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2015 Fall

Characterization of materials by experiments and computing


Heat transfer at short time and length scales

This symposium is focused on the transfer of heat in conditions where the dynamics of carriers is affected by short time and/or short length scales. The goal is to bridge the gap between experiments and modeling, fundamental issues and applications to move towards a deeper understanding of the physics and the related devices.




Thermal and radiative properties of materials at the micro/nanoscale are not well described by laws governing their properties at the macroscopic scale. The length scale and the shape of the systems affect the dynamics of the heat carriers, electrons and phonons. Furthermore, ballistic transport and scattering at boundaries and interfaces lead to deviations from Fourier’s law. Likewise, radiation emission in the subwavelength regime differs from the classical blackbody theory that characterizes the far field properties of materials.

Many applications of these effects have already been identified, ranging from energy conversion by thermoelectricity, to thermal management in nanodevices, phase change materials, magnetic memory and coherence in quantum information. Nanostructuring allows the coupling of surface waves and pave the way to the design of new monochromatic and/or directional emitters in the infrared.

Although considerable progress has been made, the fundamental understanding of heat transport at short time and length scales remains incomplete. Despite the tremendous recent advancement in thermal and radiative experimentation at the nanoscale in terms of sensitivity and accuracy, measurements with high resolution in time and space remain very challenging.. Additionally, measurements on “real” structures are preferred, deposition of heaters and sensors on given samples can completely change the thermal properties. Phonon mean-free paths may cover several length scales, from the nm to µm, thereby making the computational modeling less straightforward and calling for breatkthroughs in atomistic simulations accessible length scales. Nanostructuring is used for its benefits on thermal conductivity decrease for thermoelectricity but its effect on electronic transport is still under study. The understanding and use of coherent effects has been previously limited to low temperatures and is progressing towards room temperature. Interfaces between bio-molecules and solids are also of great interest though their study is still a challenge. Understanding the coupling between plasmons and phonons remains an important and rarely addressed issue. A lot of effort has been devoted to the thermal management of nanodevices, from the source by electron-phonon scattering, to the dissipation, thermal interface materials, for both cooling and thermal insulation of nanodevices.

Given the above context and open issues, this symposium will provide a forum to show and discuss latest advances on these topics. Our aim is to gather experimentalists and theoreticians from the fields of thermal conduction, near field and thermal radiation and photonic/phononic devices. 


Hot topics to be covered by the symposium:


  • Yann CHALOPIN, France “A Langevin approach of brownian relaxation for biological applications”
  • Teodor GOTSZALK, Poland “Thermal metrology using scanning probe microscopy related methods”
  • Nicolas HORNY, France “Experimental characterization of heat transport at interfaces, from macro- to nanoscale”
  • Samy MERABIA, France “Interfacial heat transfer: from hard to soft materials”
  • Dimos POULIKAKOS, Switzerland

With the aim of stimulating the participation especially from younger and promising scientists, additional invited talks will be selected among the best submitted abstracts.


Scientific committee members:


  • Jouni AHOPELTO, Finland
  • Francesc ALZINA, Spain
  • Olivier BOURGEOIS, France
  • Mihai CHIRTOC, France
  • Davide DONADIO, Germany
  • Younes EZZAHRI, France
  • Séverine GOMES, France
  • Karl JOULAIN, France
  • Achim KITTEL, Germany
  • David LACROIX, France 
  • Jennifer R. LUKES, USA
  • Ilari MAASILTA, Finland
  • Jean-François ROBILLARD, France
  • Miguel RUBI, Spain
  • Li SHI, USA
  • Sebastian VOLZ, France
  • Xanthippi ZIANNI, Greece
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Sesssion 1: Nanostructures : Evelyne LAMPIN
Authors : Dimos Poulikakos
Affiliations : Laboratory of Thermodynamics in Emerging Technologies (LTNT) Department of Mechanical and Process Engineering ETH Zurich CH-8092 Zurich, Switzerland

Resume : Carbon nanotubes, nanowires (such as Si or core/shell Si-Ge), graphene flakes, and metal or metal oxide nanoparticles are all minute amounts of matter with thermal, optical, mechanical and electrical properties drastically different than those of their counterpart bulk materials. Such nanomaterials are of critical importance to the development of technologies in many fields, ranging from energy and transportation to electronics and photonics. There is currently a pressing need for novel, facile, high yield methodologies for their assembly, handling, characterization and device integration. In this lecture, a remarkably simple process for the direct printing of nanoparticles of all kinds with electrohydrodynamic NanoDrip printing will be presented and the related physics and thermofluidic transport phenomena leading to the tunable formation of in- and out-of-plane functional nanostructures as single entities or large arrays will be explained. A host of applications will also be presented ranging from plasmonics, to light design through the controlled printing of quantum dots, to the printing of transparent conductive grids for solar cells and touch screen displays and to nanoscale force sensing devices for cells on surfaces with unprecedented resolution.

Authors : Y. Liu (1), D. Tainoff (1), M. Boukhari (2), A. Assy (3), J. Richard (1), A. Barski (2), P. Bayle-Guillemaud (2), E. Hadji (2), S. Gomes (3), O. Bourgeois (1)
Affiliations : 1 Université Grenoble Alpes, CNRS, Institut Néel, Grenoble F-38042, France ; 2 Institut Nanosciences et Cryogénie, SP2M, CEA-UJF, 17, Rue des Martyrs, Grenoble 38054, France ; 3 Centre d’Energétique et de Thermique de Lyon, Domaine Scientifique de la Doua, INSA de Lyon, 9 Rue de la Physique, Villeurbanne 69621, France

Resume : Engineering of thermal properties of materials by nanostructuration has made important progress in the last two decades. Besides phononics, the idea of phonon blocking as a phonon engineering approach is to reduce the lattice thermal conductivity of a material through decreasing the scale or introducing nanostructures. Once the distances between inclusions are comparable to the phonon mean free path within the material the phonons are scattered by the inclusions, resulting in a prohibited heat transport. In this paper, we present a new semi-conductor material made off Ge3Mn5 nano-inclusions embedded into an epitaxial Ge matrix. The size distribution (within 5 and 50 nm) and the concentration of the inclusions can be accorded with growth parameters. The structural features of this material have been fully studied using transmission electron microscopy. To measure the thermal conductivity of the Ge:Mn thin films, we have developed a sensitive 3-omega method adapted for measurements on thin films. Measurements have been carried out at room temperature on Ge:Mn samples having different manganese concentrations and treated at different annealing temperatures. They show that depending on the Mn concentration the thermal conductivity of the Ge:Mn thin films can be reduced by a factor of 4 to 20 comparing to the value for Ge bulk material. Numerical modeling are under way to investigate the phonon scattering mechanisms behind this significant reduction of thermal conductivity.

Authors : J.F. Robillard1,†, V. Lacatena2, M. Haras1, A. Scibetta, S. Monfray2, T. Skotnicki2 and E. Dubois1
Affiliations : 1 IEMN UMR CNRS 8520, Institut d’Electronique, de Microélectronique et de Nanotechnologie, Avenue Poincaré, F-59652 Villeneuve d’Ascq, France 2 STMicroelectronics, 850, rue Jean Monnet, F-38926 Crolles, France † Corresponding authors’ emails:

Resume : We investigate on the effect of periodic nano-holes structures etched in silicon membranes on the thermal conductivity. Such artificial crystals are promising in the scope of efficient, environmentally benign and CMOS compatible thermoelectric materials. Indeed, silicon exhibits a naturally high Seebeck coefficient and good electrical properties. However, because of its high lattice thermal conductivity, the thermoelectric efficiency remains extremely poor. The perspective of artificially introducing phonon diffusing patterns while preserving the crystalline electronic properties of silicon could renew the interest of this material from the energy harvesting point of view. Thanks to electronic lithography we have fabricated several types of silicon membranes integrated in MEMS structures. The membranes exhibit thicknesses down to 60 nm and the pitch sizes of the periodic patterns range from 60 to 100 nm. We have investigated their thermal conductivity using an electro-thermal method. Platinum heaters and sensors electrodes are used to generate and measure heats gradients through the membranes. Our results describe the important decrease in thermal conductivity as a function of pitch as compared to plain membranes.

