Symposium Organizers
Aleksandr Chernatynskiy, Missouri University of Science and Technology
Pierre-Olivier Chapuis, Center for Energy and Thermal Sciences, CNRS - INSA Lyon
Kedar Hippalgaonkar, Nanyang Technological University
Austin Minnich, California Institute of Technology
NM2.1: Thermal Transport in 2D Materials I
Session Chairs
Tuesday PM, April 18, 2017
PCC West, 100 Level, Room 101 BC
11:30 AM - *NM2.1.01
Thermal Properties of 2D Semiconductors—Theory and Application
Gang Zhang 1 , Xiangjun Liu 1 , Zhun-Yong Ong 1 , Yongqing Cai 1 , Yong-Wei Zhang 1
1 , Institute of High Performance Computing, Singapore Singapore
Show AbstractThe fruitful development and applications of graphene have inspired great interest in exploring 2D semiconducting materials, such as MoS2 and phosphorene. These 2D semiconductors possess diversified electronic and thermal properties complementary to those of graphene. For example, their thermal conductivity covers a large range from thousands W/mK to tens W/mK. Undoubtedly, their drastically different electronic and thermal conductivities present great potential for thermal management and thermoelectric energy generation.
Here we report our works in the study of thermal properties of 2D semiconductors. We first discuss the important aspects in thermal conductivity of MoS2, including the low thermal conductivity [1], anharmonic behavior of phonon [2], the contribution of spectral phonons to thermal conductivity [3], and the interfacial thermal conductance between MoS2 and metal electrode, which is important for thermal management in MoS2 devices [4]. Subsequently, we discuss the anisotropic thermal conduction of phosphorene [5-7] and phosphorene phononic crystal [8]. Finally, we present our theoretical approach for modeling phonon transmission probability in nanoscale interfacial thermal transport [9, 10], and strain engineering to enhance interface thermal conductance [11].
References:
1. X. Liu, et al., Phonon thermal conductivity of monolayer MoS2 sheet and nanoribbons, Appl. Phys. Lett., 103, 133113 (2013).
2. Y. Cai, et al., Lattice Vibrational Modes and Phonon Thermal Conductivity of Monolayer MoS2, Phys. Rev. B, 89, 035438 (2014).
3. X. Wei, et al., Phonon Thermal Conductivity of Monolayer MoS2: a Comparison with Single Layer Graphene, Appl. Phys. Lett., 105, 103902 (2014).
4. X. Liu, et al., Thermal Conduction across One-dimensional Interface between MoS2 Monolayer and Metal Electrode, Nano Research, 9, 2372 (2016).
5. Z.-Y. Ong, et al., Strong Thermal Transport Anisotropy and Strain Modulation in Single-Layer Phosphorene, J. Phys. Chem. C, 118(43), 25272 (2014).
6. Y. Cai, et al., Giant Phononic Anisotropy and Unusual Anharmonicity of Phosphorene: Interlayer Coupling and Strain Engineering, Adv. Func. Mat., 25, 2230 (2015).
7. W. Xu, et al., Direction dependent thermal conductivity of monolayer phosphorene: parameterization of Stillinger-Weber potential and molecular dynamics study, J. Appl. Phys., 117, 214308 (2015).
8. W. Xu, et al., Remarkable reduction of thermal conductivity in phosphorene phononic crystal, J. Phys.: Cond. Matt., 28, 175401 (2016).
9. Z.-Y. Ong, et al., Efficient approach for modeling phonon transmission probability in nanoscale interfacial thermal transport, Phys. Rev. B 91, 174302 (2015).
10. Z.-Y. Ong, et al., Controlling the thermal conductance of the graphene/h-BN lateral interface with strain and structure engineering, Phys. Rev. B, 93, 075406 (2016).
11. X. Liu, et al., Topological Defects at the Graphene/BN interface Abnormally Enhance Its Thermal Conductance, Nano Letters, 16, 4954 (2016).
12:00 PM - NM2.1.02
Nanoscale Characterization of the Thermal Conductivity of Supported Graphite Nanoplates, Graphene and Few-Layer Graphene
Mauro Tortello 1 , Samuele Colonna 2 , Julio Gomez 3 , Iwona Pasternak 4 , Wlodek Strupinski 4 , Fabrizio Giorgis 1 , Guido Saracco 1 , Renato S. Gonnelli 1 , Alberto Fina 2
1 Dipartimento di Scienza Applicata e Tecnologia, Politecnico di Torino, Torino Italy, 2 Dipartimento di Scienza Applicata e Tecnologia, Politecnico di Torino, Alessandria Italy, 3 , AVANZARE Innovacion Tecnologica S.L., Navarrete Spain, 4 , Institute of Electronic Materials Technology, Warsaw Poland
Show AbstractThe extraordinary properties of a single suspended layer of graphene change, sometimes dramatically, when the number of layers increases considerably or when it is supported or included as a filler in a polymer matrix. Thus, it is of utmost importance to know and control its properties in these conditions. In particular, it is highly desirable to investigate the thermal properties at the nanoscale because it is at this level that they are affected by the interfaces.
Several measurements of the thermal properties of graphene were reported [1] which employed diverse techniques like electrical methods [2] or the Raman optothermal technique [3]. Also Scanning Thermal Microscopy (SThM) [4,5] is a powerful technique for the thermal characterization and can reach a spatial resolution on the order of a few tens of nanometers while recording nanoscale topography at the same time.
Here we show that [6] i) annealing in vacuum at 1700 °C for 1 h strongly reduces the amount of defects in reduced graphite oxide (RGO) nanoplates, as shown by Raman, XRD, XPS and TGA measurements. ii) As a consequence, their thermal conductivity considerably increases, as revealed by high-resolution Scanning Thermal Microscopy (SThM) results on individual RGO flakes supported by SiO2/Si. iii) This fact is more clearly observed when the RGO nanoplates are supported by a less conducting substrate (PET). iv) Lumped parameter models and finite element analysis are discussed in order to interpret the results and try to determine the thermal conductivity and the effect of the substrate.
Moreover, SThM results are also presented for a case study of multilayer (1 to 4) CVD graphene [7], suspended or supported by different substrates like SiO2/Si, PET, Al2O3, etc. We found that a) the thermal conduction of multilayer graphene supported by SiO2/Si improves with increasing number of layers. b) In the SThM maps, the thermal contrast observed between the supported graphene and the bare substrate changes depending on the thermal conductivity of the substrate itself, possibly giving useful information on the thermal resistance at the graphene/substrate interface. Both these results, that are interesting for the potential applications of graphene for thermal management, are also discussed and compared with the above-mentioned models.
References
[1] A.A. Balandin, Nature Mater. 10 (2011) 569
[2] J.H. Seol et al., Science 328 (2010) 213
[3] H. Malekpour, et al., Nanoscale 8 (2016) 14608
[4] A. Majumdar, Annu. Rev. Mater. Sci. 29 (1999) 505
[5] S. Gomes, A. Assy, P.-O. Chapuis, Phys. Status Solidi A 212 (2015) 477
[6] M. Tortello et al., Carbon 109 (2016) 390
[7] I. Pasternak et al., AIP Advances 4 (2014) 097133
12:15 PM - NM2.1.03
Understanding and Tuning Heat Conduction in MoS2—Cross-Plane Diffusive-Ballistic Transport and Dynamic Electrochemical Tuning of Thermal Conductivity by Li Intercalation
Aditya Sood 1 , Feng Xiong 1 2 , Haotian Wang 1 , Yi Cui 1 , Eric Pop 1 , Kenneth Goodson 1
1 , Stanford University , Stanford, California, United States, 2 , University of Pittsburgh, Pittsburgh, Pennsylvania, United States
Show AbstractTwo-dimensional van der Waals bonded materials such as graphene and transition metal dichalcogenides (TMDs) like MoS2 have unusually anisotropic thermal properties. For numerous applications it is important to understand how heat flows through these materials, and how it can be controlled, particularly by tuning the cross-plane van der Waals coupling.
In this talk, we will first discuss the length scales of phonon scattering in the cross-plane direction of MoS2. Using time-domain thermoreflectance (TDTR), we measure the thermal conductivity Kz of thin-films of MoS2 with varying thickness, ranging from ~25 nm to ~ 250 nm. Through measurements at multiple pump modulation frequencies and after removing effects of thermal boundary resistance, we show that Kz increases monotonically with increasing thickness until it saturates at a constant value for thick bulk-like films. This is a signature of crossover from ballistic to diffusive transport [1], and enables an extraction of the phonon mean free path along the c-axis of MoS2 at room temperature.
In the second part, we will demonstrate a nanoscale thermal transistor using electrochemical lithium intercalation in a ~10 nm thick MoS2 device. We use TDTR to measure real-time changes in cross-plane thermal conductance of the MoS2 while subjecting it to cycles of discharge and charge, i.e. lithiation and delithiation. These experiments are performed using a novel transparent Li|LiPF6|MoS2 electrochemical cell [2] with a single MoS2 flake. The thermal conductance decreases by a factor of ~7-9 x, i.e. nearly an order of magnitude upon lithiation, and is fully reversible upon reversing the direction of current on the timescale of minutes. Further, we measure the spatial distribution of thermal conductance over the area of the flake (~ 15 x 15 µm) using a scanning TDTR technique. Area maps taken at different voltages between 3.0 and 1.0 V in the potentiostatic mode reveal significant heterogeneities in the Li concentration that evolve during the electrochemical cycle. These experiments demonstrate that in-operando measurements of thermal conductivity can provide new and useful information about spatio-temporal dynamics of intercalants within nanomaterials.
This study provides new insights into thermal transport across van der Waals bonds in layered materials, using MoS2 as a model example. Taken together, the two experiments show how boundary scattering and point defects (i.e. intercalated Li ions) can be used to achieve passive and active tuning, respectively, of cross-plane conductivity.
[1] H. Zhang et al., Nano Lett. 16, 1643 (2016)
[2] F. Xiong et al., Nano Lett. 15, 6777 (2015)
12:30 PM - *NM2.1.04
Thermal Transport in Two-Dimensional Materials and Devices
Eilam Yalon 1 , Miguel Munoz-Rojo 1 , Zuanyi Li 1 , Runjie Xu 1 , Alex Gabourie 1 , Saurabh Suryavanshi 1 , Eric Pop 1
1 Electrical Engineering, Stanford University, Stanford, California, United States
Show AbstractTwo-dimensional (2D) materials like graphene, h-BN, and transition-metal dichalcogenides (TMDs like MoS2) have shown promising applications in electronics. Their thermal properties are an area of active investigation, particularly with respect to their anisotropic and potentially tunable thermal conductivity, the thermal conductance of their interfaces, and the heat flow in nanoscale devices comparable in size to the phonon or electron mean free paths.
We found that despite its good intrinsic thermal conductivity [1], heat dissipation can be a challenge in graphene and MoS2 transistors, where heat flow is limited by interfaces with adjacent materials and thermal transients are dominated by the surrounding layers [2]. Such measurements are supported by molecular dynamics (MD) simulations, which reveal the time scales of heat dissipation. In addition, when devices are scaled below ~1 μm, experiments and theory show that graphene thermal properties, in particular, become dependent on the system size [3]. Conversely, device self-heating measurements can also be used to gain valuable information about the thermal properties of other 2D nanomaterials, such as WTe2 [4]
We also investigated the in-plane and cross-plane ballistic thermal conductance (Gb) of layered 2D materials based on full phonon dispersions. Gb is approximately one order of magnitude lower in the cross-plane vs. the in-plane direction due to weak van der Waals interactions between layers. We estimated the phonon mean free path of 2D materials, given Gb and the diffusive thermal conductivity [3,5]. We examined the size-dependent thermal conductivity and the ballistic to diffusive transition for a variety of anisotropic layered 2D materials. It is clear that most sub-micron devices and all sub-100 nm devices exhibit some degree of quasi-ballistic heat flow.
The cross-plane thermal transport in multilayer stacks of 2D materials can be tuned by the reversible intercalation of a guest atomic species in the inter-layer space. By intercalating Li, we have found that the cross-plane thermal conductance of thin MoS2 stacks can be tuned in real time (of the order of minutes) by over a factor of seven [6]. The Li atoms decrease the thermal conductance from the pristine MoS2 value due to phonon scattering at Li sites and weakening of out-of-plane vibrational modes.
These results broaden our understanding of thermal transport in 2D materials, and help us explore their applications for devices and thermal management.
[1] E. Pop et al, MRS Bull. 37, 1273 (2012).
[2] S. Islam et al, IEEE Electron Dev. Lett. 34, 166 (2013).
[3] M.-H. Bae et al, Nat. Comm. 4, 1734 (2013).
[4] M. Mleczko et al., ACS Nano 10, 7507 (2016).
[5] Z. Li et al, APS March Meeting (2014).
[6] A. Sood et al, MRS Spring Meeting (2015).
NM2.2: Multiphase Thermal Transport
Session Chairs
Tuesday PM, April 18, 2017
PCC West, 100 Level, Room 101 BC
2:30 PM - *NM2.2.01
Evaporative Processes and Mass Accommodation Coefficient via Molecular Dynamics
Pawel Keblinski 1
1 , Rensselaer Polytechnic Institute, Troy, New York, United States
Show AbstractWe use molecular dynamics (MD) simulations to investigate transport processes at liquid-vapor interfaces and processes driven by liquid-vapor interfaces. We will first describe cavitation dynamics, including vapor formation and collapse around solid nanoparticles immersed in a liquid and subjected to intense heat pulses. Second, will elucidate the nature of the merger of two liquid nanoscale droplets immersed in their own vapor and compare the result obtained by MD simulation the results obtained Volume-of-Fluid (VOF), continuum-level simulations. Third, we will show that the coalescence of nanodroplets on super hydrophobic surfaces leads to droplet jumping, despite the fact that the fluid flow associated with the coalescence of nanodroplets is highly dissipative. Throughout our presentation we discuss how the mass accommodation coefficient, i.e., the probability of the vapor atom/molecule being adsorbed upon a collision with the liquid, affects all the above-described processes.
3:00 PM - *NM2.2.02
Nanoparticle Heating to Improve Therapeutics, Diagnostics and Regenerative Medicine
John Bischof 1
1 , University of Minnesota, Minneapolis, Minnesota, United States
Show AbstractGold and iron oxide nanoparticles have unique and tunable properties that allow transduction of optical (light), or radiofrequency (RF) electromagnetic fields to affect heating of biomaterials at multiple scales. This talk will explore the underlying physics and relative advantages of each form of nanoparticle heating for therapeutic treatment of cancer or other disease by hyperthermia. Second, laser heating of gold nanoparticles will be shown to achieve an order of magnitude or more improvement in sensitivity for common point-of-care (POC) diagnostic assays (i.e. a lateral flow immunoassay or LFA) through “thermal” vs. visual contrast. This increase in sensitivity addresses the main weakness of the LFA, increasing opportunities for use in POC settings and avoiding the cost, time and labor of laboratory tests. Finally, both gold and iron oxide nanoparticle heating can be used in regenerative medicine by “nanowarming” vitrified biomaterials at sufficiently rapid and uniform rates to avoid crystallization and cracking. This addresses an important technology bottleneck for both large systems (i.e. tissues and organs) as well as smaller systems (i.e. embryos and oocytes). In summary, this talk demonstrates the growing opportunities for nanoparticle heating in biomedical applications
3:30 PM - NM2.2.03
Probing Nanoscale Heat Transport in Liquid Environments—Contact and Non-Contact Immersion Scanning Thermal Microscopy (iSThM)
Oleg Kolosov 1 , Jean Spiece 1 , Benjamin Robinson 1
1 Physics, Lancaster University, Lancaster United Kingdom
Show AbstractOperation of Scanning Thermal Microscopy (SThM) [1] in liquid environment probing thermal phenomena with nanoscale resolution could open unique opportunities for studies of biological materials, processes in the rechargeable energy storage and catalysis. Until recently such SThM operation would be deemed fully impossible, due to dominating heat dissipation from the heated probe into the surrounding liquid that thought to drastically deteriorate both the sensitivity of the probe and its spatial resolution. Nevertheless, Tovee and Kolosov [2] showed that such immersions SThM, or iSThM, is not only possible for the certain widely used type of the probe (Kelvin Nanotechnology, Scotland), but also opens the possibility to make nanoscale mapping of the heat transport with the near-field operation of SThM.
Here we show that the presence of liquid provides highly stable thermal contact between the probe tip and the sample eliminating one of the major drawbacks of the ambient or vacuum SThM’s – variability of such contact. iSThM can effectively observe the semiconductor devices and 2D materials with the resolution of few tens of nanometres, providing new tool for exploring thermal effects of chemical reactions and biological processes with nanoscale resolution. Using finite element modeling analysis we show that selecting suitable thermal conductivity of the liquid allows to to significantly enhance contrast of iSThM for the particular material. We also experimentally demonstrate that by applying of the ultrasonic vibration to the probe and by detecting a shear response of the probe it is possible to achieve near – non-contact iSThM paving the way for efficient zero-damage nanoscale thermal probing.
[1] Majumdar, A. (1999). 29, 505-585.
[2] Tovee, P., D. & Kolosov, O., V. (2013). Nanotechnology, 24, 465706.
[3] Robinson, B. J. et al, Langmuir, 2013, 29 (25), pp 7735–7742
3:45 PM - NM2.2.04
Understanding Thermal Properties in Entropy-Stabilized Oxides
Jeffrey Braun 1 , Christina Rost 1 , Ashutosh Giri 1 , Jon-Paul Maria 2 , Patrick Hopkins 1
1 , University of Virginia, Charlottesville, Virginia, United States, 2 Materials Science, North Carolina State University, Raleigh, North Carolina, United States
Show AbstractIn the search for new materials capable of withstanding extreme environments consisting of high temperatures and pressures, a new class of oxides has emerged; entropy-stabilized oxides rely on configurational disorder that is compositionally engineered into a mixed oxide by populating a single sublattice with many distinct cations. In these novel materials, thermal characterization is essential for understanding and predicting performance at elevated temperatures. Moreover, these systems provide a unique opportunity to study the nature of thermal transport and phonon scattering in multicomponent, high-entropy materials. In this study, we experimentally investigate the thermal conductivity and heat capacity of thin-film 5- and 6-component oxides using time- and frequency-domain thermoreflectance to reveal a strong reduction in thermal conductivity with inclusion of additional metallic components, beyond what is expected for mass-impurity scattering alone. Finally, we compare experimental results to analytical and computational results to understand the phonon scattering mechanisms driving these findings.
NM2.3: Phonon Properties
Session Chairs
Tuesday PM, April 18, 2017
PCC West, 100 Level, Room 101 BC
4:30 PM - *NM2.3.01
Strongly Anharmonic Materials from First Principles with the Temperature Dependent Effective Potential Method
Olle Hellman 1 2
1 , California Institute of Technology, Pasadena, California, United States, 2 IFM, Linkoping University, Linkoping Sweden
Show AbstractWe present the temperature dependent effective potential method, and discuss results for both high and low thermal conductivity applications. With a basis in ab initio calculations, we generate effective Hamiltonians that reproduce neutron scattering spectra, thermal conductivity, phonon self energies, heat capacities and free energies. The model implicitly takes all orders of non-harmonic effects into account to accurately predict thermal behaviour in strongly anharmonic materials.
5:00 PM - NM2.3.02
Phonon Properties and Slow Organic-to-Inorganic Sub-Lattice Thermalization in Hybrid Perovskites
Yi Xia 1 , Angela Chang 2 , Sridhar Sadasivam 1 , Peijun Guo 1 , Alper Kinaci 2 1 , Hao-Wu Lin 3 , Pierre Darancet 1 , Richard Schaller 1 2 , Maria Chan 1
1 , Argonne National Laboratory, Argonne, Illinois, United States, 2 , Northwestern University, Evanston, Illinois, United States, 3 , National Tsing-Hua University, Hsinchu Taiwan
Show AbstractOrganic-inorganic hybrid perovskite halide compounds have been investigated extensively for photovoltaics (PVs) and related applications. The thermal transport properties of hybrid perovskites are of significance for their PV and solar thermoelectric applications. Furthermore, the interaction among phonons and between phonons and charge carriers is important for their PV properties. The interlocking organic and inorganic sublattices can be thought of as an extreme form of nanostructuring. A result of this nanostructuring is the disparate phonon frequencies between the organic and inorganic sublattices, which is expected to create bottlenecks in phonon equilibration. In this work, we use a combination of ultrafast spectroscopy including photoluminescence (PL) and transient absorption (TA), as well as first principles density functional theory (DFT), ab initio molecular dynamics (AIMD) calculations, perturbative first principles phonon lifetimes, and non-equilibrium phonon dynamics accounting for phonon lifetimes, to determine the phonon and charge interaction processes. We find evidence that thermalization of carriers occur at an atypically slow ~50-100 ps time scale owing to the complex interplay between electronic and phonon excitations.1
Reference
1A. Y. Chang et a, Advanced Energy Materials 2016, DOI: 10.1002/aenm.201600422
5:15 PM - NM2.3.03
Direct Observation of Confined Acoustic Phonon Branches in Individual Free-Standing Semiconductor Nanowires
Fariborz Kargar 1 , Joona-Pekko Kakko 2 , Bishwajit Debnath 1 , Antti Saynatjoki 2 3 , Denis Nika 1 4 , Roger Lake 1 , Alexander Balandin 1
1 Department of Electrical and Computer Engineering, Bourns College of Engineering, University of California, Riverside, Riverside, California, United States, 2 Department of Micro and Nanosciences, School of Electrical Engineering, Aalto University, Aalto Finland, 3 , Institute of Photonics, University of Eastern Finland, Joensuu Finland, 4 Department of Physics and Engineering, Moldova State University, Chisinau Moldova (the Republic of)
Show AbstractSimilar to electron waves, the phonon states in semiconductors can undergo changes induced by external boundaries. Controlling the phonon spectrum via spatial confinement would allow for fine-tuning of the phonon interaction with electrons, spins and other phonons, particularly at low temperature [1]. However, direct experimental evidence of changes in the acoustic phonon spectrum in individual nanostructures (as opposed to periodic phononic structures) is scarce. The length scale at which the phonon confinement effects start to appear is a point of debate. Here we report results of Brillouin – Mandelstam light scattering spectroscopy, which revealed up to ten confined acoustic (CA) phonon polarization branches in GaAs nanowires with a diameter as large as 128 nm. The length scale, at which the phonon confinement effects are clearly observable, exceeds the grey phonon mean-free path in this material by almost an order-of-magnitude. The dispersion modification and energy scaling with diameter in individual nanowires are in excellent agreement with theory [2]. The phonon confinement effects result in a decrease in the phonon group velocity along the nanowire axis and changes in the phonon density of states. The obtained results can lead to more efficient nanoscale control of acoustic phonons, with benefits for nanoelectronic, thermoelectric and spintronic devices.
This work was made possible by the Spins and Heat in Nanoscale Electronic Systems (SHINES), an Energy Frontier Research Center funded by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES) under Award # SC0012670.
[1] For review, see A.A. Balandin and D.L. Nika, Materials Today, 15, 266 (2012).
[2] F. Kargar, B. Debnath, K. Joona-Pekko, A. Säynätjoki, H. Lipsanen, D.L. Nika, R.K. Lake and A.A. Balandin, Nature Communications (in print, 2016); https://arxiv.org/abs/1608.08115
5:30 PM - NM2.3.04
Monte Carlo Simulation of Thermal Transport in Fractal Nonperiodic Multilayer Structures with Power Law Layer Thickness Dependence
Amr Mohammed 1 4 , Yan Wang 2 , Xiulin Ruan 3 4 , Ali Shakouri 1 4
1 Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana, United States, 4 Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana, United States, 2 Mechanical Engineering, University of Nevada, Reno, Reno, Nevada, United States, 3 Mechanical Engineering, Purdue University, West Lafayette, Indiana, United States
Show AbstractRecently, deviations in thermal conductivity of superlattices compared to Fourier heat conduction model have been experimentally observed. Understanding thermal transport in superlattices and multilayer structures has gained a lot of interest for compound electronic devices and thermoelectric applications. Phonon Boltzmann transport equation (BTE) is a powerful technique to simulate heat conduction in multilayers taking into account full phonon dispersion and various scattering models for different phonon branches1. Molecular dynamics (MD) simulations predict a reduction in the thermal conductivity of random multilayer structures due to phonon localization and the enhanced phonon scattering2.
Here, we study thermal transport in fractal non-periodic multilayer structures (alternative high and low thermal conductivity materials) using Monte Carlo BTE under a single relaxation time approximation (i.e. gray model). The thicknesses of the high thermal conductivity layers are sampled from power law distribution while the low thermal conductivity ones have fixed thickness. The extracted thermal conductivity still follows the effective medium approximation despite that the phonon free path histogram shows slight deviation (heavy tail) from the exponential fitting expected for the relaxation time approximation. We have applied our study to both specular and diffuse interface scattering conditions.
The glass inclusions with power law size distribution inside a semi-opaque medium have shown experimentally and theoretically superdiffusive Lévy flight behavior for light propagation3. Differences and similarities between light and thermal transport in fractal multilayer structures will be discussed.
1. G. Chen, Phys. Rev. B 57, 14958 (1998).
2. Y.Wang, C. Gu, X. Ruan, Appl.Phys. Lett. 106,073104 (2015).
3. P. Barthelemy, J. Bertolotti , D.Wiersma, Nature 453, 495 (2008).
5:45 PM - NM2.3.05
Phonon Dispersion of Boron Arsenide from Inelastic X-Ray Scattering—Great Potential for Ultrahigh Thermal Conductivity
Hao Ma 1 , Li Chen 1 , Shixiong Tang 1 , Jiaqiang Yan 2 , Ahmet Alatas 3 , Lucas Lindsay 2 , Brian Sales 2 , Zhiting Tian 1
1 , Virginia Tech, Blacksburg, Virginia, United States, 2 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 3 , Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractCubic boron arsenide (BAs) was predicted to have an exceptionally high thermal conductivity (k) ~2000 Wm-1K-1 at room temperature, comparable to that of diamond, based on first-principles calculations. Subsequent experimental measurements, however, only obtained a k of ~200 Wm-1K-1. To gain insight into this discrepancy, we measured phonon dispersion of single crystal BAs along high symmetry directions using inelastic x-ray scattering (IXS) and compared these with first-principles calculations. Based on the measured phonon dispersion, we have validated the theoretical prediction of a large frequency gap between acoustic and optical modes and bunching of acoustic branches, which were considered the main reasons for the predicted ultrahigh k. This supports its potential to be a super thermal conductor if very high-quality single crystal samples can be synthesized.
NM2.4: Poster Session I: Heat Transport at the Nanoscale
Session Chairs
Wednesday AM, April 19, 2017
Sheraton, Third Level, Phoenix Ballroom
9:00 PM - NM2.4.01
Size Dictated Thermal Conductivity of GaN
Thomas Beechem 1 , Anthony Mcdonald 1 , Elliot Fuller 1 , Alec Talin 1 , Christina Rost 2 , Jon-Paul Maria 3 , John Gaskins 2 , Patrick Hopkins 2 , Andrew Allerman 1
1 , Sandia National Labs, Albuquerque, New Mexico, United States, 2 , University of Virginia, Charlottesville, Virginia, United States, 3 , North Carolina State University, Raleigh, North Carolina, United States
Show AbstractSize effects are shown to limit the thermal conductivity of gallium nitride (GaN) layers when in forms typical of device architectures. Practically, the thermal conductivity of n- and p-type doped GaN epilayers having thicknesses of 3-4 μm was investigated using time domain thermoreflectance (TDTR). Despite possessing carrier concentrations ranging across 3 decades (1015-1018 cm-3), n-type layers exhibit a nearly constant thermal conductivity of 180 W/mK. The thermal conductivity of p-type epilayers, in contrast, reduces from 160 to 110 W/mK with increased doping. These trends—and their overall reduction relative to bulk—are explained leveraging established scattering models where it is shown that, while the decrease in p-type layers is partly due to increased impurity levels evolving from its doping, size effects play a primary role in limiting the thermal conductivity of GaN layers tens of microns thick. Similarly, size effects are observed when examining the thermal conductivity versus thickness trend of more than 50 previously reported GaN thermal conductivity measurements. Device layers, even of pristine quality, will therefore exhibit thermal conductivities less than the bulk value of ~240 W/mK owing to their finite thickness.
Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.
9:00 PM - NM2.4.02
Heat Conduction Tuning Based on the Wave Nature of Phonons
Jeremie Maire 1 2 , Roman Anufriev 1 , Ryoto Yanagisawa 1 , Aymeric Ramiere 1 2 , Sebastian Volz 3 , Masahiro Nomura 1 4 5
1 , Institute of Industrial Science, the University of Tokyo, Tokyo Japan, 2 , LIMMS/CNRS-IIS, the University of Tokyo, Tokyo Japan, 3 , EM2C/CNRS, CentraleSupelec, Universite Paris-Saclay, Chatenay-Malabry France, 4 , Institute for Nano Quantum Information Electronics, the University of Tokyo, Tokyo Japan, 5 , PRESTO, JSTA, Saitama Japan
Show AbstractPhononic crystals are able to alter phonon transport properties just like photonic crystals do for light. Due to the large range of frequencies occupied by thermal phonons, the various effects achieved with photonic crystals are very challenging to demonstrate in phononic crystals. Phonon transport has been investigated in Si phononic crystals [1-3] and coherent scattering appeared at cryogenic temperatures. In this work, we elucidate the influence of disorder on thermal conduction in phononic crystals stemming from the wave nature of phonons.
Samples consist in suspended membranes and nanobeams fabricated from a single crystalline Silicon-on-insulator wafer of thickness 145 nm and patterned with circular holes by electron-beam lithography. The pitch between holes is 300 nm and their arrangement on the membrane is that of a square lattice. They are then randomly moved from their initial position. Characterization of the in-plane thermal properties was performed with our thermoreflectance system [1], in a He-flow cryostat between 4 K and room temperature.
Phonon transport — purely diffusive at room temperature — does not depend on disorder. Monte-Carlo simulations confirmed that incoherent scattering mechanisms are not significantly affected when disorder is introduced. At 4 K, experimentally measured heat diffusion times demonstrate that thermal conductivity is reduced in periodic structures compared to the disordered ones, and this difference disappears as temperature increases above 10 K. We demonstrate that these effects are caused by a coherent low-frequency range of the phonon spectrum, for which heat transport is highly suppressed. Further experiments showed that other types of disorder, such as size disorder in fishbone structures, could lead to a similar effect. These results are the first demonstration of the impact of phonons’ wave properties on thermal transport above 4 K. It paves the way towards the development of the concept of thermocrystals and the understanding of wave phononics.
References
[1] M. Nomura et al., Appl . Phys. Lett. 106, 143102 (2015).
[2] M. Nomura et al., Phys. Rev. B 91, 205422 (2015).
[3] J. Maire et al.,arXiv:1508.04574.
9:00 PM - NM2.4.03
Ballistic Phonon Transport in Si Nanowires
Jeremie Maire 1 2 , Roman Anufriev 1 , Masahiro Nomura 1 3
1 Institute of Industrial Science, University of Tokyo, Tokyo Japan, 2 LIMMS/CNRS-IIS, University of Tokyo, Tokyo Japan, 3 , PRESTO, JSTA, Saitama Japan
Show AbstractThermal conductivity is usually reduced in nanostructures, mostly due to boundary scattering [1]. However, going further than a simple reduction by using the wave properties of phonons to engineer thermal conductance [2] has proven difficult. For that purpose, phonons need to conserve their phase upon scattering on the surfaces, requiring in turn specular scattering. Such heat transport regime, called ballistic, remains difficult to observe despite the efforts in this sense. Ballistic transport has been observed in SiGe nanowires (NWs), one of the simplest nanostructure, but not yet in Si NWs, despite it being one of the most studied material. Here, we show ballistic heat transport in short nanowires at 4 K.
We fabricated Si NWs, with width ranging from 68 to 135 nm, from a 145–nm-thick SOI wafer using a classical top-down approach, including Electron-Beam lithography. An Al pad is placed in the center of each structures and serves as a heater and sensor for the thermal conductivity measurements, performed by means of micro time-domain thermoreflectance. The temperature was adjusted between 4 and 300 K with liquid helium.
First, we show that thermal conductivity decreases with decreasing width and temperature, and display a good agreement with literature data. Then, we confirm that thermal transport is diffusive at 300 K — thermal conductivity is independent of the length. At 4 K however, the thermal conductivity increases with length for short nanowires (<4 µm), demonstrating the semi-ballistic nature of heat transport at this temperature [3]. This stems from the longer phonon wavelengths as the temperature is decreased (the dominant phonon wavelength is 25 nm at 4 K versus a few nanoeters at 300 K). Lastly, we demonstrate that the modified phonon dispersion impacts thermal conductivity at 4 K, thus opening the path towards thermal conductivity control by band engineering in structures fabricated by a top-down approach.
References
[1] G. Chen, Nanoscale Energy Transport and Conversion, Oxford Press (2005).
[2] J.-K. Yu et al., Nat. Nanotech 5, 718 (2010).
[3] J Maire, R. Anufriev and M. Nomura, Sci. Rep. 7, 41794 (2017).
9:00 PM - NM2.4.04
Microelectronics Thin Films and Boundaries Characterized by Scanning Thermal Microscopy
Axel Pic 1 2 , Sebastien Gallois-Garreignot 1 , Vincent Fiori 1 , Pierre-Olivier Chapuis 2
1 , STMicroelectronics, Crolles France, 2 , CNRS - INSA Lyon, Lyon France
Show AbstractMicroelectronics Thin Films and Boundaries Characterized by Scanning Thermal Microscopy
Axel PIC(1,2), Sébastien GALLOIS-GARREIGNOT(1), Vincent FIORI(1), Pierre-Olivier CHAPUIS(2)
(1) ST Microelectronics Crolles
(2) Univ Lyon, CNRS, INSA-Lyon, Université Claude Bernard Lyon 1, CETHIL UMR5008, F-69621, Villeurbanne, France
Heat dissipation is one of the main challenges faced by microelectronics due to the increase of integration density. From Silicon-On-Insulator (SOI) technology with a very thin silicon layer confinement to 3D-stacked imagers with high sensitivity to the temperature spatial variations, accurate thermal models are needed to quantify the thermal performances of new device/package [1].
In this work, several materials (Si, SiO2, SiN, SiCN, SiOCH) and thicknesses (from 10 to 600 nm), typically used in the advanced interconnects levels of microelectronics, were thermally characterized in order to account for heat transport phenomena linked to thermal boundary resistances and ballistic conduction.
To measure thin-film thermal conductivities, we used scanning thermal microscopy (SThM), a technique based on atomic force microscopy, where a self-heated electrical resistance is added at the probe apex. In the active mode, the variation of resistance between the tip-sample contact and tip far-from-contact positions is related to both the sample thermal conductivity and dissipation from the finite heat source. To interpret the experimental data, finite-element simulations of the probe-sample interaction were performed in order to reproduce numerically the experiments. The values found were compared with semi-analytical estimations based on the materials dispersion relations and both the acoustic mismatch and diffuse models [2].
The mid-term goal is to develop a large library of effective thermal conductivities of materials used in microelectronics and subject to nanoscale heat transfer phenomena.
References
[1] S. V. Garimella, “Thermal challenges in next generation electronics systems summary of panel presentations and discussions,” IEEE Transactions on Components and Packaging Technologies, vol. 25, 2002.
[2] R. J. Stevens, J. Heat Transf. 127, 315 (2005)
9:00 PM - NM2.4.05
Effects of Grain Boundaries and Defects on Anisotropic Magnon Transport in Textured Sr14Cu24O41
Xi Chen 1 , Karalee Jarvis 1 , Sean Sullivan 1 , Jianshi Zhou 1 , Li Shi 1
1 , University of Texas at Austin, Austin, Texas, United States
Show AbstractThe strong magnetic exchange interaction in some low-dimensional magnetic materials can give rise to a high group velocity and thermal conductivity contribution from magnons. One prominent example is the incommensurate layered compounds (Sr,Ca,La)14Cu24O41, which have a large directional magnon thermal conductivity. However, the effects of grain boundaries and defects on anisotropic magnon transport in these compounds have remained to be better understood. Here we report the thermal transport properties of textured Sr14Cu24O41 samples, which are prepared by solid-state reaction followed by spark plasma sintering. The textured samples show a large anisotropy in the thermal conductivity due to the reorientation of grains during the repressing process. Transmission electron microscopy clearly reveals nano-layered grains and the presence of dislocations and planar defects. The thermal conductivity contribution and mean free paths of magnons in the textured samples are evaluated, using a kinetic model, and found to be suppressed significantly as compared to single crystals at low temperatures. Furthermore, the magnon thermal conductivity has been analyzed using a theoretical model, which provides useful insight on the magnon scattering by grain boundary and defects in these magnetic materials.
9:00 PM - NM2.4.06
Kapitza Resistance and the Thermal Conductivity of Amorphous Superlattices
Ashutosh Giri 1 , Jeffrey Braun 1 , John Duda 2 , Sean King 3 , Patrick Hopkins 1
1 , University of Virginia, Charlottesville, Virginia, United States, 2 , Seagate Technology, Bloomington, Minnesota, United States, 3 , Intel Corporation, Folsom, California, United States
Show AbstractThe electrical and optical properties of amorphous semiconductor superlattices have been a subject of scientific inquiry since Abeles and Tiedje first provided evidence that the SLs exhibit quantum size effects. In this work we report on the thermal conductivities of amorphous Stillinger-Weber superlattices as determined by non-equilibrium molecular dynamics simulations and amorphous SiOC:H/SiC:H superlattices as measured via time domain thermoreflectance technique. The results from both the computational and experimental studies sugget that thermal conductivities decrease with increasing interface density, demonstrating that interfaces contribute a non- negligible thermal resistance. Interestingly, Kapitza resistances at interfaces between amorphous materials are lower than those at interfaces between the corresponding crystalline materials. We find that Kapitza resistances within the amorphous superlattices are not a function of interface density, counter to what has been observed in crystalline superlattices. The widely used thermal circuit model is used to correctly predict the interfacial resistance within the Stillinger-Weber based amorphous superlattices and amorphous SiOC:H/SiC:H superlattices. Our results show that the significant heat carrying vibrations in these structures are diffusons, which are delocalized and non-propagating modes.
9:00 PM - NM2.4.07
Scattering of Longitudinal Acoustic Phonons in Thin Silicon Membranes
Dhruv Gelda 1 , Sanjiv Sinha 1
1 , University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Show AbstractQuantitative information on the lifetimes of THz phonons is crucial in understanding the nanoscale heat transport1. The lifetimes of such acoustic phonon modes also determine the intrinsic quality factor of nanomechanical resonators, and control the ultimate limits to sensing mass change, liquid density, charge and temperature2,3 with such devices. Recent experiments have provided direct measurements of longitudinal acoustic phonon lifetimes in the higher GHz to THz regime for silicon4,5. However, the results do not definitively resolve the relative contributions of intrinsic mechanisms (such as Akheiser) versus extrinsic mechanisms (such as boundary scattering), particularly at the higher frequencies. This work focuses on understanding how these mechanisms influence acoustic phonon transport through acoustic measurements in nanostructures with well-characterized surface morphologies. We employ a femtosecond laser pump-probe setup to excite and measure the lifetimes of longitudinal acoustic phonons in ultrathin silicon membranes with thicknesses down to 36 nm. We show that the phonon lifetime for membranes thicker than 200 nm is limited intrinsically by Akheiser mechanism. In thinner membranes, boundary scattering is the most dominant dissipation mechanism. Perturbation-based spectral scattering theory does not seem to reproduce the observed trend in phonon lifetimes. We use a surface specularity parameter based on Kirchhoff’s approximation to correctly predict the observed trend. Our results provide insights to understanding thermal and acoustic transport in nanostructures.
[1] Cahill, David G., et al. "Nanoscale thermal transport." Journal of Applied Physics 93.2 (2003): 793-818.
[2] Chaste, Julien, et al. "A nanomechanical mass sensor with yoctogram resolution." Nature nanotechnology 7.5 (2012): 301-304.
[3] Steele, Gary A., et al. "Strong coupling between single-electron tunneling and nanomechanical motion." Science 325.5944 (2009): 1103-1107.
[4] Daly, B. C., et al. "Picosecond ultrasonic measurements of attenuation of longitudinal acoustic phonons in silicon." Physical Review B 80.17 (2009): 174112
[5] Cuffe, John, et al. "Lifetimes of confined acoustic phonons in ultrathin silicon membranes." Physical review letters 110.9 (2013): 095503.
9:00 PM - NM2.4.08
Sub-Amorphous Thermal Conductivity in Amorphous Heterogeneous Nanocomposites
Jaeyun Moon 1 , Austin Minnich 1
1 , California Institute of Technology, Pasadena, California, United States
Show AbstractPure amorphous solids are traditionally considered to set the lower bound of thermal
conductivity due to their disordered atomic structure that impedes vibrational energy
transport. However, the lower limits for thermal conductivity in heterogeneous amor-
phous solids and the physical mechanisms underlying these limits remain unclear. Here,
we use equilibrium molecular dynamics to show that an amorphous SiGe nanocompos-
ite can possess thermal conductivity substantially lower than those of the amorphous
Si and Ge constituents. Normal mode analysis indicates that the presence of the Ge
inclusion localizes vibrational modes with frequency above the Ge cuto� in the Si host,
drastically reducing their ability to transport heat. This observation suggests a general
route to achieve exceptionally low thermal conductivity in fully dense solids by restrict-
ing the vibrational density of states available for transport in heterogeneous amorphous
nanocomposites.
9:00 PM - NM2.4.09
Revisiting the Theory of Disordered Alloy Thermal Conductivity
Hamidreza Seyf 1 , Asegun Henry 1
1 Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractCurrent understanding of the phonon contributions to alloy thermal conductivity is based on the phonon gas model (PGM) and the virtual crystal approximation (VCA). Using this theoretical framework, good agreement is obtained in some cases, but there are many instances where it fails – both quantitatively and qualitatively. Here, we reexamine the theory and note that a critical assumption inherent to the PGM is the notion that all of the phonons/normal modes of vibration resemble plane waves with well-defined velocities. Instead, we show that in a random alloy, the character of the normal modes changes dramatically and they more closely resemble those found in amorphous materials. We then utilize an alternative approach that can treat all types of phonons and show that it can properly predict size effects in In0.53Ga0.47As thin films. These results then illustrate that the critical missing information is the mode character, which has significant implications for neutrons, electrons and photons interacting with such phonons, since the momentum of non-propagating phonons is unknown.
