Mechanism of nanofiber crimp

Chen, Rouxi; Zhang, Li; Kong, Hai-Yan; He, Ji‐Huan; Chen, Yun

doi:10.2298/tsci1305473c

Cited by 29 publications

(39 citation statements)

References 10 publications

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“…The simulations yield results consistent with earlier lattice-dynamics based predictions which showed a reduction in the thermal conductivity due to the presence of the local resonators. Using a spectral energy density approach, in which only simulation data is utilized and no a priori information on the nanostructure resonant phonon modes is provided, we show direct evidence of the existence of resonance hybridizations as an inherent mechanism contributing to the slowing down of thermal transport in this system.Material nanostructuring has emerged as a powerful approach in the field of nanoscale heat transfer as it provides a means for direct manipulation of thermal transport properties [1]. One of the primary applications is thermoelectric materials where there is a need for new concepts and material architectures in order to attain high levels of energy conversion performance [2].…”

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confidence: 99%

“…Material nanostructuring has emerged as a powerful approach in the field of nanoscale heat transfer as it provides a means for direct manipulation of thermal transport properties [1]. One of the primary applications is thermoelectric materials where there is a need for new concepts and material architectures in order to attain high levels of energy conversion performance [2].…”

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Spectral energy analysis of locally resonant nanophononic metamaterials by molecular simulations

Honarvar

Hussein

2016

Phys. Rev. B

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A nanophononic metamaterial is a new type of nanostructured material that features an array, or a forest, of intrinsically distributed resonating substructures. Each substructure exhibits numerous local resonances, each of which may hybridize with the phonon dispersion of the underlying host material causing significant reductions in the group velocities and consequently a reduction in the lattice thermal conductivity. In this paper, molecular dynamics simulations are utilized to investigate both the dynamics and the thermal transport properties of a nanophononic metamaterial configuration consisting of a freely suspended silicon membrane with an array of silicon nanopillars standing on the surface. The simulations yield results consistent with earlier lattice-dynamics based predictions which showed a reduction in the thermal conductivity due to the presence of the local resonators. Using a spectral energy density approach, in which only simulation data is utilized and no a priori information on the nanostructure resonant phonon modes is provided, we show direct evidence of the existence of resonance hybridizations as an inherent mechanism contributing to the slowing down of thermal transport in this system.Material nanostructuring has emerged as a powerful approach in the field of nanoscale heat transfer as it provides a means for direct manipulation of thermal transport properties [1]. One of the primary applications is thermoelectric materials where there is a need for new concepts and material architectures in order to attain high levels of energy conversion performance [2]. A promising strategy for increasing the performance of thermoelectric materials, measured by the figure of merit, ZT , to levels attractive to industry is to enable a significant lowering of the total thermal conductivity in a manner that does not negatively affect the electrical conductivity and the Seebeck coefficient. In semiconductors, this may be achieved by lowering the lattice thermal conductivity, k, by nanostructuring. A common approach is to introduce obstacles, such as holes, inclusions, and interfaces, within a semiconducting material in order to enhance phonon scattering and thus reduce k [3]. However, in addition to scattering the phonons, the motion of electrons is likely to be impeded as well by the same obstacles, which diminishes improvements to the ZT value.A new avenue of research for increasing ZT is based on the concept of a nanophononic metamaterial (NPM) [4]. In a particular realization of a NPM, presented in Ref.[4], an array of nanopillars is built on top of a freestanding membrane or thin film. Each nanopillar exhibits numerous local resonances that roughly span the entire spectrum−as many as the number of atoms in the nanopillar multiplied by 3 (the number of degrees of freedom for each atom). This provides millions of resonances for a pillar that is only a few tens of nanometers in size. Each of these resonances may, in principle, couple with the phonon dispersion curves of the underlying membrane and reduce ...