Authors : Maxime VERDIER, David LACROIX, Konstantinos TERMENTZIDIS
Affiliations : Laboratoire LEMTA - Universit? de Lorraine - CNRS UMR 7563 Facult? des Sciences et Technologies, BP 70239 54506 Vandoeuvre les Nancy cedex, FRANCE

Resume : Silicon is one of the most abundant element in the world and Si based materials are involved in a broad range of application. With the evolution of the nanofabrication methods, one can tailor the physical properties of nanostructured materials and tune specific properties for specific purposes. For example, there is an increasing interest of nanostructured Si for thermoelectric applications. To enhance the poor thermoelectric conversion efficiency of bulk Si, a successful strategy is to reduce the thermal conductivity (TC) by nano-structuring the materials (nanowires, superlattices, nanopores). For nanoporous materials, the long mean free path phonons are scattered on the pores, driving to an important reduction of the TC. Nevertheless, making nano-pores in Si is often accompanied by an amorphization of the structure around the cavity. With the current work, we study with molecular dynamics simulations the effect of the amorphous edge presence on the TC. The pore size and the a-Si thickness around the pores are the study parameters. Increasing the amorphous fraction leads to the drastic decrease of the TC. Besides, phonon transport in nanoporous Silicon is also studied by the means of Boltzmann transport equation resolution through Monte Carlo method. Using this tool, several porosities are considered in order to make comparisons with other numerical studies and experimental data.

15:40 Coffee break    
Session 2: Nanocomposites : Samy MERABIA
Authors : Xanthippi Zianni
Affiliations : Dept. of Aircraft Technology, Technological Educational Institution of Sterea Ellada, 34400 Psachna, Greece Dept. of Microelectronics, INN, NCSR ‘Demokritos’, 15310 Athens, Greece

Resume : In recent works, we have explored the prospects for thermoelectric (TE) efficiency enhancement in non-uniform nanostructures above the quantum confinement regime [1-2]. In this regime, electrons and phonons can be treated as bulk-like carriers experiencing effects of the non-uniformity as they move through the nanostructure. Main effects on their transport properties originate from scattering on boundaries/interfaces and energy barriers. In one-dimensional modulated nanostructures (nanowires), a TE power factor enhancement was predicted in the presence of two phases for the electron transport and non-uniform thermal conductivity. We have explored the influence of the nanostructure dimensionality on the transport properties and the heat transfer. The two- and three- dimensional non-uniform nanostructures have been modeled by a network model. Our results indicate two regimes depending on the distribution of the non-uniformity in the nanostructures. The thermal conductivity can be interpreted by either average properties or by the formation of percolation paths for the heat transfer. We will present and discuss our findings on the heat transfer in the presence of non-uniformity due to interfaces and multiple phases in nanocomposite materials. [1] Neophytou N., Zianni X., Kosina H., Frabboni S., Lorenzi B., and Narducci D., Nanotechnology 24 (20) (2013) 205402 [2] Zianni X., Narducci D., Journal of Applied Physics 117 (2015) 035102

Authors : H. Zaoui, P. L. Palla, F. Cleri and E. Lampin
Affiliations : IEMN, UMR CNRS 8520 and University of Lille

Resume : The length dependence of the thermal conductivity is calculated in silicon nanowires and compared to silicon bulk. We use approach-to-equilibrium molecular dynamics (AEMD). AEMD is a transient temperature method for determining thermal conductivity in thermal conductors. Two delimited portions are heated at different temperatures before the temperature difference is monitored during the approach-to-equilibrium. The temperature profile has a sinusoidal form with an amplitude that slowly decreases with time. The temperature difference between the portions decays exponentially with time. We compare the numerical results with the solution of the heat equation in the same conditions. The sinusoidal form of the temperature profile and the exponential decay of the temperature difference are in agreement with the heat equation. Therefore we use the same relation to obtain the thermal conductivity. The method has been previously used to study bulk silicon supercells longer than 1 um. We apply the approach to nanowires. We first study the equilibration of the temperature difference, and show it is longer in nanowires due to surface effects. We validate the use of simultaneous Nosé-Hoover thermostats to obtain the initial temperature diffence. Finally, we obtain the thermal conductivity for several radius and lengths and compare the length dependence to the bulk.

17:10 End of session 2    
Poster session : -
Authors : V.B. Kapustianyk, B.I. Turko, M.R. Panasyuk
Affiliations : Scientific-Technical and Educational Center of Low Temperature Studies, Ivan Franko National University of Lviv, Drahomanova Str. 50, 79005, Lviv, Ukraine

Resume : For many years the ZnO micropowders are successfully and widely used as one of the main components at manufacturing a variety of, mainly low-cost, commercial thermal greases. The value of the coefficient of thermal conductivity of these greases is in the range from 0.6 to 1.5 W/(m∙K). The thermal conductivity of the composite material based on ZnO with different particle sizes (from micrometer to nanometer) and silicone oil was measured using the radial heat flow method. The thermal conductivity of the composite material based on the commercial ZnO micropowder with an average particle size of 50 μm was found to be 0.8 W/(m∙K). The thermal conductivity of the composite material based on the wet chemistry methods synthesized ZnO nanopowder with an average particle size less than 10 nm was found to be 2.5 W/(m∙K). Increased value of the thermal conductivity would be considered as a manifestation of the quantum size effect. Since the particle sizes are commensurate with the exciton Bohr radius (2 nm) and smaller than the mean free path of phonons (30 nm) and de Broglie wavelength in ZnO (14 nm), it is convenient to propose the ballistic mechanism of conductivity. When the particle sizes are commensurate with the exciton Bohr radius, their exciton binding energy on the main level is 4 times higher than those for the bulk sample. Therefore, ZnO nanocomposite material manifests a considerably higher exciton thermal conductivity.

Authors : Yuning Guo, Martin Schubert, Christoph Widmann, Thomas Dekorsy
Affiliations : Department of Physics and Center of Applied Photonics, University of Konstanz, 78457 Konstanz, Germany

Resume : Phononic crystals (PnC) make use of the fundamental properties of waves in order to manipulate the propagation of sound. Changeable periodic nanostructures provide a feasible and controllable way to modify propagation characteristics and select needed bandgaps of acoustic waves. Identifying the corresponding modes and improving efficiency of transmission in nanostructures is the key to enable further advances in this area and to enable new functionalities of potential devices. Through the computation of the band structures, acoustic displacement field and transmission of PnC which sizes are in the range of several hundred nanometers, adopting finite element method and specific boundary conditions, the characteristics of phonon transport for frequency ranges in gigahertz in PnC are shown and the propagation characteristics of Lamb waves and acoustic surface waves are investigated. Due to the ability to confine and mold acoustic waves in periodic nanostructure, acoustic nanoscale waveguides which insert defects inside or at the edge of a PnC are studied to give rise to the filtering frequencies or phononic rectification. The acoustic properties of PnC waveguide are tailored in by designing various kinds of defects, which is suitable for a wide range of applications from transducer technology to filtering and guidance of acoustic waves.

Authors : Arthur France-Lanord, Clive Freeman, Benoît Leblanc, Erich Wimmer
Affiliations : Materials Design SARL, CEA DSM-IRAMIS-SPEC; Materials Desin, Inc.; Materials Design SARL; Materials Design SARL

Resume : We present an ab initio parametrized variable charge forcefield for Si/SiO2 systems, in the third-generation Charge Optimized Many-Body (COMB3) potential framework. The fitting data, including total energies, forces and stress, comes exclusively from \it ab initio calculations of Si and SiO2 bulks, surfaces and clusters. The quality and the predictive power of the forcefield is assessed by computing properties including the cohesive energy and density of SiO2 polymorphs, surface energies of alpha-quartz, and vibrational features arising from the phonon density of states of crystalline and amorphous phases of SiO2. The results are compared to data from experiments, calculations, and molecular dynamics simulations using published forcefields including BKS, ReaxFF or COMB2. As an illustration of the strength of the new forcefield, we present results of thermal transport properties of pure crystalline and amorphous phases of SiO2, as well as of Si/SiO2 heterostructures.

Authors : A. Duzynska, A. Taube, A. Łapińska, M. Świniarski, J. Judek, M. Zdrojek
Affiliations : Faculty of Physics, Warsaw University of Technology, Koszykowa 75, 00-662 Warsaw, Poland

Resume : We herein report the determination of the intrinsic thermal conductivity (κ) and interfacial thermal conductance (g) of single-walled carbon nanotube thin films (50 nm) on top of a SiO2 substrate. The study was performed as a function of temperature (300-450 K) using the opto-thermal technique. The value of κ decreases nonlinearly by approximately 60% from a value of 26 W/Km at 300 K to a value of 9 W/Km at 450 K. This effect stems from the increase of multi-phonon scattering at higher temperatures. The g increases with temperature, reaching a saturation plateau at 410 K. These findings may contribute to a better understanding of the thermal properties of the supported carbon nanotube thin films, which are crucial for any heat dissipation applications.