9:00 PM - NM2.4.10
Synthesis and Characterization of Boron Arsenide Crystals
Fei Tian 2 , Bing Lv 3 , Yongjie Hu 4 , David Broido 1 , Gang Chen 5 , Zhifeng Ren 2
2 , University of Houston, Houston, Texas, United States, 3 , The University of Texas at Dallas, Dallas, Texas, United States, 4 , University of California, Los Angeles, Los Angeles, California, United States, 1 , Boston College, Boston, Massachusetts, United States, 5 , Massachusetts Institute of Technology, Boston, Massachusetts, United States
Show AbstractWith the rapid miniaturization of modern microelectronic devices, the need for insulators with high thermal conductivity for passive cooling is continuously growing. Recent first principle calculations have predicted that a zinc blende structure boron arsenide (BAs) can have an exceptionally high room temperature thermal conductivity above 2000 W m-1 K-1, which is comparable to that of diamond, long known to have the highest thermal conductivity of any bulk material. However, this prediction has not been experimentally realized. We have successfully synthesized BAs crystals via a chemical vapor transport method. The measured thermal conductivity, about 200 W m-1 K-1 at room temperature, is not as high as predicted, but close to that of popular high thermal conductivity materials like Si and SiC. Based on our measurement and analysis, this is mainly caused by the defects and impurities in the crystals. This indicates that the predicted ultrahigh thermal conductivity may be achieved through further optimizations of crystals with fewer defects and impurities.
9:00 PM - NM2.4.11
Calibrated Sub-Micron Temperature Measurement of an Operating Plasmonic HAMR Device by Thermoreflectance Imaging
Gregory Hohensee 1 , Dustin Kendig 2 , Ella Pek 3 , Wan Kuang 1 4 , Kazuaki Yazawa 2 5 , Ali Shakouri 5
1 , Western Digital Corporation, Fremont, California, United States, 2 , Microsanj LLC., Santa Clara, California, United States, 3 , University of Illinois at Urbana–Champaign, Urbana, Illinois, United States, 4 , Boise State University, Boise, Idaho, United States, 5 , Purdue University, West Lafayette, Indiana, United States
Show AbstractIt is difficult to measure the absolute temperature of an operating nanoscale device. Any near-field temperature probe, such as a scanning thermal AFM tip, nanoparticle, or lithographically defined thermometer, tends to influence or be influenced by the device itself. Plasmonic devices, such as heat-assisted magnetic recording (HAMR) heads for next-generation HDD storage, also emit near- and far-field radiation that overwhelm the temperature signal from near-field probes. Far-field temperature monitors to date suffer from optical diffraction limits or require TEM-sectionable devices, which is not feasible for a HAMR head. Here we describe our application of a commercial thermoreflectance imaging microscope for contact-free, sub-micron temperature mapping of an operating HAMR head. By understanding and controlling edge effects, polarization sensitivity, and thermal expansion, and by applying a transient calibration technique, we have recorded the absolute temperature of features as small as 200 nm.
9:00 PM - NM2.4.12
Pump-Probe Thermoreflectance Measurements of Critical Interfaces for Thermal Management of HAMR Heads
Gregory Hohensee 1 , Mousumi Biswas 1 , Ella Pek 2 , Chris Lee 1 , Min Zheng 1 , Yingmin Wang 1 , Chris Dames 3
1 , Western Digital Corporation, Fremont, California, United States, 2 Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 3 , University of California, Berkeley, Berkeley, California, United States
Show AbstractFor heat-assisted magnetic recording (HAMR) heads, a major reliability limiter is the peak near-field transducer (NFT) temperature. Since the NFT is nanoscale, heat sinking is controlled by materials and interfaces within a few 100 nm of the NFT. Heat sinks can be metallic to take advantage of the 10x-100x higher thermal boundary conductance (TBC) of metal/metal interfaces, versus nonmetal interfaces. Oxide formation at these interfaces can greatly decrease the TBC and contribute to NFT failure. Likewise, the thermal resistance of material between the NFT and media recording layer greatly influences the NFT operating temperature. Here we use pump-probe thermoreflectance techniques (FDTR, TDTR) to study metal-metal interfaces and detect partial oxidation of a buried metallic thin film, as well as evaluate the interface thermal conductance of amorphous-amorphous interfaces in a film stack representative of a HAMR head-media interface.
9:00 PM - NM2.4.13
Development of Polymer Imprint Thermal Mapping for AFM-Based Temperature Mapping of Plasmonic HAMR Heads
Gregory Hohensee 1 , Tan Nguyen 1 , Ella Pek 2 , Wan Kuang 1 3 , Ozgun Suzer 1 , Marc Finot 1
1 , Western Digital Corporation, Fremont, California, United States, 2 Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 3 , Boise State University, Boise, Idaho, United States
Show AbstractPolymer imprint thermal mapping (PITM) is a high-resolution thermal mapping technique that is especially valuable for nanoscale plasmonic devices. PITM leverages a 50 nm polymer film coating that crosslinks permanently upon heating, and records the peak temperature rise of the surface from the local, linear reduction in polymer film thickness. Using AFM to measure topography before and after heating, but not during operation, PITM sidesteps plasmonic artifacts seen in other near-field thermometries, where the probe tip disturbs and is heated directly by the near- and far-field radiation around the plasmonic device. This is notably troublesome for characterizing heat-assisted magnetic recording (HAMR) heads for next-generation hard disk drives. HAMR heads use near-field transducers (NFTs) to focus light on a magnetic media, heating a nanoscale region to its Curie temperature and enables magnetic writing. In this paper we further develop the PITM technique by: (1) quantifying the spatial resolution limit imposed by the polymer’s presence on the device, (2) modeling the distinction between recorded polymer temperature and actual device surface temperature, (3) presenting data on non-linearity and variability in polymer temperature response and addressing PITM signal artifacts, and (4) demonstrating robust PITM-derived temperature data on HAMR devices.
9:00 PM - NM2.4.14
Ray Tracing Simulations of Incoherent Phonon Boundary Scattering in Silicon Nanomeshes
Geoffrey Wehmeyer 1 , Jaeho Lee 2 , Woochul Lee 3 , Scott Dhuey 3 , Deirdre Olynick 3 , Stefano Cabrini 3 , Jeffrey Urban 3 , Peidong Yang 1 3 4 , Chris Dames 1
1 , University of California, Berkeley, Berkeley, California, United States, 2 , University of California, Irvine, Irvine, California, United States, 3 , Lawrence Berkeley National Laboratory, Berkeley, California, United States, 4 , Kavli Energy Nanosciences Institute, Berkeley, California, United States
Show AbstractClassical models describing the size dependence of the thermal conductivity (k) treat phonons as incoherent particles colliding with rough sample boundaries. Recently, researchers have attempted to also utilize the wave nature of thermal phonons by fabricating phononic nanostructures intended to cause phonon wave interference. A common phononic structure is the nanomesh, in which holes are etched through a silicon membrane. Several previous experiments have reported anomalous reductions in k for silicon nanomeshes even at room temperature; however, it remains controversial whether this k reduction is due to the incoherent particle boundary scattering effect or the coherent wave interference effect.
To isolate the particle effect from the wave effect, we designed a combined modeling and experimental study [1] to compare periodic and aperiodic nanomeshes and to compare nanomeshes of different hole-to-hole pitch p. In this presentation, we emphasize the incoherent particle modeling. We use ray tracing simulations and the Landauer-Büttiker formalism to quantify the boundary scattering in the silicon nanomeshes fabricated for the experiments. We find that the particle model predicts that periodic and aperiodic nanomeshes with the same average p will have the same k, and that nanomeshes with smaller p along the direction of heat flow will have slightly smaller k. We explain these boundary scattering trends using the phonon backscattering concept. We find that these particle model predictions satisfactorily explain all of our experimental measurements without requiring any consideration of wave interference effects. Our work shows that the particle boundary scattering effects must be carefully modeled using realistic 3D geometries when interpreting phonon transport measurements in heterogeneous nanostructures.
[1] J. Lee et al., Investigation of Phonon Coherence and Backscattering using Silicon Nanomeshes, Nature Communications 8, 14054 (2017).
9:00 PM - NM2.4.17
Broadening of Thermal Surface Wave Spectrum on SiO2 Thin Film from Near-Infrared to Far-Infrared due to Zenneck Modes
Sergei Gluchko 1 , Bruno Palpant 2 , Sebastian Volz 1 , Remy Braive 3 4 , Thomas Antoni 2
1 EM2C, CentraleSupelec, Paris-Saclay University, Chatenay-Malabry France, 2 LPQM, ENS Cachan, CentraleSupelec, Paris-Saclay University, Chatenay-Malabry France, 3 Sorbonne Paris Cite, Paris Diderot University, Paris France, 4 LPN, Paris-Saclay University, Marcoussis France
Show AbstractFollowing previous theoretical works uncovering the possible existence of broad band surface electromagnetic modes in thin films, we have measured and calculated the far-field thermal emission of a submicron SiO2 layer from near- to far-infrared frequencies. Thermally excited Zenneck surface waves, Surface Phonon Polaritons and guided surface waves were detected in the 882 cm−1 to 3725 cm−1 frequency range. The dispersion relation and spectral coherence length (found as large as 500 μm) are in good agreement with theoretical and numerical expectations. Optical and thermal applications are envisioned due to the photon-like behavior and the large propagation length of the observed modes. Those waves are indeed likely to open an unknown but very efficient heat channel, which can even predominate over heat conduction.
9:00 PM - NM2.4.18
Hydrogen-Induced Thermal Conductivity Change across Metal-Insulator Transition in Amorphous WO3 Film
Ayano Nakamura 1 2 , Shunta Harada 1 2 , Miho Tagawa 1 2 , Toru Ujihara 1 2
1 Department of Materials Science and Engineering, Nagoya University, Nagoya City Japan, 2 Institute of Materials and Systems for Sustainability, Nagoya University, Nagoya, Aichi, Japan
Show AbstractWe are developing “thermal switching materials”, whose thermal conductivity varies over a wide range. It has a wide range of applications such as temperature controls, thermal energy storages and so on. WO3 is expected as a thermal switching material because the electrical conductivity of WO3 can widely change owing to the metal-insulator transition (MIT) caused by hydrogen interactions. Moreover, hydrogens can be intercalated into and deintercalated from WO3 film reversibly and quickly by an electrochemical reaction. Therefore, the thermal conductivity is expected to change reversibly. Here, we report the thermal conductivity changes in WO3 film associated with hydrogen intercalations.
WO3 film was prepared on ITO coated glass at room temperature by RF magnetron sputtering method in an Ar-O2 atmosphere. The total pressure and the oxygen content of the atmosphere were 4.0 Pa and 13%, respectively. The thickness of WO3 film was 0.7-1.4 μm. Hydrogen intercalations into WO3 film on ITO coated glass were performed in an 0.5 M H2SO4 electrolyte with a Pt counter electrode and a calomel reference electrode. The structure of the films was determined by x-ray diffraction analysis. The thermal diffusivity of the films was measured by an ac calorimetric method and the thermal conductivity was calculated by the differential method using measured thermal diffusivity. The electrical conductivity was measured by a four-point probe method.
X-ray diffraction measurements showed that the WO3 films were amorphous. The value of thermal conductivity decreased with increasing hydrogen content x in HxWO3, from x = 0 to x = 0.33, and the value of thermal conductivity increased markedly with increasing x above x = 0.33. The hydrogen content of x = 0.33 is close to that of MIT. On the other hand, the electrical conductivity after MIT was 1×105 times higher than that before MIT. However, a variation of the electron thermal conductivity given from the electrical conductivity by the Wiedemann-Franz law is much smaller than a variation of the thermal conductivity. Therefore, the lattice thermal conductivity is expected to contribute to a change in the thermal conductivity. Present results indicate that the thermal conductivity of WO3 film can be controlled by hydrogen intercalations and potentialize the hydrogen-induced active control of thermal switches.
9:00 PM - NM2.4.19
The Enhancement of Thermal Conductivity of Polyvinyl Alcohol Nanofiber Membrane
Xiandong Chen 1 2 , Meng An 1 2 , Nuo Yang 1 2 , Jianfeng Zang 3 4
1 State Key Laboratory of Coal Combustion, Huazhong University of Science and Technology, Wuhan, Hubei Province, China, 2 Nano Interface Center of Energy (NICE), School of Energy and Power Engineering, Huazhong University of Science and Technology, Wuhan, Hubei Province, China, 3 School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan, Hubei Province, China, 4 Innovation Institute, Huazhong University of Science and Technology, Wuhan, Hubei Province, China
Show AbstractOrganic membranes have extensively been used to modern electronic industries such as printed circuit boards (PCBs), thermal interface materials (TIMs), and device bases/holders. However, its low thermal conductivity (∼0.1W/m-K) largely affects product reliability and functionality. Here, we prepared a new kind of polyvinyl alcohol (PVA) nanofiber membrane and measured its effective thermal conductivity using 3-Omega thermal measurement method. Interestingly, its effective thermal conductivity reaches 2.1W/m-K, about one order higher than that of spin-coating PVA membrane (0.3W/m-K) while its density is much smaller than that of PVA membrane. At last, we explored the physical mechanism of the enhancement of thermal conductivity. Our studies bring new insights in designing high thermal conductivity organic membranes and deepen the understanding of thermal transport in organic materials.
9:00 PM - NM2.4.20
The Adjustable Thermal Resistor By Reversibly Folding a Graphene Sheet
Meng An 1 2 , Qichen Song 1 2 , Nuo Yang 1 2 , Jianfeng Zang 3 4
1 State Key Laboratory of Coal Combustion, Huazhong University of Science and Technology, Wuhan, Hubei Province, China, 2 Nano Interface Center of Energy (NICE), School of Energy and Power Engineering, Huazhong University of Science and Technology, Wuhan, Hubei Province, China, 3 School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan, Hubei Province, China, 4 Innovation Institute, Huazhong University of Science and Technology, Wuhan, Hubei Province, China
Show AbstractPhononic (thermal) devices such as thermal diode, thermal transistors, thermal logical gates, and thermal memories have been studied intensively. However, the tunable thermal resistors have not been demonstrated yet. Here, we propose an instantaneously adjustable thermal resistor based on folded graphene. Through theoretical analysis and molecular dynamics simulations, we study the phonon-folding scattering effect and the dependence of thermal resistivity on the length between two folds and the overall length. Further, we discuss the possibilitiy to realize the instantaneously adjustable thermal resistor in experiment. Our studies bring new insights in designing thermal resistor and understanding thermal modulation of 2D materials by adjustable its basic structure parameters.
9:00 PM - NM2.4.22
Sound Attenuation in Amorphous Silica at Frequencies near the Boson Peak
Zhi Liang 1 , Pawel Keblinski 2
1 Mechanical Engineering, California State University, Fresno, Fresno, California, United States, 2 Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States
Show AbstractWe use molecular dynamics phonon wave packet (WP) simulations to study acoustic propagation and attenuation in amorphous silica (a-SiO2) at frequencies near the Boson peak (BP) position and compare them with the results of equilibrium molecular dynamics (EMD) simulations. The WP simulation mimics the narrow-band sound attenuation experiments by launching an acoustic wave packet in a Si substrate and monitoring its propagation and attenuation in the Si|a-SiO2 structure. The sound attenuation coefficients predicted by the WP simulations generally have good agreement with those from the EMD simulations and have reasonable agreement with the existing experimental data. Near the BP position, we found the frequency dependent sound attenuation coefficients for longitudinal and transverse modes both follow the Rayleigh-scattering fourth power law. Above the BP frequency, however, the propagating phonon is essentially attenuated in a-SiO2 within a few nanometers, and the accurate determination of the sound attenuation coefficients by the WP simulation becomes challenging. The modeling results provide a reference for future experimental investigations of sound attenuation in a-SiO2 thin film using narrow-band coherent phonons.
9:00 PM - NM2.4.23
Coherent Control of Thermal Conductance in Hole- and Pillar-Based Phononic Crystals
Roman Anufriev 1 , Masahiro Nomura 1
1 , The University of Tokyo, Meguro, Tokyo Japan
Show AbstractPhononic crystals (PnC) can effectively control heat transport at low temperatures via phonon dispersion engineered through the PnC design. PnCs, used for most of the applications, are typically two-dimensional and consist of periodic arrays of either holes in a membrane (hole-based) or pillars on top of a membrane (pillar-based). In both types of PnCs phonon dispersion can be changed due to phonon interference, which leads to the reduction of the group velocity and modifications of the density of states (DOS), thus changing thermal conductance of the structure. In this work we seek complete understanding of the processes behind the modifications of thermal transport in PnCs and systematically theoretically investigate how thermal conductance of hole- and pillar-based PnCs of realistic size depends on the various dimensions, material, lattice type and temperature.
We show that in both types of PnCs thermal conductance is suppressed in the structures of sufficiently long period (at a given temperature), yet at very low temperatures (< 0.5 K) structures with short period (< 60 nm) can on the contrary enhance thermal conductance as compared to an unpatterned membrane. In pillar-based PnCs, where the local resonances play an important role, we investigated the impact of the pillar material and size and found that the resonances actually do not suppress heat transfer, but on the contrary increase the conductance via increased DOS. Thus, the overall suppression of thermal conductance in pillar-based PnCs appears despite (not due to) the local resonances and is caused by periodicity of the structure. Next, we highlight the importance of critical membrane thickness below which the suppression of thermal conductance by PnCs starts growing as the thickness is decreased. Finally, we propose hybrid hole-pillar PnCs which combines both types of PnCs and demonstrates the strongest reduction of thermal conductance.
9:00 PM - NM2.4.24
Thermal Phonon MFP Spectrum Probing Using Phononic Crystals
Masahiro Nomura 1 2 , Junki Nakagawa 1 , Kentarou Sawano 3 , Jeremie Maire 1 , Roman Anufriev 1 , Sebastian Volz 1
1 , University of Tokyo, Tokyo Japan, 2 , Japan Science and Technology Agency, Saitama Japan, 3 , Tokyo City University, Tokyo Japan
Show AbstractWe demonstrate an experimental method to obtain information of thermal phonon mean free path (MFP) spectra in thin films using two dimensional phononic crystal nanostructures. The characteristic length of the system can be swept by changing the structural parameter of the phononic crystals. Then, thermal conductivities of 150-nm-thick single-crystalline Si, amorphous SiGe, and poly-SiGe thin films were measured for phononic crystals with different characteristic length between 20 nm and 200 nm. We observed different characteristic length dependence of the thermal conductivity among these three systems and the trend can be explained by the thermal phonon MFP spectra of the materials.
We fabricated 150-nm-thick suspended membrane by using electron beam lithography and dry/wet etching systems. The phononic crystal patterns are the circular holes periodically aligned as square or triangular lattices. The period is fixed at 300 nm and the narrowest part, from the edge of one hole to the other adjacent one, is swept from 20 nm to 200 nm to change the characteristic length. The thermal conductivities of phononic crystals formed in single-crystalline Si, amorphous SiGe and poly-SiGe were measured by micro TDTR measurement method at room temperature.
The characteristic length dependence of the thermal conductivity are largely different among three materials. Si showed large thermal conductivity change around the characteristic length of 100 nm. This result agrees with the Monte Carlo simulation in the same structure [1]. In amorphous SiGe, we found that thermal phonons are distributed mainly in 10’s of nanometers. In poly-SiGe, which was fabricated by annealing the amorphous SiGe, thermal phonons distributes mainly shorter than 20 nm and longer than 200 nm in MFP. This result indicate that the annealing process lengthen the MFP of phonons in SiGe thin films by improving the quality of thin film and this is reasonable.
The series of results on the characteristic length dependence of the thermal conductivity agree with qualitative discussion on thermal phonon MFP spectrum. Therefore, this method can be used to probe thermal phonon MFP spectrum in thin films [2].
[1] M. Nomura, et al., Phys. Rev. B 91, 205422 (2015).
[2] M. Nomura, et al., Appl. Phys. Lett. 109, 173104 (2016).
9:00 PM - NM2.4.25
Interlayer Thermal Conductance within Phosphorene and Graphene Bilayer
Yang Hong 1 , Jingchao Zhang 2 , Xiao Cheng Zeng 1
1 Department of Chemistry, University of Nebraska Lincoln, Lincoln, Nebraska, United States, 2 Holland Computing Center, University of Nebraska Lincoln, Lincoln, Nebraska, United States
Show AbstractMonolayer graphene possesses unusual thermal properties, and is often considered as a prototype system for the study of thermal physics of low-dimensional electronic/thermal materials, despite of the absence of a direct bandgap. Another two-dimensional (2D) atomic layered material, phosphorene, is a natural p-type semiconductor and it has attracted rapidly growing interests in recent years. When a graphene monolayer is overlaid on phosphorene, the hybrid van der Waals (vdW) bilayer becomes a promising candidate for high-performance thermal/electronic applications, owing to the combined direct-bandgap property of phosphorene with the exceptional thermal properties of graphene. In this work, the interlayer thermal conductance at the phosphorene/graphene vdW interface is investigated systematically using classical molecular dynamics (MD) simulation. Transient pump-probe heating method is employed to compute the interfacial thermal resistance (R) of the bilayer. The predicted R value at the phosphorene/graphene interface is 8.41 × 10-8 Km2/W at room temperature. Four different external or internal conditions, i.e., temperature, contact pressure, vacancy defect, or chemical functionalization, can all effectively reduce R at the interface. Numerical results of R reduction as functions of temperature, interfacial coupling strength, defect ratio, and hydrogen coverage are reported with the largest R reduction amounting to 56.5%, 70.4%, 34.8% and 84.5%, respectively.
9:00 PM - NM2.4.26
Non-Contact Measurement of In-Plane Thermal Anisotropy in Polymer Films Using Transient Grating Spectroscopy
Andrew Robbins 1 , Austin Minnich 1
1 , California Institute of Technology, Pasadena, California, United States
Show AbstractThermally conductive polymers are of keen interest due to their applications in light-weight heat exchangers and flexible thermal packaging. However, the mechanisms governing the upper limits of thermal conductivity are unclear, partly due to the challenge of characterizing thermal transport along the in-plane directions. Here, we demonstrate transient grating (TG) spectroscopy as a versatile tool to probe in-plane thermal transport in thin polymer films. TG possesses a number of advantages compared to other experimental methods, including non-contact measurement, no transducer layer, and simple sample fabrication. Further, for semi-crystalline or aligned polymer films that exhibit in-plane thermal anisotropy, TG is able to determine the anisotropy at a specific location of a film simply by rotating the sample. This work demonstrates TG as a powerful method to explore the limits of heat conduction in polymers.
9:00 PM - NM2.4.28
Thermal Conduction in Homologous In2O3(ZnO)ｍ Films
Junjun Jia 1 , Yuichiro Yamashita 2 , Takashi Yagi 2 , Yuzo Shigesato 1
1 Graduate School of Science and Engineering, Aoyama Gakuin University, Sagamihara Japan, 2 National Metrology Institute of Japan (NMIJ), National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Japan
Show AbstractAs a natural superlattice material, homologous In2O3(ZnO)m (m=integer) compounds have received much attention as the high temperature thermoelectric conversion material because of their structural and chemical stability at high temperature [1, 2]. We have reported that the homologous In2O3(ZnO)m thin film with a high power factor similar to bulk value at 670 °C can be fabricated on the glass substrate by dc magnetron sputtering method [3]. However, the mechanism of the thermal conducnion in the In2O3(ZnO)m superlattice is not clear until now. The present work is to investigate the thermal conduction phenomenon of the homologous In2O3(ZnO)m thin films with the different m value.
Homologous In2O3(ZnO)m with m=2, 3, 5 were deposited on the c-plane sapphire substrates at 700 °C by dc magnetron sputtering using the In2O3-ZnO ceramic target. Argon was used as the sputtering gas, and the total gas pressure was set to 0.5 Pa. All the films show the c-axis orientated epitaxial growth.
The thermal conduction phenomenon was investigated by using a front heating/front detection type picosecond pulsed light heating thermoreflectance system, and the thermal diffusivity was obtained by analyzing the phase time-response signal of the thermoreflectance measurement [4]. The thermal conductivities of the homologous In2O3(ZnO)m are 1.9, 1.8, 1.4 W(mK)-1 for m=2, m=3, and m=5 at room temperature, respectively. Thermal conductivitity decreased with m increasing in In2O3(ZnO)m thin films, which was attributed to a decreasing carrier density with an increase in m value. We also found that the thermal conductivities of the homologous In2O3(ZnO)m increase with the temperatue increasing. Furthermore, we discussed the effect of the superlattice interface (InO2/ZnO) in In2O3(ZnO)m on the phonon thermal conduction by comparing our experimetanl results and theoretical calculations, and gave an explanation about the phonon conduction along the C-axis of In2O3(ZnO)m
superlattice.
This work was supported by JSPS KAKENHI Grant-in-Aid for Young Scientists (B) 16K21338.
[1] X. Liang, and D. R. Clarke, Acta. A 34, 041507 (2016).
[2] J. Jia, N. Oka, Y. Shigesato, J. Appl. Phys. 113, 163702 (2013).
[3] J. Jia, et al., J. Vac. Sci. Technol. A 34, 041507 (2016).
[4] T. Yagi et al., Proc. 34th Jpn. Symp. Thermophys. Prop., (2013), A112.
9:00 PM - NM2.4.29
External Electric Field Driving Ultra-Low Thermal Conductivity of Silicene
Guangzhao Qin 1 , Ming Hu 1
1 , RWTH Aachen University, Aachen Germany
Show AbstractManipulation of thermal transport is on emerging demands since heat transfer plays a critical role in enormous practical implications, such as efficient heat dissipation in nano-electronics and
heat conduction hindering in solid-state thermoelectrics. It is well established that the thermal transport in semiconductors and insulators (phonons) can be effectively modulated by structure
engineering or materials processing. However, almost all the existing approaches involve altering the original atomic structure of materials, which would be frustrated due to either irreversible structure change or limited tunability of thermal conductivity. Motivated by the inherent relationship between phonon behavior and interatomic electrostatic interaction, we comprehensively investigate the effect of external electric field, a widely used gating technique in modern electronics, on the lattice thermal conductivity. Taking two-dimensional silicon (silicene) as a model, we demonstrate that, by applying electric field (Ez = 0.5V/Ang) the thermal conductivity of silicene can be reduced to a record low value of 0.091W/mK, which is more than two orders of magnitude lower than that without electric field (19.21W/mK) and is even comparable to that of most excellent thermal insulation materials. Fundamental insights are gained from the view of electronic structures. With electric field applied, due to the screened potential resulted from the redistributed charge density, the interactions between silicon atoms are renormalized, leading to the phonon renormalization and the modulation of phonon anharmonicity through electron-phonon coupling. Our study paves the way for robustly tuning phonon transport in materials without altering the atomic structure of materials, and will have significant impact on emerging applications, such as thermal managements, nano-electronics, and thermoelectrics.
9:00 PM - NM2.4.30
Methodology for Electronic Thermal Conductivity of Metals from Direct Non-Equilibrium Ab Initio Molecular Dynamics Simulation
Sheng Ying Yue 1 , Ming Hu 2
1 1 Aachen Institute for Advanced Study in Computational Engineering Science (AICES), RWTH Aachen University, Aachen, Baden-Wurttemberg, Germany, 2 Institute of Mineral Engineering, Division of Materials Science and Engineering, Faculty of Georesources and Materials Engineering, RWTH Aachen University, Aachen, Baden-Wurttemberg, Germany
Show AbstractMany physical properties of metals can be understood in terms of the free electron model which can be proved by the Wiedemann-Franz law. According to this model, electronic thermal conductivity () can be inferred from the Boltzmann transport equation (BTE). However, the BTE does not perform well for some complex metals such as Cu. Moreover, it cannot describe clearly the origin of the thermal energy carried by electrons or how the energy is transported in metals. As it is well known, the charge distribution of conduction electrons in metals reflects the electrostatic potential of the ion cores. Based on this premise, we develop a new methodology for evaluating κ el by combining the free electron model and non-equilibrium ab initio molecular dynamics (NEAIMD) simulations. In the concept of electrostatic potential oscillation, we demonstrate that the kinetic energy of thermally excited electrons originates from the energy of the spatial electrostatic potential oscillation (EPO), which is induced by the thermal motion of ion cores. Our method provides better prediction of the electronic thermal conductivity of pure metals than the traditional Boltzmann transport equation method near room temperature, without explicit recourse to any complicated scattering processes of free electrons.
9:00 PM - NM2.4.31
Out-of-Plane Thermal Transport in Multiplayer Stanene
Jingchao Zhang 1 , Yang Hong 1
1 , University of Nebraska Lincoln, Lincoln, Nebraska, United States
Show AbstractStanene, which is a two-dimensional (2D) layer of tin atoms, has spurred extensive experimental investigations due to their topological insulating behavior with a very large bandgap and near room-temperature quantum anomalous Hall effect. Those peculiar properties allow stanene to conduct electricity without losing energy as waste heat, which makes it an appealing candidate to ferry current in electronic devices. To understand the thermoelectric performance in topological insulators, their thermal properties must be investigated first. In this work, thermal transport in the out-of-plane direction of multilayer stanene is explored systematically by molecular dynamics (MD) simulation method. Ultralow out-of-plane thermal conductivities in the orders of 10-2~10-1 W/mK are calculated, which is much smaller than its lateral counterparts. Multiple internal and external factors such as system dimension, temperature, interlayer coupling strength and compression/tension strains are applied to modulate the predicted thermal properties. It is reported that thermal conductivity in the out-of-plane direction can be enhanced by 5.9 times with magnified coupling strength or 2.1 times with compressive strains. Detailed phonon power spectra analyses are conducted to reveal the underneath physical mechanism. Our predicted results provide reasonable guidelines for the design and development of next-generation stanene-based electronic circuits.
9:00 PM - NM2.4.32
Experimental Investigation of Thermal Transport in Periodic Cellular Nanotrusses
Nicholas Dou 1 , Robert Jagt 2 1 , Julia Greer 1 , Austin Minnich 1
1 , California Institute of Technology, Pasadena, California, United States, 2 , University of Groningen, Groningen Netherlands
Show AbstractMaterials with low density, low thermal conductivity, and high stiffness are desirable for structural thermal insulation applications, but achieving this combination of properties is difficult due to the coupling between them. Nanotrusses, which consist of hollow nanoscale beams architected into a periodic truss structure, can break these couplings due to their lattice architecture and nanoscale features. Simulations of phonon transport in octet nanotrusses have demonstrated their potential to reach thermal conductivities lower than aerogels while achieving 10 to 1000 times higher stiffness. Here, we use the 3-omega method to measure thermal conductivity of nanotrusses. Samples consist of a nanotruss in a line geometry coated with metal as the heater line. Our results show that nanotrusses can achieve extremely low thermal conductivity due to porosity and boundary scattering in the truss beams and thus are promising candidates for lightweight, stiff, and thermally insulating materials.
9:00 PM - NM2.4.33
The Thermal Conductivity of Actinide Materials—A New Experimental Approach
Keshav Shrestha 1 , Krzysztof Gofryk 1
1 , Idaho National Laboratory, Idaho Falls, Idaho, United States
Show AbstractA detailed knowledge of thermal properties of actinide materials, especially under extreme conditions (high pressure, low temperature, and high magnetic fields) is important due to their relevance to nuclear applications. The thermal conductivity of nuclear fuels governs the conversion of heat produced from fission events into electricity and it is an important parameter in reactor design and safety. Several methods have been implemented to determine thermal conductivity of nuclear materials. Most of them, however, require usage of large samples, which is problematic when working with single crystalline materials. In addition, most of those methods cannot be employed to measure thermal conductivity under extreme conditions, especially high physical pressure. Here, we have adapted the 3ω method, developed by Cahill [1], to measure the thermal properties of actinides. Our new approach can be used for the thermal conductivity and heat capacity measurements in wide temperature and magnetic field ranges and for both metallic and insulating actinide materials. Also, we will present our recent thermal conductivity results on UO2 and UN single crystals. In addition, some preliminary results under hydrostatic pressure will also be presented.
[1] D. G. Cahill, Review of Scientific Instruments, 61, No. 2, 1990.
9:00 PM - NM2.4.35
Dual-Mode Raman Method to Measure In-Plane and Interfacial Thermophysical Properties of 2D van der Waals Heterostructures
Qinyi Li 1 , Xing Zhang 2 3 , Koji Takahashi 1 3
1 Department of Aeronautics and Astronautics, Kyushu University, Fukuoka Japan, 2 Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, Department of Engineering Mechanics, Tsinghua University, Beijing China, 3 International Institute for Carbon Neutral Energy Research (WPI-I2CNER), Kyushu University, Fukuoka Japan
Show AbstractStacking different kinds of 2D materials layer by layer can create what is called van der Waals heterostructures with tunable properties, which has become a rapidly developing research field. The coupling with other 2D materials in the heterostructure can significantly affect the thermal transport in each layer, but there still lacks effective method to in-situ measure the in-plane and interfacial thermal properties in the layered heterostructure. This paper presents a non-contact dual-mode Raman method for the comprehensive measurement of in-plane thermal conductivity and thermal diffusivity of each layer in the heterostructure, and interfacial thermal conductance between layers, with no pre-knowledge of laser absorption. The temperature of each layer can be simultaneously detected from their temperature dependence of Raman band shifts. The term “dual-mode” refers to employing both continuous-wave (CW) laser with variable laser spot sizes and pulsed laser with variable pulse durations to heat the sample. A three-dimensional transient heat conduction model for Gaussian laser heating n layers of different 2D materials is developed with consideration of the supporting substrate and analytically solved for the temperature of each layer, showing that the in-plane and interfacial thermophysical properties can be simultaneously extracted by analytically fitting the multiple Raman-measured temperature curves of all the layers as a function of the incident laser spot radius and pulse duration, with no need of pre-knowing laser absorption. Theoretical analysis indicates high sensitivity of this method, which can be used to explore the interfacial effect in two-dimensional thermal transport and provide thermophysical data of van der Waals heterostructures in the device geometry.
9:00 PM - NM2.4.36
Breaking the Amorphous Limit to Reach Ultralow Thermal Conductivity by Nanostructuring
Yanguang Zhou 1
1 , AICES, RWTH-Aachen University, Aachen Germany
Show AbstractThermoelectrics offer an attractive pathway for addressing an important niche in the globally growing landscape of energy demand. Nanoengineering existing low-dimensional thermoelectric materials pertaining to realizing fundamentally low thermal conductivity has emerged as an efficient route to achieve high energy conversion performance for advanced thermoelectrics. The highest ZT of silicon-based structures is found to be around 1 experimentally, which is about 100 times larger than its bulk counterpart. This significant improvement of ZT of the silicon-based structures is found to be mainly related to decrease of the phonon thermal conductivity. Although the thermal conductivity of these structures is quite low, is still much larger than its amorphous limit. Meanwhile, silicon nanowires (NWs) and membranes (MBs) are two of the most popular candidates for obtaining the high figure of merit (ZT), which can be manufactured in experiments already. Here, by performing non-equilibrium and Green-Kubo equilibrium molecular dynamics simulations, we report that the thermal conductivity of Si NWs and MBs can go well below their amorphous limit by nanostructuring: introducing grain boundaries (GBs) in the structures, which are called polycrystalline form here. For the Si NWs in polycrystalline form, their thermal conductivity are found to reach a record low value substantially below the Casimir limit, a theory of diffusive boundary limit that regards the direction-averaged mean free path is limited by the characteristic size of the nanostructures. Such a low value is even only about 1/3 of the value of the purely amorphous Si NW at room temperature. For the polycrystalline Si-based MBs, the lowest thermal conductivity is only 1/2 of its amorphous limit as well. By examining the mode level phonon behaviors including phonon group velocities, lifetime etc., we identify the mechanism of breaking the Casimir limit as the strong localization of the middle and high frequency phonon modes, which leads to a prominent decrease of effective mean free path of the heat carriers including both propagons and diffusons for the structures with small grains, while for the structures with large grains, phonon-grain boundary scattering and phonon-twin scattering are corresponding to the significant decrease of thermal conductivity. Using such a strategy, we can achieve an extremely low thermal conductivity (only 1/3 of its amorphous limit) of Si NWs and MBs for structures with grain size of about 7.5 nm, which can be fabricated quite easily in experiments. Assuming the power factor as a constant, which may be achieved through doping and electron confinement, the ZT of the structures reported here can reach a value above 3 quite easily, which is thought as the value for industrial applications. Our investigation provides a deep insight into the thermal transport in polycrystalline structures and offers a promising strategy to construct thermoelectric materials with high ZT.
9:00 PM - NM2.4.37
Nonmonotonic Diameter Dependence of Thermal Conductivity of Extremely Thin Si Nanowires—Competition between Hydrodynamic Phonon Flow and Boundary Scattering
Yanguang Zhou 1
1 , ACIES, RWTH-Aachen University, Aachen Germany
Show AbstractHeat conduction in one-dimensional structures is one of the appealing fundamental thermal physics problems with enormous practical implications, for example Si nanowires (NWs) for solid-state thermoelectrics. Previous experiments have proved that the figure of merit (ZT) of Silicon nanowires (NWs) can be improved approximately 100 folders over its bulk counterpart, reaching a peak of 1 at 200 K. The significant reduction of the phonon thermal conductivity, which is caused by the strong phonon-boundary scattering, is found to be main reason for the huge improvement of ZT. Meanwhile, both experiments and theoretical models have well demonstrated that the thermal conductivity (κ) decreases with NW diameter (D) decreasing (dκ/dD 〉0), due to the enhanced phonon boundary scattering. However, when D continuously goes down to nanometer range, contradictory conclusions are drawn from previous studies even with the exactly same simulation method and model system, such as the κ~D dependence and the convergence vs. divergence of κ~length, a long debate of one-dimensional heat conduction in history. By carefully and systematically performing Green-Kubo equilibrium molecular dynamics simulations, we report that the κof Si NWs does not diverge, but converges and increases steeply when D becomes extremely small (dκ/dD 〈 0). The κ of the thinnest possible Si NWs reaches a super-high level that is as large as more than one order of magnitude higher than its bulk counterpart. The abnormally high κand the negative dκ/dD relationship can be explained in terms of the dominant normal (N) process (energy and momentum conversation) of low frequency acoustic phonons that induces hydrodynamic phonon flow in the Si NWs without being scattered. With D increasing, the downward shift of optical phonons triggers strong Umklapp (U) scattering with acoustic phonons and attenuates the N process, leading to the regime of phonon boundary scattering (dκ/dD 〉0). The two competing mechanism result in nonmonotonic diameter dependence of κ with minima at critical diameter of 2 – 3 nm. Our results unambiguously demonstrate the converged κand the clear trend of κ~ D for extremely thin Si NWs by fully elucidating the competition between the hydrodynamic phonon flow and phonon boundary scattering.
9:00 PM - NM2.4.38
Importance of the Hubbard Correction on the Thermal Conductivity Calculation of Strongly Correlated Materials—A Case Study of ZnO
Anthony Consiglio 1 , Zhiting Tian 1
1 , Virginia Tech, Blacksburg, Virginia, United States
Show AbstractThe wide bandgap semiconductor, ZnO, has gained interest recently as a promising option for use in power electronics such as thermoelectric and piezoelectric generators, as well as optoelectronic devices. Though much work has been done to improve its electronic properties, relatively little is known of its thermal transport properties with large variations in measured thermal conductivity. In this study, we examine the effects of a Hubbard corrected energy functional on the lattice thermal conductivity of wurtzite ZnO calculated using density functional theory and an iterative solution to the Boltzmann transport equation. Showing good agreement with existing experimental measurements, and with a detailed analysis of the mode-dependence and phonon properties, the results from this study highlight the importance of the Hubbard correction in calculations of thermal transport properties of materials with strongly correlated electron systems.
9:00 PM - NM2.4.40
Thermal Emission of Homogeneous Spheres—Regimes and Optimization
Khac Long Nguyen 1 , Olivier Merchiers 1 , Pierre-Olivier Chapuis 1
1 , CNRS - INSA Lyon, Villeurbanne France
Show AbstractThermal radiation of spheres is key to understanding radiative properties of more complex micro and nanostructures. Mie theory [1] considers wave diffraction and interferences, and is exact for all sphere radii. Thermal emission [2] depends on the material properties and is usually low for metals and high for dielectric spheres.
We first investigate the temperature and size dependencies of the thermal emission of spheres as a function of their dielectric properties. It is shown that the emitted power can depart strongly from the usual fourth power of temperature given by Planck’s law and from the square or the cube of the radius.
We also analyze thermal emission by selecting peculiar permittivities leading to resonances [3]. To do so, the spectral resonances of spheres are found by computing the emission as a function of the complex permittivity for different size parameters (radius over wavelength). Optimized dielectric functions are deduced for each radius by integrating over Planck’s spectrum and the contribution of each resonance to the total emissivity is investigated. Assuming that the dielectric permittivity is constant, we show that the electric dipole resonance provides a much larger total emission than the other Mie resonances due to its persistence over a large spectral range. This shows that non-interacting spheres with optimized properties are powerful thermal emitters.
[1] H.C. van de Hulst, Light Scattering by Small Particles, Dover (1981)
[2] M. Krüger et al., Phys. Rev. B 86, 115423 (2012)
[3] K.L. Nguyen et al., submitted (2016)
We acknowledge the support of the project EU FP7 QuantiHeat.
9:00 PM - NM2.4.41
Near-Field Thermal Radiation Exchanged by a Plasmonic Metal Particle and a Surrounding Bubble
Jerome Sarr 1 , Olivier Merchiers 1 , Pierre-Olivier Chapuis 1
1 , CNRS - INSA Lyon, Villeurbanne France
Show AbstractOptically-induced hyperthermia involving metallic nanoparticles is envisaged for local destruction of tumors. The principle is based on shining light onto metallic particles that heat quickly and then dissipate the energy into the surrounding medium. If the resulting medium temperature is larger than a threshold, cells located around the particles can be killed [1]. The determination of the local temperature is therefore crucial.
In these experiments, a bubble can be created around the nanoparticle, due to vaporization of water (main constituent of the human body). Precise determination of the energy exchange between the particle and the surrounding medium requires the detailed understanding of the different heat transfer mechanisms [2], among them thermal radiation from the sub-thermal wavelength gold particle (few tens of nanometers in diameter) to the nanobubble located in its near field. We compute the energy exchange by fluctuational electrodynamics and show that two effects enter into play: a reduction of thermal emission due to a decrease of the particle size, and an increase of the radiative transfer due to near-field effects. In particular, we provide the distance over which heat is absorbed in water, showing that the contributing depth is much smaller than expected from the skin depth of water.
