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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 : 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.

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.

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 : 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 : 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 : 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 : 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 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 : 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.

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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 : 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.

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.

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.

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).


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