Complex superlattice unit cell designs for reduced thermal conductivity

Landry, E. S.; Hussein, Mahmoud I.; McGaughey, Alan J. H.

doi:10.1103/physrevb.77.184302

Cited by 144 publications

(144 citation statements)

References 55 publications

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“…[19] in the study of superlattice structures. They found that the oscillation in their work is caused by specific zero-wave-vector optical phonon modes and can be removed when a different definition of the heat current based on the equilibrium atom positions is used [19].…”

Section: Core/shell Nanowire Structure and The Coherent Resonancementioning

confidence: 99%

Phonon coherent resonance and its effect on thermal transport in core-shell nanowires

Chen

Zhang

2011

The Journal of Chemical Physics

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We study heat current autocorrelation function and thermal conductivity in core-shell nanowires by using molecular dynamics simulations. Interestingly, a remarkable oscillation effect in heat current autocorrelation function is observed in core-shell NWs, while the same effect is absent in pure silicon nanowires, nanotube structures and random doped nanowires. Detailed characterizations of the oscillation signal reveal that this intriguing oscillation is caused by the coherent resonance effect of the transverse and longitudinal phonon modes. This phonon resonance results in the localization of the longitudinal modes, which leads to the reduction of thermal conductivity in core-shell nanowires. Our study reveals that a coherent mechanism can be used to tune thermal conductivity in core-shell nanowires.

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Section: Core/shell Nanowire Structure and The Coherent Resonancementioning

confidence: 99%

Phonon coherent resonance and its effect on thermal transport in core-shell nanowires

Chen

Zhang

2011

The Journal of Chemical Physics

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“…While both indicate NPM thermal conductivity reduction, the EMD predictions are higher than their counterparts from the NEMD simulations. This discrepancy between the two sets of predictions is not uncommon because the EMD and NEMD methods depend on different factors for their accuracy [20,31].…”

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confidence: 99%

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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“…(3) definition of q z exhibits fast oscillations that are associated with high-frequency optical modes. Landry et al 28 pointed out that these fast oscillations are related to the first sum in Eq. (3).…”

Section: B Nemd Determination Of Kmentioning

confidence: 99%

Molecular simulations and lattice dynamics determination of Stillinger-Weber GaN thermal conductivity

Liang

Jain

McGaughey

et al. 2015

Journal of Applied Physics

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The bulk thermal conductivity of Stillinger-Weber (SW) wurtzite GaN in the [0001] direction at a temperature of 300 K is calculated using equilibrium molecular dynamics (EMD), non-equilibrium MD (NEMD), and lattice dynamics (LD) methods. While the NEMD method predicts a thermal conductivity of 166 6 11 W/mÁK, both the EMD and LD methods predict thermal conductivities that are an order of magnitude greater. We attribute the discrepancy to significant contributions to thermal conductivity from long-mean free path phonons. We propose that the Gr€ uneisen parameter for low-frequency phonons is a good predictor of the severity of the size effects in NEMD thermal conductivity prediction. For weakly anharmonic crystals characterized by small Gr€ uneisen parameters, accurate determination of thermal conductivity by NEMD is computationally impractical. The simulation results also indicate the GaN SW potential, which was originally developed for studying the atomic-level structure of dislocations, is not suitable for prediction of its thermal conductivity.

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Complex superlattice unit cell designs for reduced thermal conductivity

Cited by 144 publications

References 55 publications

Phonon coherent resonance and its effect on thermal transport in core-shell nanowires

Phonon coherent resonance and its effect on thermal transport in core-shell nanowires

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

Molecular simulations and lattice dynamics determination of Stillinger-Weber GaN thermal conductivity

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