[1] D. Lapotko, Cancers 3, 802 (2011)
[2] J. Lombard et al., Phys. Rev. E 91, 043007 (2015)
We thank S. Merabia for useful discussions.
9:00 PM - NM2.4.42
The Role of Low Energy Phonons in Nanocrystalline Si and SiGe—An Ab Initio Based Study
Lina Yang 1 , Austin Minnich 1
1 , California Institute of Technology, Pasadena, California, United States
Show AbstractNanocrystalline thermoelectric materials based on Si have long been of interest because Si is earth-abundant, inexpensive, and non-toxic. However, a poor understanding of phonon grain boundary scattering and its effect on thermal conductivity has impeded efforts to improve the thermoelectric figure of merit. Here, we report an ab-initio based computational study of thermal transport in nanocrystalline Si-based materials using a variance-reduced Monte Carlo method with the full phonon dispersion and intrinsic lifetimes from first-principles as input. Using transmission profiles following a recent experimental report by Hua et al. [arXiv:1509.07806], we obtain excellent agreement with experimental data [Wang et al. Nano Letters 11, 2206 (2011)]. Based on these calculations, we examine transport in nanocrystalline SiGe alloys with ab-initio electron-phonon scattering rates. Our calculations show that low energy phonons still transport substantial amounts of heat in these materials, despite scattering by electron-phonon interactions, due to the high transmission of phonons at grain boundaries, and thus improvements in ZT are still possible by disrupting these modes. This work demonstrates the important insights into phonon transport that can be obtained using ab-initio based Monte Carlo simulations in complex nanostructured materials.
9:00 PM - NM2.4.43
Mode-Resolved Transmission Coefficients for Thermal Phonons at Heterogeneous Interfaces Using Atomistic Green’s Functions
Benoit Latour 1 , Austin Minnich 1
1 , California Institute of Technology, Pasadena, California, United States
Show AbstractInterfaces with exceptionally large or small thermal resistance are desirable for applications, but the rational design of such interfaces remains an open challenge. Unlike light, for which the Fresnel equations allow the straightforward design of optical elements using angular-dependent reflection and transmission coefficients, the analogous properties for phonons are not readily available. In this work, we investigate phonon transmission and reflection at heterogeneous interfaces at the atomic scale, resolved by phonon mode, using a modal version of Atomistic Green's Functions. These results provide a detailed framework in which to interpret phonon transmission at interfaces in analogy with light propagation, thereby providing a foundation to design interfaces with extreme values of thermal resistance for thermoelectricity and heat management.
9:00 PM - NM2.4.44
Transient Thermal Conduction in Nanoscale Copper Architectures with Embedded Phase Change Material
Michael Barako 1 2 , Joseph Katz 2 , Srilakshmi Lingamneni 2 , Tanya Liu 2 , Kenneth Goodson 2 , Jesse Tice 1
1 , NG NEXT, Northrop Grumman, Redondo Beach, California, United States, 2 , Stanford University, Stanford, California, United States
Show AbstractPhase change materials (PCMs) can provide nearly isothermal heat storage to buffer the operating temperature in electronic devices subjected to transient high intensity heat generation. Much like their electrochemical analogues, an ideal thermal storage medium has both a high energy density (i.e. effective heat capacity) and a large power density (i.e. thermal conductivity). However, the low thermal conductivity of many common organic (e.g. long-chain hydrocarbons) and inorganic (e.g. inorganic salts) PCMs limits the rate of heat absorption and extraction, reduces the total accessible volume of PCM, and increases the superheat temperature at the device. By combining a materials-by-design approach [1] with the mathematical framework presented by Wei and Malen [2], we synthesize hierarchical metal nano-architectures infiltrated with organic PCMs as ultrafast microscale thermal capacitors. These nanostructured composites decouple the effective material properties such that heat conducts primarily through the metal phase and diffusion lengths are minimized in the more insulating PCM phase. We use templated electrodeposition to fabricate nanoscale copper architectures, including inverse opals and three-dimensional woodpiles, and infiltrate the porous volume with paraffin wax. We then measure the composite thermal conductivity and use electrothermal hotspot devices to characterize the transient thermal response under high-intensity heating in excess of ~1 kW cm-2. In the diffusive regime, the conduction physics is well-defined by the Stefan problem under an effective medium approximation. We further discuss the limiting performance of these composites as the geometric features are reduced to the nanoscale, which increases the interfacial surface area and decreases the diffusion lengths in the PCM, but sub-continuum transport inhibits conductive heat distribution.
[1] L. Montemayor, V. Chernow, and J. R. Greer, "Materials by design: Using architecture in material design to reach new property spaces," MRS Bulletin, vol. 40, pp. 1122-1129 (2015)
[2] L. C. Wei and J. A. Malen, "Amplified charge and discharge rates in phase change materials for energy storage using spatially-enhanced thermal conductivity," Applied Energy, vol. 181, pp. 224-231 (2016)
9:00 PM - NM2.4.45
Phonon Scattering Pathways in Complex Polymers Using Anharmonic Lattice Dynamics
Peishi Cheng 1 , Austin Minnich 1
1 , Caltech, Pasadena, California, United States
Show AbstractBulk polymers typically have poor thermal conductivity, but the intrinsic thermal conductivities of polymer chains and crystals can be very high, exceeding those of many metals. Recent measurements have shown that even semi-crystalline polymers with complex unit cells still achieve high thermal conductivity, contrary to the typical guidelines for effective thermal transport which prescribe a simple unit cell with a small number of atoms. In this work, we explore the thermal conductivity and three-phonon scattering pathways of polyethylene, polythiophene, and poly(p-phenylene benzobisthiazole) using molecular dynamics and anharmonic lattice dynamics. In particular, lattice dynamics allows us to separate the influences of scattering phase space and three-phonon interaction strength, as set by the anharmonic force constants, on the thermal resistance of these complex polymer crystals. Knowledge of the three-phonon scattering pathways aids in establishing molecular-scale design principles for thermally conductive polymers.
9:00 PM - NM2.4.46
Visible and Near Infrared Absorption Characteristics of Oxygen Deficient Strontium Titanate
Sofie Ravesteijn 1 , John Tomko 1 , Daniel Long 2 , Brian Foley 1 , Brian Donovan 3 , Elizabeth Dickey 2 , Patrick Hopkins 1
1 Mechanical and Aerospace Engineering, University of Virginia, Charlottesville, Virginia, United States, 2 Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina, United States, 3 Physics, United States Naval Academy, Annapolis, Maryland, United States
Show AbstractStrontium titanate is of great interest in the field of electronics due to its material properties in both pure and processed forms. While many studies have been done to characterize this material to a great extent, gaps in our knowledge still remain. In this work, we use a Spirit OPA laser to map the trap states of SrTiO3 annealed for different time scales in oxygen deficient environments. The output of the OPA laser can be tuned from ~300 nm – 16 microns, allowing for the examining of a wide range of energies in the absorption spectrum. This allows us to quantify the location of defect states, most likely caused by oxygen vacancies, that form both in the bandgap, and near the conduction and valence band edges. The transmission of light through the samples is measured using visible and IR sensitive photodetectors connected to Zurich Instruments lock-in amplifier, which increases our signal to noise by locking into the fundamental 1 MHz output of the Spirit laser. Our results demonstrate: 1) the presence of a variety of defect states in SrTiO3 and 2) a novel and simple approach to perform absorption measurements with high signal to noise while utilizing lock-in amplification.
9:00 PM - NM2.4.47
Universality of Temperature Scaling in Self-Heated Percolating Silver Nanowires Networks
Amr Mohammed 1 2 , Suprem Das 3 4 , Kerry Maize 2 , Sajia Sadeque 1 2 , Ali Shakouri 1 2 , David Janes 1 2 , Muhammad Alam 1 2
1 Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana, United States, 2 Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana, United States, 3 Mechanical Engineering, Iowa State University, Ames, Iowa, United States, 4 Division of Materials Science and Engineering, Ames Laboratory, Ames, Iowa, United States
Show AbstractThe technological importance of 2D materials (e.g., graphene, networks of carbon nanotubes (CNT), MoS2) has driven a great surge of research for the development of atomically thin electronic1 and sensing devices2. In turn, this has encouraged fundamental exploration of these systems in terms of their electrical, optical, thermal, chemical, and mechanical properties.
Linear response theory, generally believed to be the case during a typical electrical transport, may not fundamentally hold in such nano-architect active channel materials that practically operate in the nonlinear regime. In this regard, the 2D percolating networks have emerged as powerful testbeds for linear and nonlinear percolation models. It is perceived that nonlinear statistical response of these complex structures must be irreducibly complicated, beyond the simple scaling relationships offered by percolation theory. The limitation of experimental capabilities to record the spatial and temporal evolution of nonlinear responses in these systems has perpetuated this perception.
In this work, we use high-resolution thermoreflectance imaging to spatially probe the temperature rise due to self-heating in two types of 2D networks (percolating and co-percolating networks). We initially focused on understanding how the spatially averaged temperature of hot spots differs from the spatially-averaged temperature of the network3. The appreciation that self-focusing of current can correlate the average hot-spot temperature to the global current (namely, △T∝ Ib) led to the intriguing hypothesis that perhaps the entire spatially-resolved temperature distribution (not only the average) could be described by a scaling function.
Subsequently, we carried out a detailed and systematic investigation of the hypothesis by monitoring an electrical bias dependent self-heating of the network. This generalized analysis of the temperature distribution requires thermal imaging close to the noise limit, development of new image processing algorithm based on binary masking, and positive identification of the scaling function hidden in the data. The new algorithm allowed us to pursue a quantitative statistical data analysis of self-heating of nanowire networks. For the first time, we experimentally demonstrate a spatially-resolved, reversible nonlinear electro-thermal percolation transport in network structures4. Moreover, the self-heating hotspots were demonstrated to obey a universal scaling function with the bias current that follows a Weibull distribution. Finally, we show that the emergence of hotspot dynamics is spatially correlated; a mechanism attributed to the network self-heating being similar to the physics of crystallization.
1. Q. Cao et al. Nature, 454 (7203), 495 (2008)
2. Y. Cui et al. Science, 293 (5533),1289 (2001)
3. K. Maize et al., Appl. Phys.Lett., 106, 143104 (2015)
4. S. Das et al., Nano Lett., 16 (5), 3130 (2016)
Symposium Organizers
Aleksandr Chernatynskiy, Missouri University of Science and Technology
Pierre-Olivier Chapuis, Center for Energy and Thermal Sciences, CNRS - INSA Lyon
Kedar Hippalgaonkar, Nanyang Technological University
Austin Minnich, California Institute of Technology
NM2.5: Thermal Transport in 2D Materials II
Session Chairs
Wednesday AM, April 19, 2017
PCC West, 100 Level, Room 101 BC
9:00 AM - *NM2.5.01
Probing Energy Carrier Transport and Coupling in Low-Dimensional and Complex Structures
Li Shi 1
1 , The University of Texas at Austin, Austin, Texas, United States
Show AbstractCompared to silicon and other relativley simple crystal structures with approximatley isotropic transport properties, energy carrier transport in low-dimensional structures and complex crystals remains elusive. Progresses have been made recently in steady-state measurements of both the intrinsic thermal conductance and interface thermal resistance of low-dimensional structures. New insights have been obtained based on interpretation of the measurement results by first principles phonon transport calculation. It is discovered that flexure phonons make a large and small contribution to the thermal conductivity in flat graphene and puckered phosphorene, respectively, resulting in opposite thickness dependence of the basal plane thermal conductivity of multi-layer phosphorene compared to multi-layered suspended graphene. In the presence of surface disorders and surface scattering, a phonon focusing effect in anisotropic layered two-dimensional (2D) materials causes slow decrease of the basal-plane thermal conductivity with decreasing thickness. In comparison, phonon focusing can lead to further suppression of the phonon-boundary scattering mean free path when the fast group velocity axis is aligned with the radial direction of a nanowire. Besides this effect, the presence of very low lying optical modes and numerous diffusive modes result in glass-like thermal conductivity in nanoribbon structures of incommensurate higher manganese silicides (HMS). The very low-lying optical or pseudo-acoustic modes are a general feature of aperiodic crystals with weakly coupled incommensurate substructures, as shown clearly in inelastic neutron scattering measurements of the phonon and magnon dispersions in a spin ladder compound. In addition, it is demonstrated that focused laser beam heating and inelastic light scattering measurements can be used to generate local non-equilibrium between different energy carries in graphene and magnetic crystals, and to probe the relevant coupling length scales between different phonon polarizations and magnons.
9:30 AM - NM2.5.02
Thermal Switching with Collapsible Graphene Membranes
Michelle Chen 1 , Miguel Munoz-Rojo 1 , Feifei Lian 1 , Eric Pop 1
1 , Stanford University, Stanford, California, United States
Show AbstractSocietal challenges exist pertaining to energy consumption, waste, and efficiency. Because nanomaterials demonstrate physical properties which are unique compared to their bulk counterparts, these are of interest for various energy switching and storage applications. For example, thermal energy can be stored or manipulated via phase change, however solid-state mechanisms for manipulating heat are less explored.
In this work we propose a nanoelectromechanical (NEM) switch based on graphene, which can be used to control heat dissipation in nanoelectronics. Graphene is chosen for its extraordinary flexibility and thermal conductivity [1,2], and for its ease of integration with conventional microfabrication.Our device consists of few-layer graphene microribbons suspended over insulating pillars, with the graphene electrostatically switched to modulate heat flow across the device. In the off state, the graphene is suspended, inhibiting heat flow to the conducting substrate below. Under applied bias the graphene can be electrostatically deflected to contact the underlying substrate, forming vertical heat flow paths.
We present both analytic and finite element models of the thermal switch, showing that the material of the insulating pillars (which support the graphene) is essential in limiting the heat flow on/off ratio. For example, SiO2 pillars enable ~20% change in heat flow (between the on and off states), but porous alumina and aerogel pillars could increase the on/off thermal switch ratio by more than 2x, even after accounting for realistic thermal boundary resistance. Importantly, the suspended graphene is expected to switch within nanosecond time scales [3].
We also demonstrate the CMOS-compatible fabrication of a suspended graphene thermal switch. Devices are fabricated using sequential PMMA-assisted graphene transfers to create few (<10) layer stacks from CVD-grown graphene which are transferred onto SiO2 on Si. Graphene is plasma etched into arrays of ribbons, and Cr/Au contacts are deposited to define ribbon lengths up to 24 µm. The oxide is etched under the graphene, with the contacts masking portions of the oxide to form the insulating pillars. The suspended graphene ribbons are dried in a critical point dryer to prevent damage from liquid surface tension. We compare our simulations with thermal measurements using Raman and scanning thermal microscopy (SThM).
In summary, we introduce a novel thermal switch taking advantage of unique graphene properties. Such thermal switches show promise for damping or manipulating unexpected thermal transients, such as nanosecond temperature spikes for hotspot management.
[1] Lee et al., Science, 2008, 18, 385
[2] Pop et al., MRS Bulletin, 2012, 7, 1273
[3] Zhang et al., Appl. Phys. Lett., 2016, 108, 153103
9:45 AM - NM2.5.03
Thermal Transport Measurement of Sub-10 nm Single- and Bi-Layer Graphene Nanomesh Structures by Block Copolymer Lithography
Jinwoo Oh 1 2 , Dong Su Lee 1 , Myung-jong Kim 1 , Jeong Yun Kim 3 , Jong-Chan Lee 2 , Jeffrey Grossman 3 , Jeong Gon Son 1
1 , Korea Institute of Science and Technology, Seoul Korea (the Republic of), 2 , Seoul National University, Seoul Korea (the Republic of), 3 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractThe electrical bandgap and thermal/thermoelectric properties of nanostructured graphene are significantly different from those of pristine graphene. The thermal conductivity of the nanoscale graphene structure can be significantly suppressed by edge-phonon scattering at the massive edges of nanostructure. Also, the thermoelectric property of the nanoscale graphene structure can be changed as sub-10 nm quantum confinement and bandgap opening. However, the experimental measurements of thermal/thermoelectric transport of nanostructured graphene are not reported yet due to the difficulty of preparing and handling nanoscale graphene structures. In this study, we prepared centimeter-scale graphene nanomeshs (GNMs) with sub- 10 nm neck-width from the self-assembly of polystyrene-b-poly(vinyl-2-pridine) (PS-b-P2VP) block copolymer thin film on CVD-growth single- and bi-layer graphene. And we measured the thermal conductivity using optothermal Raman technique, the Seebeck coefficient, carrier concentration and mobility, and electrical bandgap from field effect transistor. Bi-layer graphene nanomeshes with 8 nm neck width showed remarkable thermal conductivity of 78 W/m-K and Seebeck coefficient of -520 μV/K because of quantum confinement and cross-plain coupling.
10:00 AM - NM2.5.04
Thermoelectric Measurements of Graphene Antidot Lattices on Boron Nitride
Qing Hao 1 , Dongchao Xu 1 , Ximena Ruden 1 , Brian LeRoy 1
1 , University of Arizona, Tucson, Arizona, United States
Show AbstractPristine graphene has a low thermoelectric performance due to its ultra-high thermal conductivity and zero band gap. To address this critical problem, various approaches have been explored to open a band gap in graphene. One of the most effective methods is patterning periodic nanoscale or sub-1-nm pores (antidots) across graphene, called graphene antidot lattices (GALs). In GALs, a geometry-dependent band gap can be opened up to dramatically increase the Seebeck coefficient. Antidots also strongly scatter the phonons, leading to a significantly reduced thermal conductivity. The combination of these two factors results in a high thermoelectric figure of merit (ZT), predicted to be around 1.0 at 300 K [1].
For real applications, it is more practical to study GALs on a substrate instead of being suspended. Along this line, hexagonal boron nitride (h-BN) is an appealing substrate because its atomically smooth surface is relatively free of dangling bonds and charge traps. The high carrier mobility found in pristine graphene can be kept in graphene devices on h-BN [2]. For GALs on h-BN, superior electrical conductivities have been observed [3,4]. However, the corresponding Seebeck coefficient and thermal conductivity are still missing for ZT evaluation.
In this work, we have measured all three thermoelectric properties (Seebeck coefficient, electric conductivity, and thermal conductivity) of GALs on a h-BN substrate. The GALs have periodic sub-20 nm pores defined by electron beam lithography, with sub-10 nm spacing between adjacent pores. The thermoelectric properties are further tuned with a gate voltage to maximize the ZT. Our work provides new insights into the thermoelectric performance of GALs or similar antidot lattices for two-dimensional materials.
References:
[1] Yan et al., Physics Letters A 376, 2425-2429 (2012).
[2] C.R. Dean et al., Nature Nanotechnology 5, 722-726 (2010).
[3] Sandner et al., Nano Lett. 15, 8402−8406 (2015).
[4] Yagi et al., Physical Review B 92, 195406 (2015).
10:15 AM - NM2.5.05
Thermal Boundary Conductance between Monolayer MoS2 and SiO2 via In Situ Raman Spectroscopy of Functioning MoS2 Transistors
Eilam Yalon 1 , Kirby Smithe 1 , Ozgur Aslan 5 1 4 , Connor McClellan 1 , Feng Xiong 2 1 , Yong Cheol Shin 3 1 , Aditya Sood 1 , Saurabh Suryavanshi 1 , Alex Gabourie 1 , Runjie Xu 1 , Christopher Neumann 1 , Kenneth Goodson 1 , Tony Heinz 1 4 , Eric Pop 1
1 , Stanford University, Stanford, California, United States, 5 , Columbia University, New York, New York, United States, 4 , SLAC National Accelerator Laboratory, Menlo Park, California, United States, 2 , University of Pittsburgh, Pittsburgh, Pennsylvania, United States, 3 Evaluation and Planning, Korea Institute of Science and Technology, Seoul Korea (the Republic of)
Show AbstractTwo-dimensional (2D) transition-metal dichalcogenides (TMDs) are technologically attractive materials for nanoelectronics, electro-optics, thermoelectrics and energy harvesting applications. In particular, the thermal properties of their interfaces, which dominate the energy dissipation rate in nanoscale devices are of great importance, though their experimental measurement is challenging.
In this study we use Raman thermometry to study the thermal boundary conductance (TBC) between monolayer (1L) MoS2 grown by chemical vapor deposition (CVD) and SiO2 for the first time, as well as comparing it with results on exfoliated MoS2. The use of Raman thermometry for 2D materials is advantageous primarily due to its material selectivity, which enables independent and simultaneous temperature measurement of all Raman-active materials in the path of the laser.
We carry out two thermometry experiments that differ by their input power mechanism: electrical (Joule heating) and optical (Raman laser heating). For electrical heating we use as-grown 1L MoS2 patterned into field-effect transistors on a SiO2 substrate with a Si back-gate [1]. This electrical heating experiment is carried out here for the first time on 1L TMD transistors, significantly reducing the uncertainty in the input power compared with optical heating. Furthermore, Joule heating allows for probing at low laser power, thus minimizing its interference with the temperature measurement.
We find that the TBC between 1L MoS2 and SiO2 is in the range of 10-20 MW/m2/K at room temperature for transistors with CVD-grown MoS2, as well as for control devices with exfoliated flakes. These TBC values are an order of magnitude higher than previous reports for transferred MoS2 [2,3], highlighting the higher quality of our interfaces. Our results are also consistent with molecular dynamics (MD) simulations of the MoS2-SiO2 thermal interface, which similarly consider an atomically intimate interface between the two materials.
In the optical heating experiment we adopt an approach that is analogous to the one described by [3] with several key modifications, including measuring and correcting for the temperature-dependent absorption and for Raman peak shifts due to photo-carriers generated at high optical input power. Compared to electrical heating, the laser heating experiment is useful for studying the effect of capping layers, ambient temperature dependence, and annealing treatment on the TBC of the MoS2 interface.
This study highlights the importance of combining electrical with optical measurements for more comprehensive Raman thermometry of nanoscale devices. Our findings are crucial for understanding and modeling of devices based on 2D materials, as well as their interfaces with the environment.
[1] E. Yalon, et al., IEEE Device Research Conf. (2016).
[2] X. Zhang, et al., ACS Appl. Mat. & Int. 7, 25923 (2015).
[3] J. Judek, et al., Sci. Rep. 5, 12422 (2015).
10:30 AM - NM2.5.06
Ballistic Phonon Conduction in Silicon Nanobeam Labyrinths
Woosung Park 1 , Joongyeub Yeo 1 , Ethan Ahn 2 , Takashi Kodama 1 , Joonsuk Park 1 , Michael Barako 1 , Joon Sohn 1 , Mehdi Asheghi 1 , Kenneth Goodson 1
1 , Stanford University, Stanford, California, United States, 2 Electrical and Computer Engineering, The University of Texas at San Antonio, San Antonio, Texas, United States
Show AbstractNanostructuring enables the manipulation of thermal transport properties of phonon-mediated materials since energy carriers predominantly interact with nanoscale features at length scales comparable to their mean free paths (MFPs). The impact of the increased phonon-boundary scattering depends on the relative orientation of boundaries/interfaces to the major direction of heat flow, where a key geometric feature is an unobstructed line-of-sight (LOS) for propagation through the material. The nanostructures can be categorized into two groups: one with boundaries parallel to the dominant direction of heat flow and the other with boundaries normal to the direction of heat flow. For the nanostructures with the boundaries parallel to the dominant direction of heat flow, such as nanowires, the LOS is typically much longer than the phonon MFPs along the direction of heat flow. For the nanostructures with boundaries that are oriented normal to the direction of heat flow, such as superlattices, the LOS is comparable to the phonon MFPs, where the impact of ballistic and even coherent scattering has been demonstrated. While much previous research has investigated the impact for each group separately, the interplay of these two types of interfaces in practical structures remains relatively poorly understood.
Here we demonstrate the impact of a tortuous path in silicon nanobeams featuring a controlled LOS between the heat source and heat sink. A key feature of these samples is the extreme difference between the tortuous path length and the LOS, which varies in ratio between 1 and 230. Modulation of the LOS cross-sectional area and other nanobeam dimensions allow a detailed study of the impact of phonons scattering on interfaces that are either aligned with, or perpendicular to, the direction of heat flow. Combining experiments and Boltzmann transport equation calculations, we show that the most tortuous path reduces the thermal conductivity up to ~14% from the straight beam to the labyrinths despite having identical cross-sections. We use Monte-Carlo method to simulate phonon transport at cryogenic temperature, which shows that the limited LOS causes significant resistance to phonon conduction. This study suggests that the length scale of the LOS is an important metric for characterizing and modulating phonon propagation in nanostructures.
NM2.6: Phononic Crystals
Session Chairs
Wednesday PM, April 19, 2017
PCC West, 100 Level, Room 101 BC
11:15 AM - *NM2.6.01
Thermal Transport in Si Phononic Crystals
Clivia Sotomayor-Torres 1 2 3 , Bartlomiej Graczikowski 1 , Francesc Alzina 1 , Marianna Sledzinska 1 , Emigdio Chavez-Angel 1 5 , Alexandros El Sachat 1 4 , Markus R. Wagner 6 , Yunhui Wu 7 , Sebastian Volz 7
1 , Catalan Institute of Nanocience and Nanotechnology ICN2, Bellaterra Spain, 2 , ICREA, Barcelona, Barcelona, Spain, 3 MNF, KTH Royal Institute of Technology, Kista Sweden, 5 Institute of Physics, JG University of Mainz, Mainz Germany, 4 Physics, Universidad Autonma de Barcelona, Bellaterra, Barcelona, Spain, 6 Institute of Solid State Physics, Technische Universität Berlin, Berlin Germany, 7 Laboratoire d’Energetique Moleculaire et Macroscopique et Combustion, CNRS, Centrale Supelec, Chatenay-Malabry France
Show AbstractThermal transport in free-standing silicon membranes has attracted increasing attention to advance the understanding of how the volume-to-surface ratio [1], phononic crystal periodicity, disorder [2] and air convection [1] impact on thermal phonon propagation. We will discuss the physical regimes under which the dominance of each and all of the above takes place.
Our experiments were performed over a range of 300 to 1000 K [1] in purpose-designed 2D phononic crystals in the form of free-standing membranes patterned by electron beam lithography and dry etching [3]. The band structure of 2D phononic crystals was calculated using FEM [4], the experimental methods include Brillouin scattering, pump-and-probe picosecond acoustics [2] and laser Raman thermometry [5].
A preliminary insight has been obtained from comparing holey phononic structures with a periodic solid perturbation on the membranes and solid-solid phononic crystals made out metallic cones periodically positioned on a membranes.
The key parameter is found to be in the surface to volume ratio, which is affected by air convection losses and by the shape of the necks of the phononic crystal design. Furthermore, the realisation of solid-solid phononic crystals points to the possibility to tailor multiple ways of storing and retrieving energy in these periodic oscillators when coupled to Lamb waves.
[1] B. Graczykowski et al, undergoing revision
[2] M. R. Wagner et al, Nano Letters 16 5661 (2016)
[3] M. Sledzinska et al., Microelectronic Eng, 149, 41 (2016)
[4] B. Graczykowski et al., Phys. Rev. B 91 075414 (2015)
[5] ] E. Chavez Angel et al., Appl. Phys. Lett. Materials 2 012113 (2014); J. S. Reparaz et al., Rev. Sci. Instruments 85 034901 (2014).
11:45 AM - NM2.6.02
Heat Focusing by Phononic Nanostructures
Roman Anufriev 1 , Aymeric Ramiere 1 , Jeremie Maire 1 , Masahiro Nomura 1
1 , The University of Tokyo, Meguro, Tokyo Japan
Show AbstractWe experimentally and theoretically demonstrate directional ballistic heat transport in phononic nanostructures and use this phenomenon for heat guiding and focusing.
First, using micro-TDTR experiments and Monte-Carlo simulations, we studied heat transport in silicon thin films with aligned and staggered periodic arrays of holes, and demonstrated that significant difference in thermal conductivity appears when the characteristic size of the structures becomes smaller than 100 nm. This difference is attributed to ballistic phonon transport in the structures with the aligned lattice.
Next, we demonstrated that these structures can act as a media that guides and as a source that emits ballistic phonons in solids. This emission was coupled into nanowires, where the ballistic path of the phonons was continued, and corresponding nanowire length and temperature dependencies were observed.
Finally, we used this concept to create thermal lens nanostructures which can focus thermal energy in the focal point. Our theoretical and experimental results suggest that the created hotspot is smaller than 200 nm in diameter, and thus can be used in biomedicine, thermoelectrics and wherever selective heating is required.
12:00 PM - *NM2.6.03
Coherent Modification of Thermal Properties Using Phononic Crystals
Yaolan Tian 1 , Tuomas Puurtinen 1 , Zhuoran Geng 1 , Ilari Maasilta 1
1 , University of Jyvaskyla, Jyvaskyla Finland
Show AbstractControlling thermal properties in the nanoscale has become more and more relevant in recent years, in light of the strong push to develop novel energy harvesting, dissipation management and sensing techniques [1]. A lot of research has lately focused on lowering phonon thermal conductivity using nanoscale structuring of materials to increase scattering. On the other hand, less attention has been given to controlling phonon thermal conductance and heat capacity coherently by engineering the phonon dispersion relations due to Bragg scattering or local resonances. Here, we discuss our recent experimental and computational advances in this line of approach for controlling thermal conduction [2,3] and heat capacity [4], using two-dimensional phononic crystals (PnCs) at sub-Kelvin temperatures.
In our initial study [2], we observed a strong reduction of thermal conductance up to a factor of 30, with a concurrent change in the temperature dependence, agreeing quantitatively with our numerical computation based on finite element method (FEM) simulations of the modified dispersion relations of 1- 2.4 µm period hole array PnC devices. Our further calculations [3] indicate that thermal conductance can be reduced much further with larger period arrays, or can even be increased by a factor ~3 with small period arrays. We have now confirmed the further reduction experimentally in larger 4- 8 µm period arrays, demonstrating the strange theoretical prediction [2,3] that larger periods with larger neck dimensions lead to smaller thermal conductance. However, by increasing the period to 16 µm, no further reduction was seen, and in fact, the thermal conduction increased above the 4µm period results. This indicates that the fully coherent picture starts to be destroyed at such length scales. Finally, we also numerically demonstrate how the holey 2D PnC structures act as thermal metamaterials in the low temperature limit.
[1] I. J. Maasilta and A. Minnich, Phys. Today 67, 285-290 (2014)
[2] N. Zen, T. A. Puurtinen, T. J. Isotalo, S. Chaudhuri, and I. J. Maasilta, Nat. Comm. 5, 3435 (2014).
[3] T. A. Puurtinen and I. J. Maasilta, Crystals 6, 72 (2016).
[4] T. A. Puurtinen and I. J. Maasilta, AIP Advances 6, 121902 (2016).
12:30 PM - NM2.6.04
Experimental Investigation of Phonon Coherence and Backscattering Using Silicon Nanomeshes
Jaeho Lee 1 3 , Woochul Lee 3 , Geoffrey Wehmeyer 2 , Scott Dhuey 3 , Deirdre Olynick 3 , Stefano Cabrini 3 , Chris Dames 2 , Jeffrey Urban 3 , Peidong Yang 2 3
1 , University of California, Irvine, Irvine, California, United States, 3 , Lawrence Berkeley National Laboratory, Berkeley, California, United States, 2 , University of California, Berkeley, Berkeley, California, United States
Show AbstractUnderstanding heat transport in nanostructures with dimensions scaling to the phonon mean free path and even to the phonon wavelength is a frontier challenge of solid state physics. While phonons can display both wave-like and particle-like behaviors, the dominant mechanism for thermal conductivity reductions in silicon nanostructures remains unclear and is often called into doubt. The interpretation has been greatly complicated by the coupled effects of phonon coherence, boundary scattering, backscattering, and contact resistance. Here, we isolate the wave-related coherence effects by comparing periodic and aperiodic nanomeshes, and quantify the particle-related backscattering effect by comparing variable-pitch nanomeshes. The lithographically-patterned silicon nanomeshes provide a unique opportunity for this progress because the relevant dimensions including the artificial periodicity, pitch, and neck were independently controlled within a monolithic measurement device. We measure identical (within 6% uncertainty) thermal conductivities for periodic and aperiodic nanomeshes of the same average pitch, and reduced thermal conductivities for nanomeshes with smaller pitches. Our simulations based on a ray tracing technique support the measurement results. We conclude phonon coherence is unimportant for thermal transport in silicon nanomeshes with periodicities of 100 nm and higher and temperatures above 14 K. In other words, the wave nature of phonons does not need to be considered to describe transport in the regime where periodicities are greater than the dominant wavelengths but smaller than inelastic mean free paths. We also conclude that phonon backscattering, as manifested in the classical size effect, is responsible for the thermal conductivity reduction in silicon nanomeshes. This work provides valuable insights for describing phonon transport in complex nanostructured geometries and improves a fundamental understanding of nanoscale heat transport that is critical for a broad range of semiconductor technologies.
12:45 PM - NM2.6.05
Understanding and Manipulating Coherent and Incoherent Phonon Transport in Multilayered Structures
Pranay Chakraborty 1 , Yan Wang 1
1 , University of Nevada, Reno, Reno, Nevada, United States
Show AbstractA better understanding of thermal transport in multilayered structures is beneficial for improving the figure of merit of thermoelectric materials or the thermal management of optoelectronic devices. Recent studies have suggested that the coexistence of coherent and incoherent phonon conduction in layered structures leads to several interesting features of thermal transport in superlattices (SL) and random multilayers (RML), for example, the nonmontonic dependence of thermal conductivity κ on period length of certain SLs,1 the almost linearly increasing κ with total length of short SLs,2 and the much lower κ of RML than the corresponding SLs.3 The coexistence of coherent and incoherent phonons imposes challenges to the evaluation of κ of multilayered structures from first-principles. Moreover, novel strategies for manipulating thermal transport in multilayered structures are possible based on the new understanding.
In this work, we first propose an approach based on the two-phonon model3 to evaluate the thermal conductivity of superlattices and random multilayers from first-principles. The coherent length Lc is used as a criteria to determine whether a coherent phonon or incoherent phonon mode can exist in the structure. Lc also determines the speed at which the κ of coherent phonons in RMLs decay with the total length of the RML. The thermal conductivity of all possible phonon modes are evaluated from first-principles. Then the summation of them renders the total thermal conductivity. Moreover, the length dependence of the κ of SLs and RMLs can be constructed from the scattering rates, group velocities, and specific heat of all possible phonon modes obtained from our first-principles calculations. This provides an effective way to evaluate the thermal conductivity of SLs and RMLs. Secondly, molecular dynamics simulations are conducted to calculate the thermal conductivity of multilayers with various thickness distributions, degrees of randomness in layer thickness, alloy profiles, lateral confinements, etc., to optimize the existing strategies for reducing κ, so that we can achieve the lowest possible κ for a specific pair of materials.
References:
1. Simkin, M. V.; Mahan, G. D., Minimum thermal conductivity of superlattices. Phys Rev Lett 2000, 84 (5), 927-30.
2. Luckyanova, M. N.; Garg, J.; Esfarjani, K.; Jandl, A.; Bulsara, M. T.; Schmidt, A. J.; Minnich, A. J.; Chen, S.; Dresselhaus, M. S.; Ren, Z.; Fitzgerald, E. A.; Chen, G., Coherent phonon heat conduction in superlattices. Science 2012, 338 (6109), 936-9.
3. Wang, Y.; Huang, H.; Ruan, X., Decomposition of coherent and incoherent phonon conduction in superlattices and random multilayers. Physical Review B 2014, 90 (16), 165406.
NM2.7: Phonons in Materials
Session Chairs
Wednesday PM, April 19, 2017
PCC West, 100 Level, Room 101 BC
2:30 PM - *NM2.7.01
Thermal Conduction in van der Waals Materials
Fan Yang 1 , Chen-ying Wu 1 , Ke Shen 2 , Sangwook Lee 1 , Huili Liu 1 , Yabin Chen 1 , Feiyu Kang 2 , Junqiao Wu 1
1 , University of California, Berkeley, Berkeley, California, United States, 2 , Tsinghua-Berkeley Shenzhen Institute, Shenzhen, Guangdong, China
Show AbstractWe experimentally investigate thermal conduction in layered materials such as MoS2, ReS2, graphene, black phosphorus, and black arsenic, where the layers were held together by van der Waals forces. It is expected that the thermal conductivity in the in-plane (covalently bonded) direction is much higher than cross-plane (van der Waals interaction). However, thermal conduction effects in these materials are more complex and interesting than this simple prediction. For example, the in-plane thermal conductivity may exhibit a strong anisotropy between the zigzag and armchair directions, owing to lattice orientation-dependent phonon group velocity and anharmonicity; the cross-plane thermal conductivity is a strong function of interlayer coupling and sample thickness. These effects shed light on thermal physics in low dimensions, and may find applications in thermoelectrics, thermal management as well as nonlinear thermal devices.
3:00 PM - NM2.7.02
Periodicity Dependent Heat Dissipation Efficiency in 2D Confined Nanoscale Heat Source Arrays
Nico Hernandez Charpak 1 , Travis Frazer 1 , Joshua Knobloch 1 , Begona Abbad Mayor 1 , Weilun Chao 2 , Kathleen Hoogeboom-Pot 1 , Damiano Nardi 1 , Margaret Murnane 1 , Henry Kapteyn 1
1 JILA, University of Colorado at Boulder, Boulder, Colorado, United States, 2 , Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractAs miniaturization is combined with complex materials, it enables critical technologies including thermoelectrics for energy harvesting, nanoparticle-mediated thermal therapy, nano-enhanced photovoltaics, and efficient thermal management in integrated circuits. All these applications require a comprehensive understanding of energy flow at the nanoscale. However, a complete, fundamental description of nanoscale thermal transport remains elusive. Although much progress has been done in new experimental approaches to access nanoscale thermal dynamics, theoretical efforts are still limited by a lack of experimental validation and still struggle to account for newly reported behaviors.
To study the heat dissipation away from nanoscale heat sources, we use a unique pump-probe setup, which directly observes nanoscale thermal and mechanical dynamics on their intrinsic time and length scales. Substrates of interest are coated with periodic arrays of nickel nanodots as small as 20nm in width, serving as confined heat sources. In our pump-probe experimental setup, the metallic structures absorb a 25-femtosecond infrared pump pulse, and the resulting thermal expansion and relaxation is probed by the diffraction of short (<20fs) pulses of coherent extreme ultraviolet (EUV) light created by tabletop high-order harmonic generation [1]. We monitor the diffraction efficiency of the short wavelength probe pulses as a function of pump-probe delay time, allowing us to monitor picometer-scale deformations in the surface profile with sub-picosecond temporal resolution.
Past experimental work has shown that Fourier’s law for heat conduction dramatically over-predicts the rate of heat dissipation from isolated, 1-D confined heat sources with dimensions smaller than the mean free path (MFP) of the dominant heat-carrying phonons [2]. More recent work has demonstrated that the spacing between the heat sources can also significantly change the heat dissipation efficiency [3]. We reported the direct observation of a new regime of nanoscale thermal transport that dominates in 1-D confined heat sources when the separation between nanoscale heat sources is small compared with the dominant phonon MFPs. In this case, close proximity between neighboring heat sources counteracts the reduction in heat dissipation efficiency usually observed for individual heat sources. .
Here, we present new direct experimental observation of heat dissipation away from 2-D confined heat source arrays on silicon, sapphire and fused silica substrates, all with varying periodicities. Furthermore, we analyze these experimental observations both with effective theories and using the Boltzmann transport equation to show how these experimental results can be used to probe the phonon spectrum of materials and compare with existing literature results.
1. Popmintchev et al., Science 336, 1287 (2012).
2. Siemens et al., Nature Mater. 9, 26 (2010).
3. Hoogeboom-Pot et al., PNAS doi:10.1073/pnas.1503449112 (2015).
3:15 PM - NM2.7.03
Ballistic Effects on Thermal Conductivity in 1D and 2D Configurations from Single and Multiple Localized Sub Mean Free Path Heat Sources—A Numerical Investigation
Elyes Nefzaoui 1 2 , Pierre-Olivier Chapuis 3
1 , ESIEE Paris, Noisy Le Grand Cedex France, 2 , Laboratoire ESYCOM (EA2552), Noisy Le Grand Cedex France, 3 , Centre for Energy and Thermal Sciences, CNRS, Lyon France
Show AbstractThe effective thermal conductivity of materials decreases when their dimensions are comparable to or lower than the mean free path of heat carriers (phonons in dielectrics) and when the influence of the thermal boundary conductance increases. Distinguishing the two phenomena is not experimentally straightforward, while the phonon Boltzmann transport equation (BTE) in the Relaxation Time Approximation (RTA) can be used to investigate this numerically. We solve a particular form of the BTE under the RTA, the Equation of Phonon Radiative Transfer, with the Discrete Ordinates Method (DOM) in one-dimensional and two-dimensional configurations for gray and non-gray media. The simulations give access to local effective temperature and conductive heat flux fields. We consider in particular the cross-plane and the in-plane thermal conductivities through 1D and 2D calculations, respectively. Diffuse, specular and diffuse-specular reflections of the heat carriers on the boundaries are implemented. The cases of extended and localized thermal sources are studied in 2D. Reduction factors associated to the effective thermal conductivities are obtained for the different cases and compared to the predictions based on the Fuchs-Sondheimer-Casimir-Ziman theory [1–4]. Constant temperature and adiabatic boundary conditions are also distinguished and their effects on the thermal transport are highlighted. Collective effects due to multiple localized heat sources are also considered. The competition between different characteristic length-scales (heat source size, distance between heat sources, sample size) is investigated. Finally, we discuss the obtained results in light of the recent thermo-optical and electrical experiments involving 2D heat spreading from sub-mean free path heat sources [5,6].