Authors : Sonia Zampa, Pier-Luca Palla, Evelyne Lampin, and Fabrizio Cleri
Affiliations : IEMN UMR CNRS 8520 and University of Lille - CS 60069 - 59625 Villeneuve d'Ascq Cedex- France

Resume : The Approach-to-Equilibrium Molecular Dynamics (AEMD) method has been recently introduced [1] to calculate bulk thermal properties of nanomaterials. By means of a suitable application of the AEMD technique the calculation of the grain boundary thermal resistance (Kapitza resistances) in silicon has been performed as well. Taking profit from the efficiency of the AEMD both bulk and interface thermal properties have been obtained as a function of the system size and of the nanostructure. In this way a sizable scale dependence of these properties has been proved and characterized. Staring from these results a deep analysis of the thermal behavior of polycrystalline silicon is reported. In particular, a hierarchical superposition of scale-effects has been highlighted with promising applications in thermoelectronics. [1] E. Lampin, P. L. Palla, P.-A- Francioso and F. Cleri, J. Appl. Phys. 114, 033525 (2013).

Authors : Fabrizio CLERI
Affiliations : Institute of Electronics, Microelectronics and Nanotechnology (IEMN, UMR Cnrs 8520) and University of Lille I, 59652 Villeneuve d’Ascq, France

Resume : Among the variety of stress conditions organisms must survive, temperature increases or decrease damages cellular structures and interferes with cell functions. Often, indirect consequences of a temperature shift are detected. Indirect signals may be accumulation of heat shock proteins (HSPs). Also, structural proteins can denaturate at a critical temperature, as in the thermal transition of red-blood cells at 40 C: spectrin seems to be involved in the transition, as shown by its characteristic unfolding at 40 C. Cold is another temperature condition frequently encountered in nature, causing physiological problems entirely different from heat stress. Indirect effects include reduced enzyme activity, decreased membrane fluidity, stable RNA structures that interfere with translation. Induction of cold shock proteins (CSPs) enables efficient translation and maintains membrane integrity after a temperature down-shift. However, proteins, nucleic acids, lipids, can also act as direct thermosensors. Since the conformation of virtually every biomolecule is susceptible to temperature changes, all such biomolecules could act as primary thermal sensors. For example: temperature changes on DNA curvature or supercoiling can influence transcription initiation; changes to the 3-D structure of mRNA modulate translation efficiency. Here we focus on the structures of DNA and proteins susceptible to temperature changes, to show how several biomolecular thermometers may have evolved in nature.

Authors : Michal Wierzbicki
Affiliations : Faculty of Physics Warsaw University of Technology Koszykowa 75 00-662 Warszawa Poland

Resume : Thermoelectric effects in nanoribbons of two-dimensional crystals with hexagonal structure are analyzed theoretically and numerically. The influence of topological edge states and transition between the topological-insulator and conventional gap-insulator on the thermoelectric properties, and spin-related thermoelectric effects are investigated. The model includes electron-electron interaction in Hubbard the mean field approximation, spin-orbit interaction, staggered exchange field and external electric and magnetic fields. External fields lead to a nonzero thermopower in the vicinity of the gap edges and generate spin thermopower. Coulomb interaction modifies topological properties of nanoribbons, and their transport and thermoelectric properties.

Authors : Ali Alkurdi, Julien Lombard, Samy Merabia.
Affiliations : Department of Physics, Al-Baath University, Homs, Syria; Institut Lumière Matière, Université de Lyon, Villeurbanne, France.

Resume : Metallic nanoparticles heated by a laser pulse have aroused great interest due to their ability to heat up the surrounding medium as shown in recent theoretical and experimental studies [1,2,3]. This faculty opens the way to numerous applications, notably in biomedicine [4], where for instance, the destruction of a tumor may occur by means of the hyperthermia generated from a gold NP. The objective of this theoretical work is to quantify the heat transfer in a system consisting of a nanoparticle (NP) immersed in water and illuminated by a laser pulse. We investigate different types of NPs including hollow bare metallic NPs, core-shell gold-silica nanoparticles and nanomatryoshkas. For all these types, we account for interfacial resistances at the different interfaces, especially the influence of the electron-phonon interfacial conductance on thermal transport at interfaces. We compare the performance of the different types of NPs to the case of bare gold nanoparticles, with the aim to determine which type of NPs is more efficient to heat up the surrounding medium in the shortest time. We found that the core-shell gold-silica configuration may be the most efficient if the silica shell is thin. This efficiency is to a large extent explained by the electron-phonon coupling taking place at the gold-silica interface. [1]Baffou and Rigneault, PRB (2011); [2]Govorov and Richardson, NT(2007); [3]Lombard, Biben, Merabia, PRL(2014); [4]Baffou and Quidant, LPR(2013).

Authors : K. Horne(a), A. Fleming(b,e), M. Chirtoc(b), N. Horny(b), T. Antoni(c), S. Volz(c), M. Carras(d) and H. Ban(e)
Affiliations : (a)Dep. Mech. Energy Eng., Univ. North Texas, 3940 North Elm Suite 7102F, Denton TX, 76207, USA; (b)GRESPI, Univ. Reims Champagne Ardenne URCA,Moulin de la Housse BP 1039, 51687 Reims, France; (c)EM2C, Ecole Centrale Paris, PECLET, Grande Voie des Vignes, 92295 Chatenay-Malabry, France; (d)MirSense, 86 Rue de Paris, bâtiment Erable, 91400 Orsay, France; (e)Dept. Aerospace and Mech. Eng., Utah State Univ., 4130 Old Main Hill, Logan, UT 84322, USA

Resume : Quantum cascade lasers (QCLs) are constructed from superlattices of semiconductors. Increased temperatures impede their operation. Molecular dynamics (MD) simulations are used to compute the thermal conductivity through the Green-Kubo method, which takes the equilibrium heat flux variations within the system as input. The system heat flux is autocorrelated and then integrated; the result of integration is proportional to the thermal conductivity through the volume and temperature squared, as well as the Boltzman constant. The simulations provide effective bulk properties of a single period within the superlattice. These results are compared with the photothermal radiometry (PTR) measurements of similarly structured samples. Two types of irradiation configurations were used. Point irradiation with Gaussian laser beam profile has larger signal at high frequencies. Flat top beam profile ensures one-dimensional heat transfer when the thermal diffusion length increases at low frequencies. From the MD simulations the predicted thermal diffusivity of the QCL structure should be 1.77x10-^6 m^2/s, while the fitting for the PTR results measures a value of 4.70x10^-7 m^2/s. Further work must be done to reconcile this discrepancy.

Authors : 1.Paweł Janus, Andrzej Sierakowski, Krzysztof Domański, Piotr Grabiec, 2.Maciej Rudek, Teodor Gotszalk, 3. Bin Yang, Michel Lenczner
Affiliations : 1. Instytut Technologii Elektronowej al.Lotników 32/46,Warszawa, Poland 2.Wroclaw University of Technology, Wrocław, 50-372, Poland 3.FEMTO-ST, University of Technology at Belfort-Montbeliard, France

Resume : In this paper, a novel micromachined, scanning probe microscopy (SPM) micro-cantilevers with conductive, resistive tips are presented. Batch lithography and patterning process combined with focused ion beam (FIB) modification allows to manufacture thermally active, resistive tips with a nanometer radius of curvature. This design makes the proposed nanoprobes especially attractive for their application in the measurement of the thermal or/and electrical behavior of micro- and nanoelectronic devices. Developed microcantilever is equipped with piezoresistive deflection sensor. The piezoresistive deflection detector enables metrological (in other words quantitative) analysis of interactions between the microprobe and the investigated surface. Authors present results of thermal investigations of FinFet transistor under working conditions. Obtained thermal signal distribution is compared with modeling/simulation results.

Authors : Victor A. Ermakov, Andrei V. Alaferdov, Alfredo R. Vaz, Eric Perim, Pedro A. S. Autreto2, Ricardo Paupitz, Douglas S. Galvao2 and Stanislav A. Moshkalev
Affiliations : Center for Semiconductor Components, State University of Campinas, CP 6101, Campinas, SP, 13083-870, Brazil;Center for Semiconductor Components, State University of Campinas, CP 6101, Campinas, SP, 13083-870, Brazil;Center for Semiconductor Components, State University of Campinas, CP 6101, Campinas, SP, 13083-870, Brazil; Instituto de Física ‘‘Gleb Wataghin’’, Universidade Estadual de Campinas, 13083-970, Campinas, SP, Brazil; Instituto de Física ‘‘Gleb Wataghin’’, Universidade Estadual de Campinas, 13083-970, Campinas, SP, Brazil; Departamento de Física, IGCE, Universidade Estadual Paulista, UNESP, 13506-900, Rio Claro, SP, Brazil;Instituto de Física ‘‘Gleb Wataghin’’, Universidade Estadual de Campinas, 13083-970, Campinas, SP, Brazil;Center for Semiconductor Components, State University of Campinas, CP 6101, Campinas, SP, 13083-870, Brazil

Resume : Graphene, despite of being a very interesting material, presents several difficulties when our goal is to use it in applications at very high temperatures. We report here that it is possible to achieve a controlled multi-layer graphene burning, layer by layer, through a laser beam focused on suspended samples in cold-wall reactor configurations. Extremely high temperatures (up to ~ 3000K) can be attained without destroying the samples. Further insights on the details of these phenomena were gained through fully atomistic molecular dynamics simulations. These results demonstrate how to solve, with simple setup changes, two challenging graphene problems: high quality controlled thinning of multi-layer graphene and working at high temperatures, even with samples exposed directly to the air. This simple method can be very effective in the production of multi-layer graphene with controlled thickness, paving the way for new graphene applications, such as continuous radiation source and/or scaffolding material at extremely high temperatures.

