgia Institute of Technology
Deyu Li, Vanderbilt University
Amy Marconnet, Purdue University
ES09.10: Solar Thermal I
Session Chairs
Thursday AM, November 30, 2017
Hynes, Level 3, Ballroom C
8:00 AM - *ES09.10.01
Nanoengineered Materials for Liquid-Vapor Phase Change
Zhengmao Lu 1 , Daniel Preston 1 , Youngsup Song 1 , Kyle Wilke 1 , Evelyn Wang 1
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractLiquid-vapor phase change is essential in many thermal energy conversion applications. However, effectively utilizing these processes requires fine manipulation of interfacial transport. In the first part of the talk, we discuss evaporation from ultra-thin nanoporous membranes. Fundamental understanding during evaporation remains limited to date as it is generally challenging to characterize the heat and mass transfer at the interface, particularly when the heat flux is high (> 100 W/cm2). We fabricated ultra-thin (≈ 200 nm thickness) nanoporous (≈ 130 nm pore diameter) membrane devices which reduced the thermal-fluidic transport resistance and accurately monitored the temperature of the liquid-vapor interface. At steady state, we demonstrated high heat fluxes across the interface (≈ 500 W/cm2) with pure evaporation into an air ambient and elucidated the importance of convective transport caused by evaporation itself. In the second part, we discuss condensation with low surface tension liquids. Low surface tension condensates pose a unique challenge since they often form a film, even on hydrophobic coatings. Lubricant infused surfaces (LIS) represent a potential solution, where a lubricant immiscible with the low surface tension condensate is infused into a rough structure on the condenser surface to repel the condensate. We used LIS to demonstrate a 5x improvement in heat transfer for low surface tension fluids compared to filmwise condensation. These works suggest the potential opportunities for significant energy savings in device thermal management, heating and cooling, and power generation.
8:30 AM - ES09.10.02
Low-Cost, High Performance Materials and System for Solar Thermal Desalination
George Ni 1 , Hadi Zandavi 1 , Svetlana Boriskina 1 , Thomas Cooper 1 , Gang Chen 1
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractSolar thermal evaporation of water has tantalizing potential as a platform for low-cost desalination, water treatment, and other industrial processes such as distillation. Recent research has centered around the concept of a solar-thermal, energy-converting material floating on water, continuously and passively generating vapor. This vapor could then be condensed into pure water. One ultimate ambition is to rollout cheap water-harvesting farms over the world’s salty oceans, producing pure, drinkable water to quench growing water scarcity challenges. This approach represent potentially major cost savings over infrastructure-reliant conventional desalination technologies. Thus far, a wide range of materials have been tested to efficiently generate water vapor at high solar-to-vapor efficiencies (~80-90%), yet demonstrations of vapor collection and condensation into drinking water have had disappointingly lower efficiencies (~5-10%)1, even lower than traditional solar stills. In our presentation, we build upon our previous work in high-efficiency solar thermal steam generation,2 and develop a polymer film-based solar still to demonstrate a full system capable of solar thermal energy conversion, water vapor generation, and finally water condensation with high efficiency. We present a system-wide heat transfer model to explain the drastic reduction in performance from water evaporation to vapor collection. We also demonstrate a vapor generating structure that simultaneously rejects salt, allowing continuous fouling-free operation in seas and oceans. The developed system is anticipated to cost ~$5 per m2, potentially providing enough daily drinking water for an individual. Our system has the potential for immense impact on resolving drinking water problems in the developing world. Furthermore, it could be adapted to solve other challenges in wastewater treatment. This work was supported by a J-WAFS grant from MIT.
(1) Liu, Z.; Song, H.; Ji, D.; Li, C.; Cheney, A.; Liu, Y.; Zhang, N.; Zeng, X.; Chen, B.; Gao, J.; et al. Extremely Cost-Effective and Efficient Solar Vapor Generation Under Nonconcentrated Illumination Using Thermally Isolated Black Paper. Global Challenges 2017, 1, 1600003.
(2) Ni, G.; Li, G.; Boriskina, S. V.; Li, H.; Yang, W.; Zhang, T.; Chen, G. Steam Generation Under One Sun Enabled by a Floating Structure with Thermal Concentration. Nat. Energy 2016, 1, 16126.