References:
[1] Fuchs K.., The conductivity of thin metallic films according to the electron theory of metals, Math. Proc. Camb. Philos. Soc. 34, 100 (1938)
[2] Sondheimer E.H., The mean free path of electrons in metals, Adv. Phys. 1, 1 (1952)
[3] Casimir H.B.G., Note on the conduction of heat in crystals, Physica 5, 495 (1938)
[4] Ziman J.M., Electrons and Phonons (Clarendon Press), 1960
[5] Hoogeboom-Pot K., et al., A new regime of nanoscale thermal transport: Collective diffusion increases dissipation efficiency, Proc. Natl. Acad. Sci. 112, 4846 (2015)
[6] Hu Y., et al., Spectral mapping of thermal conductivity through nanoscale ballistic transport, Nat. Nanotechnol., 10 , 701 (2015)
Acknowledgements: We acknowledge the support of the project EU-FP7-LARGE QuantiHeat. We thank C. Abs Da Cruz and D. Lemonnier for discussions.
NM2.8: Thermoelectrics and Compounds
Session Chairs
Wednesday PM, April 19, 2017
PCC West, 100 Level, Room 101 BC
4:30 PM - *NM2.8.01
Structural Variations in Thermoelectric Device Geometry for Low $/W and Wearable System
Woochul Kim 1
1 , Yonsei University, Seoul Korea (the Republic of)
Show AbstractWe propose a way to lower the $/W value, while maintaining a decent power output of a thermoelectric device by changing the device architecture. We demonstrated that the $/W value can be reduced to around 10% while maintaining ~65–70% of the maximum possible power output with a given zT. A proof of concept experiment is shown as well. The device architecture we proposed should be useful to recover low quality waste heat, which is abundant and could be harvested as long as the $/W value is low enough in general. Also, we present two types of wearable thermoelectric devices based on bulk inorganic materials; one is bracelet type and the other is mat style. Utilizing high performance that can be extracted from the bulk inorganic materials, the devices based on the materials are bendable and flexible. Performance of the device attached on a human body is compared with theoretical analysis based on a human thermoregulatory model.
5:00 PM - NM2.8.02
Modulation of Thermoelectric Properties of Carbon Nanomaterials
Masato Ohnishi 1 , Takashi Kodama 1 , Takuma Shiga 1 , Junichiro Shiomi 1
1 , The University of Tokyo, Tokyo Japan
Show AbstractRecently, much effort has been made to apply carbon nanotubes (CNTs) to flexible thermoelectric devices. Because high thermoelectric performance of CNT-based networks are generated at intertube junctions between CNTs in the network, previous studies have been mainly focusing on thermoelectric properties of the intertube junctions. However, fluctuation or modulation of thermoelectric properties of individual CNTs due to internal and external factors, e.g. defects, deformation, molecular encapsulation, etc., also affect that of CNT networks. For example, the introduction of defects causes the fluctuation of both of thermal and electronic transport properties of CNTs, leading to complicated change in thermoelectric properties of CNT networks as well as individual CNTs. Furthermore, recent studies have revealed that the encapsulation of molecules such as fullerenes in CNTs modifies thermoelectric properties of CNTs. We, therefore, theoretically studied effects of crystal disorder such as deformation or interaction between outer SWNTs and encapsulated molecules using nonequilibrium molecular dynamics simulation and Green’s function approach. We revealed that while the introduction of defects deteriorate thermoelectric properties of CNT networks significantly, the molecular encapsulation can improve both electron and thermal transport properties of CNTs. While the introduction of defects can increase Seebeck coefficient by a few factors, electron conductance decreases by orders of magnitude with presumable defect concentrations and, thus, overwhelms the increase in Seebeck coefficient. The estimation of thermoelectric properties of CNT networks also revealed that this significant decrease of electron conductance also leads to the deterioration of their thermoelectric properties as well as individual CNTs. Furthermore, while previous theoretical studies have claimed that the molecular encapsulation of CNTs increases their thermal conductivity, we found that the fullerene encapsulation decreases thermal conductivity and increases Seebeck coefficient without the reduction of electrical conductivity. Our findings pave the way to control thermal and electrical properties of CNTs.
5:15 PM - NM2.8.03
Solution-Phase Processing Routes to Metal Chalcogenide Thermoelectric Thin Films
Yuanyu Ma 1 , Zhongyong Wang 1 , Prathamesh Vartak 1 , Prajwal Nagaraj 1 , Robert Wang 1
1 , Arizona State University, Tempe, Arizona, United States
Show AbstractSolution-phase processing routes to thermoelectric materials have the potential to decrease costs and enable novel device architectures. The best thermoelectric materials are crystalline inorganic semiconductors, which makes finding solution-phase routes to these materials of high interest. Unfortunately, inorganic semiconductors are generally insoluble due to their strong covalent bonds. One way around this hurdle is to create soluble semiconductor precursors that can be transformed into crystalline semiconductors after deposition.
We present our work on soluble semiconductor precursors for Cu2-xSeyS1-y and Ag-doped Cu2-xSeyS1-y, as well as our preliminary efforts on other thermoelectric metal chalcogenides (e.g. Bi2X3, PbX, SnX, etc. where X = S, Se, or Te). For our Cu2-xSeyS1-y materials, we study the effect of Cu vacancies, Se:S ratio, and Ag-doping on the room temperature thermoelectric performance. Importantly, we find that Ag-doping leads to appreciable improvements in thermoelectric performance by increasing Seebeck coefficient and decreasing thermal conductivity, while having little to no change in electrical conductivity. Overall, we find that the room temperature thermoelectric properties of these solution-processed materials are comparable to measurements on Cu2-xSe alloys made via conventional thermoelectric material processing methods. Achieving parity between solution-phase processing and conventional processing is an important milestone and demonstrates the promise of this approach to making thermoelectric materials.
5:30 PM - NM2.8.04
Effect of the High-Pressure Spin Transition in Mg-Fe-O System on Thermal Conductivity
Aleksandr Chernatynskiy 1
1 , Missouri University of Science and Technology, Rolla, Missouri, United States
Show AbstractIn this work we elucidate the effect of the spin transition on the thermal transport in ferropericlase (MgxFe1-xO) from ab-initio calculations. Ferropericlase is one of the common materials in the Earth interior and in the condition of the Earth interior, namely at elevated pressure, iron atoms substituted into the MgO rocksalt lattice experience transition from a high spin state to a low spin state. Previous work has demonstrated that account of the phonon scattering on the electronic states is important in describing thermal transport in this material at normal conditions, but no investigations have been reported at the high pressure. The spin transition itself is not sharp, and it is accompanied by a volume change, which also affects thermal conductivity. Here we report our results for lattice thermal conductivity in ferropericlase from the accurate solution of the Boltzmann Transport Equation for phonons using DFT calculations as an input. We account for impurity scattering via Virtual Crystal Approximations and take into account the effect of the electron-phonon interactions across the spin transition. Results of this work can have implications for the conditions in the Earth interior.
5:45 PM - NM2.8.05
Magnetic Martensitic Transformation and Thermal Transport in Mn1+xMGe (M = Co, Ni)
Qiye Zheng 1 , Shannon Murray 1 , Paul Braun 1 , Daniel Shoemaker 1 , David Cahill 1
1 , University of Illinois at Urbana-Champaign, Champaign, Illinois, United States
Show AbstractHeat transfer is a critical issue in almost all engineering systems, but current capabilities for the control of thermal transport are limited to the convective heat transfer by fluids and gases with low energy efficiency. Developing thermal management materials for heat dissipation and energy conversion is a fundamental step to improve the performance and efficiency of systems such as high power electronics, batteries and vehicles engines. One type of target materials is the so called “thermal switches”, i.e., materials that switch between roles of good thermal conductors and good thermal insulators as needed. Specifically, materials that could display a high contrast and reversible change in thermal conductivity near room temperature, passively controlled by temperature, would be useful for a lot of applications. Here, we report the temperature dependence of the thermal conductivity in Mn1+xMGe (M = Co, Ni) from 300 to 600 K during thermally induced magnetic and martensitic phase transition. A change of ≈8 to ≈12.5 W/mK in thermal conductivity is observed from 500 to 550 K in MnNiGe which is comparable with the 60% change of thermal in VO2 induced by the metal insulator transition. In contrast, a smaller change of ≈7 to ≈8 is found in MnCoGe near 500 K. The thermal conductivity change is strongly related to the martensitic structure transition between orthorhombic phase to hexagonal phase as confirmed by the in-situ XRD measurement. The transition temperature and thermal conductivity behavior could be effectively changed by the variation of stoichiometry and doping to meet the requirement of thermal management application.
NM2.9: Poster Session II: Heat Transport at the Nanoscale
Session Chairs
Thursday AM, April 20, 2017
Sheraton, Third Level, Phoenix Ballroom
9:00 PM - NM2.9.01
Interfacial Thermal Transport across Graphene and Organic Semiconductor
Xinyu Wang 1 , Jingchao Zhang 2 , Yue Chen 1 , Paddy K. L. Chan 1
1 , The University of Hong Kong, Hong Kong Hong Kong, 2 , University of Nebraska-Lincoln, Lincoln, Nebraska, United States
Show AbstractDue to the unique electrical and thermal properties, graphene has been widely used in the active layers or electrodes of organic electronic devices. In these devices, the energy transfer at the interfaces between the graphene and organic semiconductors are playing a critical role in the device performance and lifetime. In this study, we focus on investigating the heat transfer across the interface between graphene and small molecule organic semiconductor, dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DNTT) by classical molecular dynamics (MD). In MD simulation, an ultrafast heat pulse is imposed on the graphene, and by monitoring the energy and temperature variation of graphene and DNTT the thermal boundary resistance (TBR) values can be evaluated. Based on the simulation results, the thickness of DNTT and cross-sectional area of the graphene has no direct relationship to TBR. The TBR values of graphene and vertical stacking direction of DNTT (c-direction) is 5.23±0.51×10-8 m2-K/W, slightly smaller than interface between graphene and other two principle directions of DNTT. This is attributed to the molecule disorder at the interface of DNTT a-direction and the smaller phonon mean free path and speed of sound of DNTT b-direction. By changing the coupling strength of van Waals force at the interface from 1 to 3, the TBR decreases 45.2%, 55% and 69.8% for the interfaces between graphene and DNTT a, b, or c-directions, respectively. In addition, the temperature dependence of TBR is investigated from 100 K to 600 K. The TBR results shows a monotonous drop trend as higher frequency phonon will be excited and the stronger Umklapp scattering enhance the interfacial thermal transport. We also further investigate the vacancy effects of both graphene and DNTT. Although there is no significant effect on TBR by changing the DNTT vacancy concentration from 0% to 6.25%, the TBR between graphene and DNTT c-direction will reduce 5.23±0.51×10-8 m2-K/W to 3.37±0.26×10-8 m2-K/W when the graphene vacancy concentration increases from 0% to 5.95%. The phonon density of state (DOS) is analyzed to interpret the effect of vacancy on TBR. Our investigation about the interfacial thermal transport between graphene and organic semiconductors provides the fundamental knowledge to design and development of graphene based organic semiconductors.
9:00 PM - NM2.9.02
Monitoring Heat Dissipation from Gold Nanorods to the Ambient Water through Conjugated Ligands with Atomic Resolution
Yuexiang Yan 1 , Yee Kan Koh 1
1 , National University of Singapore, Singapore Singapore
Show AbstractDetailed knowledge of how heat is transported at atomic scale, e.g., across molecular junctions and solid/liquid interfaces, is crucial for emerging applications such as photothermal cancer therapy and organic-inorganic hybrid thermoelectric materials. Despite the importance, fundamental knowledge of heat transport at atomic scale is still limited, due to challenges to experimentally probe heat transport with atomic resolution. In this talk, we present our novel approach to monitor the picosecond-resolved temperature evolution at multiple locations along molecular chains (i.e., 4-Nitrothiolphenol and 4-Aminothiolphenol) conjugated to gold nanorods suspended in water, after the gold nanorods are heated by ultrafast laser pulses. We integrate two pump-probe techniques, the picosecond transient absorption and time-resolved Raman spectroscopy, to concurrently monitor heating and cooling of gold nanorods and bonds in the conjugated ligands.
Using this novel technique, we derive unprecedented details on atomic-scale heat transfer. We find that the bonds in the conjugated ligands are heated almost instantaneously and reach a peak temperature within ~1 ps after heating by the laser pulses. This fast heating cannot be accomplished by transmission of acoustic phonons (i.e., vibrations) across the Au-thiol bond, as commonly believed. We attribute the fast heating of the bonds to direct heating of the bonds either by hot electrons that diffuse across the Au-thiol heterojunction, or remote electron-phonon coupling at the Au-thiol interfaces as a result of extension of electron wavefunctions into the ligands. For the cooling of the bonds, we found that the bonds cool a lot faster than the gold nanorods, with a relaxation time of only ~3 ps (vs 300 ps for the gold nanorods). This indicates that coupling of the ligands to water is a lot stronger than coupling of Au-thiol heterojunctions. From our measurements, we roughly estimate that the thermal conductance of Au-thiol heterojunctions and ligand/water interfaces is 61 and 356 MW m-2 K-1 respectively.
9:00 PM - NM2.9.03
A Novel Phonon Monte Carlo Simulator for Calculating Thermal Conductivities
Abdul Shaik 1 , Dragica Vasileska 1
1 ECEE, Arizona State University, Tempe, Arizona, United States
Show AbstractA state of the art Monte Carlo device simulator has been developed to study the thermal conductivity of bulk materials. Our novel approach differs from previous studies in simulating the scattering of phonons. Phonons are allowed to undergo normal and umklapp scattering; the final state after scattering is calculated based on energy conservation and net momentum conservation by at most a unit reciprocal lattice vector. The scattering rates are verified by obtaining the phonon distribution at thermal equilibrium at a constant temperature and comparing it to Bose-Einstein statistics. The phonon distribution obtained with our method is used to study the quasi-equilibrium distribution for different applied temperature gradients. The phonon Monte Carlo solver is tested for thermal equilibrium between thermally connected bodies at different temperatures.
9:00 PM - NM2.9.04
Intrinsic Localized Mode and Low Thermal Conductivity of PbSe
Nina Shulumba 1 , Olle Hellman 1 , Austin Minnich 1
1 Division of Engineering and Applied Science, California Institute of Technology, Pasadena, California, United States
Show AbstractLead chalcogenides such as PbS, PbSe, and PbTe are of interest for their exceptional thermoelectric properties and strongly anharmonic lattice dynamics. Although PbTe has received the most attention, PbSe has a lower thermal conductivity despite being stiffer, a trend that prior first-principles calculations have not reproduced. Here, we use ab-initio calculations that explicitly account for strong anharmonicity to identify the origin of this low thermal conductivity as an anomalously large anharmonic interaction, exceeding in strength that in PbTe, between the transverse optic and longitudinal acoustic branches. The strong anharmonicity is reflected in the striking observation of an intrinsic localized mode that forms in the acoustic frequencies. Our work shows the deep insights into thermal phonons that can be obtained from ab-initio calculations that are not confined to the weak limit of anharmonicity.
9:00 PM - NM2.9.05
Phonon Heat Conduction under Large Thermal Gradient in Optically Heated Nanoline Arrays
Xiangwen Chen 1 , Chengyun Hua 2 1 , Hang Zhang 3 , Navaneetha Krishnan Ravichandran 1 , Austin Minnich 1
1 , California Institute of Technology, Pasadena, California, United States, 2 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 3 Institute of Engineering Thermophysics, Chinese Academy of Sciences, Beijing China
Show AbstractQuasiballistic heat conduction, in which thermal gradients occur over length scales comparable to mean free paths (MFPs), is of intense interest due to the failure of Fourier's law and the associated consequences for heat transport. While the diffusion and fully ballistic regimes have been extensively studied, much of the quasiballistic regime has yet to be explored due to the lack of sufficiently large thermal gradients employed in prior studies. Here, we report an experimental study of quasiballistic heat conduction under very large thermal gradients generated by optical heating of nanoline arrays maintained at cryogenic temperatures. Using a model based on the Boltzmann equation, we show that the observations can be simply interpreted based on the spatial frequencies of the heating pattern set by the nanoline geometry. Interestingly, our measurements clearly show that heat dissipation is only minimally impeded from the nanolines despite their nanoscale dimensions. Our work has important implications for heat dissipation in microelectronic devices and other applications.
9:00 PM - NM2.9.06
Thermal Measurements of Nanoporous In0.1Ga0.9N Thin Films Directly Grown by Metalorganic Chemical Vapor Deposition
Dongchao Xu 1 , Junda Yan 2 , Xuewang Wu 3 , Jie Zhu 3 , Hongbo Zhao 1 , Xiaojia Wang 3 , Xiaoliang Wang 2 , Qing Hao 1
1 , University of Arizona, Tucson, Arizona, United States, 2 Key Lab of Semiconductor Materials Science Institute of Semiconductors, Chinese Academy of Sciences, Beijing, Beijing, China, 3 Department of Mechanical Engineering, University of Minnesota, Minneapolis, Minnesota, United States
Show AbstractIn recent year, nanoporous Si thin films have been widely studied for their potential applications in thermoelectrics, in which a high thermoelectric figure of merit (ZT) can be obtained by combining both the dramatically reduced lattice thermal conductivity and bulk-like electrical properties [1,2]. Using the focused ion beam or reactive ion etching, down to ~10 nm nanopores can be drilled on a Si film to enhance its ZT. Along this line, a high ZT is also anticipated for other nanoporous thin films whose bulk counterparts have superior electrical properties but high lattice thermal conductivities.
In this work, the cross-plane thermal conductivities of nanoporous In0.1Ga0.9N thin films with varied porous patterns are measured with the time-domain thermoreflectance technique. These alloys are suggested to have better electrical properties than conventional SiGe alloys but a high ZT is hindered by the intrinsically high lattice thermal conductivity [3], which can be addressed by introducing nanopores to scatter phonons. Based on the results, the thermal conductivity of a thin film can be remarkably reduced by 300-nm-diameter pores with varying periods. Our studies provide important guidance for ZT enhancement in general nitrides and similar oxides.
References:
[1] Marconnet et al., Journal of Heat Transfer 135, 061601-1/10 (2013).
[2] Cahill et al., Applied Physics Reviews 1, 011305 (2014).
[3] Lu et al., Semicond. Sci. Technol. 28, 074023 (2013).
9:00 PM - NM2.9.07
Thermal Conductivities of Epitaxial Al-Doped and ZnO Thin Films Deposited by Magnetron Sputtering
Kaho Honda 1 , Yuichiro Yamashita 2 , Junjun Jia 1 , Takashi Yagi 2 , Shin-ichi Nakamura 2 , Naoyuki Taketoshi 2 , Yuzo Shigesato 1
1 , Aoyama Gakuin Univ, Kanagawa Japan, 2 National Metrology Institute of Japan (NMIJ), National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki, Japan
Show AbstractAl-doped ZnO (AZO) is an alternative transparent electrode material for Sn doped In2O3 because of its high electrical conductivity and transparency. Considering the heat dissipation from electrical consumption, the thermal design of electronic devices such as organic light emitting diodes becomes of critical importance, and the reliable thermophysical property data are required [1]. We have reported the thermal conductivity of polycrystalline AZO film deposited on synthetic silica substrates by magnetron sputtering in the previous report [2]. In this study, the thermal conductivities of epitaxial AZO films with c-axis orientation were investigated.
AZO films with a thickness of 200 nm were deposited on c-plane sapphire substrate by dc magnetron sputtering using a AZO target (Al2O3: 3 wt.%). Argon was used as the sputtering gas, and O2 was used as the reactive gas. The O2 flow ratio was varied from 0 to 1.5%. The non-doped ZnO film was fabricated on the c-plane sapphire substrates by rf magnetron sputtering using a ZnO target. From the XRD analysis, it was confirmed that all AZO films with c-axis orientation grew on c-plane sapphire substrate. From the X-ray pole figures, the six-fold symmetry spots ((10 1) plane) were clearly seen for AZO and ZnO films, indicating the epitaxial growth.
The thermal conductivity was analyzed using a front heating/front detection type picosecond pulsed light heating thermoreflectance system. The thermal conductivities of the epitaxial AZO films increased from 3.7 to 5.7 W m-1 K-1 with the decreasing the O2 flow ratio. The increase in thermal conductivity was proportional to electrical conductivity of epitaxial AZO films. We also compared the thermal conductivity of the epitaxial ZnO film with ones of epitaxial AZO films. The estimated phonon thermal conductivities of epitaxial AZO films were much smaller than thermal conductivities of the epitaxial ZnO films, which suggested that Al dopant of AZO might be a dominant phonon scattering source. Furthermore, the effect of grain boundary on phonon thermal conductivity was also discussed in the poster presentation.
[1] T. Ashida, K. Kimura, N. Oka, Y. Sato, T. Yagi, N. Taketoshi, T. Baba, and Y. Shigesato, J. Appl. Phys. 105, 073709 (2009).
[2] N. Oka, K. Kimura, T. Yagi, N. Taketoshi, T. Baba, and Y. Shigesato, J. Appl. Phys. 111, 093701 (2012).
9:00 PM - NM2.9.08
Influence of a nm-Sized Metallic Interlayer on Metal-Dielectric Thermal Boundary Conductance
Maite Blank 1 , Ludger Weber 1
1 , EPFL, Lausanne Switzerland
Show AbstractUnderstanding the phenomena influencing Thermal Boundary Conductance (TBC) between dissimilar materials is of prior importance in the quest for proper heat management in micro- and nano- devices. In an attempt to reach this goal, studies carried out during the last decade highlighted several parameters, which are important for nanoscale heat transport. Among others, bond strength and acoustic mismatch were found to be particularly important.
Taking advantage of this knowledge, several groups assessed the influence of a nanometric metallic interlayer with properties bridging those of the substrate and the metallic film. As a result, it was found that such layers strongly enhance TBC even if they are very thin (<1nm) and exhibit an increasing trend as the layer becomes thicker. Although several hypotheses were proposed to explain this evolution, it was always assumed that the interdiffusion between the main metallic film and the intermediate film is zero. In systems in which the two metals have a given solubility, this assumption is however not necessarily true. In the case of very thin intermediate films, this phenomenon is important because a film that is thought to be pure, might instead be an alloy and thus have properties others than the ones expected.
In this framework Ag/(nm-)Ni/Diamond and Au/(nm-)Ni/Diam systems are studied. The first system was chosen because Ag and Ni have very limited solubility and Ni has a strong tendency to segregate to grain boundaries of interfaces in silver. It should thus enable highlighting the effect of a very thin pure Ni interlayer on Ag/Diam TBC. The second system was selected because some amount of Ni can be dissolved in Au (and vice versa). It should thus provide some information on additional effects related to intermixing between Au and Ni. In particular, the electron-phonon coupling in the thin interlayer might be increased by the presence of alloying elements in solid solution
The evolution of the TBC at the interface is determined experimentally using Time Domain Thermoreflectance (TDTR) and structural features of the interface are characterized by Transmission Electron Microscopy (TEM).
9:00 PM - NM2.9.09
Four-Phonon Scattering Phase Space in Anharmonic Semiconductor Crystals
Navaneetha Krishnan Ravichandran 1 , David Broido 1
1 Physics, Boston College, Chestnut Hill, Massachusetts, United States
Show AbstractThe intrinsic lattice thermal conductivity, kL, of semiconductors and insulators is limited by phonon-phonon scattering caused by the anharmonicity in the crystal potential. In many such materials, calculations including only the lowest order anharmonic processes involving three phonons are sufficient in accurately reproducing the measured kL. However, in anharmonic materials such as those used for thermoelectric applications and those at high temperature, higher-order phonon-phonon scattering can become important [1, 2]. Furthermore, recent first principles calculations considering only three-phonon scattering have predicted that the kL of cubic boron arsenide (BAs) is exceptionally high, comparable to that of diamond. This is due to the small phase space for three-phonon scattering in BAs. The weak three-phonon interactions in BAs raise the question of whether four-phonon scattering could offer the dominant thermal resistance. As a first step towards understanding the effect of four-phonon processes on the lattice thermal conductivity in BAs, we present first principles calculations of its four-phonon phase space and compare it to results for other compounds such as silicon and diamond. We consider the different types of energy and momentum conserving four phonon processes correct to first and second orders in perturbation theory to assess the dominant four-phonon scattering channels in BAs relative to those in other compounds. We also compare the four-phonon scattering phase space to the three-phonon phase space in the studied compounds. Our work will inform the accurate evaluation of four-phonon scattering rates, which could affect the thermal conductivity of BAs and other semiconductor materials beyond that determined from considering only three-phonon interactions.
[1] D. J. Ecsedy and P. G. Klemens, Phys. Rev. B 15, 5957 (1977).
[2] Tianli Feng and Xiulin Ruan, Phys. Rev. B 93, 045202 (2016).
9:00 PM - NM2.9.10
Spherical and Cylindrical Pores with Amorphous Shells, Impact on the Thermal Transport
Konstantinos Termentzidis 1 , Maxime Verdier 2 , David Lacroix 2
1 , CNRS, Vandoeuvre les Nancy France, 2 Un. Lorraine, LEMTA, Nancy France
Show AbstractWith the rapid development of materials’ elaboration techniques, one can produce easily and controllably low dimensional nanostructures and nanostructured materials. Several emerging fields are based on this capacity and today the question is how to manipulate with precision the energy carrier transport in them. Thermal management at the nanoscale, efficient thermoelectric devices, information and communication technologies, and several other applications are seeking insights of the transport of phonons and electrons.
During the last two decades nanoporous materials have undergone important development. The synthesis methods are quite advanced today to produce uniform diameters and shapes with controllable pore size distribution as well as spatial dispersion of pores. The majority of the nanoporous materials contain amorphous phase and interfaces between the amorphous and the crystalline phases. Both affect the transport of phonons, thus the thermal conductivity in such nanostructured materials. The impact of the amorphous shells around the pores started recently to interest the scientific community.
In this theoretical work, we report results obtained with Molecular Dynamics Simulations on the impact of the amorphous shells around spherical and cylindrical pores. Two amorphous shells are modeled: a-Si and a-SiO2. The impact of amorphous silica is much more pronounced compared to amorphous silicon. A small fraction of amorphous shells can reduce the thermal conductivity to values inferior to the bulk amorphous silicon or silica. Physical insights will be presented with the use of the phonon density of states. Combined results show that there are two key parameters which control the thermal transport in nanoporous materials: the non-crystalline fraction and the total surface of interfaces between crystalline and amorphous phase to volume ratio.
9:00 PM - NM2.9.11
An Ultrathin Heat Pipe Based on Hierarchical Micro/Nanostructures for Electronic Cooling
Ramesh Shrestha 1 , Eugene Yu 1 , Sheng Shen 1
1 , Carnegie Mellon University, Pittsburgh, Pennsylvania, United States
Show AbstractWith increasing power densities, wearable electronic devices, cell phones, laptops and ultra-books require highly efficient heat rejection technologies. Micro heat pipes can be an effective solution for heat dissipation in these thin and flexible electronic devices. Here we report a large scale and low cost fabrication of an ultra-thin heat pipe (< 500 µm). In a heat pipe, one of the main components is its wick structure. For a high performance heat pipe, the wick structure should have large capillary pressure and large permeability. Smaller pore radius of a micro structure, for example, a pyramid or a pillar on the wick structure, increases the capillary pressure. However, it simultaneously decreases the permeability. In addition, increasing the hydrophilicity of the wick surface also increases the capillary pressure. We have developed a large scale and low cost technique to fabricate hierarchical micro/nanostructures on an electroplated copper surface with <5 ° contact angle. A systematic study on different pore radius of the hierarchical micro/nanostructure was also conducted to achieve optimized capillary pressure and permeability. Preliminary study of water on the wick surface using a high speed camera shows a very high proceeding speed up to 20 mm/s at a distance of a few millimeters.
9:00 PM - NM2.9.12
Size Dependent Thermal Conductivity of Single-Wall Carbon Nanotubes from Molecular Dynamics Simulations
William Yorgason 1 , Nicholas Roberts 1
1 Mechanical & Aerospace Engineering, Utah State University, Logan, Utah, United States
Show AbstractExtensive research has been done on the lattice thermal conductivity (kp) of single-wall carbon nanotubes (SWCNT), both experimentally and by use of molecular dynamics simulations. However, the research on the effects of the physical size of SWCNT on kp is lacking. The following simulations were performed using LAMMPS molecular dynamics software in order to observe the kp of SWCNT at varying lengths and diameters. The nonequilibrium molecular dynamics (NEMD) method was employed to allow the SWCNT to equilibrate before computing kp. The kp for three lengths and two diameters have been recorded, each case having results for temperatures ranging from 50 K to 500 K. For example, at 50 K, the kp for SWCNT of lengths 25, 100, and 200 nm were 1,169.883, 14,308.994, and 49,395.201 W/mK respectively. The results show an expected trend, though somewhat undocumented by current research. These results also show that changes in length and diameter affect the temperature dependent kp of SWCNT.
9:00 PM - NM2.9.13
Improvement of Thermoelectric Properties through Reduction of Thermal Conductivity by Nanoparticle Addition and Stoichiometric Change to Mg2Si
William Yorgason 1 , Arden Barnes 1 , Nicholas Roberts 1
1 Mechanical & Aerospace Engineering, Utah State University, Logan, Utah, United States
Show AbstractThermoelectric materials have been of interest for several decades due to their ability to recapture waste heat of various systems and convert it to useful electricity. One method used to improve the thermoelectric figure of merit, given by ZT = (σS2T)/(ke+kp), is to reduce the lattice thermal conductivity (kp) while not affecting the other properties. In order to reduce kp of the material, this paper introduces nanoparticles of Si in Mg2Si to manipulate phonon scattering and mean free path. LAMMPS molecular dynamics software is employed using the nonequilibrium molecular dynamics (NEMD) method to perform a series of simulations with the metal silicide thermoelectric material MgxSix. The objective of this work is two-fold: 1) to determine the optimal nanoparticle concentration and 2) to determine the optimal MgxSix stoichiometry for minimizing the thermal conductivity of the system. It should be noted, however, that the assumed reduction in thermal conductivity is only a result of reduced phonon transport and minimal impact is made on the transport of electrons. Interestingly, the uniform off-stoichiometry (41.37 percent Si) sample of MgxSix resulted in a reduction of kp of 72.39 percent, while the Si nanoparticle sample, with matching percent Si, resulted in a reduction of kp of 65.59 percent.
9:00 PM - NM2.9.14
Assessment of Convective Heat Transfer Behavior of Water Flow in Graphene Nanochannels
Drew Marable 1 , Seungha Shin 1 , Ali Yousefzadi Nobakht 1
1 MABE, University of Tennessee, Knoxville, Tennessee, United States
Show AbstractConvection heat transfer is assessed via molecular dynamics (MD) simulations of laminarly flowing liquid water through nanochannels composed of two parallel double-layer graphene (DLG) plates acting as the channel walls. Despite the presence of unrealistic axial conduction from temperature resetting and periodic boundary conditions in MD, fully developed hydro- and thermo-dynamic water flow conditions are observed. The effects of water-graphene interaction strength, channel height, water velocity, and wall temperature are evaluated in order to determine the extent of their influence on forced laminar convection between water and DLG. Microscopic interfacial behaviors, such as hydrodynamic slip and temperature jump at the solid-liquid interface are characterized for their influence on resulting behaviors. Convection heat transfer in nanochannels, characterized by the Nusselt number, is found to be considerably smaller than that at macroscale as microscopic interfacial interactions become dominant at smaller scales. Weak interaction strength of water-graphene, which results in hydrophobicity, reduction of channel height, and low channel wall temperature increase discrepancy from macroscale analysis, while velocity has minor effect.
9:00 PM - NM2.9.15
Role of Structural and Compositional Disorder in Alloys and Glasses on Thermal Conductivity
Jihui Nie 1 , Raghavan Ranganathan 1 , Zhi Liang 1 , Pawel Keblinski 1
1 Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States
Show AbstractWe use equilibrium molecular dynamics simulations to determine the relative role of compositional and structural disorder in a phononic thermal conductivity reduction by studying three 50-50 SiGe alloy structures, including ordered alloys (o-SiGe), disordered alloys (d-SiGe) and amorphous alloys (a-SiGe), as well as pure amorphous Si and Ge structures for reference. We find that while both types of disorder significantly reduce thermal conductivity, structural disorder is much more effective to this aim and compositional disorder in amorphous materials has little to no effect on thermal conductivity. The examination of phonon lifetimes in d-SiGe and a-SiGe shows high values in a low frequency regime governed by Umklapp scattering that are reduced rapidly with increasing frequency following Rayleigh scattering behavior. The local properties analysis reveals that the structural disorder leads to elastic heterogeneities, which are effective in scattering low frequency phonons. We will discuss possible strategies towards reduction of such heterogeneities and thus thermal conductivity increase of glasses.
9:00 PM - NM2.9.16
Unprecedented Increase of the Lattice Thermal Conductivity of Auxetic Carbon Crystals under Tensile Strain
Yang Han 1 , Ming Hu 1
1 , RWTH Aachen University, Aachen Germany
Show AbstractMechanical strain, representatively compression and tension, is one of the most effective ways to engineer the lattice thermal conductivity (κ) due to its flexibility and easy realization in experiments. In the past decades, a flurry of investigations of pressure (compression) effect on thermal conductivity of materials were initiated. It has been shown that, thermal conductivity of bulk materials usually increases under compression (dκ/dε <0, ε<0) and decreases under tension (dκ/dε <0, ε>0), while there are still some unusual systems, exhibiting reduced thermal conductivity when compressed (dκ/dε >0, ε<0). However, to date it has never been reported for a bulk material, whose thermal conductivity can be substantially enhanced under tensile strain, i.e. dκ/dε >0, ε>0. Herewith, we have studied thermal transport properties of three auxetic carbon crystals, namely cis-, trans-hinged polydiacetylene, and hinged polyacetylene (we call them cis-C, trans-C, and hin-C for simplicity) [Baughman et al., Nature 365, 735 (1993)], and their strain responses by performing first-principles calculations. It has been found that thermal conductivity of cis-C and hin-C decrease abnormally under compression (dκ/dε >0, ε<0). More strikingly, the thermal conductivity of trans-C (cis-C) unprecedentedly increases with tensile strain (dκ/dε >0, ε>0) up to 7% (6%) with maximum thermal conductivity of almost 7 (5) times larger than the unstrained value. The abnormal strain dependent thermal conductivity are attributed to the dominant role of the enhancement of phonon lifetime under stretching, which can be further explained from the unique atomic structure of the main chain of polydiacetylene …-C1-C2=C2-C1-… in cis-C and trans-C. The weakening of phonon anharmonicity is reflected by the enhancement of root mean-square displacement values and relevant to the potential energy surface felt by all C2 atoms in the main chain only presented in cis-C and trans-C but absent in hin-C. The electronic properties of strained auxetic carbon crystals are also analyzed and qualitatively correlated to the observed tensile dependence of thermal conductivity. Our study offers great opportunities for the carbon-based materials to be used in future stretchable electronics and presents a promising strategy towards advanced thermal management in terms of enhancing thermal transport by simple stretching.
9:00 PM - NM2.9.18
Study of Heat Transport in Metal-Coated Carbon Nanotubes Using Molecular Dynamics Atomistic Simulations
Iman Salehinia 1 , Dinesh Bommidi 1
1 , Northern Illinois University, DeKalb, Illinois, United States
Show AbstractIn view of improving the energy efficiency, thermal interface materials (TIMs) are employed to speed up the dissipation of heat in many electronics and machinery applications. So a lot of research has been carried out towards the development of TIMs with high heat dissipation efficiency and more compliance. By applying nanotechnology, high thermal conductance can be achieved at the fundamental level and it plays a pivotal role in the functioning of devices at micro or macro scale. Among a variety of choices, carbon nanotube (CNT) turfs (arrays) outstand with their exceptional mechanical and thermal properties on account of strong sp2 bonds among the carbon atoms in each CNT. They have a great strength yet are quite flexible due to their quasi-one-dimensional structure. Also, as the ballistic phonon transport is dominant in the CNTs, the thermal conductivity in an axial direction is rather large when compared to many metallic substances. However, the defects in CNTs, misaligned axial contacts between CNTs in a CNT turf, and the CNTs/substrate resistance reduce the practical thermal conductivity of the material. The application of metal coatings on each CNT in a CNT turf would help improve the overall thermal conductivity of the material and also improve the connectivity between the CNT turfs and the metallic substrate. To design an optimized metal/coated CNT turf for thermal/mechanical applications, several geometric parameters must be taken into account. As the diameter of the CNTs in a CNT turf is in the order of several nms, atomistic simulations provide a deeper understanding of the effect of various parameters on the thermal/mechanical properties of metal-coated CNT turfs. This research studied the thermal properties of metal-coated CNTs using molecular dynamics atomistic simulations. Nickel was coated uniformly on the surface of single walled and multi-walled CNTs using embedded atom potential for metal and Tersoff-Brenner potential for CNT. The interaction of the metal and carbon atoms was modeled using Morse potential. Both phonon and electron heat transport were considered as those are the main heat carriers in CNTs and metals, respectively. Through these simulations, the behavior of thermal transport in the metal-coated CNTs was investigated and the coefficient of thermal conductivity was procured. Furthermore, the effects of the metal thickness, and defects such as vacancies and Ston-walls on the thermal conductivity of the metal-coated CNTs were studied.
9:00 PM - NM2.9.19
Particle-Based Device Simulator for Modeling of Self-Heating Effects in P-Type MOSFET Transistors
Alan Carlos Junior Rossetto 1 2 , Vinicius Valduga de Almeida Camargo 1 , Dragica Vasileska 2 , Gilson Wirth 1
1 Programa de Pós-Graduação em Microeletrônica, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, Brazil, 2 School of Electrical, Computer and Energy Engineering, Arizona State University, Tempe, Arizona, United States
Show AbstractThis work aims to introduce a novel state-of-the-art Monte Carlo device simulator for p-type MOSFET transistors based on silicon which includes the capability of accounting for the effects of self-heating. Self-heating is a major reliability concern for deeply scaled CMOS technologies and it is related to the heat generation and subsequently heat confinement within the device. In short, hot-carriers interact with both acoustic and optical phonon baths transferring most of their energy to the optical and some to the acoustic phonon bath. Due to the small group velocities, optical phonons do not participate significantly in the heat diffusion when compared to the acoustic ones. Thus, thermal non-equilibrium exists between the optical and acoustic phonon baths and hot-spot forms within the device. To be able to deal with these non-uniformities, we have extended our electrical simulator by adding self-consistently a thermal solver. The carriers’ scattering rate dependence on the temperature is included through the generation of temperature-dependent scattering tables. The system starts at room temperature and the carriers’ energy (drift and thermal) and carriers’ density are sampled for each iteration. After collecting enough statistics, the energies and densities are averaged, the phonon energy balance equations are solved, the new temperature is assigned to each mesh point, and all the temperature-dependent variables in the system are updated. At that point, before performing the free-flight, each carrier is tracked and the temperature in its vicinity is used to determine the proper scattering table and scattering rate to be used, closing the loop self-consistently. This procedure is then repeated several times until the simulation reaches the desired convergence. Preliminary results obtained from our tool for a 25 nm-channel length p-MOSFET transistor at large bias condition (i.e., VGS = VDS = –1V) indicate the occurrence of a hot-spot with temperature around 30 K above the operational temperature. The hot spot is located at the drain side of the channel and it is due to the local carriers’ high energy and velocity. The increase of the temperature enhances locally the scattering rate and it has direct impact on the device’s ON-current. Thus, for the same conditions mentioned above, the drain current decreased around 2% when compared to the isothermal simulation.
9:00 PM - NM2.9.20
Metal-Insulator Metal Metamaterial Thermal Emitter with the Suppression of the Parasitic Modes
Kota Ito 1 , Hiroshi Toshiyoshi 2 , Hideo Iizuka 1
1 , Toyota Central R&D Labs Inc, Nagakute Japan, 2 RCAST, University of Tokyo, Tokyo Japan
Show AbstractMetal-insulator-metal (MIM) metamaterial thermal emitters [1][2] are attracting broad range of interests because of the simplicity of fabrication and the omnidirectional emission. The fundamental mode is generally utilized for selective thermal emission toward applications including infrared sensing of chemicals. However, several parasitic modes excited at higher frequencies are known to degrade the monochromaticy of the emitter.
Here, we present the control of the parasitic modes by utilizing the proximity interaction between resonators [3][4]. In particular, the suppression of the parasitic modes by densely tiled square resonators is discussed in detail [4]. The second-order mode, which is generally excited at twice the fundamental frequency, blue-shifts owing to the proximity interaction. Such blue-shifts suppress the amplitude of the second-order mode according to the decrease of the blackbody amplitude in this wavelength range. The other parasitic modes are also suppressed, and the parasitic emission power is reduced to one-third at an angle of 60°. The mechanism of the suppression is investigated by observing the field profile and scanning the gap width between resonators. We fabricated the metamaterial thermal emitter, whose fundamental wavelength is around 10 mm. The emission from the emitter at a temperature of 400 K experimentally validates the parasitic control presented in this work.
References
[1] X. Liu, T. Tyler, T. Starr, A. F. Starr, N. M. Jokerst, W. J. Padilla. Phys. Rev. Lett. 107, (4) 045901 (2011).
[2] J. A. Mason, S. Smith, D. Wasserman. Appl. Phys. Lett. 98, (24) 241105 (2011).
[3] K. Ito, H. Toshiyoshi, H. Iizuka, J. Appl. Phys. 119, (6) 063101 (2016).
[4] K. Ito, H. Toshiyoshi, H. Iizuka, Opt. Exp. 24, (12) 12803 (2016).
This work was partially supported by JSPS KAKENHI Grant Number JP16K17538.
9:00 PM - NM2.9.21
Degree-of-Freedom Resolved Thermal Transport in the C60 Molecular Crystal
Sushant Kumar 1 , Simon Lu 1 , Alan McGaughey 1
1 , Carnegie Mellon University, Pittsburgh, Pennsylvania, United States
Show AbstractFullerenes (e.g., C60) and their derivatives [e.g., phenyl-C60-butyric acid methyl ester (PCBM)] are molecular crystals that have application in photovoltaic, thermoelectric, and phase change memory devices. For example, fullerene-functionalized graphene can be integrated into conjugated polymers to enhance their thermoelectric properties. This enhancement comes partly from the low thermal conductivity of fullerenes. Though their thermal conductivities have been measured, the mechanisms of thermal transport are not well understood. We use molecular dynamics (MD) simulations to investigate the different ways that heat can travel in the C60 crystal.