Authors : Anna Łapińska, Andrzej Taube, Anna Dużyńska, Michał Świniarski, Mariusz Zdrojek
Affiliations : Faculty of Physics, Warsaw University of Technology, Koszykowa 75, 00-662 Warsaw, Poland

Resume : The low dimensional materials are becoming one of the most promising for modern electronic due to their outstanding properties. One of them is germanium selenide, a IV - VI narrow band chalcogenide, which could be an alternative for the lead chalcogenides due to its environmental sustainability and high stability and also its less toxicity. We have produced thin films of this materials via mechanical exfoliation and performed temperature-dependent Raman measurements in temperature range of 70 ? 350 K for the germanium selenide thin films. We have observed temperature-dependent non-linear phonon shift in low temperature which could be explained by optical phonon decay onto two or three acoustic phonons with equal energies. The first order temperature coefficient χ for higher temperature for B3g mode is χ = -0.025 cm-1/K, for Ag(1) mode is χ = -0.0197 cm-1/K and for Ag(2) mode is χ = -0.0288 cm-1/K and their values are comparable to those noticed for graphene or phosphorene. Our results are useful for further analysis of phonon and thermal properties of germanium selenide.

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Session 3: Experimental studies : interface resistances : Jerzy Bodzenta
Authors : Nicolas Horny
Affiliations : Multiscale Thermophysics Lab. GRESPI-CATHERM, Universit? de Reims Champagne Ardenne URCA, Moulin de la Housse BP 1039, 51687 Reims, France

Resume : Despite recent progress in the comprehension and modeling of heat transfer across interfaces, experimental values of interfacial thermal resistance Rth in various systems present large deviations from theoretical predictions. Moreover, a large variability of Rth with the condition of the interface at micro- and nano-scale is observed. However, such data are necessary for the validation of theoretical models and computations. Measuring Rth is often a challenge for the experimentalist because the available methods have to be adapted to the features of the samples. This work presents several experimental approaches including photothermal radiometry (PTR) and 3omega hot wire to evaluate Rth and thermal properties in solid/solid and solid/liquid systems having planar, cylindrical, spherical or random geometries. For simple configurations, Rth is obtained directly from the experiment and then it can be compared to theoretical predictions. On the other hand, in the case of nanocomposites and nanofluids, Rth is determined as a fit parameter in the frame of effective medium approximation (EMA) models.

10:30 Coffee break    
Session 4: Experimental studies : SThM : Mihai CHRISTOC
Authors : Teodor Gotszalk; Piotr Grabiec; Paweł Janus; Ivo W. Rangelow
Affiliations : Wroclaw Univesrity of Technology, Wyb. Wyspianskiego 27, 50370 Wroclaw, Poland; Insitute of Electron Technology, Al. Lotników 02-668 Warsaw, Poland; Ilmenau University of Technology, Gustav-Kirchhoff-Straße 1, 98693 Ilmenau, Germany

Resume : Metrology of thermal phenomena at the nanoscale is of big importance for the today progress in nanotechnology. The thermal effects, including heating and selfheating in the microelectronical integrated circuits (ICs) have become one of the most important factors limiting the system reliability. In very large scale integration (VLSI) devices, of power often reaching even 100 W the current density in the connection lines of nanometer width is in the range of 107 A/cm2, which leads to the electromigration in the wiring and system failure. Characterization of the local temperature variations makes it possibly to study the energy transfer and heat generation mechanisms and enables the analysis of the thermophysical phenomena. It should be also noted, that not only investigations of temperature distribution are of importance but also the locally resolved imaging of thermal conductivity can improve the system design and operation. Although the need for the high sensitive and high resolution imaging and measurement methods of thermal properties is clear their accessibility is quite limited. Methods based on infrared microscopy are limited to lateral resolutions in the micrometer range. A much higher resolution can be obtained using scanning thermal microscopy (SThM) which is one of the scanning probe microscopy (SPM) technologies. In the SPM methods the interactions between the nanotip and the surface are used to describe the surface parameters. The SThM technology relies on detection of the thermal flux between the thermal nanotip sensor and the investigated sample. In general two basic types of the tip sensors can be distinguished. In the thermocouple technology the nanotip is formed as a thermojunction, whose output voltage depends on the temperature difference between the tip sample contact point and the reference junction. In the thermoresistive technology the nanotip is formed as a the resistor, whose resistance depends on the sample temperature. Both thermal tips can be used in the so called passive and active SThM investigations. In the passive technology the temperature of the nanotip is detected, whereas in the active technology the energy dissipated from the thermal nanotip is used to determine the thermal resistance between the investigated sample. The investigation resolution of the SThM system is determined predominantly by the properties of the thermal microprobe, which is formed by a mechanical cantilever at the end of which a thermal nanosensor is integrated. The ideal SThM probe should exhibit low stiffness and integrate a force sensor enabling metrological (in other words quantitative) investigations of the load force acting between the microprobe and the surface. Moreover, the thermal resistance of the cantilever must be as high as possible to isolate thermally the nanotip from the spring beam and cantilever supporting body. In order to ensure the high operation frequency the mass of the thermal tip should be small as possible, which additionally ensures the high local resolution of the surface thermal imaging. The thermal nanotip should be wear resistant, which leads to reliable and repeatable surface imaging. Many designs of the SThM probes have been reported in the last two decades. However, all of them do not comprise all described above desired features. The reported systems suffered from the low endurance of the nanotip, did not include the integrated deflection sensors and the thermomechanical setup was not optimized. In this article we present a family of novel SThM probes integrating piezoresistive deflection sensor and resistive nanotips. We will present sensor metrology and control environment and the methods for sensor and entire system calibration.

Authors : F. Menges 1, H. Schmid 1, P. Mensch 1, U. Drechsler 1, S. Karg 1, V. Schmidt 1, A. Stemmer 2, H. Riel 1, and B. Gotsmann 1
Affiliations : 1) IBM Research - Zurich, 8803 Rueschlikon, Switzerland 2) Nanotechnology Group, ETH Zurich, 8803 Rueschlikon, Switzerland

Resume : A key-missing piece in the tool-box of scanning probe techniques is a reliable method to quantify temperature. The primary challenge is that thermal probes can typically not equilibrate with the sample, but acquire heat-flux-related signals that are disturbed by contact-related thermal resistance variations. This has limited the reliability of scanning probe microscopy for nanoscale thermometry and established as major hurdle for understanding of thermal effects in nanoscale devices. Here, we introduce a novel method to map nanoscale temperature distribution using a scanning thermal microscope. Contact-related artifacts are minimized by simultaneously probing a time-dependent and a time-averaged heat flux signal between a self-heated scanning probe sensor and a temperature-modulated sample. The method is applied to image self-heating of a nanoscale metal interconnect and a semiconducting nanowire. Local Joule and Peltier effcts are quantified with 7mK sample-temperature resolution, corresponding to a pico-Watt tip-sample heat flux sensitivity.

Authors : Ali Assy, Stéphane Lefèvre and Séverine Gomès
Affiliations : Centre d’Energétique et de Thermique de Lyon (CETHIL), UMR CNRS 5008, INSA Lyon, UCBL, Université de Lyon, Villeurbanne, France

Resume : Scanning Thermal Microscopy (SThM) has been used to investigate heat transfer at nano-contacts. The heat conduction from the heated probe to the sample through water meniscus, solid-solid contact and air was quantified and will be presented in details. Experimental results were obtained with two resistive probes: the Wollaston wire probe (5 µm in diameter) and the Pd/Si3N4 tip (apex radius < 100 nm). From experiments performed under ambient conditions, the capillary forces at the tip-sample contact were measured as a function of the tip temperature. The water meniscus evaporation appears dependent on the sample spreading resistance. The meniscus dimensions and the thermal conductance of the water meniscus were determined accounting for the meniscus-solid interfacial thermal conductance. The thermal conductance through solid-solid contact was identified from SThM measurements performed under vacuum conditions. Assuming perfect interfaces, the thermal boundary resistance and phonon transmission coefficient for various contacts were determined. Based on the previous results, the thermal conduction through air was quantified from measurements performed under ambient conditions and reference samples. It appears to be strongly dependent on the sample thermal conductivity. The results show the limits of sensitivity of thermal conductivity measurements with the two used probes.

