Frequency-dependent phonon mean free path in carbon nanotubes from nonequilibrium molecular dynamics

Sääskilahti, Kimmo; Oksanen, Jani; Volz, Sébastian; Tulkki, Jukka

doi:10.1103/physrevb.91.115426

Cited by 200 publications

(130 citation statements)

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“…(4) are mode-averaged and projected along the direction of heat transfer. 9 They are also independent of the system length and correspond to the bulk values. 9 We note that the MFPs determined from Eq.…”

Section: Simulation Setup and Methodsmentioning

confidence: 99%

“…Equation (4) can be analytically derived, e.g., from the frequency-dependent relaxation time approximation 21 and has been successfully used to describe the length-dependence of heat flux in various systems. 9,11,12,22 Both q 0 (ω) and Λ(ω) in Eq. (4) are determined from the fitting procedure.…”

Section: Simulation Setup and Methodsmentioning

confidence: 99%

“…1). 9,11 The SDHC q i→j (ω) between particles i and j located on opposite sides of this plane is given by the pair-wise SDHC equation 10 …”

Section: Simulation Setup and Methodsmentioning

confidence: 99%

“…This restriction to the first-order current term at the plane of decomposition does not, however, mean that anharmonic scattering in the bulk is neglected, because all anharmonic effects are included in the NEMD simulations. 9,10 Frequency-dependent MFPs Λ(ω) are calculated by determining q(ω, L) for different system lengths L and fitting the length-dependent q(ω, L) to the equation 9,11 …”

Section: Simulation Setup and Methodsmentioning

confidence: 99%

“…11 We previously used the spectrally-decomposed MFP method to calculate the non-equilibrium MFPs in low-dimensional systems such as carbon nanotubes, 9 anharmonic chains, 11 and nanowires with resonant scatterers. 12 We demonstrated that the non-equilibrium MFPs transparently describe the ballistic-to-diffusive transition in the length-dependence of thermal conductivity 9,11,12 and reveal the effects of structural modifications such as alloying on frequency-dependent phonon transport. 12 Compared to previous calculations for a-Si, the spectrally-decomposed MFP method has several advantages.…”

Section: Introductionmentioning

confidence: 99%

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Vibrational mean free paths and thermal conductivity of amorphous silicon from non-equilibrium molecular dynamics simulations

et al. 2016

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The frequency-dependent mean free paths (MFPs) of vibrational heat carriers in amorphous silicon are predicted from the length dependence of the spectrally decomposed heat current (SDHC) obtained from non-equilibrium molecular dynamics simulations. The results suggest a (frequency) 2 scaling of the room-temperature MFPs below 5 THz. The MFPs exhibit a local maximum at a frequency of 8 THz and fall below 1 nm at frequencies greater than 10 THz, indicating localized vibrations. The MFPs extracted from sub-10 nm system-size simulations are used to predict the length-dependence of thermal conductivity up to system sizes of 100 nm and good agreement is found with independent molecular dynamics simulations. Weighting the SDHC by the frequency-dependent quantum occupation function provides a simple and convenient method to account for quantum statistics and provides reasonable agreement with the experimentally-measured trend and magnitude. © 2016 Author(s)

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Section: Simulation Setup and Methodsmentioning

confidence: 99%

Section: Simulation Setup and Methodsmentioning

confidence: 99%

“…1). 9,11 The SDHC q i→j (ω) between particles i and j located on opposite sides of this plane is given by the pair-wise SDHC equation 10 …”

Section: Simulation Setup and Methodsmentioning

confidence: 99%

Section: Simulation Setup and Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Vibrational mean free paths and thermal conductivity of amorphous silicon from non-equilibrium molecular dynamics simulations

et al. 2016

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Moiré Pattern Controlled Phonon Polarizer Based on Twisted Graphene