8:45 AM - ES09.10.03
Artificial Transpiration for Water Purification
Xiuqiang Li 1 , Jia Zhu 1
1 College of Engineering and Applied Sciences, Nanjing University, Nanjing, Jiangsu, China
Show AbstractRecently, efficient solar steam and vapor generation[1-2] is attracting a lot of attention for its potential applications in desalination, sterilization and chemical purification with minimum carbon footprint. In the process of solar steam and vapor generation, there are several outlets for the input solar energy: total enthalpy of liquid-vapor phase change, optical losses and thermal losses (including radiation, convection, conduction losses). Therefore, it is clear that there are two key elements to enable efficient solar steam and vapor generation: broadband and efficient solar absorption and minimized thermal losses. (1) We demonstrate that, when water path is confined to be two dimensional (2D), both efficient water supply and suppressed conduction loss can be achieved simultaneously. With a graphene oxide(GO) film with 94% absorption as absorbers, over 80% solar vapor efficiency under one sun irradiation can be achieved. More strikingly, because of minimized conduction loss, high efficiency is independent of the water quantity and can be maintained without thermal insulation of the container.[3] (2) We firstly reported a new concept “artificial transpiration” and achieved it with a GO film based 3D hollow cone structure inspired by transpiration processes of trees. In this device, the conduction loss was suppressed by designing 1D water path. The radiation and convection losses were also suppressed by designing morphology of device. Over 85% solar vapor efficiency under one sun irradiation was achieved. It is also found that this technology can enable efficient waste water treatment through two pathways, producing clean water and recycling heavy metals as Au, Cu.[4]
References:
[1] Zhou L, Jia Zhu et al. Nat. Photon. 2016; 10: 393-8.
[2] Zhou L, Jia Zhu, et al. Sci. Adv. 2016; 2: e1501227 1-8.
[3] Xiuqiang Li, Jia Zhu, et al. PNAS. 2016; 113:13953-8.
[4] Xiuqiang Li, Jia Zhu, et al. Nat. Sci. Rev. 2017; doi:https://doi.org/10.1093/nsr/nwx051.
9:00 AM - ES09.10.04
Thermal Energy Utilization by Stabilized 2D Water Films in Polymer Membranes as Evaporative Cooling Curtains
Mario Stucki 1 , Christoph Ruedi Kellenberger 2 , Michael Loepfe 1 , Wendelin Stark 1
1 , ETH Zürich, Zürich Switzerland, 2 , Novamem AG, Zürich Switzerland
Show AbstractGlobal energy demand is rising. In the United States alone more than 40 % of the consumed energy can be assigned to thermal energy involved with building utilities of which a vast part is cooling, heating and air movement alone.[1] Further increase is expected as countries develop in hot and arid regions on this planet.[2] Passive systems are sustainable solutions to reduce energy demand by using abundant thermal and radiation energy. Water, with its high enthalpy of evaporation of about 2.3 MJ/kg and its ubiquitous presence in human environment, makes it the transport-, storage- and cooling-liquid of choice. Evaporation of water over a large surface area by solar energy, might replace some or the current electric air conditioning.
In the templating method, found in our laboratory in 2012, dispersed hard salt template particles are used as templates for pores down to a size of a few nanometers. The scale-up of the technology has been shown up to the m2 scales at precise pore formation control.[3]–[6] The immense scaling benefits in creating porous surface area were exploited towards a passive cooling system in order benefit from the thermal properties of water evaporation. We stabilized 2D water in a hydrophilic porous membrane sandwiched in two hydrophobic porous cover membranes. A layer-by-layer built up strategy afforded a seamless combination of the three layers and porosity was maintained throughout the interfaces. Within the hydrophilic middle layer the water moves passively by capillary forces. It is fed through cut sides, as the outer layers remain dry in the application of a cooling curtain. These outer layers are porous enough to allow equal evaporation compared to a sample consisting only of the hydrophilic middle layer. In a laboratory scale cooling setup at 30°C and 50 % relative humidity 1427 ± 295 g/m2 of water were evaporated. This corresponds to a passive cooling rate of about 38 W/m2 at double-sided evaporation. In a model calculation it was shown that a cubic house of 10 m side length and 80 m2 of window area, equipped with the passive cooling curtain, could actively be cooled. [7]
[1] U.S. Energy Information Administration, 2011.