Authors : Anna Kaźmierczak-Bałata1), Justyna Juszczyk1), Jerzy Bodzenta1), Piotr Firek2)
Affiliations : 1)Institute of Physics-CSE, Silesian University of Technology Konarskiego 22 B, 44-100 Gliwice, Poland; 2)Institute of Microelectronics and Optoelectronics, Warsaw University of Technology Koszykowa 75, 00-662, Warsaw, Poland

Resume : A nanofabricated thermal probes (NThP) were used to measure the thermal conductivity of ultra-thin SiO2 and BaTiO3 films. The SiO2 film thicknesses were from 4.1 to 15.6 nm. The BaTiO3 films were 100 nm thick. The films were grown (SiO2) or deposited (BaTiO3) on Si substrates. The main issue in such SThM measurements is to take into account the influence of thermal properties of the substrate on measured signal and to elaborate correction procedure allowing to extract information about thin film thermal conductivity from measurements carried out for layered sample. To study the substrate influence on the signal a thermo-electrical model of the sample-probe system was built in COMSOL MultiPhysics. According to the model the voltage of the dc driven NThP was calculated as a function of the layer thickness and its thermal conductivity. The analysis of results from numerical simulations allowed to propose a correction procedure reestablishing the actual value of thermal conductivity according to the apparent value. The apparent thermal conductivity of the sample was determined from calibration curve bulit on experimental data for reference samples. The experimental method based on earlier elaborated methodology allowing determination of dynamic and static resistances of the NThP. The ratio of the difference between dynamic and static probe resistances is proportional to the thermal resistance for the heat flux from the NThP to the sample.

12:40 Lunch break    
Session 5: Cohence effects : Severine GOMES
Authors : T. A. Puurtinen, Y. Tian, N. Zen, T. J. Isotalo, S. Chaudhuri, I. J. Maasilta
Affiliations : Nanoscience Center, Department of Physics, P.O. Box 35, University of Jyväskylä, FI-40014, Finland

Resume : A lot of research has lately focused on lowering phonon thermal conductivity using nanoscale structuring of materials to increase scattering. On the other hand, much less attention has been given to controlling phonon thermal conductance by engineering the phonon dispersion relations, in other words the phonon ‘band structure’. Here, we discuss this line of approach for controlling thermal conduction [1] and heat capacity and present our recent experimental and computational studies in two-dimensional phononic crystals (PnCs) at sub-Kelvin temperatures. A typical sample consists of a periodic array of holes etched into a 0.5 µm thick silicon nitride membrane. We compared the results of two PnCs with different periodicities to an uncut membrane sample and 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 the PnC devices. As our calculation of the thermal conduction was performed in the fully ballistic limit, we draw the conclusion that coherent, interference-based phonon band structure modification is behind the observations and thus phonon thermal conduction can be controlled by using the wave-properties of phonons, instead of just the particle (scattering) properties. [1] N. Zen et al., Nat. Commun. 5, 3435 (2014).

Authors : Benoit Latour, Yann Chalopin
Affiliations : Laboratoire EM2C, CNRS Ecole Centrale Paris

Resume : In harmonic systems, phonons are plane waves with infinite mean free path and spatial extension. When anharmonic interactions are present, a complex frequency is associated at each phonon mode [1], as the phonon lifetime becomes finite. The imaginary part of the frequency is related to the relaxation time due to phonon/phonon scattering, so to the mean free path. The spatial extension of the phonon modes, defined by the spatial coherence length [2], is also affected by the presence of the anharmonicity. Consequently, a complex wave vector can be introduced for each mode. Using Equilibrium Molecular Dynamics, a comparison between the phonon mean free path and the spatial coherence length spectra is first provided for single layer graphene, where phonons acts as particles. Then, these two characteristic lengths are computed for superlattices, where wave effects are known to be a key property. We will show that bringing a complex wave vector in the phonon mode allows to quantitatively assess phonon localization phenomena. [1] A.A. Maradudin and A.E. Fein, Phys. Rev. 128, 2589 (1962). [2] B. Latour, S. Volz and Y. Chalopin, Phys. Rev. B 90, 014307 (2014).

Authors : B. Graczykowski, M. Sledzinska, J.S. Reparaz, A. El Sachat, F. Alzina, M.R. Wagner, C.M. Sotomayor Torres
Affiliations : B. Graczykowski, (1) ICN2 - Catalan Institute of Nanoscience and Nanotechnology, Campus UAB, 08193 Bellaterra (Barcelona), Spain; M. Sledzinska, (1) ICN2 - Catalan Institute of Nanoscience and Nanotechnology, Campus UAB, 08193 Bellaterra (Barcelona), Spain; J.S. Reparaz, (1) ICN2 - Catalan Institute of Nanoscience and Nanotechnology, Campus UAB, 08193 Bellaterra (Barcelona), Spain; A. El Sachat, (1) ICN2 - Catalan Institute of Nanoscience and Nanotechnology, Campus UAB, 08193 Bellaterra (Barcelona), Spain. (2) Dept. Of Physics, Universitat Autónoma de Barcelona, Campus UAB, 08193 Bellaterra (Barcelona), Spain; F. Alzina, (1) ICN2 - Catalan Institute of Nanoscience and Nanotechnology, Campus UAB, 08193 Bellaterra (Barcelona), Spain; M.R. Wagner, (1) ICN2 - Catalan Institute of Nanoscience and Nanotechnology, Campus UAB, 08193 Bellaterra (Barcelona), Spain; C.M. Sotomayor Torres, (1) ICN2 - Catalan Institute of Nanoscience and Nanotechnology, Campus UAB, 08193 Bellaterra (Barcelona), Spain. (3) Institució Catalana de Recerca i Estudis Avançats (ICREA), 08010 Barcelona, Spain

Resume : The research from the last 10 years has shown that nanoscale phononic crystals (PnCs) can be efficiently applied for the control of hypersound and engineering of the thermal transport in solids. Herein the thermal conductivity can be significantly decreased with respect to bulk, e.g., down to two orders of magnitude for Si based PnCs. In this study we consider two types of 2D PnCs, solid-air and solid-solid, made of thin Si membranes. The results obtained by Brillouin spectroscopy show how the volume reduction or local resonances both accompanied by a periodicity modify the dispersion of GHz acoustic phonons. The experimentally observed features, such as zone folding, frequency bad gaps, 3D localization, are compared with results of finite element method calculations. Regarding the heat transport in such materials, contrarily to the previous studies, we use a novel and non-contact technique based on Raman thermometry, where two lasers are used to heat and probe the sample. The results obtained for a wide range of temperatures show a clear reduction of thermal conductivity as a function of porosity of the holey PnCs. A comparative study of membranes with and without a periodic array of Al pillars touches the, so far, open question regarding the role of the phonon dispersion of PnCs on the thermal conductivity. Moreover, we consider the important issue, in the viewpoint of potential applications, of the influence of air convective cooling on the heat dissipation in PnCs.

Authors : Haoxue Han, Baowen Li, Yuriy A. Kosevich and Sebastian Volz
Affiliations : CNRS UPR 288 Laboratoire d’Energétique Moléculaire et Macroscopique Combustion (EM2C) Ecole Centrale Paris France, National University of Singapore, Russian Academy of Sciences Russia, CNRS UPR 288 Laboratoire d’Energétique Moléculaire et Macroscopique Combustion (EM2C) Ecole Centrale Paris France

Resume : We introduce an atomic-scale phononic metamaterial producing two-path phonon interference antiresonances to control the heat flux spectrum. We show that a crystal plane partially embedded with defect-atom arrays can completely reflect phonons at the frequency prescribed by masses and interaction forces. We emphasize the predominant role of the second phonon path and destructive interference in the origin of the total phonon reflection and thermal conductance reduction in comparison with the Fano-resonance concept. The random defect distribution in the plane and the anharmonicity of atom bonds do not deteriorate the antiresonance. The width of the antiresonance dip can provide a measure of the coherence length of the phonon wave packet. All our conclusions are confirmed both by Green's function studies of the equivalent quasi-1D lattice models and by numerical molecular dynamics simulations of realistic 3D lattices. Haoxue Han, et al., Phys. Rev. B 89, 180301(R) 2014 Haoxue Han, et al., Phys. Rev. Lett. 114, 145501 2015 Zhang, Haoxue Han*, et al., Adv. Funct. Mater. in press

15:40 Coffee break    
Session 6: Graphene : Sebastian VOLZ
Authors : Xiaoliang Zhang1, Ming Hu1,2
Affiliations : 1 Institute of Mineral Engineering, Division of Materials Science and Engineering, Faculty of Georesources and Materials Engineering, Rheinisch-Westfaelische Technische Hochschule (RWTH Aachen University), 52064 Aachen, Germany; 2 Aachen Institute for Advanced Study in Computational Engineering Science (AICES), RWTH Aachen University, 52062 Aachen, Germany.