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Spectral energy analysis of locally resonant nanophononic metamaterials by molecular simulations

Honarvar

Hussein

2016

Phys. Rev. B

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“…This provides an opportunity to introduce significant changes to the thermal transport properties by direct engineering of the phonon characteristics−which are shaped primarily by the phonon band structure and the nature of the underlying scattering mechanisms [2]. Recent reviews survey developments in theory, computation, and experiment pertaining to nanoscale thermal transport in a variety of materials and point to the remarkable possibilities for using nanostructuring as a means for phonon engineering [3].…”

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Thermal transport size effects in silicon membranes featuring nanopillars as local resonators

Honarvar

Yang

Hussein

2016

Applied Physics Letters

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Silicon membranes patterned by nanometer-scale pillars standing on the surface provide a practical platform for thermal conductivity reduction by resonance hybridization. Using molecular simulations, we investigate the effect of nanopillar size, unit-cell size, and finite-structure size on the net capacity of the local resonators in reducing the thermal conductivity of the base membrane. The results indicate that the thermal conductivity reduction increases as the ratio of the volumetric size of a unit nanopillar to that of the base membrane is increased, and the intensity of this reduction varies with unit-cell size at a rate dependent on the volumetric ratio. Considering sample size, the resonance-induced thermal conductivity drop is shown to increase slightly with the number of unit cells until it would eventually level off.In semiconducting materials, heat is carried mostly by phonons which are quanta of lattice vibrations [1]. This provides an opportunity to introduce significant changes to the thermal transport properties by direct engineering of the phonon characteristics−which are shaped primarily by the phonon band structure and the nature of the underlying scattering mechanisms [2]. Recent reviews survey developments in theory, computation, and experiment pertaining to nanoscale thermal transport in a variety of materials and point to the remarkable possibilities for using nanostructuring as a means for phonon engineering [3].Thermoelectric energy conversion stands to benefit profoundly from the ability to alter the phonon properties by nanostructuring [4], as well as by reducing the material dimensionality [5]. Thermoelectric materials, which generate electricity from heat and vice versa, are characterized by a figure of merit defined as ZT = σT S 2 /k, where S is the Seebeck coefficient, σ is the electrical conductivity, k is the thermal conductivity (consisting of a lattice component and an electrical component), and T is absolute temperature [6]. One strategy to improve the value of ZT , particularly in semiconductors, is to reduce the lattice thermal conductivity and attempt to do so without negatively affecting S and σ. A promising approach for achieving this goal is to introduce nanoscale local resonators as intrinsic substructures within, or attached to, a host crystalline material [7,8]. The emerging system, called nanophononic metamaterial (NPM), exhibits unique properties that are not attainable in conventional nanostructured media such as nanocomposites [9] or nanophononic crystals [10]. The substructure resonances, which could be numerous for relatively large substructures, may be tuned to couple with all or most of the heat-carrying phonon modes of the underlying host medium. This atomic-scale coupling mechanism is essentially a resonance hybridization between the wavenumberdependent wave modes of the host medium (phonons) and the wavenumber-independent vibration modes of the local substructure (vibrons). The outcome is significant reductions in the phonon group velocities across roughly ...

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“…However, according to (16), the main cause of variation of the thermal conductivity is, besides the thermal boundary resistance of the interface, the dimension of the nanoparticles: the smaller is the radius, the smaller is the effective heat conductivity.…”

Section: Si-ge Composite; Comparison With Monte Carlo Simulationsmentioning

confidence: 99%

Effective Thermal Conductivity of Spherical Particulate Nanocomposites: Comparison with Theoretical Models, Monte Carlo Simulations and Experiments

Machrafi

Lebon

2014

Int. J. Nanosci.

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The purpose of this work is to study heat conduction in systems that are composed out of spherical micro-and nanoparticles dispersed in a bulk matrix. Special emphasis will be put on the dependence of the effective heat conductivity on various selected parameters as dimension and density of particles, interface interaction with the matrix. This is achieved by combining the effective medium approximation and extended irreversible thermodynamics, whose main feature is to elevate the heat flux vector to the status of independent variable. The model is illustrated by three examples: Silicium-Germanium, Silicaepoxy-resin and Copper-Silicium systems. Predictions of our model are in good agreement with other theoretical models, Monte-Carlo simulations and experimental data.

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Mechanism of nanofiber crimp

Cited by 29 publications

References 10 publications

Spectral energy analysis of locally resonant nanophononic metamaterials by molecular simulations

Spectral energy analysis of locally resonant nanophononic metamaterials by molecular simulations

Thermal transport size effects in silicon membranes featuring nanopillars as local resonators

Effective Thermal Conductivity of Spherical Particulate Nanocomposites: Comparison with Theoretical Models, Monte Carlo Simulations and Experiments

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