[2] M. Kassas, J. Arid Environ. 1995, 30, 115.
[3] C.R. Kellenberger, N.A. Luechinger, A. Lamprou, M. Rossier, R.N. Grass, W.J. Stark, J. Membr. Sci. 2012, 387–388, 76.
[4] S.C. Hess, A.X. Kohll, R.A. Raso, C.M. Schumacher, R.N. Grass, W.J. Stark, ACS Appl. Mater. Interfaces 2015, 7, 611.
[5] M. Stucki, W.J. Stark, WATERPROOF AND BREATHABLE, POROUS MEMBRANES, 2015, PCT/EP2016/079939.
[6] M. Stucki, C.R. Kellenberger, M. Loepfe, W.J. Stark, J. Mater. Chem. A 2016.
[7] M. Stucki, W.J. Stark, Adv. Eng. Mater. 2017.
9:15 AM - ES09.10.05
On-Sun Demonstration of a Solar-Thermal Aerogel Receiver (STAR)
Lee Weinstein 1 , Thomas Cooper 1 , Sungwoo Yang 1 , Bikram Bhatia 1 , Lin Zhao 1 , Elise Strobach 1 , George Ni 1 , Svetlana Boriskina 1 , Evelyn Wang 1 , Gang Chen 1
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractSolar energy is a critically important renewable energy technology, due to the abundance of available solar energy on Earth. To provide a constant supply of electricity, solar energy technologies must be paired with storage, due to the intermittency of sunlight from weather and diurnal cycling. Solar-thermal systems, in which sunlight is converted to high temperature thermal energy before being converted to electricity, are promising in this regard, as thermal energy can be stored more inexpensively than electricity. We have developed optically transparent, thermally insulating silica aerogels, which enable a novel Solar-Thermal Aerogel Receiver (STAR). The receiver is comprised of a transparent aerogel layer covering the high temperature absorber, which insulates the absorber from thermal losses while still allowing sunlight to reach it. STAR offers a number of advantages over traditional vacuum tube receivers: it achieves high efficiency without the use of spectrally selective coatings or vacuum, which could lead to better reliability and enables non-cylindrical receiver geometries. This flexibility in geometry is particularly useful for receivers paired with linear Fresnel reflector (LFR) concentrating optics. In order to demonstrate performance in on-sun operation, we have built a prototype 1-m long, 10-cm wide STAR, along with a 33x concentration ratio LFR array. In this presentation we will report the optical and thermal efficiencies achieved by the STAR prototype. This work is supported by the U.S. Department of Energy through Advanced Research Projects Agency−Energy (ARPA-E) Award No. DE-AR0000471.
9:30 AM - ES09.10.08
Exploring Ultimate Water Capillary Evaporation in Nanoscale Conduits
Yinxiao Li 1 , Mohammad Alibakhshi 1 , Chuanhua Duan 1
1 Department of Mechanical Engineering, Boston University, Boston, Massachusetts, United States
Show AbstractCapillary evaporation in nanoscale conduits is an efficient heat/mass transfer strategy that has been widely utilized by both nature and mankind. Despite its broad impact, the ultimate transport limits of capillary evaporation in nanoscale conduits, governed by the evaporation/condensation kinetics at the liquid-vapor interface, have remained poorly understood. Here we report experimental study of the kinetic limits of water capillary evaporation in single nanochannels and nanopores using a novel hybrid channel design. This design converts challenging evaporation rate measurements at the entrance of the nanochannel/nanopore into optical measurements of the receding meniscus in the reference nanochannel. We investigate the effect of confinement, curvature, humidity and temperature on the kinetic-limited ultimate evaporation flux. Our results show that the kinetic-limited evaporation fluxes in single nanochannels break down the limits predicated by the classical Hertz-Knudsen equation by an order of magnitude, reaching values up to 37.5 mm/s at 40°C with corresponding heat fluxes up to 8500 W/cm2. The measured evaporation flux increases with decreasing channel height and relative humidity, but decreases as the channel temperature decreases. Our results also show that the evaporation fluxes in single nanopores are even larger than those in single nanochannels with similar confinements. These findings have implications for further understanding evaporation at the nanoscale and developing capillary evaporation-based technologies for thermal management, membrane distillation, solar steam generation, and lab-on-a-chip.