The different types of degrees of freedom present in the C60 crystal make thermal transport interesting. Apart from the intramolecular and intermolecular (i.e., collective) vibrational degrees of freedom, which one would find in any molecular crystal, the molecules have rotational degrees of freedom at room temperature. These rotational degrees of freedom, in fact, lead to orientational disorder in the crystal, which causes glass-like thermal transport behavior. We use equilibrium and non-equilibrium MD simulations to quantify the relative contributions of each of these types of degrees of freedom to thermal conductivity. Different cases are considered wherein one or more of the types of degrees of freedom are prohibited and the resultant thermal conductivity is predicted. To study crystal-like behavior, both rotational and intramolecular degrees of freedom are removed. To study the effect of rotation, the rotational degrees of freedom are disallowed. Similarly, to study the significance of intramolecular vibrations, a rigid body approximation is made.
9:00 PM - NM2.9.22
Nanoscale Thermal Transport in the Kinetic Collective Model
F. Xavier Alvarez 1 , Pol Torres Alvarez 1 , Alvar Torello 1 , Javier Bafaluy 1 , Juan Camacho 1 , Amir Ziabari 2 , Ali Shakouri 2
1 , Universitat Autonoma de Barcelona, Bellaterra Spain, 2 , Purdue University, West Lafayette, Indiana, United States
Show AbstractRecent ultrafast heating experiments using nanostructured patterns have revealed that at small length scales Fourier law fails to interpret the results even using an effective thermal conductivity [1-3]. Anisotropy and collective transport have emerged as possible explanations [1,3], but to date no single model has been able to quantitetively predict the data from various sample geometries and experimental configurations.
We present the ab initio Kinetic Collective Model (KCM), a generalization of Fourier law that combines the inclusion of memory and nonlocality terms with ab-initio calculations using an accurate treatment of normal scattering. Recent publications have shown that the introduction of the normal processes and collective regime is the key point to predict the thermal transport for a large number of bulk and nanostructured materials [4-5].
KCM equations are much simpler than the full Boltzmann model and thus solutions for complex geometries can be obtained using a finite element approach. We describe the full landscape of thermal transport phenomenology in terms of the kinetic and collective regimes for different 3D and 2D configurations and compare with the experimental results. This model can be used in the design and optimization of nanoscale devices predicting their thermal behaviour prior to fabrication.
References:
[1] R. B. Wilson and D. G. Cahill, Nature communications 5 5075 (2014)
[2] J. A. Johnson et al. Physical Review Letters 110, 025901 (2013)
[3] K. M. Hoogeboom-Pot et al. PNAS 112, 201503449 (2015)
[4] C. de Tomas et al. Journal of Applied Physics 115, 164314 (2014).
[5] C. de Tomas et al. Proceedings of the Royal Society A 470, 20140371 (2014) .
9:00 PM - NM2.9.23
Enhancement of the Thermophysical Properties of Suspended Silica Thin Films Supporting the Propagation of Surface Phonon-Polaritons
Laurent Tranchant 1 , Jose Ordonez-Miranda 2 , Sebastian Volz 3 , Koji Miyazaki 1
1 , Kyushu Institute of Technology, Kitakyushu Japan, 2 , Institut Pprime, CNRS, Université de Poitiers, ISAE-ENSMA, Futuroscope Chasseneuil France, 3 , Laboratoire EM2C, CNRS, Centrale-Supélec, Université Paris-Saclay, Châtenay-Malabry France
Show AbstractSilica thin films are widely used in microelectronics and are very common insulating materials. The reduction of the unwanted overheating of microelectronic devices thus requires the improvement of their thermal performance driven by the thermophysical properties of the involved materials. In suspended silica nanomembranes, this could be achieved by means of surface phonon-polaritons (SPhPs), which are evanescent electromagnetic waves propagating along the surface of the membranes and are able to significantly enhance their in-plane thermal conductivity. Based on theoretical predictions, this enhancement occurs due to the increase of the longitudinal propagation length as the film thickness decreases and the broadening of the frequency spectrum of these surface waves for amorphous materials such as glass.
In this work, we intend to experimentally prove the aforementioned theoretical results by making several experiments: measure the enhancement of the thermophysical properties of suspended glass thin films and then link this increase to the enhanced propagation of SPhPS for these devices. First the main experiment is the measurement of the in-plane thermal conductivity of silica thin films by means of the AC calorimetry. This is done by heating the film through Joule effect generated by an electric current flowing along an aluminum wire deposited on the film surface, and measuring the increase of the film steady-state temperature. This increase is directly related to the film thermal conductivity through a thermal model that takes into account the radiative losses. Preliminary results show a thermal conductivity of 1.25 W/(m.K) for a 500 nm-thick silica film, which is in agreement with usual bulk values of glass. Higher values are expected for thicknesses smaller than 200 nm, for which the SPhP energy contribution is expected to be dominant. In addition, we also explore the measurement of the SPhP propagation length by means of the attenuated total reflection technique, as well as the observation of the SPhP spectrum broadening by studying the interaction of light with rough glass surfaces. Roughness can indeed induce the light absorption and is linked to the frequencies of SPhP propagation. We have generated roughness on glass surface by depositing silica microspheres on the surface of a glass plate. These two latter experiments will support the conclusion that the increase of the thermophysical properties of suspended glass membranes is due to the enhancement of the SPhPs propagation along their surfaces.
9:00 PM - NM2.9.24
Wavevector Dependent Transmission Coefficient at Si/Ge Interfaces and across Vacuum Gaps from First Principles Lattice Dynamics Calculations
Merabia Samy 1 , Ali Alkurdi 1
1 , Universite de Lyon, CNRS, UCBL, ILM, UMR5306, Villeurbanne France
Show Abstract
Thermal boundary conductance is basically dictated by phonon transmission at interfaces, and an accurate prediction at nanoscale is of a great importance for many applications where thermal management is a vital issue. In microelectronics there is a strong need to know how energy can be exchanged across small vacuum gaps having separation distances of few nanometers.
Recently, experimental studies found giant heat flux transfer between gold and silica at nanometer sepraration distance [1].
Theoretically, it is expected that at such nanometer distances, heat is exchanged primarily by acoustic waves [2], while radiative heat transfer dominates when the gap is larger than a few nanometers [3]. To our knowledge, since Young and Maris' work, few studies reported lattice dynamics calculations at interface using interatomic force constants from density functional theory as inputs (ab initio), even though it has been proved to be an excellent method to describe bulk phonon dispersion.
In this communication, we have performed lattice dynamics calculations at silicon/germanium interfaces and across vacuum gaps using ab initio interatomic force constants [4]. This analysis allows to predict the interfacial phonon transmission coefficient as a function of both the phonon wavevector and the frequency. As a result, we have quantified the energy flowing in a given scattered direction, depending on the phonon energy. Our simulations show that, quite generally a large contribution of the transmitted energy flux corresponds to small scattered angles, close to the direction normal to the interface. Conversely, the energy flux that is not transmitted is found to be much more isotropic. These results are robust to a change in the bonding strength, and also to the interaction range between Si and Ge, in the situation where there is no gap. The lattice dynamics calculations allow us to characterize also the localized modes close to the interface, and we demonstrate that these modes may have penetration depths greater than a few nanometers, and that they propagate in the direction parallel to the interface.
Finally, we have used these calculations to probe heat transfer across vacuum gaps. We first characterize the thermal conductance due to phonons for different interfaces including Silicon/Silicon and Silicon/Germanium interfaces, but also interfaces between Silicon and noble metals, including Gold and Aluminium. We characterize in all cases the probability for phonons to be transmitted across the gap, and show that the cone of transmission is very narrow and corresponds to a scattered direction normal to the interface. Moreover, we demonstrate how the presence of a nanoscale gap enhance the amplitude of localized modes.
[1] Konstantin Kloppstech et al., arxiv1510.06311
[2] V. Chiloyan, J. Garg, K. Esfarjani and G. Chen, Nat. Comm. 6, 6755 (2015)
[3] B. V. Budaev and D. B. Bogy, Appl. Phys. Lett. 99, 053109 (2011)
[4] A. Alkurdi and S. Merabia, submitted
9:00 PM - NM2.9.25
Spin Mediated Thermal Transport in 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.
Symposium Organizers
Aleksandr Chernatynskiy, Missouri University of Science and Technology
Pierre-Olivier Chapuis, Center for Energy and Thermal Sciences, CNRS - INSA Lyon
Kedar Hippalgaonkar, Nanyang Technological University
Austin Minnich, California Institute of Technology
NM2.10: Radiative Heat Transport
Session Chairs
Thursday AM, April 20, 2017
PCC West, 100 Level, Room 101 BC
9:00 AM - *NM2.10.01
Radiative Heat Transfer at the Nanoscale
Pramod Sangi Reddy 1
1 , University of Michigan, Ann Arbor, Michigan, United States
Show AbstractRadiative heat transfer between objects separated by nanometer-sized gaps is of considerable interest due to its promise for non-contact modulation of heat transfer and for several energy conversion applications. Although radiative heat transfer at macroscopic distances is well understood, radiative heat transfer at the nanoscale remains largely unexplored. In this talk, I will describe ongoing efforts in our group to experimentally elucidate nanoscale heat radiation. Specifically, I will present our recent experimental work where we have addressed the following questions: 1) Can existing theories accurately describe radiative heat transfer in single nanometer sized gaps1? 2) What is the role of film thickness on nanoscale radiation2? and 3) Can radiative thermal conductances that are orders of magnitude larger than those between blackbodies be achieved3? In order to address these questions we have developed a variety of instrumentation including novel nanopositioning platforms and microdevices, which will also be described. Finally, I will briefly outline how these advances can be leveraged for future investigations of nanoscale radiative 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, Y. Ganjeh, S. Sadat, D. Thompson, A. Fiorino, V. Fernández-Hurtado, J. Feist, F. J. García-Vidal, J. C. Cuevas, P. Reddy and E. Meyhofer, “Enhancement of near-field radiative heat transfer using polar dielectric thin films“, Nature Nanotechnology 10, 253-258 (2015).
[3] 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).
9:30 AM - NM2.10.02
Near-Field Thermal Radiation and Gas Conduction in a Nanostructured Gap Measured by Frequency Domain Thermoreflectance (FDTR)
Minyoung Jeong 2 , Cheng-Ming Chow 1 , Turga Ganapathy 3 , James Bain 1 , Jonathan Malen 3
2 Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States, 1 Electrical and Computer Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States, 3 Mechanical Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States
Show AbstractThermoreflectance techniques that have advanced our study of heat conduction in solids and liquids are applied for the first time to measure heat transfer by near-field radiation and gas conduction. To study these heat transfer mechanisms, we created nanoscale gaps between dielectric layers by etching an intermediate layer of SiO2. The conductance across these gaps was measured by frequency domain thermoreflectance (FDTR) where periodic surface heating by an intensity modulated pump laser generates periodic temperature variation that is measured by thermoreflectance. One challenge for these measurements is identifying an acceptable lateral spacing for the supporting structures that bridge the gap to support the top layers such that these structures will not divert heat that must cross the gap to enable measurement. To evaluate the radial spreading length scale, a heat conduction model considering periodic heating of an annular fin was developed and the support structures were placed at conservative distances. Preliminary FDTR measurements on 20 nm gaps between AlN dielectric layers with lateral support spacing of 10 mm identify temperature amplitudes nearly twice as large in vacuum, relative to air environments, suggesting that the near field conductance is of order ~104 W/m2-K, which is the magnitude of predicted near field radiative heat transfer. Measurements of the temperature dependence of near field thermal conductance across gaps ~10 nm in size will be presented. Such temperature dependence of near field radiative heat transfer has not been measured before.
9:45 AM - NM2.10.03
Radiation at the Nanoscale—A Heat Transfer Measurement between Parallel Plates
Anthony Fiorino 1 , Dakotah Thompson 1 , Linxiao Zhu 1 , Pramod Sangi Reddy 1 2 , Edgar Meyhofer 1
1 Mechanical Engineering, University of Michigan , Ann Arbor, Michigan, United States, 2 Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States
Show AbstractThermal radiation is well-described by Planck’s law and by the Stefan-Boltzmann law when the radiating bodies are separated by distances greater than ~10 micrometers at room temperature. When the spacing between the bodies is decreased to the nanoscale, electromagnetic energy can tunnel via exponentially-decaying, “evanescent” modes which would otherwise be confined to the surfaces of the bodies. These additional modes are expected to lead to orders-of-magnitude enhancement in the radiative heat flux as compared to that predicted by the Stefan-Boltzmann law. This phenomenon, called near-field radiative heat transfer (NFRHT), has been extensively explored in theoretical and numerical works and is expected to have important implications in the development of various technologies.
Past experimental investigations have primarily focused on characterizing NFRHT between a tip and a plate or between a sphere and a plate because these configurations are relatively tractable in performing experiments. Indeed, those studies have been instrumental in clarifying our understanding of the physics, but systematic measurements of NFRHT between parallel plates are required in order to realize many promising new technologies. Our own past work [Nature Nanotech. 11, 509–514 (2016)] recently addressed this challenge using a pair of planar microdevices separated by tens of nanometers.
In this talk, I describe our new measurements of NFRHT between extremely flat and parallel plates. In comparison with our past approach which required two microdevices, our new technique requires just a single microdevice emitter/thermometer situated across from a macroscopic receiver. I will discuss how, using this technique, we have been able to attain smaller nanoscale gaps and higher radiative heat flows (more than 2000-fold enhancement over the far field) than has previously been possible between planar surfaces. A comprehensive comparison with theory will be made within the framework of fluctuational electrodynamics. If time permits, novel technological applications of this phenomenon will also be discussed.
10:00 AM - NM2.10.04
Daytime Radiative Cooling Using Glass Slides
Junlong Kou 1 , Austin Minnich 1
1 , California Institute of Technology, Pasadena, California, United States
Show AbstractRecent works have demonstrated that daytime radiative cooling under direct sunlight can be achieved using multilayer thin films designed to emit in the infrared atmospheric transparency window while reflecting visible light. Here, we demonstrate that a simple glass mirror, as a near-ideal blackbody in the mid-infrared and near-ideal reflector in the solar spectrum, achieves radiative cooling below ambient air temperature during both daytime (4.2 degrees Celsius) under direct sunlight and at night (7.4 degrees Celsius). Its performance is comparable to previous results obtained using multilayer thin film stacks fabricated using vacuum deposition methods. Furthermore, an average net cooling power of about 60 W/m2 is estimated according to field measurements even considering the significant influence of external conduction and convection. Our work demonstrates that extremely simple materials that can be fabricated in large scale can be used to achieve radiative cooling, advancing applications such as dry cooling of thermal power plants.
10:15 AM - *NM2.10.05
Contactless Thermotronics with Photons
Philippe Ben-Abdallah 2 3 , Svend-Age Biehs 1
2 , Laboratoire Charles Fabry CNRS/ Institiut d'Optique, Palaiseau France, 3 , Université de Sherbrooke, Sherbrooke, Quebec, Canada, 1 , Institut für Physik, Carl von Ossietzky Universität, Oldenburg, Select State/Province, Germany
Show AbstractThe next-generation of the “internet of things” has the potential to change the way people and systems live in a world of massive and disparate data sources, and to provide opportunities for connectivity at different scales. Instead of using electrical signals, purely thermal signals could be used. The development of such technology requires the existence of thermal analogs of basic electronic building elements such as transistors, memories and logic gates which work with heat flow rather than with electronic currents.
An important step forward in this direction has been carried out in 2006 by Baowen Li and his co-workers [1] who have introduced phononic analogs of electronics devices. However, this transport of heat with phonons in solid networks suffers from some weaknesses of fundamental nature which intrinsically limit its performances. One of these limitations is linked to the speed of acoustic phonons itself which is limited by the speed of sound in solids.
In this presentation we will discuss the possibility to develop, radiative analogs of fundamental building blocks for controlling the flow of heat with thermal photons, instead of the flow of phonons.
After describing the operating mode of radiative transistor which have been recently introduced [2] we will describe a mechanism of thermal bistability [3] which is at the origin of the very first radiative memory. Next, we will show the possibility to develop, contactless thermal logic gates [4] to process heat flows with thermal photons using complex architectures.
Finally, we will discuss some of new challenges we are going to face to combine these basic elements and to control heat flux [5] in order to conceive thermal circuits.
References
[1] B. Li and L. Wang and G. Casati, Appl. Phys. Lett. 88, 143501 (2006). B. Li and L. Wang and G. Casati, Appl. Phys. Lett. 88, 143501 (2006).
[2] P. Ben-Abdallah and S.-A. Biehs, Phys. Rev. Lett. 112, 044301 (2014).
[3] V. Kubytskyi, S.-A. Biehs, and P. Ben-Abdallah, Phys. Rev. Lett. 113, 074301 (2014)
[4] P. Ben-Abdallah and S.-A. Biehs, arXiv:1608.01791, (2016).
[5] P. Ben-Abdallah, Phys. Rev. Lett. 116, 084301 (2016).
NM2.11: Computational Methods
Session Chairs
Thursday PM, April 20, 2017
PCC West, 100 Level, Room 101 BC
11:15 AM - *NM2.11.01
First Principles Calculations of Thermal Conductivity with out of Equilibrium Molecular Dynamics Simulations
Giulia Galli 1 , Marcello Puligheddu 1
1 , University of Chicago, Chicago, Illinois, United States
Show AbstractWe present a method [1] to compute the thermal conductivity of solids by performing ab initio molecular dynamics at non equilibrium conditions. Our formulation is based on a generalization of the approach to equilibrium technique, using sinusoidal temperature gradients, and it only requires calculations of first principles trajectories and atomic forces. We discuss results and computational requirements for a representative oxide -- bulk and nano-crystalline MgO-- and we compare with experiments and data obtained with classical potentials.
[1] Marcello Puligheddu and Giulia Galli (submitted for publication).
11:45 AM - *NM2.11.02
Modeling Thermal Transport from First-Principles—Nanostructures, Defective Materials, Novel Compounds and Beyond
Natalio Mingo 1 , Jesus Carrete 1 2 , Ankita Katre 1 , Ambroise van Roekeghem 1 , Bjorn Vermeersch 1
1 , CEA, Grenoble France, 2 , TU Wien, Vienna Austria
Show AbstractAfter a decade of development, accurate ab-initio predictions of thermal conductivity in bulk crystalline materials are close to becoming standard practice, partly thanks to several recently released open source codes. To go beyond the single crystal case, however, means dealing with all the features that break translational symmetry in real materials. I will present several examples to illustrate how this can be done in an ab-initio fashion.
In the case of materials with point defects, such predictive modeling allows us to determine what kinds of antisite defects are dominant in a material like half-heusler ZrNiSn [1], or the expected reduction due to vacancies in novel material BAs [2]. I will also discuss the roles of segregation, compositional profiles, and sizes, on the thermal conductivity of thin films and superlattices. I will then present exfoliable structures like germanane and black phosphorus, where ab-initio modeling provides valuable insight as to the main scattering mechanisms determining the measured thermal conductivity of sub-micrometer thick samples [3]. Finally, I will show how to calculate the thermal conductivity of phases that are not mechanically stable at zero kelvin, making it impossible to use standard approaches. In some cases, temperature dependent phonon dispersions, and soft modes in particular, can lead to negative thermal expansion, and anomalous thermal conductivity [4]. Results of a high throughput study of oxide and fluoride perovskites will be discussed [5]. I will also give a quick overview of our public code AlmaBTE, www.almabte.eu , used to obtain many of the aforementioned results.
[1] A. Katre, J. Carrete, and N. Mingo, “Unraveling the dominant phonon scattering mechanism in the thermoelectric compound ZrNiSn,” J. Mater. Chem. A, 2016.
[2] N. H. Protik, J. Carrete, N. A. Katcho, N. Mingo, and D. Broido, Ab initio study of the effect of vacancies on the thermal conductivity of boron arsenide,” Phys. Rev. B, vol. 94, no. 4, p. 45207 (2016).
[3] G. Coloyan et al., “Basal-plane thermal conductivity of nanocrystalline and amorphized thin germanane,” Appl. Phys. Lett., vol. 109, no. 13, p. 131907 (2016).
[4] A. van Roekeghem, J. Carrete, and N. Mingo, “Anomalous thermal conductivity and suppression of negative thermal expansion in ScF3,” Phys. Rev. B, vol. 94, no. 2, p. 20303 (2016).
[5] A. van Roekeghem, J. Carrete, C. Oses, S. Curtarolo, and N. Mingo, “High throughput thermal conductivity of high temperature solid phases: The case of oxide and fluoride perovskites,” ArXiv160603279 Cond-Mat Physics, (2016).
12:15 PM - NM2.11.03
Theory of Substrate-Directed Cross-Plane Heat Dissipation from Two-Dimensional Crystals
Zhun-Yong Ong 1 , Yongqing Cai 1 , Gang Zhang 1
1 , Institute of High Performance Computing, Singapore Singapore
Show AbstractPhonon-mediated heat dissipation to the substrate is a major factor in the effective thermal management and design of electronic devices based on two-dimensional (2D) materials (e.g. graphene and MoS2). We present a theoretical description of flexural phonon-mediated thermal boundary conductance (TBC) at the interface between a single-layer 2D crystal and its substrate [1]. We show how intrinsic flexural phonon damping is necessary for obtaining a finite Kapitza resistance and how the encasement of the 2D crystal with a superstrate (such as a top oxide layer) greatly increases the TBC through the introduction of additional low-frequency phonon transmission channels. To illustrate our theory, we calculate the TBC for bare and SiO2-encased graphene and MoS2 on a SiO2 substrate using input parameters from first-principles calculations. The estimated room temperature TBC for bare (encased) single-layer graphene and MoS2 on OH-terminated SiO2 are 34.6 (105) and 3.10 (5.07) MWK-1m-2, respectively, in good agreement with published experimental data [2, 3, 4, 5]. We also find that H-termination (OH-termination) of the SiO2 surface improves the TBC for graphene (MoS2) and that MoS2 is especially sensitive to the type of surface termination. Finally, we generalize the theory to multilayer 2D crystals and calculate the layer-dependent TBC for graphene on SiO2. Our results show that the TBC increases with the layer number, agreeing quantitatively with published experimental data [2] and MD simulation results [6]. We discuss the physics underlying this layer number dependence.
References:
1. Z.-Y. Ong, Y. Cai, and G. Zhang, “Theory of substrate-directed heat dissipation for single-layer graphene and other two-dimensional crystals,” submitted.
2. K. F. Mak, C. H. Lui, and T. F. Heinz, “Measurement of the thermal conductance of the graphene/SiO2 interface,” Appl. Phys. Lett. 97, 221904 (2010).
3. Z. Chen, W. Jang, W. Bao, C. N. Lau, and C. Dames, “Thermal contact resistance between graphene and silicon dioxide,” Appl. Phys. Lett. 95, 161910 (2009).
4. M. Freitag, M. Steiner, Y. Martin, V. Perebeinos, Z. Chen, J. C. Tsang, and P. Avouris, “Energy Dissipation in Graphene Field-Effect Transistors,” Nano Lett. 9, 1883 (2009).
5. A. Taube, J. Judek, A. Lapinska, and M. Zdrojek, “Temperature-Dependent Thermal Properties of Supported MoS2 Monolayers,” Appl. Mater. Interfaces 7, 5061 (2015).
6. Y. Ni, Y. Chalopin, and S. Volz, “Few layer graphene based superlattices as efficient thermal insulators,” Appl. Phys. Lett. 103, 141905 (2013).
12:30 PM - NM2.11.04
Molecular Dynamics Study of the Influence of Individual Dislocation and Density of Dislocations on the Thermal Conductivity
Konstantinos Termentzidis 1 , Mykola Isaiev 3 , Joseph Kioseoglou 2
1 , CNRS, Vandoeuvre les Nancy France, 3 , Taras Shevchenko National University of Kyiv, Kyiv Ukraine, 2 Department of Physics, Aristotle University of Thessaloniki, Thessaloniki Greece
Show AbstractIII-V semiconductors are the base of micro/nano optoelectronics, high efficient LEDs and lasers, as well as active elements of high-frequency devices. All these devices can be significantly overheated during operation, and the thermal properties of their basic elements play a crucial role for the further improvement of the quality of the devices and to increase their life time. The crystalline bulk GaN has high thermal conductivity, which is an important advantage for a variety of devices. Threading dislocations comprise the major type of defects in heteroepitaxial GaN. The influence of threading dislocations on thermal conductivity has not been elucidated in deep till now. With Molecular Dynamics simulations we studied the influence of three edge configurations and two screw threading dislocations on the thermal conductivity of individual GaN nanowires. It has been proved that the screw dislocations reduces thermal conductivity of pristine nanowires by a factor of two while the influence of edge dislocations is less pronounced. The impact of each of the five types of dislocations is related to the nature of the bonds at the core of the dislocations. The relative reductions are correlated via the linear elasticity theory to the elastic energy of dislocations. Furthermore the influence of the density of dislocation in bulk GaN has been studied. The thermal conductivity dependence on the density of dislocations is different between the two types of dislocations (edge, screw).
12:45 PM - NM2.11.05
Lattice Thermal Conductivity of PbTe-Based Materials Driven Near Ferroelectric Phase Transition
Ivana Savic 1 , Ronan Murphy 1 , Eamonn Murray 2 , Stephen Fahy 1
1 , Tyndall National Institute, Cork Ireland, 2 , Imperial College London, London United Kingdom
Show AbstractNanostructuring has proven to be a very successful strategy to design materials with low lattice thermal conductivity [1]. Here we propose an alternative strategy to block heat conduction that does not rely on the concept of nanostructuring, and exploits the proximity to soft mode phase transitions of certain materials like PbTe. Using first principles simulations, we show that driving PbTe near the transition from the rocksalt to a rhombohedral structure will significantly reduce the lattice thermal conductivity. We illustrate this concept by applying biaxial tensile (001) strain to both PbTe and its alloy with rocksalt PbSe, and also by alloying PbTe with rhombohedral GeTe [2]. Furthermore, our calculations show that the lattice thermal conductivity of (Pb,Ge)Te alloys changes continuously between rocksalt and rhombohedral structures, and reaches a minimum at the phase transition [3]. The large conductivity reductions of these materials near the phase transition occur as a result of the increased acoustic-soft optical mode interaction. The proposed concept may open new opportunities for the design of materials with low lattice thermal conductivity.
[1] K. Biswas, J. He, I. D. Blum, C.-I. Wu, T. P. Hogan, D. N. Seidman, V. P. Dravid, and M. G. Kanatzidis, Nature 489, 414 (2012).
[2] R. M. Murphy, E. D. Murray, S. Fahy, and I. Savic, Phys. Rev. B 93, 104304 (2016).
[3] R. M. Murphy, E. D. Murray, S. Fahy, and I. Savic, in preparation.
NM2.12: Junctions and Couplings
Session Chairs
Thursday PM, April 20, 2017
PCC West, 100 Level, Room 101 BC
2:30 PM - *NM2.12.01
Heat Transport through Atomic Contacts
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, Ruschlikon Switzerland
Show AbstractMetallic atomic junctions pose the ultimate limit to the scaling of electrical contacts. They serve as model systems to probe electrical and thermal transport down to the atomic level as well as quantum effects occurring in one-dimensional systems. Charge transport in atomic junctions has been studied intensively in the last two decades. However, heat transport remains poorly characterized because of significant experimental challenges. Specifically the combination of high sensitivity to small heat fluxes and the formation of stable atomic contacts has been a major hurdle for the development of this field. We report on the realization of heat transfer measurements through atomic junctions and analyze the thermal conductance of single atomic gold contacts at room temperature. Simultaneous measurements of charge and heat transport reveal the proportionality of electrical and thermal conductance, quantized with the respective conductance quanta. This constitutes an atomic scale verification of the well-known Wiedemann-Franz law. 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.
3:00 PM - NM2.12.02
Investigation of a Topography-Free Composite Sample Using a Combined Scanning Thermal Microscopy/Scanning Electron Microscopy Instrument
Severine Gomes 1 , David Renahy 1 , Sanna Arpiainen 2 , Jonathan Weaver 3 , Pascal Vincent 4 , Mika Prunnila 2 , Antonin Massoud 1
1 , CETHIL, UMR 5008, CNRS - INSA Lyon - Université Claude Bernard Lyon 1, Villeurbanne France, 2 , VTT Technical Research Centre of Finland Ltd, Espoo Finland, 3 Department of Electronics and Electrical Engineering, University of Glasgow, Glasgow United Kingdom, 4 , ILM, UMR5306, CNRS - Université Claude Bernard Lyon 1, Villeurbanne France
Show AbstractNanometer-scale thermal measurements using Scanning Thermal Microscopy (SThM) techniques are increasingly performed under vacuum conditions. Reducing the number of thermal channels by which the probe-sample heat flux may be transferred to that of channels localized at the near probe-sample mechanical contact this enables the improvement of the spatial resolution of the technique and a simplification of the modeling used to interpret the measurements. The investigation of thermal conduction at solid-solid mechanical nanocontacts and near-field radiation are then possible [1-4]. However, the real conditions of the contact between the tip apex and the sample surface remain a riddle also its description is often partly a matter of the imagination. To go beyond this issue, we developed a combined SThM/scanning electron microscope (SEM) instrument allowing the real-time observation of the shape and size of the tip, and of the sample surface during the acquisition of a thermal image. We have demonstrated that this constitutes a significant advantage for characterizing more in depth the measurement with SThM.
In this work we also applied the instrument to investigate a nanocomposite sample comprising in its subsurface Poly-Si (n+) structures of various thicknesses covered successively by two nanolayers of Al203 and thermal SiO2, and embedded in a SiO2 matrix. The thermal SiO2 sample surface is free of topography: features have height lower than 2 nm. Topography and thermal imaging were realized simultaneously in contact mode with a resistive SThM probe from Kelvin Nanotechnology heated by Joule effect. The analysis of the both obtained images has demonstrated that the SThM can probe the subsurface of the sample in the case of measurements performed under vacuum conditions and is sensitive to the buried structures. As there is no topography artefact in the thermal contrast, the sample appears to be a good candidate to characterize the thermal nanomeasurement using SThM. The boundary resistance at the probe-sample thermal contact is determined using a modeling established in the light of the observations of the probe apex-sample contact made possible using SEM.
References [1] S. Gomes, A. Assy, P.-O. Chapuis, Physica Status Solidi (a), 2015, 212, 477-494. [2] A. Assy, PhD Thesis, INSA de Lyon, 2015. [3] B. Gotsmann, M. A. Lantz, A. Knoll and U. Dürig, Nanotechnology, 2010. [4] Kittel, W. Müller-Hirsch, J. Parisi, S.-A. Biehs, D. Reddig and M. Holthaus, Physical review letters, 2005, 95, 224301.
Acknowledgements The research leading to these results has received funding from the European Union Seventh Framework Programme FP7-NMP-2013-LARGE-7 under grant agreement n° 604668.
3:15 PM - NM2.12.03
Heat Transport in Isotopically Engineered Nanowires
Samik Mukherjee 1 , Oussama Moutanabbir 1
1 Department of Engineering Physics, Ecole Polytechnique-Montreal, Monteal, Quebec, Canada
Show AbstractIsotope engineering in nanoscale materials is a powerful paradigm to investigate and manipulate some of their important physical properties and exploit them in innovative device structures. For instance, the subtle changes in lattice dynamics between the isotopes can be exploited to manipulate the phonon transport in nanowires. Till date however, isotope engineering has mostly been restricted to bulk semiconductors and thin films with no experimental investigations of the influence of stable isotope impurities on the basic characteristics of nanoscale materials. With this perspective, we report in this work on phonon engineering in metal catalyzed silicon nanowires with tailor-made isotopic compositions grown using isotopically enriched silane precursors 28SiH4, 29SiH4, and 30SiH4 with purity better than 99.9%.1 The phonon behavior in isotopically mixed 28Six30Si1-x nanowires with a composition close to the highest mass disorder were investigated and compared to that in isotopically pure 29Si nanowires having a similar reduced mass. The disorder-induced enhancement in phonon scattering in isotopically mixed 28Six30Si1-x nanowires was found to be unexpectedly much more significant than in bulk crystals of similar isotopic compositions. Using Raman nanothermometry, the ratio of thermal conductivities between the two sets of nanowires was obtained suggesting a ~30% decrease in the thermal conductivity around room temperature of isotopically mixed 28Six30Si1-x nanowires as compared to isotopically pure 29Si nanowires.
1 S. Mukherjee, U. Givan, S. Senz, A. Bergeron, S. Francoeur, M. de la Mata, J. Arbiol, T. Sekiguchi, K.M. Itoh, D. Isheim, D.N. Seidman, and O. Moutanabbir, Nano Lett. 15, 3885 (2015).
3:30 PM - NM2.12.04
Correlation of Heat Transport and Shear Forces in Nanoscale Junctions
Benjamin Robinson 1 , Oleg Kolosov 1
1 , Lancaster University, Lancaster United Kingdom
Show AbstractNanoscale solid-solid contact defines a wealth of materials behaviour from the friction in micro- and nanoelectromechanical systems to electrical and thermal conductivity in modern electronic devices. For modern, ultra-high integration processor chips and power electronic devices one of most essential, but thus far most challenging, aspects is the heat transport in nanoscale sized interfaces. The Highest spatial resolution to date, achieved via nanoscale probes in scanning thermal microscopy (SThM)1, is often devalued by the poorly defined nature of the nanoscale contacts2. However truly uunderstanding the thermal properties of such nanoscale junctions is of fundamental importance for the development of next generation nanodevices, where ballistic transport is expected to dominate bulk-like diffusive and convective transport and may, indeed, be quantised.
Here we show that simultaneous measurement of shear forces and heat flow between the probe and the studied material elucidates the key parameters of solid-solid contact. Our analysis indicates the ballistic nature of heat transport via nanoscale contacts in such a system. Furthermore, in analogy to the Wiedemann-Franz law linking electrical and thermal conductivity in metals3, we show that a generalised relation exists linking shear forces and thermal resistance in nanoscale contacts via fundamental material properties such as heat capacity and heat carrier group velocity. These factors, together with the clearly observed anti-correlation of the thermal resistance and shear forces, demonstrate a quantitative approach for the experimental characterisation of thermal transport in nanoscale junctions.
References:
1. Gomès, S., Assy, A. & Chapuis, P.-O. Scanning thermal microscopy: A review. physica status solidi (a) 212, 477-494 (2015).
2. Gotsmann, B. & Lantz, M. A. Quantized thermal transport across contacts of rough surfaces. Nat Mater 12, 59-65 (2013).
3. Franz, R. & Wiedemann, G. Ueber die Wärme-Leitungsfähigkeit der Metalle. Annalen der Physik 165, 497-531 (1853)
3:45 PM - NM2.12.05
Probing the Mean-Free-Paths of Phonons in Semiconductors and Dielectrics by Fourier-Transform Time-Domain Thermoreflectance (FT-TDTR)
Yuexiang Yan 1 , Puqing Jiang 1 , Yee Kan Koh 1
1 , National University of Singapore, Singapore Singapore
Show AbstractTime-domain thermoreflectance (TDTR) is a pump-probe technique that has been widely employed to study heat conduction at micro- and nano-scales. Over the past decade, TDTR measurements at high frequencies have been explored to probe the mean-free-paths of heat-carrying phonons in crystals and alloys. However, due to the limitations of the instruments, the highest frequency at which temperature responses could be measured is limited to ~200 MHz, which affects the usefulness of the approach. We, however, propose that high frequency temperature responses up to 500 MHz can be derived from TDTR measurements by performing Fourier transform on the TDTR measurements. Since samples are heated by a train of modulated laser pulses in TDTR measurements, heating induced by the laser pulses is composed of components at the sidebands of multiples of laser repetition rate (80 MHz). Thus, in principle, temperature oscillations due to the high frequency heating could be derived from the Fourier-transform of TDTR measurements. These high frequency signals are, however, not registered in prior TDTR measurements, because the signals are filtered out by thick metal transducer films usually deposited in the samples. We thus use a thin transducer film (~30 nm Al) and ensure a good transducer/substrate interfacial thermal conductance (>300 MW m-2 K-1) to reduce the filtering effect. We successfully extract the apparent thermal conductivity of Si, Si0.992Ge0.008, GaAs, In0.89Ga0.11N and sapphire as a function of frequency up to ~500 MHz with uncertainty <20% from the frequency domain analysis of the FT-TDTR measurements. We have carefully considered various factors that could possibly affect the extracted effective thermal conductivities. We interpret the apparent thermal conductivity as the cumulative thermal conductivity of phonons with mean-free-paths up to twice the thermal penetration depth, and we achieved good agreements with previously reported first-principles calculations. Thus, the FT-TDTR could be a convenient tool to probe the phonon mean-free-paths of different semiconductors and dielectrics.
NM2.13: Thermal Transport in Organic Materials
Session Chairs
Thursday PM, April 20, 2017
PCC West, 100 Level, Room 101 BC
4:30 PM - *NM2.13.01
Dynamic Disorder Controls Thermal Transport in Superatomic Crystals and Organic-Inorganic Perovskites
Jonathan Malen 1 , Wee-Liat Ong 2 , Evan O'Brien 2 , Giselle Elbaz 2 , Daniel Paley 2 , Fred Higgs 1 , Alan McGaughey 1 , Xavier Roy 2
1 , Carnegie Mellon University, Pittsburgh, Pennsylvania, United States, 2 , Columbia University, New York, New York, United States
Show AbstractThe thermal conductivity of several superatomic crystals (SACs) and organic-inorganic halide perovskites are measured across a wide range of temperatures. A superatom is a cluster of atoms that acts as a stable entity [e.g., fullerenes (C60)]. Organic-inorganic superatoms can assemble into unary SACs or co-crystallized with C60 superatoms into binary SACs. Organic-inorganic perovskites are hybrid materials of the form APbX3 (where A = methylammonium, formamidinium or Cs cations and X = Cl, Br or I). Both of these material sets exhibit unique thermal transport properties that bear on their potential application in solar cells and thermoelectric materials.
The k of the SACs and APbX3 are measured using the frequency domain thermoreflectance setup. The room temperature thermal conductivities (k) of different SACs are found to be below 0.3 W/mK and trend with their measured sound speeds obtained independently using nano-indentation. The APbX3 crystals exhibit higher room temperature k values (below 0.7 W/mK) that trend with their sound speeds when the cation group is the same. All crystals, however, exhibit different temperature dependent thermal conductivity behaviors according to the activation/deactivation of dynamic disorder.
Unary SACs exhibit an almost invariant k trend down to a temperature of 150 K. Binary SACs, however, show different k trends depending on the type of superatoms. The CoSe.C60 SAC shows a crystalline-like increase in k with decreasing temperature while the CoTe.C60 SAC shows an amorphous-like decrease. These contrasting trends result from the dynamic disorder/order induced by the C60 cages that spin freely but get ordered after a phase change. Similarly, the dynamic disorder of the molecular cations in APbX3 becomes deactivated with phase changes at lower temperatures. The k trends for the different APbX3, however, showed slightly different behaviors, perhaps signifying the different extent of deactivation or influence of the dynamic disorder on k.
5:00 PM - NM2.13.02
C60 Based Molecular Self-Assemblies with On-Demand Thermal and Mechanical Properties
Abduljabar Alsayoud 1 , Joshua Vita 1 , Stefan Bringuier 1 , Pierre Deymier 1 , Keith Runge 1 , Krishna Muralidharan 1
1 , University of Arizona, Tucson, Arizona, United States
Show AbstractRecent advances in crystal engineering techniques have enabled the ability to obtain shape-controlled self-assemblies of C60 molecules. Further, the self-assemblies are shown to undergo pressure-induced, photo-induced or electric-field induced polymerization. In particular, it has also been shown that under an electric field, the polymerization is reversible. In this context, using molecular dynamics simulations that employ a relevant and an accurate long-range bond order potential (LCBOB), we demonstrate that reversible polymerization properties of the C60 self-assemblies can be suitably exploited to control phonon propagation and phonon life-times, which in turn provide a ready-made platform for developing new phononic metamaterials with applications in the GHz-THz regime. Specifically, we show that by dynamically controlling the spatial extent of polymerization, the elastic moduli, as well as the wave-propagation properties can be suitably tuned leading to new phononic functionalities of C60 nanostructures. Applications of these systems for developing thermal rectifiers and surface acoustic wave filters and detectors will also be discussed.
5:30 PM - NM2.13.04
Real Time Thermal Conductivity Measurement during Growth of Ultrathin Layers
Pablo Ferrando-Villalba 1 , Daisuke Takegami 1 , Aitor Lopeandia 1 , Joan Rafols-Ribe 1 , Libertad Abad 2 , Gemma Garcia 1 , Javier Rodriguez-Viejo 1
1 Physics Department, Universitat Autónoma Barcelona, Cerdanyola del Valles Spain, 2 , Institut de Microelectrònica de Barcelona- Centro Nacional de Microelectrònica − CSIC, Cerdanyola del Valles, Barcelona, Spain
Show AbstractHere, we present a real-time study of the growth kinetics of materials prepared from the vapour phase, from incipient clustering to continuous film formation and growth. We demonstrate that the high sensitivity of phonons with microstructure permits to use the variation of thermal conductance as a probe of microstructure evolution during film growth stages. Growth monitoring during the early stages of vapour deposition is of prime importance to understand the growth process, the microstructure and thus overall resulting films, as well as nanoparticle assemblies’ properties. In-plane thermal conductivity of organic and metallic films deposited on an amorphous silicon nitride membrane is measured during growth. This thermal sensor, based on the 3ω-Völklein method, shows extremely high accuracy and a resolution of △(κ×t) =0.065 Wm-1K-1, enabling the measurement of ultra-thin films with very low thermal conductivity. At early stages of growth, we observe a reduction of the thermal conductance, K, related to nucleation and cluster formation. As cluster coalescence advances, K reaches a minimum to rise up at the percolation threshold. Subsequent island percolation produces a sharp increase of the conductance and once the surface coverage is completed, K increases linearly with thickness. Values of thickness where percolation threshold and complete coverage are achieved vary as a function of the material and its growth conditions.
5:45 PM - NM2.13.05
Tuning Thermal Conductivity of Metal-Organic–Frameworks
Luping Han 1 , Wenxi Huang 1 , Laura de Sousa Oliveira 1 , Alex Greaney 1
1 , University of California, Riverside, Riverside, California, United States
Show Abstract
Metal-organic frameworks (MOFs) have an open nanoporous architecture that make them suitable for applications in gas storage and gas separation. In many of these applications a MOF’s thermal conductivity is an important contributor to the material’s performance, where the delivery or removal of latent heat is essential for the material’s function. However, the open molecular architecture of MOFs leads to unusual vibrational behavior not seen in fully dense crystals. Concomitantly MOFs carry heat through a mixture of propagating and non-propagating modes, and their open and in some cases flexible architecture provide numerous avenues for engineering thermal transport properties. In this work we show thermal conductivity can be tuned by gas intercalation, network interpenetration, and structural transition. We show how these different mechanisms can be used to turn on or off different channels for heat conduction. Additionally we examine the extent to which simple network models, often used to understand mechanical behavior of MOFs, can be applied to intuitively understand MOF thermal transport properties.
