Publications by authors named "David Lacroix"

10 Publications

  • Page 1 of 1

Nanowire forest of pnictogen-chalcogenide alloys for thermoelectricity.

Nanoscale 2019 Jul;11(28):13423-13430

Institut Néel, CNRS, 25 avenue des Martyrs, F-38042 Grenoble, France. and Univ. Grenoble Alpes, Grenoble, France.

Pnictogen and chalcogenide compounds have been seen as high-potential materials for efficient thermoelectric conversion over the past few decades. It is also known that with nanostructuration, the physical properties of these pnictogen-chalcogenide compounds can be further enhanced towards a more efficient heat conversion. Here, we report the reduced thermal conductivity of a large ensemble of Bi2Te3 alloy nanowires (70 nm in diameter) with selenium for n-type and antimony for p-type (Bi2Te3-ySey and Bi2-xSbxTe3 respectively). The nanowire growth was carried out through electrodeposition in nanoporous aluminium oxide templates with high aspect ratios leading to a forest (109 per centimetre square) of nearly identical nanowires. The temperature dependence of thermal conductivity for the nanowire ensembles was acquired through a highly sensitive 3ω measurement technique. The change in the thermal conductivity of nanowires is largely affected by the roughness in addition to the size effect due to enhanced boundary scattering. The major factor that influences the thermal conductivity was found to be the ratio of the rms roughness to the correlation length of the nanowire. With a high Seebeck coefficient and electrical conductivity at room temperature, the overall thermoelectric figure of merit ZT allows the consideration of such forests of nanowires as efficient potential building blocks of future TE devices.
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http://dx.doi.org/10.1039/c9nr01566cDOI Listing
July 2019

Thermal conductivity in disordered porous nanomembranes.

Nanotechnology 2019 Jun 12;30(26):265401. Epub 2019 Mar 12.

Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and The Barcelona Institute of Science and Technology Campus UAB, Bellaterra, E-08193 Barcelona, Spain.

In this work we study the effects of disorder on the thermal conductivity of porous 100 nm thick silicon membranes, in which the size, shape and position of the pores were varied randomly. Measurements using two-laser Raman thermometry on both non-patterned and porous membranes revealed more than a 10-fold reduction of the thermal conductivity compared to that of bulk silicon and a six-fold reduction compared to non-patterned membranes for the sample with random pore shapes. Using Monte Carlo methods we solved the Boltzmann transport equation for phonons and compared different possibilities of pore organization and its influence on the thermal conductivity of the samples. The simulations confirmed that the strongest reduction of thermal conductivity is achieved for a distribution of pores with arbitrary shapes that partially overlap. Up to a 15% reduction of the thermal conductivity with respect to the purely circular pores was predicted for a porous membrane with 37% filling fraction. The effect of the pore shape and distribution was further studied. Maps of temperature and heat flux distributions clearly showed that for particular pore placement heat transport can be efficiently blocked and hot spots can be found in narrow channels between pores. These findings have an impact on the fabrication of membrane-based thermoelectric devices, where low thermal conductivity is required. This work shows that for porous membranes with a given filling fraction the thermal conductivity can be further modified by introducing disorder in the shape and placement of the pores.
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http://dx.doi.org/10.1088/1361-6528/ab0ecdDOI Listing
June 2019

Enhanced thermal conductivity in percolating nanocomposites: a molecular dynamics investigation.

Nanoscale 2018 Nov;10(46):21732-21741

Univ Lyon, CNRS, INSA-Lyon, Université Claude Bernard Lyon 1, CETHIL UMR5008, F-69621, Villeurbanne, France.

In this work we present a molecular dynamics investigation of thermal transport in a silica-gallium nitride nanocomposite. A surprising enhancement of the thermal conductivity for crystalline volume fractions larger than 5% is found, which cannot be predicted by an effective medium approach, not even including percolation effects, the model systematically leading to an underestimation of the effective thermal conductivity. The behavior can instead be reproduced if an effective volume fraction twice larger than the real one is assumed, which translates into a percolation effect surprisingly stronger than the usual one. Such a scenario can be understood in terms of a phonon tunneling between inclusions, enhanced by the iso-orientation of all particles. Indeed, if a misorientation is introduced, the thermal conductivity strongly decreases. We also show that a percolating nanocomposite clearly stands in a different position than other nanocomposites, where thermal transport is dominated by the interface scattering and where parameters such as the interface density play a major role, differently from our case.
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http://dx.doi.org/10.1039/c8nr05734fDOI Listing
November 2018

Impact of screw and edge dislocations on the thermal conductivity of individual nanowires and bulk GaN: a molecular dynamics study.