10:15 AM - *ES09.10.07
Pyroelectric Energy Conversion for Waste Heat Harvesting
Laurent Pilon 1
1 Mechanical and Aerospace Engineering, University of California, Los Angeles, Los Angeles, California, United States
Show AbstractThis talk presents different strategies to exploit the unique properties of pyroelectric materials for direct energy conversion of waste heat into electricity. Pyroelectric energy conversion can be divided into linear and cycle-based methods. Linear pyroelectric energy conversion consists of subjecting a pyroelectric material to periodic heating and cooling in absence of an electric field bias. It is easy to implement both in terms of hardware and electronics. However, the energy and power densities generated and the associated efficiency are relatively small. Pyroelectric energy conversion cycles consist of performing a closed cycle in the electric displacement, electric field, temperature, and stress phase diagram. These cycles typically take advantage of the large change in displacement associated with solid-state phase transitions, induced by changes in temperature and/or compressive stress, to achieve large energy and power densities. Practical implementations and performance of linear and cycle-based pyroelectric energy conversion methods proposed to date will be reviewed critically. Particular attention will be paid to experimental demonstrations and performance of the Olsen cycle, also known as the electric Ericsson cycle on materials and in devices.
10:45 AM - ES09.10.06
Cold-Side Engineering of a Thermophotovoltaics System
Yi Huang 1 , Yoichiro Tsurimaki 1 , Svetlana Boriskina 1 , Gang Chen 1
1 Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show Abstract
In thermophotovoltaics (TPV) systems, photons radiated from a hot emitter are converted to electricity using photovoltaic devices operating close to the ambient temperature. Photon management is critical to achieve high efficiency. Simulations show that by reducing the sub-bandgap losses via cell design can yield high TPV efficiency, exceeding 30% for an ultrathin InSb cell with a 1000K spectrally-selective emitter (J. Tong, Sci. Rep. 5, 10661, 2015) and 47.7% for a thin-film GaAs cell with a 1800K blackbody emitter (V. Ganapati, T. P. Xiao, E. Yablonovitch, arXiv:1611.03544). In this work, we simulate several cold-side designs to achieve significant improvements to TPV system efficiencies. We carry out electrical and optical simulations on In0.53Ga0.47As cell to show a TPV system efficiency of above 35% without any additional spectral filters when coupled with a graybody emitter at 1700K. Several key parameters to push up the system efficiency will be discussed, such as minimization of free-carrier absorption due to high dopant concentration in PV cell back/front surface fields and emitters, increasing radiative recombination efficiency in base region of the PV cell and enhancement of collection efficiency at contacts. We also explore other material systems on the coldside of the TPV system, including conventional Si PV cells.
This work is supported by DOE BES under Award # DE-FG02-02ER45977.
11:00 AM - ES09.10.09
Solar-Thermal Energy Harvest Enabled by Dispersed Optical Medium
Peng Tao 1 , Zhongyong Wang 1 , Yingying Chen 1 , Qinxian Ye 1 , Tao Deng 1
1 School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai China
Show AbstractSolar-thermal technology has emerged as an attractive way to harness abundant clean solar energy not only because of its high conversion efficiency, but more importantly, the facile storage of converted solar-thermal energy. Current solar-thermal energy harvesting technology typically relies on a solar receiver to convert solar energy into heat and slow heat diffusion to charge thermal storage media. Herein, we directly convert and store solar-thermal energy within the storage media by homogenously dispersed with nanoscale photothermal converters. By using plasmonic metal nanoparticles as the photothermal converter, we demonstrate that the optical media uniformly dispersed with volumetric ppm level gold nanocrystals exhibited a much faster charging rate, higher heating temperature and larger heating area than conventional heat diffusion based approach under illumination of green laser and solar light. Poor dispersion stability of the optical media is one of the main obstacles to practical application of such technology for solar-thermal storage, in particular at higher operation temperatures. To this end, we further report a facile and effective strategy to prepare stably dispersed silicone oil-based optical nanofluids by using Fe3O4 nanoparticles as the model photothermal converter. Through a series of processes including controlled high-temperature synthesis of nanoparticles, surface modification of particles, and post-modification particle size partition, stably dispersed silicone oil nanofluids have been prepared and successfully utilized for consistent volumetric harvesting of solar thermal energy at more than 110 oC.