NM2.14: Poster Session III: Heat Transport at the Nanoscale
Session Chairs
Friday AM, April 21, 2017
Sheraton, Third Level, Phoenix Ballroom
9:00 PM - NM2.14.01
Local Thermal Calibration for Quantitative Measurement Using Thermoresistive Micro and Nanoprobes
Eloise Guen 1 , David Renahy 1 , Pierre-Olivier Chapuis 1 , Severine Gomes 1
1 , CETHIL-UMR5008, CNRS, INSA Lyon, Villeurbanne France
Show AbstractScanning thermal microscopy (SThM) is a technique that allows thermal imaging of solid material surfaces with a sub-micrometric spatial resolution and sub-kelvin thermal sensitivity [1]. In addition of its imaging mode, SThM allows in its active mode the characterization of thermal and temperature-dependent properties of materials by following the response of a resistive probe during its controlled heating while its apex remains in contact with the sample surface. As an example the goal can be to determine the thermal conductivity or the phase transition temperature of the sample. Nevertheless, obtaining quantitative measurements is very challenging because of the complex probe-sample interaction occurring at nanoscale [2-4]. The main heat transfer channels are conductions through the surrounding gas and through the tip-sample contact. They are strongly dependent on various parameters such as the size, geometry and surface of probe and sample.
In this work, we studied the possibility to calibrate the technique using specimens of well-known thermal conductivity and surface controlled in terms of roughness and nanomechanical properties so that quantitative measurement of an unknown sample is possible. Two different surrounding environments were considered, ambient air and vacuum, and three thermoresistive SThM probes were used: the first sensor is made of an etched Wollaston microwire, the second one of a palladium nanoelement and the third one of low-doped silicon. For each probe and each environment we performed local-point SThM measurements following a precise protocol on fourteen samples comprising metals, semiconductors and polymers. The changes of the electrical probe resistance and that of the derived effective thermal conductance at the probe apex were studied as a function of the sample thermal conductivities. Ultimately SThM measurements were shown to be strongly dependent on the environment and probe, and the nanoprobes response did not necessarily follow the thermal conductivity trend as they are much more sensitive to the tip-sample contact physical parameters.
References: [1] S. Gomès et al. Phys. Status Solidi Appl. Mater. Sci., 212, 3, 477–494 (2015) [2] K. Kim et al. Appl. Phys. Lett., 105, 20 (2014) [3] Y. Ge et al. Nanotechnology, 27, 32, 325503 (2016) [4] F. Menges et al. Rev. Sci. Instrum., 87, 7, 74902 (2016)
Acknowledgements: The research leading to these results has received funding from the European Union Seventh Framework Programme FP7-NMP-2013-LARGE-7 under grant agreement n°604668.
9:00 PM - NM2.14.02
Monte Carlo Simulation of Phononic like Silicon Nanostructures—Comparison to Experiments and Models
Maxime Verdier 1 , Romuald Jucquin 1 , Konstantinos Termentzidis 1 , David Lacroix 1 , Roman Anufriev 2 , Aymeric Ramiere 2 3 , Masahiro Nomura 2 4
1 , University of Lorraine, LEMTA, Vandoeuvre les Nancy France, 2 Institute of Industrial Science, University of Tokyo, Tokyo Japan, 3 LIMMS/CNRS-IIS, University of Tokyo, Tokyo Japan, 4 PRESTO, Japan Science and Technology Agency, Saitama Japan
Show AbstractRecent developments of elaboration techniques allow the design of low dimension systems and nanostructured materials with periodic pattern. Among them, phononic crystals structures (PnC) drew the attention of several research groups due to their ability to strongly hinder heat transport and possibly to control heat fluxes. Potential applications in new technologies are numerous and there is a need of understanding the physic of phonon transport in such devices.
In the present work, following experimental studies carried in this field by M. Nomura et al (1) or J.F. Robillard et al (2), we investigate heat transfer within PNC at room temperature. The proposed methodology lies on the use of Monte Carlo modeling of phonon transport, solving the BTE in the frame of the relaxation time approximation, for realistic structures with characteristic lengths of several microns. For the latter, periodicity and diameter of cylindrical pores are varied for aligned and staggered configurations. Simulation results show good agreement between experiments and numerical modeling. On this basis, an attempt to model and define universal parameters that link the thermal conductivity of the nanostructure to its key geometrical parameters is proposed.
(1) R. Anufriev et al., PRB, 93, 045411, 2016
(2) V. Lacatena et al., APL, 106, 114104, 2015
9:00 PM - NM2.14.03
Ultrafast Interferometric Measurement of Plasmonic Field in a Hot Spot by Thermoreflectance
Martin Berthel 1 , Olga Lozan 1 , Buntha Ea-Kim 2 , Philippe Ialanne 3 , Stefan Dilhaire 1
1 , University of Bordeaux, Talence France, 2 , IOGS LCF, Palaiseau France, 3 , IOGS LP2N, Talence France
Show AbstractRecent advances in nano-photonics lead to extreme light confinement (ELC) and light manipulation. This progress has spawned a variety of new important technological possibilities for the efficient delivery, control and manipulation of optical radiation on the nanoscale. Although the physical principles of ELC with plasmons i.e. nano-focusing has been clearly demonstrated in several studies, further fundamental studies are needed to optimise these processes and control losses in plasmonic devices for viable technological applications.
The unprecedented ability of plasmonic structures to concentrate light in deep-subwavelength volumes has driven their use in numerous nanophotonics technologies [1]. In particular, the ability to concentrate large amounts of energy at nanometer and femtosecond scales has led to a recent emerging field based on plasmon-induced hot carriers (HC), as well as the emergence of new applications by stimulating complex electrical, thermal, mechanical, and chemical processes [1-3]. These recent advances have raised the demand for understanding and characterising the ELC on the nanometer and femtosecond scales. The generation of plasmon-induced HC in metals, i.e. carriers far from the equilibrium with energies significantly larger than the average thermal energy, can be achieved by appropriately concentrating the photon energy at the apex of a metal tip [4-9]. It has been shown that by using such a technique, HC can be extracted with an efficiency of about 30% and then be used as extremely localised sources, but the physical processes induced in such confinements are not yet understood. Many practical applications also need a complete understanding of physical phenomena involved in ELC from the quantum aspect at nanometric and femtosecond scales up to the macroscopic behaviour.
This work is devoted to the characterization of the plasmonic field adiabatically focused to produce a hot nanometric spot. We probed the hot electrons heated by the plasmon dissipation via a femtosecond pump-probe thermoreflectance approach. We have measured and characterised through the hot carriers generated in the hot spot the plasmon field the autocorrelation of the plasmoninc field.
[1] M. Moskovits, Nature Nanotechnology, 10 (2015), 6-8.
[2] M. J. Kale et al, Science, 349 (2015), 587-88.
[3] Brongersma,et al. Nat. Nanotechnol. 10, 25–34 (2015).
[4] Chalabi, H. & Brongersma, M. L. Nat. Nanotechnol. 8, 229–230 (2013).
[5] Clavero, C. Nat. Photonics 8, 95–103 (2014).
[6] A. Giugni, et al, Nature Nanotechnology, 8 (2013), 845-52.
[7] Mukherjee, S. et al. Nano Lett. 13, 240–247 (2012).
[8] G. Baffou, and R. Quidant, Laser and Photonics Reviews, 7 (2013), 171-87.
[9] O. Lozan, M. Perrin, B. Ea-Kim, J.M. Rampnoux, S. Dilhaire, and P. Lalanne, Phys. Rev. Lett. 112, 193903 (2014)
Acknowledgements, This study was carried out with financial support from “the Investments for the future” Programme IdEx Bordeaux–LAPHIA (ANR-10-IDEX-03-02).
9:00 PM - NM2.14.05
Probing In-Plane Phonon Mean Free Paths of MoS2
Taeyong Kim 1 , Bo Sun 1 , Austin Minnich 1
1 , California Institute of Technology, Pasadena, California, United States
Show AbstractThermal transport properties of MoS2 have attracted tremendous attention, not only due to their importance for the thermal management of MoS2 devices but also because of the interesting physics of phonon transport in highly anisotropic solids. A deep understanding of phonon transport in MoS2 requires knowledge of its phonon mean free path (MFP) distribution, which is still unknown due to experimental challenges. Here we report the first experimental measurement of phonon MFPs of MoS2 at 80 K – 300 K obtained using transient grating spectroscopy. By systematically varying the grating period, the characteristic length of in-plane heat transport can be varied from 1 - 60 µm. The phonon MFP distributions can then be reconstructed from the measured thermal conductivities observed at different grating periods using the method of Minnich [Phys. Rev. Lett., 109, 205901, 2012]. Our work provides a new microscopic perspective of heat transport in highly anisotropic solids.
9:00 PM - NM2.14.06
Radiative Heat Transfer between Plasmonic Nanospheres
David Becerril 1 , Cecilia Noguez 1
1 , Universidad Nacional Autonoma de Mexico, Cd de Mexico, FDM, Mexico
Show AbstractThe excitation of surface plasmon resonances determines, among other properties, the optical response of metallic nanospheres (NSs), as well as the dispersive forces between them. The number and frequency of surface plasmon resonances of interacting NSs depend on geometrical parameters that generate an inhomogeneous electromagnetic field. Surfaces plasmons are evanescent waves which, explained in terms of near field fluctuations, are known to enhance by several orders of magnitude the radiative heat exchange between bodies at nanometric distances. Therefore, we want to study the effect of geometrical parameters, such as size and distance of NSs on the near electromagnetic field, and consequently in the radiative heat transfer between them.
We present a spectral representation formalism to obtain the surface plasmon resonances of interacting NSs, which is applied to study the exact near field between two neighboring spherical NPs, where an exact solution is found using a full-multipolar expansion. The spectral representation separates the geometrical parameters from the dielectric contributions, which has the advantage over other methodologies to allow for a systematic analysis of the system in terms of the geometrical properties independently of the dielectric properties or viceversa. Then, the spectral representation is introduced in the fluctuation-dissipation theorem to determine the radiative heat transfer between two or more spherical NSs, where the fluctuating electromagnetic fields are due to the non-zero temperature of each NS. This methodology allows us the identification of the main geometrical and dielectric conditions to optimize the radiative heat transfer between plasmonic NSs.
9:00 PM - NM2.14.07
2D Ballistic Phonon Heat Conduction from Single Metallic Line Investigated with Electrical Means
Wassim Jaber 1 , Celine Chevalier 2 , Pierre Cremillieu 2 , Elyes Nefzaoui 3 , Pierre-Olivier Chapuis 1
1 , CETHIL, Villeurbanne France, 2 , UMI LN2 France-Sherbrooke Grenoble and Ecole Centrale de Lyon, Lyon France, 3 , ESIEE ESYCOM, Marne-la-Vallée France
Show AbstractFourier’s diffusive law fails predicting the heat transfer when the mean free paths (MFPs) of energy carriers are comparable to, or larger than, the characteristic dimensions of a material. In silicon, the average mean free path is estimated to be close to 300 nm at room temperature and increases strongly up to millimeters when the temperature decreases. As an example, ballistic transport takes place in the cross-plane direction of thin films. While this has been largely investigated numerically, it is difficult to split its effect from the one associated to thermal boundary conductances in practice. In contrast, 2D ballistic dissipation from arrays of heat sources standing on substrates has been investigated by optical means in the recent years, with the purpose of determining phonon mean free path distributions [1-2]. In our work, we study experimentally the heat transfer from a single source excited by electrical means [3], a situation closer to that faced by metallic lines in microelectronics, in strongly-ballistic configurations.
Electron-beam lithography patterned gold lines on top of silicon substrates are measured by an electrical setup close to that known as the 3omega method. The thermal conductance associated to heat dissipation from a heated metallic line to the substrate is reported as a function of width and temperature down to 20 K. This allows reaching average Knudsen numbers (Kn), defined as the ratio of the average mean free path to the line width, larger than 5000 (while Kn<<1 is required for the diffusive regime). It is shown that the thermal conductance behavior follows that of the specific heat and not that of the thermal conductivity, as expected in the ballistic case. The results obtained for a single line are compared to previous experimental investigations [4] obtained on similar devices involving ridges expected to be far from equilibrium [5], and to results obtained for arrays of lines [1-2]. They are also compared to numerical simulations based on the Boltzmann transport equation for phonons solved with the discrete–ordinate method (DOM) [6].
[1] K. M. Hoogeboom-Pot et al., Proceedings of the National Academy of Sciences 112, 4846 (2015)
[2] L. Zeng et al., Scientific Reports 5, (2015)
[3] M. E. Siemens et al., Nature Materials 9, 26 (2010)
[4] P.O. Chapuis et al., Proceedings of THERMINIC, 2010
[5] S. Volz and P.O. Chapuis, J. Appl. Phys. 103(3), 034306 (2008)
[6] W. Jaber et al., submitted (2016)
We acknowledge the support of projects ANR NanoHeat and EU FP7 QuantiHeat. We thank the NanoLyon platform (K. Ayadi, J. Grégoire, P. Pittet, J. Degouttes, N. Terrier, J.L. Leclercq), P. Bevilacqua (Ampere) and I. Peck (CIME).
9:00 PM - NM2.14.08
Surface Nanoscale Engineering to Tune Phonon Dispersion and Lifetimes in Low-Dimensional Semiconductors
Sanghamitra Neogi 1 , Davide Donadio 2
1 Department of Aerospace Engineering Sciences, University of Colorado Boulder, Boulder, Colorado, United States, 2 Department of Chemistry, University of California Davis, Davis, California, United States
Show AbstractTo achieve control of phonons, especially at micro- and naoscale, has an ever increasing importance in a broad range of technological applications, encompassing nanoelectronics, renewable energy harvesting, nano- and opto-mechanics, quantum technologies and medical therapy, imaging and diagnostics. When the system size reaches nanoscale, phonon transport in ultrathin silicon membranes can be tuned by surface characteristics at nanoscale [1]. In addition, inclusion of local surface resonators in the nanophononic metamaterials (NPMs) is shown to engender the emergence of unique nanoscale subwavelength properties at the nanoscale [2].
We carried out a systematic spectral analysis of the impact of band structure hybridization on phonon scattering and consequentially, on phonon transport in locally resonant silicon membrane-based NPMs with two surface nanopattern geometries--nanopillars and nanoridges that extrude off the surfaces of these membranes. We used an approach based on the Boltzmann transport equation with relaxation time approximation as well as classical equilibrium molecular dynamics to investigate the phononic thermal transport in nanopatterned silicon membranes with thicknesses of the order of 20 nm and below. The phonon relaxation times are calculated using Fermi’s Golden Rule and taking into account the contribution of three-phonon processes using anharmonic lattice dynamics. We find that the presence of local surface resonators has a significant effect on the phonon dispersion and has a direct consequence of suppression of phonon group velocities in nanostructured silicon membranes. In addition, the surface structures have unique effects on the phonon relaxation times in these membranes based on their nanoscale character. Our study establishes the relationship between surface nanoscale geometry and spectral contribution to in-plane phonon transport in ultrathin silicon membranes and provides insight for materials design for future phononic applications with controlled phonon transport in materials.
[1] S. Neogi et al, “Tuning Thermal Transport in Ultrathin Silicon Membranes by Surface Nanoscale Engineering.” ACS nano, 9(4), 3820-3828 (2015).
[2] B. L. Davis and M. I. Hussein, Physical review letters 112, 055505 (2014).
9:00 PM - NM2.14.09
Comparison of Monte Carlo Methods for Phonon-Boundary Scattering in Nanoporous Silicon Films
Kevin Parrish 1 , Justin Abel 1 , Ankit Jain 1 , Jonathan Malen 1 , Alan McGaughey 1
1 , Carnegie Mellon University, Pittsburgh, Pennsylvania, United States
Show AbstractThe thermal conductivity of silicon thin films with periodic pore arrays are calculated using two Monte Carlo-based techniques that treat phonons as particles. The first method is a path sampling technique that modifies the intrinsic bulk mean free paths. The second method uses ray tracing to calculate a boundary scattering mean free path that is agnostic of the material and uses the geometry alone. The boundary scattering mean free path then is combined with the intrinsic bulk mean free path using the Matthiessen rule. The bulk phonon properties are obtained from first-principles driven harmonic and anharmonic lattice dynamics calculations. The path sampling technique predicts the largest mean free path to be an order of magnitude greater than the ray tracing method. We attribute this difference to the modal detail provided by the path sampling technique. The thermal conductivity predictions are compared to existing measurements on a series of structures. While both modeling techniques predict a thermal conductivity reduction in agreement with the measurements, the path sampling technique more accurately reproduces the relative reduction between different structures.
9:00 PM - NM2.14.10
Effect of Anharmonicity on Thermal Conductance at Solid/Solid Interfaces with an Intermediate Layer
Rouzbeh Rastgarkafshgarkolaei 1 , Jingjie Zhang 4 , Carlos Polanco 4 2 , Nam Le 1 3 , Avik Ghosh 4 , Pamela Norris 1
1 Mechanical and Aerospace Engineering, University of Virginia, Charlottesville, Virginia, United States, 4 Electrical and Computer Engineering, University of Virginia, Charlottesville, Virginia, United States, 2 Materials Theory Group, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 3 , Naval Research Laboratory, Washington DC, District of Columbia, United States
Show AbstractMolecular dynamics (MD) simulations are utilized to investigate the effect of anharmonicity on thermal transport at mismatched solid/solid interfaces with an added mass-graded intermediate layer. It has been shown that adding an intermediate thin layer can enhance thermal boundary conductance [1]. Maximum enhancement can be achieved when the atomic mass of the intermediate layer is close to the geometric mean of the two contacts’ atomic masses [2]. Thus we setup a system with mass-graded intermediate layer which consists of several layers within the intermediate layer and atomic mass of each layer is the geometric mean of the two neighboring layers’ atomic masses. Our preliminary results show that adding a mass-graded intermediate layer can further enhance the thermal transport at these interfaces. By comparing thermal boundary conductance calculations in presence of inelastic processes with those of harmonic systems, we show that anharmonicity can play a major role in this enhancement. Inelastic phonon processes are naturally included in our MD simulations due to the anharmonic interatomic potentials. Furthermore, we compare our MD results with those of non-equilibrium Green’s function formalism (NEGF), which are solely harmonic, to isolate the contribution from inelastic phonon scattering. We have already shown that our calculations from these two methods are in agreement at very low temperatures where energy transport is dominated by harmonic phonon interactions. We prescribe different levels of anharmonicity by changing the atomic mass, and thickness of the intermediate layer and also varying the temperature. Moreover, we will further study anharmonicity in a more systematic fashion where we vary harmonic and anharmonic force constants (up to 4th order) in 1D and 3D systems. This approach can provide us with a better understanding of anharmonic contribution to thermal transport at such interfaces.
[1] English, T. S.; Duda, J. C.; Smoyer, J. L.; Jordan, D. A.; Norris, P. M. & Zhigilei, L. V.; Enhancing and tuning phonon transport at vibrationally mismatched solid-solid interfaces; Phys. Rev. B, American Physical Society, 2012, 85, 035438.
[2] Polanco, C. A.; Rastgarkafshgarkolaei, R.; Zhang, J.; Le, N. Q.; Norris, P. M.; Hopkins, P. E. & Ghosh, A. W.; Role of crystal structure and junction morphology on interface thermal conductance; Phys. Rev. B, American Physical Society, 2015, 92, 144302.
KEYWORDS: Anharmonicity, Green’s function, Molecular dynamics, Phonon Transport, Thermal boundary conductance.
9:00 PM - NM2.14.12
Understanding the Origins of Large Negative Thermal Expansion in Ferroelectric Perovskites from First Principles
Ethan Ritz 1 , Nicole Benedek 1
1 , Cornell University, Ithaca, New York, United States
Show AbstractMany of the functional properties of ABO3 perovskite oxides (for example, ferroelectricity) are strongly linked to particular phonon modes in the material. In addition, in many cases it is possible to formulate simple guidelines or ‘rules of thumb’ that link crystal structure and chemistry to specific lattice dynamical characteristics. The thermal transport properties of perovskites are thus potentially highly tunable and dynamically controllable with external fields. Unfortunately, compared to the main group semiconductors, little is understood of the thermal transport properties of perovskites at a detailed (phonon mode) level. We use first-principles density functional theory to reveal new details related to the origin of the large negative thermal expansion (NTE) observed for ferroelectric PbTiO3. Although the origin of NTE in this material is often ascribed to ferroelectricity (which arises from the freezing in of a soft, zone-center optical phonon), our results suggest that zone-boundary modes play a major role in driving NTE. In addition, hybridization between different electronic states has a significant effect on the lattice dynamics of PbTiO3 in general, and its NTE behavior in particular. Our work has implications for the understanding of, discovery and design of NTE in perovskites and other families of inorganic materials.
9:00 PM - NM2.14.13
Quantitative Measurements of Intrinsic Thermal Conductivity of Surface and Buried Nanoscale Layers via Cross-Sectional Scanning Thermal Microscopy – X-SThM
Jean Spiece 1 , Charalambos Evangeli 1 , Alexander Robson 1 2 , Benjamin Robinson 1 , Francesc Alzina 3 , Oleg Kolosov 1 2
1 Physics, Lancaster University, Lancaster United Kingdom, 2 , Lancaster Materials Analysis Ltd, Lancaster United Kingdom, 3 , ICN, Barcelona Spain
Show AbstractMeasuring thermal conductivity of nanoscale thin layers in a multilayer device is a fundamental task critical for the semiconductors (processors and memory), energy storage and nanoscale sensors. Unfortunately, major questions – getting access to a particular buried layer, and how to decouple boundary thermal resistances from the intrinsic material thermal conductivity, present significant challenge for the quantitative measurements.
Here we present a new paradigm combining a a cross-section of the material or device via Ar ion polishing followed by the quantitative measurement of the heat transport via scanning thermal microscopy – cross-sectional SThM, or x-SThM. The studied multilayer structure is first polished via “beam-exit cross-sectional polishing” (BEXP), that unlike traditional ion polishingwith beam impinging on the surface, directs polishing Ar-ion beam to the side of the sample [1] that exits the front surface at a glancing angle of about 50 creating a close to open angle wedge cross-sectioning the inner layers at the oblique angle. Glancing incidence produces a minimal damage to the layer and excellnt close-to atomic flat surface.
The thermal resistance R for the heat transferred through this wedge to the substrate is directly measured by the SThM [2] as a function of the wedge thickness d. The increase of the thermal resistance with thickness Rx=dR/dt reflects only the thermal conductivity of the sample, eliminating both the SthM tip-layer thermal resistance and layer-substrate thermal resistance, two notorious unknown parameters that render majority of SThM measurements to be merely qualitative. By comparing Rx with the same value for the known material – e.g. SiO2 wedge on Si substrate – RSiO2 we obtain true quantitative data for the thermal conductivity of the unknown material.
We applied x-SThM in vacuum and air environments to measure the thermal conductivity of SiGe alloys of gradient composition with a few 10-nm lateral resolution, for SiGe layer grown on a Si substrate with Ge composition varying from 0 to 23%. While SiGe is a highly promising material for both high speed processors demonstrating 0.8 THz transistors and future thermoelectric applications [3] fully compatible with Si processing, its nanoscale thermal conductivity remains a big unknown, providing a major challenge for development of advanced chips and nano-thermoelectrics.
x-SThM allows to measure and map thermal conductivity of a wide range of organic and inorganic nanoscale layers. Being suitable for almost any material, ranging from simple compounds to nanodevices, the high flexibility of the process opens wide scopes of research in nanothermal transport realm and beyond.
References
[1] Kolosov OV, Grishin I Method and apparatus for ion beam polishing. USA patent 9,082,587. 2015 July 14, 2015.
[2] Pumarol, M., Rosamond, M., Tovee, P., Petty, M., Zeze, D., Falko, V., & Kolosov, O. Nano letters, 12(6), 2906 (2012).
[3] Lee EK et al. Nano Letters. 2012;12(6):2918-23.
9:00 PM - NM2.14.14
Roles of Interface and Substrate Properties on Through-Plane Heat Dissipation in 2D-Material-Based Devices
Poya Yasaei 1 , Amirhossein Behranginia 1 , Ahmed El-Ghandour 1 , Craig Foster 1 , Amin Salehi-Khojin 1
1 , University of Illinois at Chicago, Chicago, Illinois, United States
Show AbstractThe generated heat in current high-performance devices based on two-dimensional (2D) materials primarily dissipates through the plane into the substrate rather than in-plane. In the through-plane direction, the interface and substrate resistances comprise the overall thermal dissipation resistance to the environment (RTH), but the relative importance of these resistances are just qualitatively known in 2D-based devices. In this work, we utilized a custom-designed electrical thermometry platform to investigate the thermal transport across chemical vapor deposited (CVD) graphene and molybdenum disulfide (MoS2) monolayers stacked between Au/Ti electrodes and different technologically-viable substrates over a temperature range of 85-295K. Thermometry experiments and extensive finite element analyses are employed to precisely quantify the roles of the interface (boundary) and substrate resistances (comprised of bulk and dielectric resistances) on the RTH on various substrates including diamond, sapphire, aluminum nitride (AlN), Si/SiO2 (thin oxide), and Si/Al2O3. Our results and analyses suggest that the interface and bulk properties of the substrate must be simultaneously designed in accord with the 2D materials and to provide the highest heat dissipation capability.
9:00 PM - NM2.14.15
Quantifying the Propagon Contribution to Thermal Conductivity in Free-standing Amorphous Germanium Films
Ruiqiang Guo 1 , Jaeyun Moon 1 , Austin Minnich 1
1 , California Institute of Technology, Pasadena, California, United States
Show AbstractThermal transport in amorphous solids is of crucial importance for applications such as photovoltaic solar cells, thermal insulation, and infrared detectors used for space science. However, the physics of heat-carrying vibrations in these solids remain poorly understood due to both computational and experimental challenges. Here, we use transient grating spectroscopy to probe heat conduction in free-standing amorphous Ge films over micron length scales. We find that propagons contribute substantially to the thermal conductivity despite the atomic disorder of the film. Our results expand the fundamental understanding of thermal transport mechanisms in amorphous solids and identify the characteristic length scales for further manipulation of thermal conductivity in amorphous Ge using structure engineering.
9:00 PM - NM2.14.16
Validity of the Isotropic Thermal Conductivity Assumption in Supercell Lattice Dynamics
Ruiyuan Ma 1 , Jennifer Lukes 1
1 , University of Pennsylvania, Philadelphia, Pennsylvania, United States
Show AbstractSuperlattices and nano phononic crystals have attracted significant attention due to their low thermal conductivities and their potential application as thermoelectric materials. A widely used expression to calculate thermal conductivity, presented by Klemens and expressed in terms of relaxation time models by Callaway and Holland, is derived from the Boltzmann transport equation. In its most general form, this expression involves a direct summation of the heat current contributions of individual phonons of all wavevectors and polarizations in the first Brillouin zone. In common practice, the expression is simplified by making an isotropic assumption that converts the summation over wavevector to an integral over wavevector magnitude. The isotropic expression has been applied to superlattices and phononic crystals, but its validity for different supercell sizes has not been studied. In this work, the isotropic and direct summation methods are used to calculate the thermal conductivities of bulk Silicon, Si/Ge superlattices, and Si/Ge quantum dot superlattices. Group velocities for the calculations are obtained using lattice dynamics, and the calculations are validated against previous work (Tamura et al., 2000). The results show differences between the two methods that depend substantially on supercell size.
9:00 PM - NM2.14.17
Viability of HfN Transducers for High Temperature Thermal Measurements Using Time Domain Thermoreflectance
Christina Rost 1 , Kevin Ferri 2 , Lavina Backman 3 , Elizabeth Opila , Jon-Paul Maria 2 , Patrick Hopkins 1
1 Mechanical and Aerospace Engineering, University of Virginia, Charlottesville, Virginia, United States, 2 Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina, United States, 3 Materials Science and Engineering, University of Virginia, Charlottesville, Virginia, United States
Show AbstractTime domain thermoreflectance (TDTR) is a non-destructive, optical pump-probe technique used to measure the thermal properties of material systems. Samples are typically coated with a thin metal transducer layer, such as aluminum or gold. At temperatures approaching 2,000°C, such transducer materials are limited by their respective melting temperatures, making thermal measurements at extreme temperatures incredibly difficult. Hafnium Nitride (HfN) is a conductive ceramic material with a melting point of approximately 3300°C. Additionally, HfN is estimated to have a constant reflectance of 17% and 64% at 400nm and 800nm, respectively, making it a potential candidate for a robust high temperature transducer. This work characterizes the thermal properties of HfN and investigates its viability as a high temperature transducer for TDTR measurements of ultra-high temperature materials. Room temperature thermal conductivity is measured for HfN grown on a variety of substrates including amorphous SiO2, c-Sapphire, MgO, and diamond. Temperature dependent thermal conductivity is measured and compared to that of aluminum, gold, and platinum up to the point of failure. Results and implications for future high temperature TDTR measurements are discussed.
9:00 PM - NM2.14.19
Breaking Network Connectivity Leads to Ultralow Thermal Conductivities in Fully Dense Amorphous Solid
Jeffrey Braun 1 , Sean King 2 , Ashutosh Giri 1 , John Gaskins 1 , Masanori Sato 3 , Takemasa Fujiseki 3 , Hiroyuki Fujiwara 3 , Patrick Hopkins 1
1 , University of Virginia, Charlottesville, Virginia, United States, 2 , Intel Corporation, Hillsboro, Oregon, United States, 3 , Gifu University, Gifu Japan
Show AbstractWe demonstrate a method to reduce the thermal conductivity of fully dense (above the rigidity percolation threshold) amorphous thin films below the minimum limit by systematically changing the coordination number through hydrogenation. Studying a-SiO:H, a-SiC:H, and a-Si:H thin films, we measure thermal properties using time-domain thermoreflectance to show that thermal conductivity can be reduced below the amorphous limit by a factor of up to two. By experimentally investigating the parameters that determine thermal conductivity, we show that sound speed, number density, and heat capacity cannot explain the measured reduction in thermal conductivity, revealing that coordination number can significantly alter the scattering length scale of heat carriers. Reformulating the minimum limit to consider the propensity for energy to transfer through the non-hydrogen network of atoms, we observe greatly improved agreement with experimental data.
9:00 PM - NM2.14.20
Non-Equilibrium Molecular Dynamics Simulations of Thermal Boundary Conductance in Stacked Two-Dimensional Materials
Klas Karis 1 , Arman Fathizadeh 1 , Fatemeh Khalili-Araghi 1
1 Physics, University of Illinois at Chicago, Chicago, Illinois, United States
Show AbstractIn the design of nano-electronic devices using two dimensional (2D) semiconductors, precise knowledge of the thermal boundary conductance at interfaces is crucial from a thermal management perspective. However, experimentally, it is not possible to determine the contribution of each interface in a multi-layered 2D structure. We have carried out non-equilibrium molecular dynamics (NEMD) simulations to calculate the boundary (Kapitza) conductance of molybdenum disulfide (MoS2) sandwiched between crystalline titanium (Ti) and amorphous silicone dioxide (SiO2). This simulated structures resemble the experimental platforms developed for cross-plane thermal measurements of 2D materials. Our results indicate that in the triple-stacked structure, the Kapitza conductance of each interface (Ti-MoS2 and MoS2-SiO2) increases compared to that of the same interface in a double-stacked system. The Ti-MoS2 interface increases in conductivity by a factor of 1.7 while the MoS2-SiO2 interface conductance increases by 3.7. Our results uncover that once sandwiched between two substrates, the interfacial properties of the MoS2 are affected in a non-trivial fashion, such that the results of single interface measurements cannot be translated to a multilayered system.
9:00 PM - NM2.14.21
Characterizing and Controlling the Anisotropic Nanoscale Heat Transfer in 2D van der Waals Materials
Joon Sang Kang 1 , Ming Ke 1 , Yongjie Hu 1
1 Department of Mechanical and Aerospace Engineering, University of California, Los Angeles (UCLA), Los Angeles, California, United States
Show AbstractTwo-dimensional (2D) layered materials have been of great research interest recently due to their rich potential for energy conversion, storage, and electronics. The mechanism of the energy transfer process, in particular, the coupling effects between structure surfaces, dimensions, interfaces, and thermal properties, remain to be explored. Here, we describe our current progress on experimentally quantifying and controlling the thermal properties of 2D materials under chemical synthesis and modifications. Our work focuses on the fundamental understanding and manipulation of the unique thermal transport phenomena and phonon spectra in 2D materials. We expect our study will bring further the promise of rational material design to achieve high performance through a synergistic experiment-modeling approach. The significant impact of this research in improving the efficiency of thermal energy conversion, storage, and thermal management, as well as developing novel thermal devices will also be discussed.
9:00 PM - NM2.14.22
Deterministic Simulation of Frequency Dependent Phonon Transport in Nuclear Materials
Jackson Harter 1 , Aria Hosseini 2 , Todd Palmer 1 , Alex Greaney 2
1 , Oregon State University, Corvallis, Oregon, United States, 2 , University of California, Riverside, Riverside, California, United States
Show AbstractPredicting thermal conductivity in nuclear fuels under irradiation is an important component in the safe operation of nuclear power plants and research reactors. The code Rattlesnake solves the Boltzmann transport equation (BTE) for neutrons in the Self-Adjoint Angular Flux formulation with a variety of spatial and angular discretizations. We use a modified implementation of Rattlesnake to simulate phonon transport in 3D heterogeneous materials with defects and compute thermal conductivity using moments of angular phonon radiance.
We solve the phonon BTE using the method of source (or Richardson) iteration, which has a rich history in neutron transport. As the Self-Adjoint form of the BTE with the discrete ordinates angular discretization involves the solution of a linear system of equations generated from the discretization of an elliptic operator for each ordinate in the angular quadrature, we are able to take advantage of mature and efficient numerical solution techniques. Specifically, we employ the generalized minimum residual (GMRes) method, preconditioned with multigrid. For acoustically thick problems, more efficient transport iteration schemes may be necessary. Rattlesnake also provides the option of nonlinear diffusion acceleration (NDA), which solves a low-order diffusion equation to rapidly generate an improved scattering source for the Boltzmann transport equation.
We have previously solved the phonon BTE in a gray formulation in both homogeneous and mixed media, an approach which does not account for mean free path dependence on the phonon frequency spectra. We are implementing multi-frequency transport which permits contributions from temperature-dependent frequency spectra to influence the phonon radiance. We demonstrate the effectiveness of this predictive approach by solving the phonon BTE in a bulk material with defects.
9:00 PM - NM2.14.23
Light-Induced Temperature Control in Solid-State Nanopores
Hirohito Yamazaki 1 , Rui Hu 2 , Robert Henley 1 , Meni Wanunu 1
1 , Northeastern University, Boston, Massachusetts, United States, 2 , Peking University, Beijing China
Show AbstractThe ability to interrogate single molecules using nanopores has resulted in a wide spectrum of applications, from macromolecular identification to DNA and RNA sequencing. Nanopores in synthetic materials offer other attractive benefits, such as the ability to tailor the material properties and the sensor robustness. In this work, we present a method to instantaneously (sub-microsecond timescales) affect the temperature of a nanopore, thereby enabling extremely fast temperature-jump experiments on individal molecules. We will provide a cutting-edge proof that thermal effects dominate when nanopore is irradiated with light. A very compelling application for this effect is to study kinetics and thermodynamics of single molecule unfolding, which we will demonstrate in this presentation.
9:00 PM - NM2.14.24
Synthesis and Thermal Analysis of Vertically Aligned CNTs Grown on Copper Substrates
Qiuhong Zhang 1
1 , University of Dayton, Dayton, Ohio, United States
Show AbstractDue to the low degree of contact area and weak interfacial adhesion between CNTs and the growth substrate (Cu), large thermal contact resistance is the largest challenge preventing the use of vertically aligned CNTS (VACNTs) as a thermal interface material (TIM). Although significant research has been done (this group’s previous work) regarding the growth of CNTs on reactive substrates by using an appropriate buffer layer in, there are many unanswered questions associated with using VACNTs as a thermal interface material beyond CNT synthesis. Very little has been reported regarding interfacial thermal properties, especially regarding direct growth of VACNTs on Cu substrates. This effort extends the work done previously on carbon nanotube growth, by concentrating on ways to evaluate/measure CNT-based nanocomposite thermal resistance. In this study, with the use of a laser flash measurement system, the influence of buffer layer (thickness and material) and CNT array properties (layer height and density) on the thermal diffusivity and thermal resistance of the CNT composite has been investigated. Test results identify a correlation between the CNT array density/thickness and its thermal resistance on a Cu substrate.
9:00 PM - NM2.14.25
Novel Scanning Thermal Microprobe for Co-Registered Seebeck Coefficient and Thermal Conductivity
Nicholas Kempf 1 , Yanliang Zhang 1
1 , Boise State University, Boise, Idaho, United States
Show AbstractScanning thermal microscopy (SThM) is a powerful tool for the characterization of material properties on the micro- and nanoscale. For instance, SThM is very useful in areas where traditional measurement techniques cannot quantify property changes, such as in irradiation experiments where the damage depth is limited to 10’s of microns or less. It can also be used to quickly determine the optimal properties, and thus the optimal composition, of combinatorial films. Despite these exciting applications, most micro- and nanoscale SThM hot-probes for thermal conductivity measurement are not capable of making electrical contact on samples with resistive oxide layers. In certain fields, it is extremely desirable to quantify both thermal and electrical properties with a single probe at the same location and with minimal sample preparation.
SThM probes based on a heated resistive wire have been demonstrated to simultaneously measure thermal conductivity and Seebeck coefficient on bismuth telluride and other bulk thermoelectric materials. However, through extensive study we have found that the conventional Wollaston wire microprobe has several limitations, including high thermal contact resistance, low measurement repeatability and sensitivity, and the inability to establish electrical contact through nanoscale oxide layers – greatly limiting the range of samples that can be measured.
Here we present the development of a scanning thermal probe based on the Wollaston wire with novel support structure. While maintaining microscale spatial resolution, the probe exhibits enhanced sensitivity, lower thermal contact resistance, and simultaneous electrical and thermal measurements on materials with >20 nanometer thick oxide layers. Furthermore, the probe is capable of measuring a wide range of materials with thermal conductivity up to 20 W/m-K. The power of the probe is demonstrated with quantified thermal conductivity and Seebeck coefficient measurements on combinatorial thermoelectric films and on proton-irradiated thermoelectric materials.
9:00 PM - NM2.14.26
Epitaxial Metal-Semiconductor Interfacial Thermal Conductance
Ning Ye 1 , Joseph Feser 1
1 Mechanical Engineering, University of Delaware, Newark, Delaware, United States
Show AbstractAs the development of nano-electronic devices, the interfacial thermal resistance begins to play a much more important role than the film thermal resistivity on the heat transport of the devices. Therefore, understanding the interfacial thermal conductance (resistance) would be substantial to design and modify the thermal transport properties of the devices with better performance. In this work, thermal conductance of epitaxial NiAl/GaAs, Al/AlxGa1-xAs and silicides/silicon interfaces were studied by time domain thermoreflectance (TDTR) at different temperatures. In addition, these experimental results were carefully compared to the modeling results of the acoustic mismatch model (AMM) and diffuse mismatch model (DMM) in order to understand the dominate mechanisms of heat transportation across these metal-semiconductor interfaces.
9:00 PM - NM2.14.27
Characterization of Thermal Transport in Amorphous Germanium
Freddy DeAngelis 1 , Asegun Henry 1
1 , Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractThe development of frameworks such as the phonon gas model (PGM) and lattice dynamics have led to significant improvement of our understanding of thermal transport in well-ordered solid materials. Thermal tranport in disordered materials, such as amorphous solids, is less well-understood. Due to the lack of periodic, long-range order in amorphous substances, a group velocity cannot be definied, and the PGM therefore cannot be applied to study such systems, necessitating the use of methods such as molecular dynamics (MD). Using density functional theory, we have generated accurate interatomic potentials to describe the interactions of atoms in amorphous germanium. By implementing these potentials in MD simulations, in combination with Green-Kubo Modal analysis, we have analyzed the means by which heat propagates in amorhpous germanium. Our analysis includes analysis of the full spectrum of "phonon-like" vibrational modes, categorizing such modes as propagons, diffusons, or locons, and determining the extent of their contribution to thermal conductivity within amorphous germanium. Such analysis can allow for improved thermal management in applications in which amorphous germanium is used.
9:00 PM - NM2.14.28
Temperature Dependent Thermal Conductivity of Aluminum Rich AlGaN Alloys
Christopher Saltonstall 1 , Andrew Allerman 1 , Thomas Beechem 1
1 , Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractTemperature dependent thermal conductivity is examined as a function of aluminum composition in AlGaN alloys to assess the dominant phonon scattering mechanisms. AlGaN is being increasingly pursued as the active material for power electronics where its “ultra” wide-bandgap and thus large break down voltage result in advantages over either GaN or SiC. In such devices, large voltages, frequencies, and currents induce significant self-heating that can limit both performance and reliability. Understanding the evolution of this heating necessitates an understanding of the underlying thermal physics of the active materials. Despite this fact, there are few experimental quantifications of AlGaN’s thermal conductivity. Consequently, the dominant phonon scattering mechanisms remain the subject of debate. In response, the thermal conductivity of AlGaN alloys possessing aluminum compositions ranging from 0.26 to 0.7 is measured from 80-500 K utilizing time domain thermoreflectance (TDTR). Results are compared to established phonon scattering models for alloys under the virtual crystal approximation to identify the dominant factors dictating thermal transport.
Sandia National Laboratories is a multi-mission laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.