Resume : Graphene and its bilayer form have attracted a great deal of attention due to their promising applications. Using equilibrium molecular dynamics, we investigated the effect of inter-layer covalent bonding on the in-plane thermal conductivity of bilayer graphene. We found that, on one hand, the introduction of inter-layer covalent bonding can lead to the reduction of the thermal conductivity of bilayer graphene; on the other hand, the reduction of the thermal conductivity dependent on not only the inter-layer bonding density but also the detailed topological configuration of the inter-layer bonds. For randomly distributed inter-layer bonding the thermal conductivity of bilayer graphene decreases monotonically with inter-layer bonding density; however, for regularly arranged inter-layer bonding the thermal conductivity of bilayer graphene surprisingly possesses a non-monotonic dependence on the inter-layer bonding density. This non-intuitive non-monotonic dependence is further explained by performing phonon spectral energy density analysis. We also found the similar results for the bilayer BN. These results suggest the application of inter-layer covalent bonding can be effectively used for rational designing nanoscale devices with precisely tunable thermal conductivities.

Authors : Maxime Gill-Comeau, Laurent J. Lewis
Affiliations : Département de physique, Université de Montréal

Resume : We use molecular dynamics (MD) simulations to study heat conductivity in single-layer graphene and graphite. More precisely, we analyse the MD trajectories through a time-domain modal analysis. We show that the use of the time-domain formulation (in contrast to the frequency-domain formulation) is essential to obtain a faithful representation of heat flow in graphene and related materials as it allows the proper treatment of collective vibrational excitations. Our temperature-dependent results display very good agreement with experiment and, for temperatures in the range 300-1200 K, we observe that the ZA branch allows more heat flow than all the other branches combined while the contributions of the TA, LA and ZO branches are fairly similar to one another at every temperature. Conductivity mappings indicate strong collective excitations associated with low frequency ZA modes. We find that these collective effects are a consequence of the quadratic nature of the ZA branch as they also appear in graphite but are absent in strained graphene where the dispersion becomes linear.

17:10 End of session 6    
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Session 7: Membranes : Yann CHALOPIN
Authors : M. Sledzinska (1), B. Graczykowski (1), D. Saleta Reig (1), M. Placidi (2), A. El Sachat (1), J.S. Reparaz (1), F. Alsina (1) and C. M. Sotomayor Torres (1)(3)
Affiliations : (1) Catalan Institute of Nanoscience and Nanotechnology (ICN2) Edifici ICN2 08193 — Bellaterra (Barcelona) Spain; (2) Catalonia Institute for Energy Research (IREC) Jardin de les Dones de Negre 1, 08930, Sant Adrià del Besòs, Spain; (3) Institucio Catalana de Recerca i Estudis Avancats (ICREA) 08010 Barcelona, Spain;

Resume : Transition metal dichalcogenides, such as MoS2, are one of the 2D materials that have recently attracted a lot of attention because of their optical properties, such as the thickness-dependent band-gap transition and large optical absorption, which covers almost the whole visible spectrum. At the same time they show excellent room-temperature carrier mobility with a high on-off ratio making them perfect candidates for nano-electronics. Here we report a technique for transferring large areas of the CVD-grown, few-layer MoS2 from the original substrate to another arbitrary substrate and onto holey substrates, in order to obtain free-standing structures. The method consists of a polymer- and residue-free, surface-tension-assisted wet transfer, in which we take advantage of the hydrophobic properties of the MoS2. The methods yields better quality transferred layers, with fewer cracks and defects, and less contamination than the widely used PMMA-mediated transfer and allows fabrication of few-layer, fee-standing structures with diameters up to 100 µm. So-fabricated samples are ideal for performing thermal conductivity measurements using non-contact, Raman thermometry. Understanding thermal properties of MoS2 can give an insight on the thermal transport in ultra-thin semiconducting films, especially taking into account amount of layers and grain sizes in polycrystalline materials.

Authors : A. El Sachat1,2, J. S. Reparaz1, B. Graczykowski1, M. Sledzinska1, F. Alzina1, M. Wagner1, A. Shchepetov3, M. Prunnila3, J. Ahopelto3 and C. M. Sotomayor Torres1,4
Affiliations : 1 ICN2 Catalan Institute of Nanoscience and Nanotechnology, Edifici ICN2, Campus UAB, 08193 Barcelona, Spain; 2Dept. of Physics, Universitat Autònoma de Barcelona, Campus UAB, 08193 Bellaterra (Barcelona), Spain; 3 VTT Technical Research Centre of Finland, PO Box 1000, FI-02044 VTT, Espoo, Finland; 4 ICREA, Passeig Lluis Companys 23, 08010 Barcelona, Spain;

Resume : Contactless tools for thermal conductivity determination have attracted considerable attention in the last years. In the case of nanomebranes, 2-dimensional geometries with thicknesses below few hundreds nanometres, the ability to map the temperature field upon a localized thermal excitation provides a full picture of the thermal properties of these systems. Besides avoiding expensive and time consuming fabrication processes and the presence of thermal resistances arising from the contacts used in electrical methods, two-laser Raman thermometry provides self-consistently the temperature dependence of the thermal conductivity from a single measurement of the decay of the thermal field in a broad temperature range (100 K up to the melting point). In particular, this technique is especially suitable to study the temperature range over 1000 K where other techniques cannot be applied since experiments at such high temperatures always represent an experimental challenge. We provide examples of the application of this technique in case of free-standing Si membranes with thicknesses ranging from 9 nm to 200 nm, Si phononic crystal membranes, and free-standing graphene.

10:30 Coffee break    
Session 8: Thermoelectricity : Jean-Francois ROBILLARD
Authors : K.Zberecki, R.Swirkowicz, J. Barnaś
Affiliations : Faculty of Physics, Warsaw University of Technology;Faculty of Physics Warsaw University of Technology; Faculty of Physics, Adam Mickiewicz Universityand Institute of Molecular Physics, Polish Academy of Sciences

Resume : Electronic and transport properties of narrow boron-nitride nanoribbons (BNNRs) asymmetrically passivated with hydrogen atoms have been investigated using theoretical methods based on ab initio calculations and non-equilibrium Green function formalism. The spin conductance Gs, spin Seebeck coefficient Ss, and spin thermoelectric efficiency described by the spin figure of merit ZTs, have been determined for zigzag BNNRs with B-edges dihydrogenated and N-edges mono-hydrogenated, Such nanoribbons exhibit ferromagnetic ordering of the edge magnetic moments. The corresponding band structure calculations show that one spin channel becomes non-conductive for chemical potentials above the Fermi level of the corresponding charge neutral BNNRs, which has a strong influence on thermoelectric properties and, more importantly, leads to interesting spin related effects. Numerical calculations performed for BNNRs of different widths in a wide region of temperatures show that the Seebeck coefficient Ss, and especially the spin efficiency ZTs, can achieve high values even at room temperatures. Interestingly, the maximum of ZTs only weakly depends on the temperature and nanoribbon width, which makes the system interesting for applications in spintronic devices.

Authors : Tito Huber, Scott Johnson, Tina Brower, Albina Nikolaeva, Leonid Konopko
Affiliations : Howard University;Academy of Sciences of Moldova

Resume : We are interested in hybrid interfaces applicable to energy conversion problems. We report on the fabrication and photoresponse of devices composed of nanowire arrays of thermoelectric bismuth, which is capped with transparent conducting films such as indium tin oxide (ITO). The front surface is highly absorbing over a broadband because of the light-trapping property of the nanowire array. Under infrared illumination the photoresponse can be described by thermoelectric effects caused by the heating of the front surface. At low frequencies, quasi-equilibrium across the nanowire array is achieved but at high frequencies the signal rises to high values proportional with the square root of the frequency. This is because the energy is delivered to the front surface, where the thermoelectric junctions between the nanowires and the transparent film are located. The response can be fast, with a response time much shorter than the array thermalization time, only limited by optical penetration length and thermalization time of the front surface. Preliminary results have been presented by Huber et al, Appl. Phys. Lett. 103:041114 (2013). The photoresponse of devices capped with graphene will be discussed also. The detection arrays may find future optoelectronic application as fast nanoscale thermopiles.