11:15 AM - ES09.10.10
Solar Energy Storage via Thermochemical Metal Oxide/Metal Sulfate Water Splitting Cycle
Rahul Bhosale 1 , Gorakshnath Takalkar 1 , Anand Kumar 1 , Fares AlMomani 1 , Majeda Khraisheh 1
1 Department of Chemical Engineering, Qatar University, Doha Qatar
Show AbstractSolar thermochemical water splitting cycles are considered as one of the most promising options for hydrogen production. In a long list of solar thermochemical water splitting cycles, the sulfur-iodine cycle and its variation the hybrid sulfur cycle are more appealing as the required operating temperatures are lower as compared to other thermochemical cycles. For both cycles, the most energy intensive step is the dissociation of SO3 into SO2 and O2, which is possible only under catalytic conditions. As sulfation poisoning is a major concern related to such reactions, simply the noble metal catalysts were observed to be active towards the endothermic dissociation of SO3. Although, the noble metal catalysts are attractive for such reactions, they are less preferable due to the limited availability and high cost. To overcome this issue, we propose a solar driven metal oxide – metal sulfate (MO-MS) based water-splitting cycle for the production of hydrogen. In this study, the thermodynamic and experimental analysis of the MO-MS based water splitting cycle was studied. At first, the computational thermodynamic analysis was performed to identify the required temperatures, pressures, and inert gas flowrates to operated MO-MS water splitting cycle. This analysis also helps to find the efficiency of this cycle in terms of the conversion of solar energy into hydrogen. After performing the computational thermodynamic analysis, the MO-MS based water splitting cycle was experimentally investigated using a high temperature TGA and a packed-bed reactor set-up. Obtained thermodynamic and experimental results will be presented and compared with other thermochemical cycles in detail.
11:30 AM - ES09.10.11
Reversible Water Insertion in Rare Earth Sulfates—A New Material for Thermochemical Heat Storage
Kunihiko Shizume 1 , Naoyuki Hatada 1 , Tetsuya Uda 1
1 , Kyoto University, Kyoto Japan
Show AbstractThermal energy storage based on chemical reactions (thermochemical heat storage) is a prospective technology for the reduction of fossil fuel consumption by storing and reusing industrial waste heat. For widespread application, a critical challenge is to identify appropriate reversible reactions which occur below 250 °C where abundant low-grade waste heat might be available. The dehydration reactions of alkali-earth metal hydroxides such as Mg(OH)2 and Ca(OH)2 are promising reactions for thermochemical heat storage; heat is stored by the endothermic dehydration reaction and released by the exothermic reverse reaction. However, the dehydration of these materials generally occurs at higher than 250 °C, which makes it difficult to utilize low-grade waste heat.
In this work, we have focused on rare earth sulfate Ln2(SO4)3 (Ln: rare earth element) as a new candidate material for thermochemical heat storage. Ln2(SO4)3 has many hydrated forms Ln2(SO4)3*nH2O, where n represents the hydration number typically ranging from 1 to 9. We conducted thermogravimetry (TG) on La2(SO4)3*nH2O during heating/cooling under a humidified argon atmosphere (Ar – 1.2% H2O). The results revealed that the following dehydration/hydration reaction occurred reversibly at between 50-250 °C:
La2(SO4)3*H2O (s) = La2(SO4)3 (s) + H2O (g)
The gap between dehydration and hydration temperatures (thermal hysteresis) of La2(SO4)3*H2O was smaller than that of Mg(OH)2 (~40 °C vs. ~200 °C at 20 °C min-1) suggesting its high hydration activity. In addition, the dehydration/hydration behavior of La2(SO4)3*H2O did not change significantly through the 100 cycles of heating/cooling, while other candidate systems often suffer from degradation during several reaction cycles. These characteristics of La2(SO4)3*H2O are promising for thermochemical heat storage for utilizing low-grade waste heat.