Phys Chem Chem Phys 2018 Feb;20(7):5159-5172

CNRS, CETHIL, UMR 5008, 69100 Villeurbanne, France.

We report the thermal transport properties of wurtzite GaN in the presence of dislocations using molecular dynamics simulations. A variety of isolated dislocations in a nanowire configuration are analyzed and found to considerably reduce the thermal conductivity while impacting its temperature dependence in a different manner. Isolated screw dislocations reduce the thermal conductivity by a factor of two, while the influence of edge dislocations is less pronounced. The relative reduction of thermal conductivity is correlated with the strain energy of each of the five studied types of dislocations and the nature of the bonds around the dislocation core. The temperature dependence of the thermal conductivity follows a physical law described by a T variation in combination with an exponent factor that depends on the material's nature, type and the structural characteristics of the dislocation core. Furthermore, the impact of the dislocation density on the thermal conductivity of bulk GaN is examined. The variation and absolute values of the total thermal conductivity as a function of the dislocation density are similar for defected systems with both screw and edge dislocations. Nevertheless, we reveal that the thermal conductivity tensors along the parallel and perpendicular directions to the dislocation lines are different. The discrepancy of the anisotropy of the thermal conductivity grows with increasing density of dislocations and it is more pronounced for the systems with edge dislocations. Besides the fundamental insights of the presented results, these could also be used for the identification of the type of dislocations when one experimentally obtains the evolution of thermal conductivity with temperature since each type of dislocation has a different signature, or one could extract the density of dislocations with a simple measurement of thermal anisotropy.
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http://dx.doi.org/10.1039/c7cp07821hDOI Listing
February 2018

High-throughput heterodyne thermoreflectance: Application to thermal conductivity measurements of a Fe-Si-Ge thin film alloy library.

Rev Sci Instrum 2017 Jul;88(7):074902

Laboratoire Ondes et Matière d'Aquitaine (LOMA), UMR 5798, CNRS-Université de Bordeaux, 33400 Talence, France.

A High-Throughput Time-Domain ThermoReflectance (HT-TDTR) technique was developed to perform fast thermal conductivity measurements with minimum user actions required. This new setup is based on a heterodyne picosecond thermoreflectance system. The use of two different laser oscillators has been proven to reduce the acquisition time by two orders of magnitude and avoid the experimental artefacts usually induced by moving the elements present in TDTR systems. An amplitude modulation associated to a lock-in detection scheme is included to maintain a high sensitivity to thermal properties. We demonstrate the capabilities of the HT-TDTR setup to perform high-throughput thermal analysis by mapping thermal conductivity and interface resistances of a ternary thin film silicide library FeSiGe (20
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http://dx.doi.org/10.1063/1.4986469DOI Listing
July 2017

Scaling behavior of the thermal conductivity of width-modulated nanowires and nanofilms for heat transfer control at the nanoscale.

Nanotechnology 2014 Nov 31;25(46):465402. Epub 2014 Oct 31.

Department of Aircraft Technology, Technological Educational Institution of Sterea Ellada, 34400 Psachna, Greece. Department of Microelectronics, INN, NCSR'Demokritos', 153 10 Athens, Greece.

We report on scaling behavior of the thermal conductivity of width-modulated nanowires and nanofilms that have been studied with the phonon Monte Carlo technique. It has been found that the reduction of the thermal conductivity scales with the nanostructure transmissivity, a property entirely determined by the modulation geometry, irrespectively of the material choice. Tuning of the thermal conductivity is possible by the nanostructure width-modulation without strict limitations for the modulation profile. In addition, a very significant constriction thermal resistance due to width-discontinuity has been identified, in analogy to the contact thermal resistance between two dissimilar materials. The constriction thermal resistance also scales with the modulated nanostructure transmissivity. Our conclusions are generic indicating that a wide range of materials can be used for the modulated nanostructures. Direct heat flow control can be provided by designing the nanostructure width-modulation.
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http://dx.doi.org/10.1088/0957-4484/25/46/465402DOI Listing
November 2014

Thermal properties of amorphous/crystalline silicon superlattices.

J Phys Condens Matter 2014 Sep 8;26(35):355801. Epub 2014 Aug 8.