9:00 PM - NM2.14.29
Heat Conduction Analysis Involving the Effect Arising from Phonon Coherence
Takuma Shiga 1 , Junichiro Shiomi 1 2
1 , The University of Tokyo, Tokyo Japan, 2 , National Institute for Materials Science, Tsukuba Japan
Show AbstractKnowledge on characteristic lengths for phonons such as coherence length and mean free path is indispensable for thermal conductivity manipulation by structural control. While recent anharmonic phonon calculations have quantitatively revealed order of phonon mean free path, investigations on coherence length, being a length scale for wave nature of phonon, are still limited. In this work, by performing molecular dynamics simulations to model crystals, we have calculated frequency-dependent coherence length of phonon at given temperature. Furthermore, from the obtained knowledge on coherence length, we have separately evaluated contributions of coherent and incoherent phonons to overall thermal conductivity in frequency space, which facilitates understanding of heat conduction in phononic crystal exploiting wave nature of phonon and leads to design low-coherence-loss phononic crystal.
9:00 PM - NM2.14.30
How are Phonons Scattered at the Interface between Inorganic Nanoparticles and Polymers?
Christian Huebner 1 , Kevin Voges 1 , Miriana Vadala 1 , Doru Lupascu 1
1 Institute for Materials Science, University of Duisburg-Essen, Essen Germany
Show AbstractPolymers are used in a broad variety of fields – from daily domestic uses to high-tech applications. To further enhance the spectrum of polymer properties, inorganic nanoparticles can be incorporated into polymer matrices. This can improve certain material specific properties like hardness, abrasion resistance, chemical stability and others.
Our work is focused on the integration of inorganic nanoparticles into polymer matrices and the thermal properties of the resulting composite materials. As nanoparticles we use commercial as well as custom synthesized SiO2, Al2O3, and carbon black. Thermoplastic polymer matrices like polyvinyl alcohol (PVA), polyetherimide (PEI), polyvinylidene fluoride (PVDF) and polystyrene were used. To match the chemical properties at the interface of the nanoparticles and the polymers, the surface of the particleswas modified with organo-silyl coupling agents. De-agglomeration experiments were performed by high-energy ball milling and sonication to enable a fine and equal distribution of the nanoparticles in the polymers. The results of the de-agglomeration step have been investigated by dynamic light scattering technique (DLS) to compare particle sizes. The success of the functionalization was analyzed by infrared spectroscopy (FT-IR). Thermal conductivity of the hot- and cold-pressed composite materials were measured by transient hot bridge THB-100.
To improve our knowledge of the thermal properties of these composite materials, it is important to obtain a better understanding how the phonons are scattered at the interfaces within the materials. Furthermore the influence of the chemical functionalization of the nanoparticle surface on the phonon scattering processes have to be understood.
9:00 PM - NM2.14.31
Controlling Thermal Transport in Porous Nanocomposite for Thermoelectric Applications
Yue Wu 1
1 , Iowa State University, Ames, Iowa, United States
Show AbstractHollow nanostructures have received continuous interests in diverse fields, such as batteries, supercapacitors, biomedical, catalysis (reactor), photocatalysis, sensors and optics, because their hollow interiors can act as containers and/or provide a large number of reactive sites. To synthesize hollow nanostructures, hard templating (e. g. against silica nanoparticles or polystyrene nanobeads) and self-templating (e.g. Kirkendall effect) are widely investigated and the underlying growth mechanism has been extensively studied. Self-templating synthesis is considered to be cost-effective and easy to scale up. The large-scale synthesis, together with exploring new ways to utilize hollow nanostructures will finally push them into practical use.
In this talk, we report the scalable synthesis of hollow nanostructures and the subsequent sintering of them into a highly porous thermoelectric nanocomposite. The as-sintered material has high porosity and holds a record low thermal conductivity, however, its zT is comparable to or even better than the state-of-the-art. The relative density leads to the less cost in raw material and better portability. We foresee that this large-scale approach can be extended to other types of thermoelectric materials and will inspire the utilization of hollow nanostructure in other fields.
9:00 PM - NM2.14.32
A Detailed Wave-Packet Study of Phonon Scattering at Surfaces—Effect of Roughness and Morphology
Cheng Shao 1 , Qingyuan Rong 1 , Ming Hu 2 , Hua Bao 1
1 , Shanghai Jiao Tong University, Shanghai China, 2 , RWTH Aachen University, Aachen Germany
Show AbstractA better understanding of nanoscale heat transport is important to a wide range of technologies and applications, such as thermoelectric energy conversion, phase change memories, and thermal management of microelectronics. Numerical solving the Boltzmann transport equations under the relaxation time approximation with phonon relaxation time that considering the phonon-phonon and phonon-boundary scattering is a powerful method to model heat transport processes at those nanostructures. While the phonon-phonon scattering processes are well understood and the scattering rates could be calculated with desirable accuracy, the understanding on phonon-boundary scattering is limited, especially when the roughness of the boundary is comparable to the wavelength of phonon. An approximate formula derived by Ziman was widely used to calculate the fraction of specularly scattered phonon at the boundary. However, the derivation of the Ziman’s formula was under the condition that the asperity of the boundary is small and thus will underpredict the specularity in most of the real situations. In this work, a phonon wave packet dynamics method is adopted to study the phonon scattering at boundaries with different asperity. This method could inherently model the scattering process at the boundary with no assumption and provide many scattering details. With the goal of a better understanding of phonon-boundary scattering, we consider surfaces with different characteristic parameters, namely surfaces with different root mean square roughness and correlation length. Special attention will be placed on the differences between phonon with different polarizations and the detailed mode conversion processes at the scattering. The results are compared with that predicted from the Ziman’s formula and some specularity values used in previous works.
9:00 PM - NM2.14.33
Anharmonic Lattice Dynamics Prediction of Thermal Conductivity of 2D Materials—A Discussion on the Accuracy
Han Xie 1 , Hua Bao 1
1 , Shanghai Jiao Tong University, Shanghai China
Show AbstractFirst-principles based anharmonic lattice dynamics calculation is believed to be an accurate method for predicting the thermal conductivity of three-dimensional materials. With the increasing research interest in low-dimensional material, this method has also been directly applied to predict the thermal conductivity of typical two-dimensional materials, such as graphene, silicene, phosphorene, and MoS2. However, previous calculations show quite contradicting results for these two-dimensional materials. We demonstrate that such discrepancy arises from the inaccuracy of the input second-order and third-order force constants. For 2D materials, the force constants must be extremely accurate to obtain a well-converged results. Our investigation improves the predictive power of anharmonic lattice dynamics method and sheds light on the understanding of thermal transport in low-dimensional materials.
9:00 PM - NM2.14.34
Thermal Properties of Half Heusler Superlattices
Emigdio Chavez-Angel 1 2 , Niklas Reuter 1 , Paulina Komar 1 , Gerhard Jakob 1 3
1 , Johannes Gutenberg-Universität Mainz, Mainz Germany, 2 , Catalan Institute of Nanoscience and Nanotechnology, Barcelona Spain, 3 , Graduate School Materials Science in Mainz, Mainz Germany
Show AbstractThermoelectric materials possess a huge potential at industrial levels due to the fact they can be actuators for cooling or warming, as well as for energy harvesting to convert the waste heat into electricity. The long quest to improve their figure of merit values has mainly followed the roadmap of spoiling the thermal conductivity, k. Traditionally, the reduction of k has been achieved through the introduction of structural defects (e.g. porous, boundaries, alloying and so on). Although, the mechanisms have shown to be an effective means for the decrease of k, such incorporations will also have an impact in the electronic properties. In the present work we study the thermoelectric properties of TiNiSn-HfNiSn half Heusler superlattices. A systematic and dramatic decrease of the cross-plane κ has been measured by the 3ω technique. The transition between coherent-incoherent (wave-particle) transport was observed as a minimum in k as a function of period thickness, p. This minimum comes from the competition between the phonons diffusively scattered by each interface and the band-folded phonons [1-4]. These findings open a novel approach for the manipulation of the thermal conductivity based in the control of coherent phonons in SLs.
References
[1] P. Holuj et al, “Reduced thermal conductivity of TiNiSn/HfNiSn superlattices,” Phys. Rev. B 92(2015), p. 125436.
[2] P. Komar et al. " Tailoring of the electrical and thermal properties using ultra-short period non-symmetric superlattices", APL Materials 4(10), p. 104902.
[3] P. Komar et al., "Half Heusler superlattices as model systems for nanostructured thermoelectrics", PSS A, 213(2016), p. 732.
[4] E. Chavez-Angel et al., "Alloy-like behaviour of the thermal conductivity and an estimation of the thermal boundary resistance in superlattices", Preprint Arxiv: 1607.08017 (2016).
9:00 PM - NM2.14.35
The Effect of Nanotube Length and Temperature on Phonon Transport and Thermal Conductivity of Graphyne Nanotubes
Ali Ramazani 1 , Alireza Soleimani 2 , Amin Reihani 1 , Veera Sundararaghavan 1 , Ronald Larson 1
1 , University of Michigan, Ann Arbor, Michigan, United States, 2 , Amirkabir University of Technology, Tehran Iran (the Islamic Republic of)
Show AbstractGraphyne is generated when one-third of the C-C bonds in the graphene are replaced with one acetylene unit, which is structurally stable and synthetically approachable. The presence of acetylene groups reduces the binding energy and modulates optical, electronic, thermal and mechanical properties in different ways. Currently, there are limited theoretical efforts on predicting thermal conductivity of graphyne. In the current study, the effect of nanotube length as well as temperature effect is studied on the phonon transport and thermal conductivity of graphyne nanotubes (GNT) using non-equilibrium molecular dynamics (NEMD) simulations. The results indicate that for all α-, β-, and γ-GNTs, the thermal conductivity increases with the nanotube length, while decreasing with temperature. The highest thermal conductivity is observed for γ-GNT. Additionally, compared to CNTs, all three GNT structures (α, β, γ) demonstrate lower thermal conductivity in all studied lengths and temperatures. Finally, all the calculated thermal properties are interpreted using phonon dispersion relation and density of states. The outcome of this study provides insight into the effect of acetylene bond and crystallographic structure of carbon based materials on their phonon transport and thermal properties in different length and temperature scales.
9:00 PM - NM2.14.36
Parallel Measurement of Conductive and Convective Thermal Transport of Micro/Nanowires Based on Raman Mapping
Yanan Yue 1 , Jingchao Zhang 2
1 , Wuhan University, Wuhan China, 2 , University of Nebraska, Lincoln, Nebraska, United States
Show AbstractThermal transport in one-dimensional structures has been studied extensively in the past two decades for the unique properties. Among different heat transfer modes, heat conduction and convection are of most importance and are studied separately with different experimental techniques. However, they are coupled effects in thermal transport of low-dimensional materials especially at micro/nanoscale. The comprehensive study of the coupled effect requires a parallel measurement, which is still a challenge due to the limitation of characterization pathways. In this research, we report a novel method to study conductive and convective thermal transport of micro/nanowires simultaneously by using steady-state Joule-heating and Raman mapping. In this experimental setup, the wire is suspended between electrodes and supplied with joule heating. Under room environment, the heat dissipates along the sample to the electrodes via heat conduction and to the air through the sample surface via heat convection. The temperature profile along the sample represents the portion of heat conduction and convection, and thus, the corresponding thermophysical property can be characterized from the single temperature profile which can be monitored by simultaneous Raman mapping along the sample. To examine this method, a carbon nanotubes (CNTs) fiber is characterized for its thermal conductivity and convection coefficient with air. The temperature dependence of thermal properties of CNTs fiber including thermal conductivity and convection coefficient is studied. This method features a fast/convenient way for parallel measurement of both heat conduction and convection which is beneficial to comprehensively understanding the coupled effect in micro/nanoscale heat transfer. It can not only be employed to directly measure thermophysical property of low dimensional materials, but also be used for analyzing physical fundamentals in thermal transport under different environment.
9:00 PM - NM2.14.37
Molecular Dynamics Study on Thermal Transport at Carbon Nanotube Interface Junctions—Effects of Mechanical Force and Chemical Functionalization
Wen Chen 1 , Jingchao Zhang 2 , Yanan Yue 1
1 , Wuhan University, Wuhan China, 2 , University of Nebraska, Lincoln, Nebraska, United States
Show AbstractClassical molecular dynamics (MD) simulations are performed in this work to investigate the interfacial thermal transport across stacked carbon nanotube (CNT) junctions. Various approaches are implemented to increase the thermal conductance (G) between CNTs. Effects of crossing angle, contact area, bonding strength, external force and hydrocarbon functionalization on G are investigated. A remarkably increase of thermal conductance is achieved by connecting two CNTs with hydrocarbon chain linkers CH2. The predicted G changes from 229 pW/K without linkers to 4901 pW/K with an optimized linker number, which increases by a factor of 20. Meanwhile, thermal conductance is found to increase monotonically with contact area but decrease inversely with crossing angle. The van der Waals (vdW) bonding strength has similar effects with applied external force on thermal conductance, both of which facilitate the interfacial thermal transport by enhancing the contact pressures. Synthesized relationship of internal coupling strength, external force and final separation distance between CNTs is explored to illustrate the variation of thermal conductance and intermolecular potential energy.
9:00 PM - NM2.14.38
Carbonized Electrospun Nanofiber Sheets for Thermophones
Ali Aliev 1
1 , University of Texas at Dallas, Richardson, Texas, United States
Show AbstractThermoacoustic performance of thin freestanding sheets of carbonized poly(acrylonitrile) and polybenzimidazole nanofibers are presented as promising candidates for thermophones. We analyze thermodynamic properties of sheets using transport parameters of single nanofibers and their aligned and randomly electrospun thin film assemblies. The electrical and thermal conductivities, thermal diffusivity, heat capacity, and infrared blackbody radiation are investigated to extract the heat exchange coefficient and enhance the energy conversion efficiency. Spectral and power dependencies of sound pressure in air are compared with carbon nanotube sheets and theoretical prediction. Despite lower thermoacoustic performance compared to that of CNT sheets, the advanced mechanical strength and cost-effective production technology make them very attractive for large-size sound projectors. The advantages of carbonized electrospun polymer nanofiber sheets are in the low frequency domain (<1000 Hz), where the large thermal diffusion length diminishes the thermal inertia of thick (~200 nm) nonbundled fibers and the high intrinsic thermal conductivity of fibers enhances the heat exchange coefficient. Applications of thermoacoustic projectors for loudspeakers, high power SONAR arrays, and sound cancellation are discussed. .
9:00 PM - NM2.14.39
Interatomic Potentials for Mechanical Properties via Machine Learning
Andrew Rohskopf 1
1 Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractThermal properties of matter emerge from underlying processes at the atomic level. A better understanding of such properties in terms of underlying nanoscale processes is crucial for more rational design and manufacturing of modern devices. Atomistic simulations can be used to predict mechanical properties with atomic insight, mainly via molecular dynamics (MD) simulations where the atomic forces are calculated every time step to predict atomic motions. Accurate dynamics requires an accurate method of sampling the potential energy surface (PES), the system potential energy as a function of atomic positions , in order to obtain the force on each atom as the gradient of the PES. For practical atomistic studies of thermal properties across relevant length ( > 103 nanometers) and time scales ( > 102 nanoseconds), a model of the PES with the following Requirements is needed:
1) Calculation of PES must be fast ( < 0.01 second/atom) so that MD simulations of relevant length and time scales can be performed with reasonable cost on modern computers.
2) Calculation of PES must be chemically accurate ( < 1 kcal/mol) with respect to the true energy, so that simulations are chemically meaningful and forces will be accurate.
3) Requirement 2 must be transferrable to mechanically relevant regions of the PES. This includes atomic positions associated with thermal vibrations across a wide range of temperatures.
Quantum mechanical (QM) methods such as density functional theory (DFT) satisfy Requirements 2 and 3, but greatly fail Requirement 1. Many attempts to bypass the computational costs of QM include development of models that mimic the QM PES, but these models often fail in Requirements 2 and 3. These models include analytical functions of position and fitting parameters known as empirical interatomic potentials (EIPs), which can be fit to reproduce data from experiments or QM methods. Many EIPs fail Requirement 3 because no simple analytical expression can capture the complicated function , which is ideally a solution of the many-body Schrödinger equation. EIPs therefore lack transferability to many atomic scenarios . My initial solution for a method to satisfy Requirements 1-3 involved the creation of an open-source program Pops that uses a genetic algorithm to parameterize any EIP in an EIP database to reproduce DFT forces, energies and stresses of various atomic configurations associated with Requirement 3. I dubbed these optimized EIPs as “phonon optimized potentials” (POPs) since they reproduce phonon dispersion relations, and therefore thermal properties, quite well. My method satisfies Requirements 1 and 2, while 3 is satisfied to a certain extent due to the aforementioned limitations of EIPs. In order to overcome this limitation of transferability, a model that accurately reproduces the complicated function for all mechanically relevant is needed (Requirement 3).
9:00 PM - NM2.14.40
Study of Radiative Heat Transfer in Ångström and Nanometer Sized Gaps
Longji Cui 1 , Wonho Jeong 1 , Victor Fernandez-Hurtado 2 , Johannes Feist 2 , Francisco Garcia-Vidal 2 , Juan Carlos Cuevas 2 , Edgar Meyhofer 1 , Pramod Sangi Reddy 1
1 , University of Michigan, Ann Arbor, Michigan, United States, 2 , Universidad Autónoma de Madrid, Madrid Spain
Show AbstractRadiative heat transfer in the extreme near-field (gap-sizes <10 nm) is of great current
interest. Here, we report studies of radiative heat transfer for gap-sizes of a few Å to 5
nm, performed under ultra-high vacuum conditions between a stiff Au-coated probe
featuring embedded Au-Cr thermocouples and a heated planar Au substrate. Past
measurements performed in ultra-high vacuum conditions showed large apparent nearfield
conductances that are more than three orders of magnitude above the predictions of
state-of-the-art fluctuational electrodynamics calculations. In order to understand the
source of this discrepancy we systematically studied extreme near-field radiative heat
transfer after subjecting Au surfaces to various surface cleaning procedures. We found
that insufficiently cleaned samples lead to unexpectedly large thermal conductances and
feature a small apparent tunnel barrier height (1 eV) suggesting the presence of surface
contamination. When the probe and substrate were systematically cleaned following
protocols involving plasma-cleaning or locally pushing the tip into the substrate by a few
nanometers the apparent barrier heights were found to increase to values as large as 2.5 eV
and the observed near-field conductances decreased to extremely small values—below the
detection limit of our probe—as expected by our computational results. Our results show
that surface contaminants, that confound the interpretation of near-field radiative heat
transfer measurements, can be reproducibly eliminated paving the way for systematic
future studies.
9:00 PM - NM2.14.41
Analysis of the Temperature Dependence of the Thermal Conductivity in Single Crystal Oxides
Eric Langenberg 1 , Elias Ferreiro-Vila 1 , Victor Leboran 1 , Adolfo Otero-Fumega 2 , Victor Pardo 2 , Francisco Rivadulla 1
1 , Centro de Investigación en Química Biolóxica e Materiais Moleculares (Universidade de Santiago de Compostela), Santiago de Compostela Spain, 2 Física Aplicada, Universidade de Santiago de Compostela, Santiago de Compostela Spain
Show AbstractWe report the temperature dependence of the thermal conductivity, k(T), of 27 different single crystal oxides, including 20 perovskites, as well as spinel, corundum and rock-salt structures. They have been selected among the most common substrates for growing epitaxial thin-film oxides, and span over a large range of lattice parameters (from »3.7 Å to »12.5 Å). The experimental data from 20 K to 350 K are analyzed on the basis of the Debye model, in order to understand the different contributions to the phonon relaxation time. We found that k(T) is governed by intrinsic phonon scattering processes in most of the non-perovskite oxides studied (Gd3Ga5O12, and Gd3Ga5O12, MgAl2O4, MgO, etc), while random atomic substitutions and vacancy scattering dominates in complex LSAT and NSAT, and Y2O3-stabilized ZrO2. More surprisingly, intrinsic random atomic vacancies are also responsible of the very low thermal conductivity in REScO3, in spite of their excellent crystalline quality. Our analysis proves that phonon scattering by rare-earth magnetic moments is only of secondary importance in k(T) of REScO3. The effect of ferroelectric domains over k(T) is also discussed by comparison of LiTaO3 with incipient ferroelectrics KTaO3 and SrTiO3.
The analysis reported in this work serves as a guide to understand the relative magnitude of the different factors affecting thermal conductivity in oxides. It also provides a fundamental database for the selection of appropriate substrates for thin-film growth according to their desired thermal properties, for applications in which heat management is important.
9:00 PM - NM2.14.43
Synthesis of Fe1-xCoxS2 Nanoparticles Using Hot-Injection Method for Use in Thermoelectric Applications
Rick Eyi 1 , Seungyong Lee 1 , Andreu Cabot 2
1 , University of Arkansas, Bedford, Texas, United States, 2 , Catalonia Inst Energy Res, Barcelona Spain
Show AbstractFeS2, also known as iron pyrite or “fool’s gold” has been widely investigated because of its interesting characteristics that made it suitable for various energy applications, from solar cells, to batteries. Regarding solar cell applications, its unique properties are a high adsorption coefficient allowing it to absorb most of the visible light at thicknesses lower than 100 nm, and its price as it is the most common sulfide mineral. Despite these advantages, making viable solar cells based on iron pyrite proves to be a daunting task. Many defects arise during and after the synthesis and cause the low performances of the cells. One of the defect results in the metal like conductivity of the FeS2 films. The idea was to use this defect and investigate the thermoelectric properties of the FeS2 nanoparticles. They were synthesized by rapidly injecting in a flask containing iron (II) chloride dissolved in hexadecylamine, elemental sulfur dissolved in diphenylether. The native hexadecylamine ligands were replaced by (NH4)2S ligands to improve the electrical properties of the material. The nanoparticles were dried in vacuum, and crushed to make a powder. The powder was then pressed to make a pellets. The thermoelectric properties of the pellets were measured. The seebeck of the FeS2 showed a p type conductivity but its electrical conductivity was low resulting in a figure of merit in the order of 10-3. To increase the electrical conductivity, FeS2 was doped with cobalt. The nucleation temperature of CoS2 is lower than the nucleation temperature of FeS2, making it difficult to synthesize Fe1-xCoxS2 using hot-injection method. The doping was therefore done in two parts. First a nucleation process involving only Fe and sulfur precursor, followed by a growth process at a temperature lower than the nucleation temperature of CoS2, where Co, Fe, S precursors were introduced in the flask. The Fe1-xCoxS2 nanoparticles with different concentrations of Co (5, 10, 15 and 20 percent) were characterized using XRD, SEM-EDX. The cobalt doped FeS2 nanoparticles were also dried, crushed and pressed to make pellets and their thermoelectric properties were measured. As expected the conductivity of the nanoparticles switched from p-type to n-type after introduction of cobalt. The electrical conductivity gains two orders of magnitude, while the thermal conductivity just slightly increased. The figure of merit gained more than one order of magnitude. More work needs to be done to further improve the figure of merit but it is the highest reported figure of merit from FeS2 nanoparticles reported so far to the best of our knowledge.
9:00 PM - NM2.14.44
Thermal Conductivity of Oxide-Based Thin Films Measured by Frequency Domain Thermoreflectance (FDTR)
Alexandros Sarantopoulos 1 , Minyoung Jeong 2 , Wee-Liat Ong 2 , Francisco Rivadulla 1
1 CIQUS, Universidad de Santiago de Compostela, Santiago de Compostela, A Coruña, Spain, 2 Mechanical Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States
Show AbstractThe extremely large electron mobility in lightly doped SrTiO3 (STO)[1], along with its characteristic band degeneracy at the center of the Brillouin zone[2], makes this oxide an interesting material from the thermoelectric point of view. Ohta et al. showed that its thermoelectric efficiency can be largely increased by reducing its dimensionality [3]. This, along with the possibility to support a two-dimensional electron gas at the interface with LaAlO3, launched the interest in the thermoelectric properties of SrTiO3 thin-films. However, an experimental determination of the complete figure of merit of this system, including the effect of epitaxial stress on the electronic and thermal properties of well characterized thin-films, is lacking.
Here we report the thermoelectric properties of SrTiO3 (STO) and CaTiO3 (CTO) thin-films prepared by Pulsed Laser Deposition, under different degrees of epitaxial stress. Measurements of the thermal conductivity by Frequency Domain Thermoreflectance (FDTR) [5] show that cationic defects determine the thermal conductivity in these films. Moreover, we observed a clear influence of epitaxial stress on the thermal transport, which can be used to further optimize the thermoelectric performance of the films. We show that different growth conditions allow the control of the final concentration of defects in the sample[4], which also determine the electrical conductivity and Seebeck coefficient.
These results show that a careful control of the concentration of defects (namely cation and anion vacancies) during growth can be used to optimize the thermoelectric figure of merit of these oxides.
[1] D. W. Reagor, V. Y. Butko, Nature Materials 4, 593 (2005)
[2] A. F. Santander-Syro et al., Nature 469, 189 (2011).
[3] H. Ohta , S. Kim, Y. Mune, T. Mizoguchi, K. Nomura, S. Ohta, T. Nomura, Y. Nakanishi, Y. Ikuhara, M. Hirano, H. Hosono & K. Koumoto, Nature Materials 6, 129 - 134 (2007)
[4] A. Sarantopoulos, E. Ferreiro-Vila, V. Pardo, C. Magen, M.H. Aguirre, F. Rivadulla, Phys. Rev. Lett. 115, 166801
[5] JA Malen, K Baheti, T Tong, Y Zhao, JA Hudgings, A Majumdar, Journal of Heat Transfer 133 (8), 081601
9:00 PM - NM2.14.45
Magnetic Polariton Enhanced Localized Heating for Heat Assisted Magnetic Recording Applications
Xiaoyan Ying 1 , Liping Wang 1
1 School for Engineering of Matter, Transport & Energy, Arizona State University, Tempe, Arizona, United States
Show AbstractOne of the promising technologies being researched in recent years to increase storage density is heat-assisted magnetic recording (HAMR), this technology leverages the temperature sensitivity of magnets, specifically the fact that coercively and non-linearly decrease at Curie temperature. In HAMR, plasmonic nanostructures acting as near field transducers (NFTs) locally heat up a sub-diffraction-limited writing section above Curie temperature so that data can be written at a lower magnetic field. In most previous HAMR researches, which utilize localized surface plasmon polariton (LSPP) generated by thin lollipop antennas or nano-apertures to produce local heat confinement, efficiencies are hindered due to SPP frequency dependency towards light incidence angles. We proposed a HAMR structure with local heating obtained by Magnetic Polariton (MP) confinement, as MP is not affected by incidence light direction, higher confinement efficiency can possibly be obtained in practice. Here we simulate using ANSYS HFSS the spherical NFT under varies dielectric constants to illustrate material effects on MP driven HAMR confinements. Influence of tuning plasmon frequency and scattering rate in Drude model is discussed and electric fields are compared to optimize MP local confinement in HAMR structures. Furthermore, we present a geometric study of the HAMR structure, including NFT size, structure and gap distance within NFT and Iron-platinum (FePt) writing layer. These parametric studies facilitate understanding of MP driven local confinement and offer new perspective for HAMR NFT designs. Moreover, transient thermal analysis of various designs is included and temperature distributions are obtained in ANSYS Thermal Solver coupled with HFSS module.
9:00 PM - NM2.14.46
Thin Silica Micro-Grating Coating for Enhancing Radiative Cooling of Solar Cells
Linshuang Long 1 2 , Yue Yang 1 , Liping Wang 1
1 School for Engineering of Matter, Transport & Energy, Arizona State University, Tempe, Arizona, United States, 2 Department of Thermal Science and Energy Engineering, University of Science and Technology of China, Hefei, Anhui, China
Show AbstractWith the raising demand for renewable energy, solar cells, which are able to convert the solar radiation to electricity, play a very important role in the energy industry. With the primary goal to improve the conversion efficiency of solar cells, the temperature of the cells needs to be sustained at a low value while in practice the cell performance is usually degraded by overheating with excessive temperatures. Recently, the idea of radiative cooling by dumping infrared thermal energy to the cold space through the atmospheric window from 8 to 13 µm in wavelength has become an attractive way to cool down the solar cells and thereby improve the practical performance. While researchers have proposed and demonstrated different types of structured surfaces in order to enhance infrared emittance within the atmospheric window, most of them involve expensive materials and complex nanostructures, which requires expensive fabrication processes. Here we propose economical thin silica (SiO2) micro-gratings as visibly-transparent but radiatively cooling coatings for lowering the temperatures of solar cells. By using finite-different time-domain (FDTD) method, we have optimized the design of the SiO2 micro-gratings atop heavily doped silicon substrate as solar cells, which could remarkably enhance the infrared emittance up to 100% in a broad band within the atmospheric window. For a heavily doped silicon cell, the cooling power or the emitted thermal energy within the atmospheric window is increased by more than twice compared with the cell without the silica gratings. The well-design silica micro-gratings will be fabricated on a 4-inch silicon wafer with low-cost plasma-enhanced chemical vapor deposition, photolithography, and reactive ion etching processes. The spectral-directional radiative properties will be characterized by a Fourier Transform Infrared Spectrometer as well as spectral-hemispherical ones by a gold-coated integrating sphere. Thermal characterizations will also be carried out to measure the surface temperatures during different times of the day in comparison to the sample without the silica micro-gratings in order to experimentally demonstrate the radiative cooling effect.
9:00 PM - NM2.14.47
Plasmonic Light Trapping for Enhanced Infrared Photon Absorption in Ultrathin Wide-Bandgap Semiconductors
Qing Ni 2 1 , Hassan Alshehri 2 , Liping Wang 2
2 School for Engineering of Matter, Transport & Energy, Arizona State University, Tempe, Arizona, United States, 1 , University of Science and Technology of China, Hefei, Anhui, China
Show AbstractMuch effort has been devoted to the investigation of the thin-film solar cells with thickness of a few micrometers or even less for reduced cost, while the challenges in the weak light absorption have been treated by lots of different strategies such as cavity resonance, surface plasmon, grating diffraction, etc. However, few studies have looked into how to improve the absorption of infrared photons in ultrathin wide-bandgap semiconductors for infrared detectors or thermophotovoltaic energy conversion applications. While sharing the common challenges in weak light absorption with solar cells, wide-bandgap semiconductors with thickness less than 100 nm could significantly reduce the cost, possibly increase the response time, or enable wider applications due to flexibility and light weights. Based on our recent fundamental study for plasmonic light trapping in sub-50nm GaAs solar cells with film-coupled metamaterial structures [2015 AIP Advances, 5, 027104], we propose to study similar effect for enhancing infrared photon absorption in an ultrathin cell such as GaSb or InGaSb, which is sandwiched by subwavelength metallic concave grating covering and a metal film backing. Note that the proposed film-coupled metamaterial structure can not only excite so-called magnetic polariton (MP) modes for spectrally enhanced photon absorption above bandgap, but also serve as top and bottom electrodes for photon-generated charge collection. The radiative properties of the metamaterial structure will be numerically modelled by the rigorous coupled-wave algorithm and finite-difference time-domain methods. Our preliminary results indicate that the normal absorptance in the ultrathin GaSb cell layer of 30 nm can be as high as 95% around the bandgap in compassion to 4% absorption of the same GaSb layer without the top subwavelength grating covering, which clearly demonstrates greatly enhanced infrared photon absorption with the film-coupled metamaterial absorber structure. The underlying mechanism for the enhanced absorption is elucidated to be the excitation of MP with the help of the electromagnetic field distribution at the resonance wavelength. Besides, surface plasmon polaritons can also be excited to enhance the energy absorption at shorter wavelengths. An inductor-capacitor model is utilized to further confirm the excitation of MP, while dispersion relation is used to understand SPP behaviors. Effects of grating period, width, height as well as the cell thickness will be systematically investigated to understand the behaviors of MP and SPP on the light absorption. Different electrode materials like Ag, Au and ITO will be studied as well. This work will facilitate the development of next-generation ultrathin low-cost infrared TPV cells or detectors.
9:00 PM - NM2.14.49
Heat Pulse Propagation in Silicon Phononic Crystals
Weixuan Li 1 , Xiang Chen 1 , Yang Li 1 , Zexi Zheng 1 , Adrian Diaz 1 , Youping Chen 1
1 Department of Mechanical & Aerospace Engineering, University of Florida, Gainesville, Florida, United States
Show AbstractIt has been revealed by experiments that the phononic crystals, with periodic arrays of inclusions or pores, exhibit ultra-low thermal conductivity compared to the bulk crystals. Various computational simulations of nano-sized models using atomistic methods have been reported to investigate the mechanism underlying the thermal conductivity reduction. However, the periodicity of experimentally studied phononic crystals is from hundreds of nanometers to microns, which is beyond the length scale that atomistic simulations can effectively handle. Also, formation of phononic bandgaps and phonon wave interference are reported in various experimental works, indicating the role of long wavelength phonons on the thermal transport behavior in phononic crystals. Thus, to understand the thermal transport in phononic crystals necessitates the need of mesoscale simulation methods, such as the concurrent atomistic-continuum (CAC) method, to provide a complementary study. In this talk, we present a CAC study of heat pulse propagation in silicon phononic crystals at low temperature. Micron-sized computer models are constructed and a coherent phonon pulse model is applied to simulate and visualize the propagation of the heat pulses. For verification and validation purpose, we first simulate single crystalline silicon to reproduce the phonon focusing phenomenon observed in experiments. We then perform CAC simulations to monitor the evolution of the kinetic energy in space and time and to measure the dependence of the energy transmission on the phonon wavelength. Simulation results are presented to provide a quantitatively understanding of the effect of phononic structure in thermal conductivity reduction and the role of long wavelength phonons on the thermal transport.
9:00 PM - NM2.14.50
Dynamical Thermal Conductivity in Single-Crystalline Graphene Ribbons
Arnab Majee 1 , Zlatan Aksamija 1
1 , University of Massachusetts Amherst, Amherst, Massachusetts, United States
Show AbstractThe steady-state behavior of thermal transport in bulk and nanostructured semiconductors has been widely studied, both theoretically and experimentally. On the other hand, fast transients and frequency response of thermal conduction has been given less attention. The frequency response of thermal conductivity has become more crucial in recent years, especially because of the constant increase in the clock frequencies in microprocessors and other terahertz applications. It has been theoretically predicted in 3-d materials that thermal conductivity in response to a time-varying temperature gradient, starts decaying when the frequency of the temperature gradient (f) exceeds a cut-off (fc), where fc has been found to be in the order of phonon relaxation time. The phonon relaxation time in semiconductors like silicon is short, on the order of 2-10 ps, leading to thermal conductivity that is independent of frequency up to very high values exceeding 10 GHz. In contrast, 2-d materials like graphene have much longer phonon relaxation times. Therefore, in suspended graphene ribbons, fc can be expected to be much lower than that of silicon.
We calculate frequency-dependent thermal conductivity of graphene ribbons from the solution of phonon Boltzmann transport equation using improved Callaway model. The phonon dispersion is calculated from the first principles using Quantum Espresso and the scattering rates are taken from our previous work.[1] We observe that thermal conductivity remains constant at low frequencies of temperature gradient and exhibits a decaying behavior at higher frequencies, therefore behaving like low-pass thermal filters. We define cut-off frequency to be the frequency of the temperature gradient at which thermal conductivity becomes less than 70% of its dc value. The cut-off frequency in graphene ribbons is found to be relatively low as compared to that of silicon, ranging from few μHz to 100 μHz at 20 K and in the order of GHz at room temperature, thereby showing dependence on both temperature and size of the ribbons. However, the rate of decay of thermal conductivity beyond cut-off frequency is, surprisingly, found to be independent of temperature and size of ribbons. At low temperatures (20 K), dynamical thermal conductivity as well as the cut-off frequency is dominated by the resistive contribution, and at room temperature, the contribution from non-resistive (normal) processes governs the behavior of thermal conductivity with frequency. We also found that out-of-plane (ZA) modes contribute the most to dynamical thermal conductivity as compared to in-plane modes (LA and TA) at low temperatures, with narrow spectral distribution of phonon mean free path, whereas at room temperature the contribution from in-plane modes dominates the dynamical thermal conductivity, with spectral phonon mean free path spread over a much wider range as compared to that of low temperature.
[1] A.K. Majee and Z. Aksamija, Phys. Rev. B 93, 235423, 2016.
9:00 PM - NM2.14.51
Phonon Transport Dynamics in SiGe Alloy Nanowires and Nanocomposites
Meenakshi Upadhyaya 1 , Zlatan Aksamija 1
1 , University of Massachusetts Amherst, Amherst, Massachusetts, United States
Show AbstractSilicon-germanium (SiGe) alloy nanowires (NWs) and nanocomposites (NCs) have been proposed as candidates for highly efficient thermoelectric (TE) conversion in waste heat recovery applications. The TE conversion efficiency in NWs is limited by the large lattice contribution to thermal conductivity (κ). We study the combined effects of alloying and nanostructuring on phonon transport using a full-band description of the phonon dispersion to capture the anisotropy and a momentum-dependent specularity model for the partially diffuse boundary roughness scattering. We employ the Monte Carlo method to sample the phonon lifetimes and track a large ensemble of phonons through a sequence of scattering events to fully capture the interaction between roughness scattering at the boundaries and intrinsic scattering inside the wire. The strong alloy scattering primarily affects the upper portion and boundary scattering affects the middle of the phonon spectrum, whereas the phonons in the lower portion remain unaffected, resulting in a broad distribution of phonon mean-free-paths. We find that the phonon flights are comprised of a mix of large free-flights over several µm interrupted by bursts of short flights, resulting in a heavy-tailed distribution, characteristic of Levy walk dynamics. We also find that phonon transport is these systems is neither entirely ballistic nor diffusive but falls into an intermediate superdiffusive regime, where Fourier’s law is violated and κ diverges with the length of the system as κ ∝ Lα. This exponent of length dependence α ≈ 0.33 over a broad range of wire lengths 10 nm < L < 10 µm regardless of roughness or diameter. We conclude that it is possible to tune the lattice conductivity of SiGe NWs by length even in the µm range, thereby enhancing the TE figure of merit for higher conversion efficiency. Si-Ge NCs could potentially be a cost effective replacement to superlattice structures due to their simple and inexpensive mechanical processing techniques such as ball-milling and sintering. We model NC structures using a Voronoi tessellation to mimic the grains and their distribution in the composite. Our results show highly anisotropic transport with conductivity values well below their bulk alloy counterparts, in agreement with experimentally observed values. We show that NCs can be optimized to improve ZT by reducing the thermal conductivity by a combination of approaches including scattering of phonons from the interfaces between nanoscale grains, alloys of varying composition, and roughness. We study the κ dependence on average grain size and find that κ decreases with average grain size, analogous to the thickness dependence in superlattices; we then proceed to study the impact of grain size distribution and disorder on κ. We also study conductivity dependence on the total length of the composite material, and explore mixed composites made up of grains having two or more different alloy compositions.
9:00 PM - NM2.14.52
Enhanced Thermal Conductivity and Low Permittivity of Resin Based Composites Modified by Mesoporous-SiO2 and Mesoporous-SiO2@Al2O3 Microspheres
Jun Zhou 1
1 , Xi'an Jiaotong University, Xi'an China
Show AbstractUnderstanding of surface thermal conductivity and surface potential at the nanoscale is very important for composite polymers. In this study, mesoporous-SiO2 and mesoporous-SiO2@Al2O3 microspheres were successfully synthesized by tetraethylorthosilicate (TEOS) hydrolysis method. The synthesized SiO2@Al2O3 microspheres were subsequently characterized by FTIR spectroscopy, XRD, scanning electron microscopy (SEM), and transmission electron microscope (TEM). The results indicated that the particle size of SiO2@Al2O3 microspheres is about 500 nm, and the SiO2 microsphere is uniformly coated by Al2O3 shell (about 100-200 nm in thickness). SiO2@Al2O3 /CE/ER composites were prepared with SiO2@Al2O3 microspheres as fillers.Thermal conductivity of SiO2@Al2O3 /CE/ER composite increases 131% by adding 1.0 wt% ofSiO2@Al2O3 microspheres. The volume resistivity of composites decreased with increasing of the loading of SiO2@Al2O3 fillers and still keeping an excellent insulating performance. We also discuss the time and temperature evolution of the nanometer-scale interface tested by an atomic force microscope (AFM) tip scanning across surfaces of several amorphous polymers.
9:00 PM - NM2.14.53
Heat Transfer in Porous Crystals Containing Adsorbed Gases
Hasan Babaei 1 2 , Alan McGaughey 2 , Christopher Wilmer 1
1 , University of Pittsburgh, Pittsburgh, Pennsylvania, United States, 2 , Carnegie Mellon University, Pittsburgh, Pennsylvania, United States
Show AbstractHeat transfer in porous crystals containing adsorbed gases is an important process for many industrial applications, but it is poorly understood on a fundamental theoretical level. We have studied the mechanisms of heat transfer in a porous crystal/gas mixture system, motivated by the challenge of quickly dissipating heat generated in metal-organic frameworks (MOFs) due to gas adsorption. Our study reveals that the thermal conductance of the system is dominated by lattice thermal conductivity in the crystal, and that conductance is reduced as the concentration of gas in the pores increases. This mechanism was observed from molecular dynamics simulations of a monatomic gas in an idealized porous crystal structure. We show that the decreased conductivity associated with increased gas concentration is due to phonon scattering in the crystal due to interactions with gas molecules. Calculations of scattering rates for two phonon modes reveal that scattering of the lowest frequency mode scales linearly with gas density. This result suggests that the probability of a phonon-gas collision is simply proportional to the number of gas molecules in the pore.
We also investigate the effect of pore size and shape on the thermal conductivity of porous crystals containing adsorbed gas. With no gas present, the thermal conductivity decreases with increasing pore size. In the presence of adsorbed gas, MOFs with smaller pores experience reduced thermal conductivity due to phonon scattering introduced by gas-crystal interactions. In contrast, for larger pores (>1.7 nm), the adsorbed gas does not significantly affect thermal conductivity. This difference is due to the decreased probability of gas-crystal collisions in larger pore structures. In contrast to MOFs with simple cubic pores, the thermal conductivity in structures with triangular and hexagonal pore channels exhibits significant anisotropy. For different pore geometries at the same atomic density, hexagonal channel MOFs have both the highest and lowest thermal conductivities, along and across the channel direction, respectively.