The dehydration/hydration mechanism of La2(SO4)3*H2O was further analyzed by High-temperature X-ray diffraction during heating under a humidified oxygen atmosphere (O2 – 3% H2O). The diffraction patterns revealed that the lattice volume decreased progressively with temperature at between 50-250 °C, where dehydration took place. These results suggest that water can be removed from, or inserted in, the stable crystal lattice of La2(SO4)3*xH2O with progressive change in hydration number x (0 ≤ x ≤ 1). This mechanism is unusual for sulfates and could be the reason for the high hydration activity of La2(SO4)3.
Reactivity with other gaseous species has also been studied by TG. Ammonia was found to react with La2(SO4)3 at between 230-330 °C under ammonia atmosphere and the observed weight change corresponded to formation of La2(SO4)3*0.12NH3. It suggests that reaction temperatures and heat storage capacity of La2(SO4)3 can be controlled by choosing appropriate gas species as working medium, although ammonia is not very suitable in terms of reacting weight.
11:45 AM - ES09.10.12
Atmospheric Water Capture and Delivery with Metal-Organic Frameworks Powered by Natural Sunlight
Hyunho Kim 1 , Sameer Rao 1 , Sungwoo Yang 1 , Shankar Narayanan 2 , Eugene Kapustin 3 , Hiroyasu Furukawa 3 , Omar Yaghi 3 , Evelyn Wang 1
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 , Rensselaer Polytechnic Institute, Troy, New York, United States, 3 , University of California, Berkeley, Berkeley, California, United States
Show AbstractUp to thirteen thousand trillion liters of water exist in air at any one time. This is equivalent to about ten percent of all fresh water in lakes on earth. However, an efficient process by which water can be captured from air, especially at low humidity levels (down to 20%), and delivered has not been developed. In this talk, we present the design framework and demonstration of a device based on porous metal-organic framework-801 [Zr6O4(OH)4(fumarate)6] that captures water from the atmosphere at ambient conditions using low-grade heat from natural sunlight below one sun (1 kW m-2). With an optimized design, we predicted ~2.8 L kg-1 or ~1 L m-2 of daily water harvesting capability of this device at relative humidity levels as low as 20% without additional input of energy.
ES09.11: Solar Thermal II
Session Chairs
Laurent Pilon
Evelyn Wang
Thursday PM, November 30, 2017
Hynes, Level 3, Ballroom C
1:30 PM - *ES09.11.01
Photothermally Driven Nanoscale Optical Motor
Min Qiu 1
1 State Key Laboratory of Modern Optical Instrumentation, Zhejiang University, Hangzhou China
Show AbstractOptical force usually comes from momentum exchange during the light-matter interaction, and it can manipulate microscopic objects typically in ambient liquids. While photophoretic force, coming from light-induced thermal effect, provides a more effective way to transport light-absorbing particles in ambient gases. Optical force and photophoretic force usually function independently as the working environments are different. Recently, we demonstrate experimentally a configuration which can drive a micron-size metallic plate moving back and forth on a tapered fiber with supercontinuum light in ambient air. Optical pulling and oscillation of the metallic plate are experimentally realized, which is the synergy effects of optical force and photophoretic force. This idea can further employed to realize optical motors, and other interesting devices.
2:00 PM - *ES09.11.02
Radiation by Nanoscale Resonant Emitters
Zongfu Yu 1
1 , University of Wisconsin, Madison, Wisconsin, United States
Show AbstractThermal emission by resonant emitters can be significantly different that from non-resonant emitters. The emission power and the spatial coherence will be discussed. We will also discuss the impact of the dispersion of the continuum on thermal emission. The interaction among resonant emitters can also lead to interesting coherent effects on thermal emission, where more emitters do not necessarily lead to higher emission power.