Université de Lorraine, LEMTA, CNRS-UMR7563, Faculté des Sciences et Technologies, BP 70239, 54506 Vandoeuvre-les-Nancy Cedex, France. Materials Design SARL, 92120 Montrouge, France. CEA, DSM-IRAMIS-SPEC, Saclay, 91191 Gif-sur-Yvette Cedex, France.

Thermal transport properties of crystalline/amorphous silicon superlattices using molecular dynamics are investigated. We show that the cross-plane conductivity of the superlattices is very low and close to the conductivity of bulk amorphous silicon even for amorphous layers as thin as ≃ 6 Å. The cross-plane thermal conductivity weakly increases with temperature which is associated with a decrease of the Kapitza resistance with temperature at the crystalline/amorphous interface. This property is further investigated considering the spatial analysis of the phonon density of states in domains close to the interface. Interestingly, the crystalline/amorphous superlattices are shown to display large thermal anisotropy, according to the characteristic sizes of elaborated structures. These last results suggest that the thermal conductivity of crystalline/amorphous superlattices can be phonon engineered, providing new directions for nanostructured thermoelectrics and anisotropic materials in thermal transport.
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http://dx.doi.org/10.1088/0953-8984/26/35/355801DOI Listing
September 2014

Atomistic amorphous/crystalline interface modelling for superlattices and core/shell nanowires.

J Phys Condens Matter 2014 Feb;26(5):055011

In this paper we present a systematic and well controlled procedure for building atomistic amorphous/crystalline interfaces in silicon, dedicated to the molecular dynamics simulations of superlattices and core/shell nanowires. The obtained structures depend on the technique used to generate the amorphous phase and their overall quality is estimated through comparisons with structural information and interfacial energies available from experimental and theoretical results. While most of the related studies focus on a single planar interface, we consider here both the generation of multiple superlattice planar interfaces and core/shell nanowire structures. The proposed method provides periodic homogeneous and reproducible, atomically sharp and defect free interface configurations at low temperature and pressure. We also illustrate how the method may be used to predict the thermal transport properties of composite crystalline/amorphous superlattices.
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http://dx.doi.org/10.1088/0953-8984/26/5/055011DOI Listing
February 2014

Cluster agglomeration induced by dust-density waves in complex plasmas.

Phys Rev Lett 2012 Dec 10;109(24):245002. Epub 2012 Dec 10.

Institut Jean Lamour, Département CP2S UMR 7198 CNRS, Université de Lorraine, BP 70239, 54506 Vandoeuvre-les-Nancy Cedex, France.

Experimental results showing the agglomeration of large carbonaceous particles in a dusty plasma are reported. Experiments were performed in a capacitively coupled rf argon plasma. Acetylene was injected to produce dust particles. When a sufficient amount of nanoparticles is present in the cathodic sheath, self-excited dust-density waves occur. The latter ones induce the motion of larger clusters, which vertically oscillate with the displacement of wave fronts. In some cases, the relative velocity of large particles was high enough to overcome the Coulomb repulsion forces, and agglomeration can be observed. The mechanisms underlying this process are discussed.
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http://dx.doi.org/10.1103/PhysRevLett.109.245002DOI Listing
December 2012

Finite-difference time-domain and near-field-to-far-field transformation in the spectral domain: application to scattering objects with complex shapes in the vicinity of a semi-infinite dielectric medium.

J Opt Soc Am A Opt Image Sci Vis 2011 May;28(5):868-78

Nancy Université-LEMTA-CNRS UMR 7563, Faculté des Sciences et Technologies, BP 70239-54506 Vandoeuvre Cedex, France.

We present the study of a spectral-domain near-field-to-far-field (NFTFF) transformation, taking into account an interface in the vicinity of a particle. This technique is associated with a three-dimensional finite-difference time-domain (FDTD) model, which solves the Maxwell equations in the time domain. Moreover, material properties are considered with the use of dispersion models. First, particular attention is paid to the description of the modeling, especially concerning the NFTFF transformation using the dyadic Green tensors. Second, several simulation cases are considered to evaluate the ability of the developed technique to model the scattering by different kinds of "particles/interface" configurations and for various illuminating waves. Then validation test cases are used in order to assess the model accuracy through comparisons with T-matrix simulations. Finally, perspectives to this work and its application to near-field detection devices are discussed.
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http://dx.doi.org/10.1364/JOSAA.28.000868DOI Listing
May 2011
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