Authors : Tao Ouyang and Ming Hu
Affiliations : Institute of Mineral Engineering, Division of Materials Science and Engineering, Faculty of Georesources and Materials Engineering, RWTH Aachen University, 52064 Aachen, Germany Aachen Institute for Advanced Study in Computational Engineering Science (AICES), RWTH Aachen University, 52062 Aachen, Germany

Resume : Pressure tuning and exploration of high pressure phase are effective approaches to modulate the electronic properties and optimize the thermoelectric performance [1-7]. For example, the researchers found that the pressure can significant improve the power factor S^2 σ of some potential thermoelectric materials, e.g., PbTe, Bi2Te3 and Sb2Te3 [1-5]. The high pressure phase of PbTe and HgTe are also predicted to possess superb thermoelectric efficiency [6,7]. However, in these works the phononic thermal conductivity is simply estimated by the Wiedemann-Franz relation or assumed to be the same value for all different phases, which will gives rise to the inaccuracy of thermoelectric performance. In order to describe the thermoelectric property more accurately, it is desirable to investigate the lattice thermal transport through the first-principles-based approach. In this work [8-10], taking some potential thermoelectric materials as example, e.g., HgTe and CdTe, we investigate the thermal conductivity with different pressure and phases by using the first-principle based phonon Boltzmann transport equation. The results show that the lattice thermal conductivity of HgTe presents abnormal pressure dependence. That is, it decreases as the pressure increases which is in contrast with that of the traditional bulk systems. Meanwhile, we also find that the thermal conductivity of high pressure phase of HgTe is an order of magnitude lower than that with normal pressure. Based on the modified thermal conductivity, the figure of merit of HgTe is re-calculated and the max value is found to approach 1.4 at room temperature, which further qualifies the potential application of HgTe in thermoelectrics. As for the CdTe, however, the pressure dependence of thermal conductivity displays a quite different behavior as compared to HgTe although they belong to the same group. Through analyzing the microscopic mechanism, e.g. mode dependent phonon group velocity, relaxation time, Grüneisen parameters and three phonon scattering phase space, we can explain these novel thermal transport phenomena in HgTe and CdTe. Our studies shed light on the thermal transport of the telluride based materials with different pressures and phases and could offer useful guidance for engineering the thermal transport properties in terms of enhancing their thermoelectric performance.

Authors : Eun Kyung Lee1, Jong Woon Lee2, Junho Lee3, Dongmok Whang2, Byoung Lyong Choi4
Affiliations : 1. Samsung Electronics, Samsung Advanced Institute of Technology, Computer Aided Engineering Group, Korea 2. Sungkyunkwan University, School of Advanced Materials Science and Engineering, Korea 3. Samsung Electronics, Samsung Advanced Institute of Technology, Analytical Engineering Group, Korea 4. Samsung Electronics, Samsung Advanced Institute of Technology, Nano Electronics Lab, Korea

Resume : During the last decade, low dimensional nanostructures have been considered to be effective for thermoelectric materials by decreasing of thermal conductivity due to suppressing the lattice phonon contribution. Particularly, silicon-germanium alloy nanowires are one of the promising candidates as efficient thermoelectric materials because they have low thermal conductivity and the excellent electrical properties. In this presentation, we will discuss the thermal properties of silicon-germanium nanowires with nano particles embedded in shell and their structure formation mechanism. Nano particles in outer shell can play an important role to maximize the depletion of heat-carrying phonons in nanowires. Ultra low thermal conductivity which is nearly alloy limit of the silicon-germanium nanowire will be presented. At the same time, the electrical conductivity of nanowires shows to be sustained due to the smooth transport of charge carrier through the core region.

Authors : Mykola ISAIEV 1, Joseph KIOSEOGLOU 2, Imad BELABBAS 3, David LACROIX 1, Konstantinos TERMENTZIDIS 1
Affiliations : 1. Laboratoire LEMTA - Universit? de Lorraine - CNRS UMR 7563 Facult? des Sciences et Technologies, BP 70239 54506 Vandoeuvre les Nancy cedex, FRANCE 2. Department of Physics, Aristotle University of Thessaloniki, GR-54124 Thessaloniki, Greece 3. Groupe de Cristallographie et de Simulation des Mat?riaux, Laboratoire de Physico-Chimie des Mat?riaux et Catalyse, Facult? des Sciences Exactes, Universit? de Bejaia, Bejaia 06000, Alg?rie

Resume : The III-V semiconductors are very important materials for micro/nano-optoelectronics. In particular, gallium nitride was firstly used for the fabrication of high-efficient blue LEDs and lasers. In addition, this material is successfully used as active element of high-frequency devises. These devices can be significantly overheated during operation. Therefore, the thermal properties of their basic elements play a crucial role for the further improvement of the quality of the devices and their life time, as well their range of functional frequency. The bulk GaN has high thermal conductivity (~150 W/(m K)) and this is an important advantage of this material for certain devices. In addition, the threading dislocations comprise the major type of defects in heteroepitaxial, polar c-plane GaN layers. Their role on the electronic properties has been a matter of extensive investigation. However, the influence of threading dislocations on thermal conductivity has not been elucidated till now. By means of Equilibrim Molecular Dynamics simulations; the influence of the a-edge and c-screw threading dislocations on the thermal conductivity of bulk GaN has been investigated. The dependence of the thermal conductivity on the Burgers vector of dislocations will be presented and physical insights will be given. In addition, the influence of dislocation density will by analyzed.

12:40 Lunch break    
Session 9: Soft matter : Bernd GOTSMANN
Authors : Yann Chalopin
Affiliations : ECP, Paris-France

Resume : The thermal relaxation phenomena in nano-objects of biological interest is introduced from the microscopic time-fluctuations point of view. The three modes of heat transfers are presented. The first part details some results on the IR-dielectic properties of lipid membranes. A second step is devoted to the numerical prediction of the thermal interface resistance of metallic nano-particles interfaced with polymers. The third line of the talk will explore the brownian relaxation mechanisms in magnetic spin lattices formed by magnetic nano-particles. From the Langevin equation, the prediction of the magnetic susceptibility spectra of strongly coupled magnetic nano-clusters damped in a viscous fluid and under external field is introduced. We will illustrate how this practically allows to accurately map the heat dissipation and its propagation in a cell in contact with magnetic nano-particles.

Authors : Samy Merabia
Affiliations : ILM - Lyon - France

Resume : Heat transport at interfaces is of prime importance for heat management at the nanoscale. On the fundamental side, our understanding of interfacial energy transport is still partial. In the first part of this contribution, we discuss energy transport across metal-silicon interfaces. We present results of ab-initio lattice dynamics calculations which allow us to predict the phonon-phonon transmission coefficient as a function of the phonon frequency and wavevector. We discuss the possibility to filter high-frequency phonons through a change of the orientation of the interface. Finally, comparison between our theoretical predictions and available experimental data permits to discuss the effect of the bonding strength on interfacial heat transport. In the second part of the talk, we will briefly review our recent efforts to model heat dissipation in soft materials. This encompasses heat transfer from hot plasmonic nanoparticles in water and the thermal conductivity of polymer nanocomposites, with the aim to make polymer good conductors. We will stress the importance of viscoelastic effects in the heat transport of soft materials.

15:20 Coffee break    
Session 10: Modeling and simulations I : Konstantinos TERMENTZIDIS
Authors : L. Rebohle 1, T.Schumann 1, S. Prucnal 1, W. Skorupa 1, T. Henke 2,3
Affiliations : 1 - Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden - Rossendorf, Bautzner Landstraße 400, 01328 Dresden, Germany; 2 - Institute of Semiconductors and Microsystems, Technische Universität Dresden, 01062 Dresden, Germany; 3 - Center for Advancing Electronics Dresden, Technische Universität Dresden, 01062 Dresden, Germany

Resume : Flash lamp annealing (FLA) is a modern annealing technique which takes advantage of the millisecond- and microsecond time scale. However, in many cases a direct temperature determination is sophisticated and complex, and sometimes an a priori guess of the temperature is desirable. In this work we simulate the space and time dependent temperature distribution during FLA and compare it with experimental results, e.g. with observable phase changes during the crystallization of amorphous Si layers on insulator for thin film transistor applications. In detail, we will address the following items: (i) the influence of multiple reflections within the layer system as well as between sample and chamber walls, (ii) the influence of lateral and transversal temperature gradients, and (iii) the edge overheating problem. Simulations were performed with the help of both in-house and commercial software tools.