2:30 PM - *ES09.11.03
Metasurface-Based Approaches for Controlling and Harnessing Heat Flow in Nanostructured Materials
Jason Valentine 1
1 Department of Mechanical Engineering, Vanderbilt University, Nashville, Tennessee, United States
Show AbstractIn this talk, I will discuss our recent efforts to manage and harness heat flow and heat generation using nanostructured metasurfaces. I will first discuss how we can use dynamic metasurfaces to manage thermal radiation. Dynamic control is based on optically generated carriers in zinc oxide thin films which are embedded in a metasurface architecture. Importantly, a long carrier lifetime in the zinc oxide allows us to achieve modulation of the metasurface’s emissivity using low power light emitting diodes as the illumination source opening the door to large area modulation. In the second half of the talk I will discuss the use of heat generation in phase change materials, specifically vanadium dioxide (VO2), to dynamically control the properties of metasurfaces. In this approach, we take advantage of the field concentration within the metasurface to utilize nanoscale patches of VO2. The small patch size and thermal mass of the VO2, compared to past demonstrations using thin films, allows us to greatly decrease both the switching time and power consumption of the device.
3:30 PM - ES09.11.04
NIR Photothermoelectric Effect of Highly Crystalline Conductive Polymer Films
Byeonggwan Kim 1 , Minsu Han 1 , Lim Hanwhuy 1 , Jong Un Hwang 1 , Eunkyoung Kim 1
1 , Yonsei Univ, Seoul Korea (the Republic of)
Show AbstractPhotothermoelectric effect of conductive polymer films were explored by controlling the polymerization composition for poly(3,4-ethylenedioxythiophene)s (PEDOT) and their derivatives. Highly crystalline conductive polymer films were synthesized in the presence of polymeric surfactant under an optimized polymerization temperature. As prepared polymer films showed high photothermal effect by NIR light, which led photothermally induced thermoelectric conversion. The effect from the crystallinity of the polymer films on the photothermoelectric output was correlated to the electronic state and morphology of the polymer films obtained under different composition. Efficient visible to NIR absorption, photon to heat, and heat to electric conversion have been realized in one transparent film, which could benefit in exploiting invisible NIR sensors and night vision display.
3:45 PM - ES09.11.05
Design and Benchmark of a Hybrid Thermophotovoltaic (HTPV) Device for Energy Recovery in Industrial Applications
Pablo Araya 1 , Amador Guzman 1 , Jose Lincoleo 1 , Paulina Escobar 1 , Francisco Montero 1 , Tomas Salinger 1
1 , Universidad Catolica de Chile, Santiago Chile
Show AbstractAn experimental Thermophotovoltaic (TPV) conceptual device is designed and tested with the final goal developing a Hybrid Thermophotovoltaic (HTPV) device that offers improvements on efficiencies obtained with standard Thermophotovoltaic devices. The HTPV shall use inexpensive and simple components such as commercial photovoltaic cells, graphite absorber/emitters, thermoelectric modules, and custom made microchannel-based cooling units. Special attention is given to the selection of specific absorber/emitter components, placed between a radiative heat source and a receiving Photovoltaic Cell (PVC).
The experiment is designed and constructed to measure the temperatures that will be reached by the absorbing/emitting element and lower PVC placed under a controlled heat concentrating device. The objective is to determine heat input and resulting surface temperatures that will be reached under steady state conditions. Conduction, convection and radiative heat transfer will be present in the device. The resulting power generated by the PVC will be used to determine the device efficiency. Design of the experiment is uses heat transfer simulations of conduction, natural convection and radiation of the device are performed using Computational Fluid Dynamics software in order to predict temperatures that will be reached by the test device as a function of input power, before its actual construction. Simulations allow for the selection of appropriate components and experimental results are compared to the numerical.
Results show that using three cartridge heat elements running at 150 W results in absorber/emitter temperatures of 750°C. At this temperature, radiation the PVC, the output power is used to determine efficiencies of the device. Results are benchmarked against experiments conducted by others. Although the HTPV underperforms with respect to TPV experiments performed by others, it exceeds the performance of common solar photovoltaic cells, and may be used for other applications in the housing, agriculture and mining sectors, that do not necessarily require solar radiation.