9:00 PM - NM2.14.54
Thermal Conductivity Mapping of Ternary Material Libraries Using High-Throughput Time-Domain Thermoreflectance (HT-TDTR) Technique
Quentin d'Acremont 1 2 , Andrej Furlan 3 , Matthias Wambach 3 , Jean-Michel Rampnoux 1 , Alfred Ludwig 3 , Stefan Dilhaire 1 , Gilles Pernot 4
1 LOMA, Université de Bordeaux, Talence France, 2 , Amplitude Systèmes, Pessac France, 3 Institute for Materials, Ruhr-Universitat, Bochum Germany, 4 LEMTA, Université de Lorraine, Vandoeuvre Les Nancy France
Show AbstractIn this work, we present a new High-throughput Time Domain Thermoreflectance (HT-TDTR) technique to perform high-speed thermal characterization of ternary silicide libraries.
Our novel method relies on a femtosecond pump-probe set-up using two synchronized femtosecond lasers associated with an amplitude modulation and a lock-in detection of the thermal signal. We demonstrate that this technique reduces by a factor of 10 the typical acquisition time of TDTR experiments while keeping a high sensitivity to thermal properties.
We have studied Fe-Si-Ge and Ti-Ni-Sn ternary libraries deposited by multi-wedge multilayer and hot-substrate co-deposition methods. Those sputtering methods allow the synthesis of a wide range of compositions between three different materials on a single 4 inches wafer called library.
Applying HT-TDTR method, we show the results of thermal conductivity mapping on those libraries for a complete range of alloys. Multi-wedge deposited library exhibits low thermal properties [2-20]W/mK revealing the existing amorphous phases. While hot substrate co-deposition method exhibits higher thermal conductivity results from [10-50]W/mK revealing tailored crystalline phases suitable for future thermoelectricity and energy harvesting applications.
9:00 PM - NM2.14
NM2.14.04 TRANSFERRED TO NM2.13.04
Show Abstract
Symposium Organizers
Aleksandr Chernatynskiy, Missouri University of Science and Technology
Pierre-Olivier Chapuis, Center for Energy and Thermal Sciences, CNRS - INSA Lyon
Kedar Hippalgaonkar, Nanyang Technological University
Austin Minnich, California Institute of Technology
NM2.15: Thermal Measurement Techniques
Session Chairs
Friday AM, April 21, 2017
PCC West, 100 Level, Room 101 BC
9:00 AM - *NM2.15.01
Mode-Resolved Phonon Scattering Rates across the Brillouin Zone with Neutron and X-Ray Scattering
Olivier Delaire 1 2
1 , Duke University, Durham, North Carolina, United States, 2 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show Abstract
A detailed understanding of atomic dynamics is of broad interest for the design of efficient energy materials, for example to establish reliable microscopic models of thermal transport and thermodynamics in thermoelectric materials. The dominant contribution of phonons to thermal conductivity in thermoelectrics needs to be suppressed to enhance the conversion efficiency, but little is known about the respective contributions of different phonon modes. As demonstrated in our recent studies [1-5], inelastic neutron/x-ray scattering (INS/IXS) measurements of crystalline samples enable us to map phonon dispersions and phonon linewidths throughout the Brillouin zone. In addition, density functional theory (DFT) simulations enable the rationalization of extensive experimental datasets. In this presentation, I will illustrate how our approach, combining comprehensive INS measurements on single-crystals with detailed DFT simulations, has achieved novel insights into the microscopic underpinings of thermal conductivity in a number of important thermoelectric materials, such as PbTe, SnTe, AgSbTe2, SnSe, or Mo3Sb7 [1-5]. Our studies provide wavevector- and mode-resolved mean-free-paths of heat-carrying phonons, and reveal dominant scattering mechanisms, including anharmonic phonon-phonon scattering, electron-phonon coupling, and scattering by defects or nanostructures. In particular, we identify the importance of incipient lattice instabilities in achieving low thermal conductivities in PbTe, SnSe [1,3] and more recently in SnSe [4], and trace the electronic origin of this behavior with DFT. Using first-principles simulations of phonon-phonon interactions, we also show how the anomalous double-peak in the phonon spectral function of the TO mode in rocksalt chalcogenides arises from a resonance in the phonon self-energy [3]. This deeper understanding of phonon scattering is critically needed to design future thermoelectric materials with higher conversion efficiency, and is also applicable to a wide array of other energy materials.
[1] O. Delaire, J. Ma, K. Marty, A. F. May, M. A. McGuire, M.-H. Du, D. J. Singh, A. Podlesnyak, G. Ehlers, M. Lumsden, B. C. Sales, Nature Materials 10, 614 (2011).
[2] J. Ma*, O. Delaire*, A. May, C. Carlton, M. McGuire, L. VanBebber, D. Abernathy, G. Ehlers, Tao Hong, A. Huq, Wei Tian, V. M. Keppens, Y. Shao-Horn, and B. C. Sales, Nature Nanotechnology 8, 445 (2013).
[3] C.W. Li, O. Hellman, J. Ma, A.F. May, H.B. Cao, X. Chen, A.D. Christianson, G. Ehlers, D.J. Singh, B.C. Sales, and O. Delaire, Physical Review Letters (2014).
[4] C.Li,* J. Hong,* A.May, D. Bansal, S. Chi, T. Hong, G. Ehlers and O. Delaire, Nature Physics 11, 1063 (2015).
[5] D. Bansal, C. Li, A. Said, D. Abernathy, J.-Q. Yan, and O. Delaire, Physical Review B 92, 214301 (2015).
Funding from the US DOE BES, Materials Science and Engineering Division, through the Office of Science Early Career program, and as part of the S3TEC EFRC.
9:30 AM - NM2.15.02
Individual Upconverting Nanoparticles as Nanoscale Heaters and Thermometers
Andrea Pickel 1 , Jacob Kilbane 1 , Emory Chan 2 , Christian Monachon 1 , Nicholas Borys 2 , Elizabeth Levy 2 , Jeffrey Urban 2 , P James Schuck 2 , Chris Dames 1
1 , University of California, Berkeley, Berkeley, California, United States, 2 , Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractWe demonstrate a far-field optical thermometry technique based on the temperature-dependent luminescence of single upconverting NaYF4 nanoparticles doped with Er3+ and Yb3+ [1]. While lanthanide-doped upconverting nanoparticles are commonly used for thermometry, most measurements employ large ensembles of particles. Single particle measurements are far less common, and prior to this work the smallest isolated particle used for thermometry was several hundred nanometers in diameter. Although single particle measurements require excitation intensities orders of magnitude higher than those used for ensemble imaging, it is typically assumed that self-heating effects are negligible. In this work, we identify individual 20 x 20 x 40 nm3 particles using only far-field optics, which is confirmed with subsequent scanning electron microscopy. The spatial resolution of our single-point measurement technique is governed by the nanoparticle size and is thus far below the diffraction limit.
Simple thermal models based on experimentally determined Yb3+ absorption cross-sections suggest that any self-heating effects should be negligible. However, experiments in which we vary the power of a continuous wave excitation laser show a linear increase in the ratio of emitted intensity from two coupled energy levels in Er3+ that, if interpreted as thermal, represents a temperature rise of over 60 K for sub-150 nm particles. Alternatively, it is possible that the complex energy transfer pathways of the upconverting nanoparticles give rise to a non-thermal excitation intensity dependence. To decouple these two effects, we employ a time-periodic scheme in which we modulate the excitation laser and measure the apparent temperature as a function of the modulation frequency. We believe the ability to use NaYF4:Yb3+,Er3+ nanoparticles as dual-purpose nanoscale heaters and thermometers offers exciting possibilities for both fundamental thermal measurements and metrology in industry.
[1] Kilbane et al., Far-field optical nanothermometry using individual sub-50 nm upconverting nanoparticles, Nanoscale (2016).
9:45 AM - NM2.15.03
Scanning Thermal InfraRed Microscopy (STIRM) a New Method for Measuring Thermal Conductivity and Chemical Composition at the Nanoscale
Andrea Centrone 1
1 Center for Nanoscale Science and Technology, National Institute of Standard and Technology, Gaithersburg, Maryland, United States
Show AbstractThe atomic force microscope (AFM) is widely used because, in addition to the topography, it can provide nanoscale electrical, thermal, chemical etc., properties of the sample, which are important for engineering nanomaterials towards numerous applications (photovoltaics, sensing, thermoelectrics, etc.).
In this work, we introduce a novel AFM-based technique named Scanning Thermal InfraRed Microscopy (STIRM)1 that provides correlated thermal conductivity and chemical composition with nanoscale resolution. STIRM uses nanofabricated temperature sensitive AFM probes in combination with IR-tunable lasers to measure locally, the temperature raise in the sample due to light absorption. The amplitude of the STIRM signal is proportional to the absorbed energy and yields the local chemical composition, thus enabling the identification of unknown samples by comparison with FTIR databases. Additionally, the temporal evolution of the STIRM signal (exponential decay) can provide the local thermal diffusivity of the sample without a probe specific calibration and, if the density and heat capacity of the sample are known, its local thermal conductivity.
Proof of principle demonstration will be given on polymer samples and on Metal-Organic Framework (MOF materials). MOFs are nanoporous materials composed by inorganic ions connected by organic linker to for 3D porous crystalline structures. Engineering MOFs at the molecular level allows design of promising new materials for catalysis, chemical separation and sensing. The development of electrically conductive MOFs2 opens a new pathway for engineering those materials towards thermoelectric and electronics applications.
Because STIRM provides access to the sample thermal conductivity only if the probe thermalization time is faster than the thermalization of the sample, in the last part of the talk, I will introduce custom nanofabricated probes that thermalize 150 times faster that commercially available probes, thus providing access to samples with a broad range of the thermal conductivities.
1. Katzenmeyer, A.M. et al. Mid-infrared spectroscopy beyond the diffraction limit via direct measurement of the photothermal effect. Nanoscale 7, 17637-17641 (2015).
2. Talin, A.A. et al. Tunable Electrical Conductivity in Metal-Organic Framework Thin-Film Devices. Science 343, 66-69 (2014).
10:00 AM - NM2.15.04
Calibrated Scanning Thermal Microscopy for Nanolayered and Micropatterned Samples
Antonin Mouhannad Massoud 1 , Jean-Marie Bluet 1 , Valeria Lacatena 2 , Maciej Haras 2 , Jean-Francois Robillard 2 , Pierre-Olivier Chapuis 1
1 , CNRS - INSA Lyon, Villeurbanne France, 2 , IEMN, Lille France
Show AbstractScanning thermal microscopy (SThM) is a technique allowing to determine the local effective thermal conductivity with an expected submicron-scale spatial resolution [1]. When the atomic force microscope thermal probe is operated in vacuum, the resolution is only limited by the tip-sample nanometric contact. However, ambient-condition operation is mostly used, and the spatial resolution is then micrometric because of the tip-to-sample heat transfer which spreads through the air around the contact.
Here, we present a way to split the air and contact contributions [2]. First, it is shown that heat convection can be neglected in comparison to diffusion. Second, a calibration is performed with bulk materials, which is compared to temperature levels simulated with finite elements. This allows us to demonstrate that the Wollaston-wire probe can be sensitive to effective thermal conductivities up to 60 W/m.K if the surface is patterned, in contrast to ~10 W/m.K for unpatterned surfaces.
By thermally characterizing nanometer-thin suspended membranes with various micrometric lengths, we find that the spatial resolution is reduced to 300 nm when appropriately considering the air contribution. The results also indicate that a probe temperature resolution below 50 mK is achieved under these conditions.
[1] S. Gomes et al., Physica status solidi (a) 212, 477-494 (2015)
[2] A. M. Massoud et al., submitted (2016)
We acknowledge the support of projects EU FP7 QuantiHeat, ERC StG UPTEG; Nano 2017; and INSA BQR Ma NaTherm.
10:15 AM - NM2.15.05
Full-Field Thermal Imaging of Submicron Heat Transport in InGaAs and Silicon
Amir Ziabari 1 , Pol Torres Alvarez 2 , Alexander Shakouri 3 , Yi Xuan 1 , Mengwei Si 1 , Bjorn Vermeersch 4 , Je-Hyeong Bahk 5 , Yee Rui Koh 1 , Peide Ye 1 , F. Xavier Alvarez 2 , Ali Shakouri 1
1 , Purdue University, West Lafayette, Indiana, United States, 2 , Universitat Autonoma de Barcelona, Barcelona Spain, 3 , University of California San Diego, San Diego, California, United States, 4 , LITEN, CEA-Grenoble, Grenoble France, 5 , University of Cincinnati, Cincinnati, Ohio, United States
Show AbstractThermal transport at nanoscale is crucial for the design and optimization of high power electronic and optoelectronic devices. Departure from Fourier Law for heat conduction have been reported at submicron scales. Non-local and non-equilibrium effects due to phonons carrying heat ballistically away from the heat source are among the main causes the Fourier law breaks down. Previous studies have shown that as the characteristic length of thermal transport is reduced, ballistic effects manifest as a reduction in apparent thermal conductivity of material (Modified Fourier Theory). Despite substantial advancement in the field, most of the measurements relied on single point temperature or average temperature measurements.
In this work, high spatio-temporal resolution of thermoreflectance thermal (TR) imaging microscopy is used to obtain full-field 2D temperature distribution of submicron devices under both steady-state and transient operation. The TR imaging technique directly probes an electrically biased device where the amount of Joule heating is precisely estimated using four-probe electrical measurements. This bypasses the complexities of some of the common femtosecond laser pump-probe techniques. A set of heater lines are fabricated ranging in width from 100nm to 10µm on both Silicon substrate and on 5-microns thick InGaAs layer on InP substrate. The heater lines are electrically isolated from the substrate using thin Al2O3 insulating layer. Thermoreflectance imaging is used to measure temperature change, due to Joule heating, on the heater line as well as the temperature profile on the substrate near the heater. The TR imaging measurements were performed in both static and transient domains with 50ns time resolution. Identical structure were fabricated on thin film InGaAs on InP substrate as well as directly on Silicon. The width of the heater lines is the parameter that controls the characteristic length of thermal transport.
Experimental thermal images suggest that the modified Fourier theory ceases to explain the full thermal distribution of submicron size heat sources. For both Silicon and InGaAs, as the width of heat sources decreases the temperature of the heater lines exceed predictions of Fourier heat diffusion equation. The non-diffusive behavior is also apparent within 1-3µm outside the heater lines. It is noted that full temperature distribution cannot be explained with modified Fourier theory using a reduced apparent thermal conductivity. Silicon and InGaAs show different behavior as the size of the heat source decreases. They both need a lower thermal conductivity to explain temperature change on top of the metal heater line. However, tails of the temperature distribution around the heater lines can’t be explained with the same thermal conductivity. We will describe the implication of these results and provide a possible theoretical explanations using Kinetic Collective phonon transport model.
10:30 AM - NM2.15.06
Developing Superior Alloy Contacts Optimized for Electrical and Thermal Transport at Metal-Graphene Interfaces
Dipanjan Saha 1 , Xiaoxiao Yu 2 , Mohamed Darwish 4 , Minyoung Jeong 3 , Justin Freedman 3 , Andrew Gellman 2 , Jeffrey Weldon 4 , Jonathan Malen 1
1 Mechanical Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States, 2 Chemical Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States, 4 Electrical and Computer Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States, 3 Material Science and Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States
Show AbstractWe present high throughput measurements of electrical and thermal contact resistance in metal-alloy/dielectric interfaces as a function of alloy composition and adhesion layer thickness. Pure metals are used almost exclusively as contacts in modern electronic devices, where the metal/semiconductor interfaces inhibit the flow of both electrons and phonons, quantified by the electrical contact resistance and thermal contact resistance. In next generation short channel 2D devices that exhibit ballistic carrier transport in the channel, the electrical and thermal contact resistances become even more detrimental to performance. The alloy design space in these applications and others has been completely overlooked due to a focus on pure elements.
To make high throughput measurements, metal films with a continuous alloy composition gradient spanning two pure metals were deposited on Al2O3 substrates. The alloys considered include Au-Cu and Au-Pd alloys that form solid solutions at all compositions, and Cr-Pd that has intermediate phases. Frequency domain thermoreflectance was used to measure thermal contact resistance as a function of alloy composition. While the thermal contact resistance for the solid solutions varied monotonically between the pure metals, the intermediate phases of Cr-Pd resulted in non-monotonic behavior with a local minimum at 35% Cr. Likewise, we studied the thermal contact resistance as a function of adhesion layer thickness for Cu and Cr adhesion layers sandwiched between Au films and Al2O3 substrates. We show that a 1-nm-thick adhesion layer of Cu or Cr is sufficient to reduce the thermal interface resistance by more than a factor of 2 or 4, respectively, relative to the pure Au/Al2O3 interface. These results on Al2O3 led us to deposit compositionally spread alloy films of Au-Pd with a Cr adhesion layer on single layer graphene patterned with transmission line measurement structures, so that simultaneous measurements of electrical and thermal contact resistance can be made as a function of adhesion layer thickness and alloy composition.
NM2.16: Interfacial Thermal Transport
Session Chairs
Friday PM, April 21, 2017
PCC West, 100 Level, Room 101 BC
11:15 AM - *NM2.16.01
Manipulating Interfacial Thermal Transport Using Surface Chemistry
Ravi Prasher 1
1 , Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractThermal interfaces play a significant role in variety of technologies such as microelectronics, Li-Ion batteries, and thermal insulation of buildings. In many applications such as microelectronics large interfacial conductance is desired whereas in some applications very low interfacial conductance is desired. Thermal interface conductance can be tuned by orders of magnitude by manipulating phonon transmissivity. Surface chemistry can either make the interfacial bond strength very weak (van der Waals) or very strong (covalent) leading to significant changes in phonon transmissivity. In this talk the speaker will discuss both theoretical and experimental research on the impact of surface chemistry on interfacial thermal transport.
11:45 AM - NM2.16.02
Cooperative Molecular Behavior Enhances the Thermal Conductance of Binary Self-Assembled Monolayer Junctions
Shubhaditya Majumdar 1 , Jonathan Malen 1 , Alan McGaughey 1
1 , Carnegie Mellon University, Pittsburgh, Pennsylvania, United States
Show AbstractHybrid materials composed of organic-inorganic heterojunctions are gaining popularity as alternatives to conventional semiconductors for energy-conversion applications, thus requiring detailed study of the properties of their internal interfaces. Previous studies have isolated the organic-inorganic interface thermal properties using self-assembled monolayer (SAM) junctions between two inorganic substrates and characterized them based on interfacial bonding strength, vibrational mismatch, and molecule length. Here, we investigate the effect of having a binary SAM layer on the thermal conductance of the SAM junction.
The binary SAMs are built from a mixture of alkanethiol and alkanedithiol species sandwiched between gold leads. This setup creates a tailorable bonding environment at one interface either through varying the ratio of strongly- and weakly-bonded end groups or by decreasing surface coverage of the molecules by changing their length. Thermoreflectance measurements and molecular dynamics simulations demonstrate that the thermal conductances of the binary SAM junctions vary with molecular composition and are greater than predictions of a parallel resistance model. The enhancement results from increased thermal transport through the alkanethiols, whose terminal methyl groups are confined by the anchored alkanedithiols. This confinement effect extends over length scales that are more than twice the range of the van der Waals interactions between molecules and are commensurate to the sizes of experimentally-observed molecular domains. Conversely, for a partially-packed (i.e., sub-monolayer) alkanedithiol unary SAM, increasing the molecular packing density decreases the per molecule thermal conductance. This finding indicates that thermal transport measurements of SAMs cannot be used to predict the thermal transport properties of single molecules.
12:00 PM - NM2.16.03
Thermal Phonon Diffraction from Atomically Rough Surfaces
Navaneetha Krishnan Ravichandran 2 1 , Hang Zhang 2 , Austin Minnich 2
2 Engineering and Applied Science, California Institute of Technology, Pasadena, California, United States, 1 Physics, Boston College, Chestnut Hill, Massachusetts, United States
Show AbstractReflection of thermal phonons from free boundaries is a key physical process that strongly influences the thermal resistance of thin films. Despite much effort, the specularity parameter, which quantifies the probability of specular phonon reflection, has not been experimentally measured while theory is often based on Ziman’s model introduced over 50 years ago. Here we report the first direct measurement of the phonon wavelength-dependent specularity parameter at a free surface with atomic-scale roughness. Our approach employs the optical transient grating experiment on free-standing silicon membranes over temperatures from 80 - 450 K. In our experiment, we probe different parts of the thermal phonon spectrum by systematically varying the grating period over length scales commensurate with phonon mean free paths. We rigorously extract the specularity parameter from the measured data by using Bayesian inference to invert a transfer function derived from the Boltzmann equation with ab-initio bulk phonon properties as input. We find that thermal phonons with wavelength longer and even comparable to the atomic surface roughness amplitude are frequently specularly reflected, far above the rate predicted by Ziman’s theory. Our work provides direct experimental insights into the diffraction-like interaction of phonons at free rough surfaces that will impact efforts to improve the performance of thermoelectrics and LEDs.
12:15 PM - NM2.16.04
Thermal Boundary Resistance-Limited Performance of High-Frequency Photodiodes—Towards In Situ Thermoreflectance Measurements without Metal Transducers
Patrick Hopkins 1 , John Gaskins 1 , Ramez Cheaito 1 , Jeffrey Braun 1 , Ashutosh Giri 1 , Ethan Scott 1 , Yang Shen 1 , Joe Campbell 1
1 , University of Virginia, Charlottesville, Virginia, United States
Show AbstractTypical solutions to thermal mitigation of high power, high frequency devices have traditionally relied on solutions high thermal conductivity submounts/heat sinks, such as diamond, to mitigate unwanted temperature rises and resulting device inefficiencies. In this work, we show that the output power of our current state of the art (SOA) Modified Uni-Traveling Carrier (MUTC) photodiode is not dictated by the thermal conductivity of the substrate heat sink, but limited by the resistance intrinsic to the contact at the substrate/heat sink interface. Using Time-Domain ThermoReflectance (TDTR), we measure the thermal boundary resistance (TBR) across a series of Au/Ti/heat sink interfaces that are employed in our radio frequency (RF) MUTC photodiodes. Through a combination of TBR engineering and substrate thermal conductivity selection, we improve the power density at failure of the MUTC photodiodes.
This work highlights the importance of mitigating, and understanding, device thermal resistances, and specifically demonstrates the need for on-wafer thermal diagnostics. Towards this goal, while TDTR and FDTR provide robust platforms to measure the thermophysical properties of a wide array of systems on varying length scales, routine in the implementation of these techniques is the application of a thin metal lm on the surface of the sample of interest to serve as an opto-thermal transducer. Motivated by our results on the MUTC photodiode, we demonstrate a method to directly measure the thermal conductivities of bulk and thin film materials without using a metal transducer layer using a standard TDTR/FDTR experiment.1 Using this approach, we demonstrate the ability to measure the thermal conductivity on three semiconductors, intrinsic Si (100), GaAs (100), and InSb (100), the results of which are validated with FDTR measurements on the same wafers with aluminum transducers. Finally, we use this approach to measure the thermal resistances of silicon-on-sapphire chips, quantifying the TBR at the silicon/sapphire interface and the thermal conductivity of the silicon thin film with FDTR without the use of a metal film transducer.
1. L. Wang, R. Cheaito, J. L. Braun, A. Giri, P. E. Hopkins, “Thermal conductivity measurements of non-metals via combined time- and frequency-domain thermoreflectance without a metal film transducer,” Rev. Sci. Instrum., 87, 094902 (2016).
12:30 PM - NM2.16.05
A Numerical Test of the Diffuse Mismatch Model—Wavevector-Resolved Modeling of Phonon Transmission across Rough Interfaces
Rohit Kakodkar 1 , Joseph Feser 1
1 , University of Delaware, Newark, Delaware, United States
Show AbstractWe probe the applicability of the diffuse mismatch model to realistic interfaces by direct numerical simulation, using a computationally efficient frequency-domain atomistic simulation tool enabled by perfectly matched layer boundary conditions. The simulation technique can obtain wavevector-resolved phonon transmission coefficients for atomistic systems with millions of atoms in 3D. In analogy with analytic approaches for determining transmission coefficient, it works by preparing an incident phonon wave that satisfies the dispersion equation in the emitting medium, and seeking a scattered wave solution that allows the interface and any other defects to satisfy each atomistic equation of motion. A perfectly matched layer is used to absorb waves that propagate away from the interface/scattering region, and to measure the scattered energy via the rate of energy dissipation in the perfectly matched layer. The method is able to distinguish the transmission coefficient for individual incident wavevectors and, through recent advances, can resolve the spectrum of modes that energy is transmitted into, and can by used to obtain quantum-correct thermal interface resistance for interfaces with complex structures.
We use this to study the effect of chemical roughness on the phonon transmission coefficient and thermal interface conductance of an otherwise abrupt interface. By varying the characteristic interdiffusion distance, we show that less than a monolayer of interdiffusion is all that is required to relax phonon scattering selection rules and increase mode conversion, thereby increase phonon transmission coefficients. Thus, defective interfaces have the ability to raise thermal interface conductance, a key feature of the DMM. On the other hand, further chemical interdiffusion does not recover a transmission coefficient consistent with the diffuse mismatch model, regardless of the degree of interdiffusion. Failure is confirmed to be persistent throughout simulations performed in 1D, 2D, and 3D, and we use the mode-resolved features of the simulation method to demonstrate the mechanism of failure.
12:45 PM - NM2.16.06
Fabrication and Characterization of Copper Nanowire Arrays as Thermal Interface Materials
Wei Gong 1 , Sheng Shen 1
1 , Carnegie Mellon University, Pittsburgh, Pennsylvania, United States
Show AbstractModern high-power microelectronics, such as microprocessors, solid-state lasers, and LED modules, require highly effective, compact and reliable heat removal solutions. In order to thermally connect various components in these thermal solutions, thermal interface materials (TIMs) are commonly employed for filling up interfacial gaps and increasing the heat flux uniformity along interfaces. The thermal resistance of TIMs can constitute more than 50 % of the total thermal resistance in many high-power electronics. Greases and solders are widely used TIMs. However, they have their respective drawbacks. The low thermal conductivity of thermal greases is the main obstacle limiting their applications. For solders, their poor compliance which cannot withstand large thermal stress, will cause cracks or even failure of devices. In this work, we fabricated vertically aligned copper nanowire arrays on silicon substrates as a new kind of TIM. First, a 100nm copper is sputtered on silicon wafer as seed layer. Then a piece of anodic aluminum oxide (AAO) nanoporous template is adhered on substrate by the surface tension of water. The wafer substrate with the template are fixed on a wafer holder with O-ring. Next, electroplating is applied to grow copper nanowire array. At the beginning of electroplating, copper form a thin layer under the template. Then nanowires begin to grow in the pores of AAO template. Finally copper grows out of the pores and forms a continuous layer at the top of template. The density of nanowire array is controlled by choosing AAO template with different porosities. Chemical mechanical planarization (CMP) is applied to obtain a smooth top surface and control the height of nanowire arrays. Finally, supercritical drying is used to remove liquid in order to obtain separated nanowire without agglomeration. After fabrication, mechanical and thermal properties of copper nanowire array are characterized. The effective Young’s modulus of copper nanowire arrays is measured by applying nanoindentation tests. The results show that for copper nanowire with 35% density and 50μm height, the effective Young’s Modulus is about 1.958 GPa, which is 2 orders of magnitudes smaller than that of bulk copper. The effective thermal conductivity of copper nanowire array is measured using Phase-Sensitive Transient Thermoreflectance (PSTTR) method. For copper nanowire with 60% density and 27.5μm height, the effective thermal conductivity can be as large as 164.2W/(m.K), which reaches 40.1% of bulk copper. These results indicate the excellent mechanical compliance and thermal conductivity of copper nanowire arrays, which make them promising for TIM applications.
NM2.17: Radiative Thermal Devices and Key Parameters
Session Chairs
Friday PM, April 21, 2017
PCC West, 100 Level, Room 101 BC
2:30 PM - *NM2.17.01
Near-Field Radiative Heat Transfer—Multiscale Modeling and Measurement between Macroscale Planar Surfaces
Mathieu Francoeur 1
1 , Department of Mechanical Engineering, University of Utah, Salt Lake City, Utah, United States
Show AbstractNear-field radiative heat transfer has received significant attention due to potential applications to thermophotovoltaic (TPV) power generation (DiMatteo et al., Appl. Phys. Lett. 79, 1894, 2001), thermal rectification (Otey et al., Phys. Rev. Lett. 104, 154301, 2010), localized radiative cooling (Guha et al., Nano Lett. 12, 4546, 2012), and near-field thermal spectroscopy and imaging (Babuty et al., Phys. Rev. Lett. 110, 146103, 2013; O’Callahan et al., Phys. Rev. B 89, 245446, 2014). The application of near-field thermal radiation to engineering systems requires robust modeling techniques and reliable experimental data. In this Invited Talk, modeling and experimental aspects of near-field thermal radiation will be overviewed.
In the first part of the Talk, the challenging problem of modeling near-field radiative heat transfer in multiscale, arbitrary and three-dimensional geometries will be discussed. Specifically, the thermal discrete dipole approximation (T-DDA) with surface interaction, which is a numerically exact approach for predicting near-field radiative heat transfer between objects of arbitrary shape and size and an infinite surface, will be detailed (Edalatpour and Francoeur, Phys. Rev. B 045406, 2016). The specific problem of near-field radiative heat transfer between a complex-shaped probe and a surface, which is important for near-field thermal spectroscopy, will be presented. The results will be compared against a simplified model involving a prolate spheroidal electric dipole, and the limit of validity of this approximation will be assessed. The potential of employing the T-DDA with surface interaction for predicting the thermal response of metamaterials made of complex, periodic inclusions will be discussed.
The second portion of the Talk will focus on the measurement of near-field radiative heat transfer between two macroscale surfaces separated by a nanosize vacuum gap. Many technologies may greatly benefit from the enhancement of radiative heat transfer between surfaces separated by a sub-wavelength vacuum gap. Yet, potential applications capitalizing on thermally generated evanescent modes such as near-field TPVs are currently limited by the lack of devices capable of transferring radiation between two large surfaces separated by a nanosize gap. Radiative heat transfer measurements made with a custom-fabricated device consisting of two 5 by 5 mm2 intrinsic silicon surfaces separated by a gap that can be modulated from 3500 nm down to 150 nm via a compliant membrane and mechanical actuation will be presented. This device allows probing regimes dominated by either propagating or evanescent modes, and leads to a maximum radiative heat transfer enhancement of 8.4 relative to the blackbody limit (Bernardi et al., Nat. Commun. 7, 12900, 2016). The potential application of the device architecture to TPV power generation, in which the near-field enhancement is as important as the size of the surfaces, will be discussed.
3:00 PM - NM2.17.02
Multi-Length Scale Coupled Phonon-Electron Monte Carlo Simulations of Three-Dimensional GaN Transistors
Hongbo Zhao 1 , Yue Xiao 1 , Qing Hao 1
1 , University of Arizona, Tucson, Arizona, United States
Show AbstractIn recent years, tremendous efforts have been dedicated to GaN-based transistors for high-power and high-frequency applications. However, the device performance is largely restricted by the significant overheating at nanoscale “hot spots” within the device [1].
To provide theoretical guidance for better thermal designs, a multi-length scale simulation for the coupled electron-phonon system in a GaN transistor is needed. The length scale spans from few nanometers in the hot spot region to hundreds of micrometers across the device substrate. It is critical to ensure self-consistence in the coupled electron and phonons simulations. Here hot electron scattering and thus phonon generation depend on the local phonon temperature, whereas the resulting phonon generation further affects the local temperature. However, two major drawbacks should be emphasized in recent electrothermal simulations [2-4]. First, the temperatures of three subsystems (i.e., electrons, acoustic phonons, and optical phonons) are used for these equations, which hides the detailed energy and spatial distribution of individual phonons. Second, bulk lattice thermal conductivities are still used for acoustic phonons, which becomes invalid at the nanoscale.
The energy-dependent electron and phonon transport can be considered in electron and phonon Monte Carlo (MC) simulations that track the movement and scattering of individual charge and heat carriers. In this work, a recently developed deviational phonon MC technique [5] is introduced to dramatically improve the computational efficiency and thus enable simulations of the micrometer hot region around a transistor. For regions away from the transistor, the thermal diffusion equation is employed to find the heat dissipation into the substrate and is couple with the phonon MC simulation for the transistor region.
As demonstration, the proposed electron and phonon simulations are carried out for a three-dimensional GaN-based transistor. The frequency dependence of interfacial phonon transmissivity and phonon mean free paths is fully incorporated within the phonon simulations. Self-consistence is achieved between the electron and phonon simulations that are coupled with temperature-dependent electron-phonon scattering. Unrestricted to GaN transistors, the presented method can be widely applied to nanoelectronics devices to predict their device performance and provide important guidance for the thermal management of such devices.
References:
[1] Y.-R. Wu & J. Singh, J. Appl. Phys. 101, 113712 (2007).
[2] T. Sadi et al. J. Comput. Electron. 6, 35-39 (2007).
[3] S. Sinha et al. J. Heat Transfer 128, 638-647 (2006).
[4] K. Raleva et al. IEEE Trans. Electron Devices 55, 1306-1316 (2008).
[5] J.-P. M. Péraud and N. G. Hadjiconstantinou, Phys. Rev. B 84, 205331 (2011).
3:15 PM - NM2.17.03
Toward Radiative Thermal Information Processing—Multilevel Memory and Near-Field Effect
Kota Ito 1 , Kazutaka Nishikawa 1 , Atsushi Miura 1 , Hiroshi Toshiyoshi 2 , Hideo Iizuka 1
1 , Toyota Central R&D Labs Inc, Nagakute Japan, 2 RCAST, University of Tokyo, Tokyo Japan
Show AbstractThermal rectifiers[1], thermal transistors[2], and thermal memories[3] have been theoretically studied by utilizing radiative heat transfer. The unique radiative properties of polar materials[1] and phase-change materials[2][3] have brought various functionalities toward thermal information processing. Such functionalities are further enhanced by utilizing the near-field coupling across a nanometric gap[1][2]. Both the heat flux enhancement and the spectral selectivity are achieved for sophisticated devices.
We have been experimentally realized such novel thermal devices [4]. For instance, we experimentally demonstrate a radiative thermal memory for the first time, by utilizing the phase-change of vanadium dioxide [5]. The hysteresis, which has not been highlighted in the theoretically community, enables a multilevel memory. The hysteresis is modelled by the Preisach representation, and the measured transient response is well reproduced by the model.
In order to further enhance the memory effect, we also present a gap formation methodology for the near-field radiative heat transfer [6]. A gap width of 500 nm is obtained over an area larger than 1 cm2, while the gap uniformity is monitored by optical interferometry. Micromachined spacers are placed sparsely to maintain the gap, and the parasitic heat conduction through spacers is suppressed to be smaller than the radiative heat flux. Further optimization of the design of the pillar array, as well as the combination of vanadium dioxide and near-field radiative heat transfer, are discussed in the presentation.
References
[1] C. Otey, W. T. Lau, S. Fan. Phys. Rev. Lett. 104, (15) 154301 (2010).
[2] P. Ben-Abdallah, S. A. Biehs. Phys. Rev. Lett. 112, (4) 044301 (2014).
[3] V. Kubytskyi, S. A. Biehs, and P. Ben-Abdallah. Phys. Rev. Lett. 113, (7) 074301 (2014).
[4] K. Ito, K. Nishikawa, H. Iizuka, and H. Toshiyoshi. Appl. Phys. Lett. 105, (25) 253503 (2014).
[5] K. Ito, K. Nishikawa, and H. Iizuka. Appl. Phys. Lett. 108, (5) 053507 (2016).
[6] K. Ito, A. Miura, H. Iizuka, and H. Toshiyoshi. Appl. Phys. Lett.106, (8) 083504 (2015).
This work was partially supported by JSPS KAKENHI Grant Number JP16K17538.
3:30 PM - NM2.17.04
Near-Field Thermophotovoltaic Energy Conversion by Excitation of Magnetic Polaritons inside Nanometer Vacuum Gaps with Nanostructured Drude Emitters
Payam Sabbaghi 1 , Yue Yang 1 , Liping Wang 1
1 School for Engineering of Matter, Transport & Energy, Arizona State University, Tempe, Arizona, United States
Show AbstractIt has been demonstrated during the last decade that radiative heat transfer could be significantly enhanced when the distance between two objects is smaller than the characteristic thermal wavelength due to the coupling of evanescent waves. Moreover, it has been recently demonstrated that the excitation of magnetic polaritons (MP) between metal grating metasurfaces can spectrally enhance the near-field radiative heat flux [1]. In this study, we aim to improve the electrical power output and conversion efficiency of a near-field thermophotovoltaic (TPV) system by exciting MP in a nanometer-thick vacuum gap and TPV cell between a nanostructured Drude emitter and a perfect metal. Fluctuational electrodynamics that incorporates scattering matrix theory with rigorous coupled-wave analysis is employed to rigorously calculate the near-field radiative flux in the near-field TPV system. An internal quantum efficiency of 100% is assumed for ultra-thin TPV cells by assuming the depletion region occupies the entire sub-100 nm-thick cell. The Drude emitter is considered as 1D nanostructured gratings for possibly exciting MP for spectrally enhanced near-field radiative flux above the cell bandgap. On the other hand, the perfect metal backing, which could practically serve as electrodes for charge collection besides reflecting photons into the cell for recycling, is considered lossless in the Drude model possibly for the upper limit of performance. By considering a TPV cell made of InGaSb, our preliminary results show that an enhancement of spectral heat flux just above the cell bandgap could occur due to the MP excitation, which is verified by the contour plots of transmission coefficient and an inductor-capacitor circuit model. As a result, compared with the case of a planar Drude emitter, the conversion efficiency of the near-field TPV with a nanostructured grating emitter is improved from 29.6% to 31.6% at a vacuum gap distance of 50 nm under the emitter and cell temperatures of 2000 K and 300 K, respectively. Effects of emitter geometric parameters like grating period, width, height, as well as the material properties like plasma frequency and scattering rate, in addition to vacuum gap distances and nanometer cell thickness, on the near-field radiative flux, electrical power output and conversion will be systematically investigated. This work would open up a new scope to improve the performance of TPV devices with nanostructures and near field effect.
[1] Yang, Y. and Wang, L., 2016 "Spectrally enhancing near-field radiative transfer between metallic gratings by exciting magnetic polaritons in nanometric vacuum gaps," Phys. Rev. Lett., 117, p. 044301.
3:45 PM - NM2.17.05
A Full Drift-Diffusion Model for Near-Field Radiation Mediated Thermophotovoltaic Devices
Etienne Blandre 1 , Pierre-Olivier Chapuis 1 , Rodolphe Vaillon 1 2
1 , Univ Lyon, CNRS, INSA-Lyon, Université Claude Bernard Lyon 1, CETHIL UMR5008, Villeurbanne, F-69621, France, 2 Radiative Energy Transfer Laboratory, Department of Mechanical Engineering, University of Utah, Salt Lake City, Utah, United States
Show AbstractNear-field radiation mediated thermophotovoltaic (NFR-TPV) devices are expected to convert more radiative energy into electrical power than usual far-field thermophotovoltaic devices due to the additional energy transferred by the evanescent waves [1]. Up to now, the most advanced modeling of the electrical behavior of such energy converters was made under the low-injection approximation which assumes that the photogenerated electrical charge densities are much lower than the doping densities [2, 3]. This condition may not be always met, especially near the front surface of the device where the contribution of the evanescent modes to the photogeneration of electron-hole pairs can be very large [4].
To analyze its validity, a full drift-diffusion model that applies to all injection conditions is developed. It consists of solving the coupled Poisson’s, transport and continuity equations to derive the electric field, electron and hole density profiles in a one-dimensional p-n junction. Fluctuational Electrodynamics is used to calculate the local rate of electron-hole pair photogeneration in the junction.
As a result, the conditions of high-injection are determined in the case of a GaSb p-n junction, as a function of distance between the radiator and the photoconverter, temperature and type of radiator, and doping and size of the n and p layers [5]. Furthermore, the full drift-diffusion model is applied to the design of InSb diodes selected for building an experimental demonstrator of the near-field enhancements of NFR-TPV converters.
Acknowledgments: this work is sponsored by the French National Research Agency (ANR) under grant ANR-16-CE05-0013. The authors are thankful to colleagues from the Nanomir team of Institut d’Electronique et des Systèmes (IES, Montpellier, France) for fruitful discussions.
References:
[1] M.D. Whale and E.G. Cravalho, IEEE TEC 17, 130 (2002)
[2] K. Park et al., J. Quant. Spectrosc. Radiat. Transfer 109, 305 (2008)
[3] M. Francoeur et al., IEEE TEC 26, 686 (2011)
[4] M. Bernardi et al., Sci. Reports 5, 11626 (2015)
[5] E. Blandre et al., in preparation (2017)
4:00 PM - NM2.17.06
Characterizing Electron Phonon Coupling in Elemental Metals with Picosecond Electrical Pulses
Richard Wilson 1 , Yang Yang 2 , Jon Gorchon 3 , Jeffrey Bokor 3
1 , University of California, Riverside, Riverside, California, United States, 2 Materials Science, University of California Berkeley, Berkeley, California, United States, 3 Electrical Engineering, University of California Berkeley, Berkeley, California, United States
Show AbstractElectron-phonon interactions play a dominant role in transport phenomena in metals. For example, electron-phonon coupling determines the mean-free-paths of electrons in pure elemental metals, contributes to the thermal interface resistance between metals and dielectrics, and can govern energy flow in metal multilayers on time-scales ranging from 0.1 to 100 picoseconds. Despite their fundamental importance, the most common method for experimentally quantifying electron-phonon interactions is flawed. Electron-phonon interactions are most commonly measured by analyzing time-domain thermoreflectance measurements with a two-temperature model. In thermoreflectance experiments, an optical pulse excites electrons to eV scale energies and the energy distribution is initially nonthermal. However, the two-temperature model erroneously assumes the distribution of electron energies is well described by Fermi-Dirac statistics on all time scales. This assumption causes significant errors in experimentally derived values for the electron-phonon energy transfer coefficient. We present an alternative pump/probe method for quantifying electron-phonon interactions that does not suffer from these errors. We heat the electrons with a picosecond electrical pulse from a photoconductive Auston switch. In contrast to the laser experiments, the distribution of electrons is thermal at all times and therefore the two-temperature model can provide an accurate description of the dynamics. We observe large differences in the cooling rate of electrons following electrical vs. optical heating. For example, Pt electrons cool approximately twice as fast when heated electrically vs. optically. Our study is an important step towards a unified understanding of thermal transport in metals at the nanoscale.