Authors : Etienne Blandre (1)*, Pierre-Olivier Chapuis (1), Mathieu Francoeur (2), Rodolphe Vaillon (1)
Affiliations : (1) Université de Lyon, CNRS, INSA-Lyon, UCBL, CETHIL, UMR5008, F-69621, Villeurbanne, France; (2) Department of Mechanical Engineering, University of Utah, Salt Lake City, UT 84112, USA

Resume : We investigate the impact of interferences on thermal radiation of layered structures. In a previous study [1] of a semi-infinite thermal radiator emitting toward a thin film, we showed in particular how interferences affect the spatial and spectral distributions of the flux absorbed by the film due to Fabry-Pérot cavity effects. In the present work, we investigate one-dimensional multilayered structures deposited on a substrate composed of at most two transparent semiconductor films and one metallic reflective thin layer. Using fluctuational electrodynamics, we calculate the radiative heat flux emitted by the structure, its spectral and total emissivities, as a function of temperature. In particular, we show that the emission of a substrate can be enhanced by the deposition of a silicon layer of appropriate size. We also determine the temperature maximizing the total emissivity for a given layer thickness. For multilayers, we analyze the contribution of each layer to the emission, and observe that it depends strongly on the structure. This work improves our understanding of the radiative heat transfer between layered bodies and paves the way for new optimizations in thermophotovoltaic applications. [1] E. Blandre et al., AIP Advances, 5, 057106 (2015)

Session 11: Polaritons : Pawel KEBLINSKI
Authors : Jose Ordonez-Miranda 1, Laurent Tranchant 2, Sergei Gluchko 1, Thomas Antoni 1,3, and Sebastian Volz 1,
Affiliations : 1 Laboratoire d’Energétique Moléculaire et Macroscopique, Combustion, UPR CNRS 288, Ecole Centrale Paris, Grande Voie des Vignes, 92295 Chatenay Malabry, France. 2 Department of Mechanical and Control Engineering, Kyushu Institute of Technology, 1-1 Sensui-cho, Tobata-ku, Kitakyushu 804-8550, Japan. 3 Ecole Centrale Paris, Laboratoire de Photonique Quantique et Moléculaire, CNRS (UMR 8537), Ecole Normale Supérieure de Cachan, Grande Voie des Vignes, F-92295 Châtenay-Malabry cedex, France.

Resume : Surface phonon-polaritons (SPhPs) are coupled states of optical phonons and electromagnetic waves, which can significantly enhance the thermal energy transport along the interface of polar nanomaterials. Theoretical results showed that the SPhP contribution to the thermal conductivity of nanofilms [1,2] and the thermal conductance of nanowires [3] could be comparable to or even higher than the corresponding ones of phonons, especially at room temperature. This is explained by the comparatively long SPhP propagation length, which can be tuned by the permittivity of the material, its geometry, and its surrounding media. [4,5] These three variables can be used to classify different polar structures, as good or bad materials for the SPhP energy transport, and therefore to define a SPhP figure of merit, which is not established yet. In this work, a SPhP figure of merit (ZSPhP) of polar structures is proposed as a quality factor for the energy transport of SPhPs. This is defined as a benefit-to-cost ratio, where the benefit is the propagation length (Λ) and the surface confinement of these energy carriers, and the cost is their transversal attenuation (δ). Taking into account that the surface confinement can be measured by the difference (β-k0) of wave vectors of the SPhPs (β) and light (k0), which are given by the SPhP dispersion relation, the non-dimensional SPhP figure of merit is defined by ZSPhP= Λ(β/k0-1)/δ. This frequency-dependent parameter is then used to assess and compare the SPhP response of SiO2, SiC, and boron nitrite, which are three commonly used polar materials to excite and propagate SPhPs. Explicit expressions of ZSPhP are obtained for a single polar-dielectric interface and a polar nanofilm sandwiched by dielectric media. Furthermore, the SPhP thermal conductivity of this nanofilm is determined and its direct correspondence with the figure of merit is analyzed for the three polar materials. The proposed SPhP figure of merit is analogous to that of thermoelectric materials and could have great applications in the classification, design, and fabrication of polar structures involved in electronics and photonics. [1] D. Z. A. Chen, A. Narayanaswamy, and G. Chen, Phys. Rev. B 72, 155435 (2005). [2] J. Ordonez-Miranda, L. Tranchant, T. Tokunaga, B. Kim, B. Palpant, Y. Chalopin, T. Antoni, and S. Volz, J. Appl. Phys. 113, 084311 (2013). [3] J. Ordonez-Miranda, L. Tranchant, B. Kim, Y. Chalopin, T. Antoni, and S. Volz, Phys. Rev. Lett. 112, 055901 (2014). [4] J. Ordonez-Miranda, Laurent Tranchant, Sergei Gluchko, Thomas Antoni, and Sebastian Volz, Phys. Rev. B 90, 155416 (2014). [5] X. J. G. Xu, B. G. Ghamsari, J. H. Jiang, L. Gilburd, G. O. Andreev, C. Y. Zhi, Y. Bando, D. Golberg, P. Berini, and G. C. Walker, Nat. Commun. 5, 1 (2014).

Authors : Armande Hervé 1, Jérémie Drévillon 1, Younès Ezzahri 1, Karl Joulain1* and Domingos de Sousa Meneses 2
Affiliations : 1 Insitut Pprime, Université de Poitiers-CNRS-ENSMA, UPR3346, ENSIP Bâtiment B25, 2, Rue Pierre Brousse TSA41105, 86073 Poitiers, France. 2 CNRS-Conditions Extrêmes et Matériaux Haute Température et Irradiation, 1D, Av. de la Recherche Scientifique, F-45071 Orléans, France. *

Resume : By ruling a grating on a polar material that supports surface phonon-polaritons such as SiC or SiO2, it is possible to create directional and monochromatic thermal sources [1]. So far, most of the studies have considered only materials with room temperature properties as the ones tabulated in Palik’s handbooks [2]. Experimental measurements performed at CEMHTI laboratory in Orleans have provided us experimental data of the dielectric function at different temperatures, for SiC and SiO2 (glass). We study, numerically, the effect of temperature dependence of the dielectric function on the thermal emission of these two materials, either by heating or through designing a grating (1D grating, in a first approach) at the surface. When materials are heated, the position of the grating emissivity peak shifts towards higher wavelength values. Room temperature designed gratings can also not be optimum for higher temperatures. However, we could find an emission peak for each material and each temperature, by modifying the grating parameters. We tried first to catch some patterns in the emissivity variation. Then, we tried to obtain a design of the grating, which is optimum for all temperatures for SiC. The best found grating, not quite isotropic but with relatively thin peaks, can be completed by other ones with different properties. [1] J. J. Greffet, et al. Nature, 416, 61 (2002). [2] E.D. Palik, “Handbook of Optical Constants of Solids”, Academic Press, Boston, USA (1985).

17:30 End of session 11    
18:00 Best Student Presentation Awards Ceremony and Reception (Main Hall)    
Start atSubject View AllNum.
09:00 Plenary Session - Main Hall    
12:30 Lunch break    
Session 12: Modeling and simulations II : Xanthippi ZIANNI
Authors : Pawel Keblinski
Affiliations : Rensselaer Polytechnic Institute

Resume : An interface scatters phonons and thus poses resistance to the heat flow, in addition to the bulk resistance of the material. The associated interfacial thermal resistance can dominate the overall heat flow when the density of the interfaces is high, such as in nanoscale and interfacial materials. When two (or more) interfaces or junctions are at a distance smaller than the phonon mean path, the interfacial resistances of each interface are not independent. Using molecular dynamics simulations and phonon scattering based analysis we will study heat flow mechanisms across proximal interfaces in various systems including self-assembled organic monolayers between two solids, nanoscopic solid adlayer on a substrate and molecular junctions. We will demonstrate the presence and role of multiple phonon scattering and interference effects on individual phonons and overall interfacial thermal transport.

Authors : K. Saaskilahti1, A. Rajabpour,2 J. Oksanen1, J. Tulkki1, S. Volz3
Affiliations : 1 Department of Computational Science,Aalto University, Finland 3 EM2C Laboratory, CNRS and Ecole Centrale Paris, France

Resume : In a first step, we derive a theoretical model providing access to the frequency dependent interfacial resistance based on the spectral decomposition of the heat flux defined in terms of the mechanical microscopic quantities. By using Molecular Dynamics (MD), the main phonon processes involved in the heat transfer are revealed in an Argon-like system. In a second step, we develope a theoretical approach based on the fluctuation-dissipation theorem showing a time dependence of the thermal interfacial resistance and its convergence at high frequencies towards a universal thermal resistance. We demonstrate this dependence and the universal number by MD computations.

Authors : Shiyun Xiong, Sanghamitra Neogi, Davide Donadio
Affiliations : Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany

Resume : Using equilibrium molecular dynamics (EMD) simulations, the thermal conductivities (TC) of Si membranes of different thickness with Ge alloying and/or SiO2 coating have been calculated. It is demonstrated that TC can be greatly reduced down to 5 W/mK with SiO2 coating for the thickness of 3.2 nm, which is about 2.5% of the bulk value. This value can be further reduced down to 2.3 W/mK, with a combination of only 5% Ge alloying. The results reveal that SiO2 coating and Ge alloying can serve as ideal sources to block the phonon transport. To separate the contributions from SiO2 coating and Ge alloying, we performed non-equilibrium molecular (NEMD) dynamics simulations for all the samples of different lengths. From NEMD simulations, TCs of samples of different lengths are calculated to identify which range of phonon mean free path is most responsible for the total TC. In addition, the length dependent transmission functions are obtained to evaluate phonon contribution by frequency. With the quantities obtained from NEMD, one can identify the effect of SiO2 coating and Ge alloying on phonon transport, respectively. This analysis can provide a convenient avenue for TC design.

15:20 End of session 12    

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