4:00 PM - ES09.11.06
Active Radiative Heat Switching with Graphene Plasmon Resonators for Thermal Management on the Nanoscale
Ognjen Ilic 1 , Harry Atwater 1
1 , California Institute of Technology, Pasadena, California, United States
Show AbstractRadiative heat transfer on the nanoscale holds promise for next-generation energy conversion technologies, including heat-to-electricity conversion platforms such as near-field thermophotovoltaics and near-field solid-state refrigeration. A key enabler is the idea that closely separated objects – specifically, objects at separation distances much smaller than the characteristic thermal wavelength – can exhibit order-of-magnitude increase in the radiatively exchanged energy relative to the energy that can be transferred in the far field. Materials and interfaces that can support thermally excited surface electromagnetic modes are of particular interest, owing to large local density of states that can facilitate efficient evanescent coupling.
Here we propose a means of active thermal management by way of radiative heat switching with graphene plasmon nano-resonators. In contrast to those of their bulk counterparts, the optical properties of low-dimensional materials (such as graphene) can be highly tunable, providing a large degree of active control of absorption and thermal emission. Specifically, here we study the extremes of the radiative thermal conductance between two graphene structures that are accessible by actively controlling (via gate-voltage) the relevant carrier concentrations in graphene. The two conductance extremes constitute the respective “ON” (i.e. largest conductance) and “OFF” (i.e. smallest conductance) states of the proposed thermal switch.
We present the idea of a thermal switch in several relevant configurations, including thermal switching between (a) graphene sheets, (b) multilayer graphene stacks, (c) hybrid disk resonator–multilayer structure, and (d) dipolar graphene resonators. In each of these scenarios, finding the “ON” and “OFF” states presents a nonlinear optimization problem over a parameter space of all allowable gate voltages. For the case of multilayer (two or more) graphene stacks, we find that there exists an optimal value of graphene carrier mobility (μ~2000cm2/Vs, for T=300K) that maximizes the thermal conductance in the “ON” state (which, normalized to the black-body limit, equals to Hon/Hbb~300 for 100 nm separation). At the same time, the switching ratio (Hon/Hoff) monotonically increases with increasing mobility (e.g. Hon/Hoff~40, for μ~104cm2/Vs). In contrast to the coupling between extended multilayer structures, dipolar graphene resonators (such as disks or ellipses) can exhibit much stronger heat flux (Hon) as well as larger switching ratios (Hon/Hoff>103). In addition, these structures have a very high degree of switching sensitivity, which makes them particularly suitable for low-power thermal switching applications. These results show that the combination of resonator geometry and material properties of graphene—specifically its strong optical response and tunability in the thermal IR range—can enable active control of thermal transport on the nanoscale.
4:15 PM - ES09.11.07
Warming up Human Body by Nanoporous Metallized Polyethylene Textile
Lili Cai 1 , Alex Song 1 , Peilin Wu 1 , Po-Chun Hsu 1 , Yucan Peng 1 , Jun Chen 1 , Chong Liu 1 , Peter Catrysse 1 , Yayuan Liu 1 , Ankun Yang 1 , Shanhui Fan 1 , Yi Cui 1
1 , Stanford University, Stanford, California, United States
Show AbstractSpace heating accounts for the largest energy end-use of buildings that imposes significant burden on the present energy and environmental issues. The large energy waste for heating the vast empty space of the entire building can be greatly saved by passively heating the immediate environment around the human body for maintaining thermal comfort. Here, we demonstrate a nanophotonic structure textile with tailored infrared (IR) property for passive localized personal heating using nanoporous metallized polyethylene. By constructing an IR-reflective layer on an IR-transparent layer with embedded nanopores that are smaller than the IR wavelength but larger than the water molecule, the nanoporous metallized polyethylene textile achieves a minimal IR emissivity of 10.1% on the outer surface that effectively suppresses heat radiation loss from the human body to the environment without sacrificing wearing comfort. This enables 7.1 oC decrease of the ambient temperature set-point needed for maintaining thermal comfort in buildings as compared to normal textile, greatly outperforming all the existing radiative heating textiles by more than 3 oC. This large set-point expansion can potentially result in heating energy savings of more than 35% in buildings in a cost-effective way, and ultimately contribute to the relief of global energy and climate issues.