Qin,

Dai,

et al. 2024

Advanced Materials

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Atomically twisted van der Waals materials featuring Moiré patterns present new design possibilities and demonstrate unconventional behaviors in electrical, optical, spintronic, and superconducting properties. However, experimental exploration of thermal transport across Moiré patterns has not been as extensive, despite its critical role in nanoelectronics, thermal management, and energy conversion. Here, we conduct the first experimental investigation into thermal transport across twisted graphene, demonstrating the concept of a phonon polarizer achieved by manipulating the rotational misalignment between adjacent stacked layers. Our approach includes thorough structural characterizations and atomistic modeling of various twisted graphene configurations, along with direct measurements of thermal and acoustic transport using ultrafast spectroscopies. For the first time, we have measured a significant modulation – up to 631% – in the thermal conductance of twisted graphene by reducing phonon transmissions as a function of Moiré angles, while a high acoustic transmission maintains across all twist configurations. By comparing experiments with first‐principles calculations using density functional theory and molecular dynamics simulations, mode‐dependent phonon transmission between monolayer graphene are quantified based on the angle alignment of phonon band structures. We investigate mode‐specific phonon transmission and attribute the pronounced polarizing effect to the distortion over the coupling phase space especially from flexural phonon modes. The modeling results agree with experimental data, verifying the dominant tuning mechanisms in adjusting phonon transmission from high‐frequency thermal modes while negligible effects on low‐frequency acoustic modes near Brillouin zone center. This study offers crucial insights into the fundamental thermal transport in Moiré structures, opening avenues for the invention of advanced thermal devices and new design methodologies based on manipulations of vibrational band structures and phonon spectra.This article is protected by copyright. All rights reserved

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A Facile Strategy to Densify Aligned CNT Films with Significantly Enhanced Thermal Conductivity and Mechanical Strength

Liang

et al. 2022

Adv Materials Technologies

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conductivity as a single assessment indicator for thermal management materials, often with simultaneous requirements for mechanical and other properties. Thus, carbon nanotubes (CNTs) possess outstanding thermal conductivity, satisfactory mechanical strength, and good chemical stability, which share huge potential in thermal management especially after the CNT fibers with higher tensile strength than any other fibers and ultralong length were reported. [2] In practical scenarios, mechanical traction of aligned CNT arrays followed by combining them into macroscopic aligned film is the main way for applying the superior performance of CNTs so that they can perform expected heat conduction. However, macroscopic CNT bodies normally exhibit dramatically reduced thermal conductivity and mechanical strength due to the low stacking density and unsatisfactory alignment of individual CNTs. [3] The degradation of thermal performance is mainly due to the weak van der Waals forces between the neighboring CNTs which originates from the preparation process of CNT films. [4] Meanwhile, the weak interfacial bonding also affects the effective transfer of loads among CNTs, resulting in comparatively poor mechanical strength. Researchers have achieved some progress on CNT densification, with the main ideas to introduce covalent bonds among CNTs via chemical cross-linking or to enhance the van der Waals forces by shortening the distance between the neighboring CNTs via external forces. [2b,5] Chemical cross-linking is the most effective method for densifying CNT films, but this method suffers from difficult operation, strict reaction conditions and high cost in large-scale treatment. In some cases, the introduction of polymer cross-linkers can also seriously affect the thermal conductivity of CNT films. In contrast, densification via liquid capillary forces or mechanical external forces is simple, mild, and more suitable for commercial and large-area treatment, that is, liquid infiltration and subsequent densification, [5a,b] and mechanical densification, [5c,d] in which the enhancement of performance relies on denser stacking and enhanced inter-tube interaction of CNTs rather than polymer adhesive. Previous studies normally apply a single means of densification, or involve time-consuming and Aligned carbon nanotube (CNT) films with outstanding thermal and mechanical properties are promising for thermal management in electronics and mechanical enhancement in composites. One main challenge toward aligned CNT films is the loose stacking and unsatisfactory orientation of individual CNTs within the macroscopic assemblies, resulting in unsatisfactory performance. In this study, a facile strategy to densify commercial aligned CNT films with nearly doubled stacking density increasing from 0.63 to 1.17 g•cm −3 , where the densification process involves infiltration of ethanol, CNT protonation along with mechanical stretching, is proposed. The densification strategy makes CNTs compactly aligned at the macro level, and enables CNTs to ...

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Frequency-dependent phonon mean free path in carbon nanotubes from nonequilibrium molecular dynamics

Cited by 200 publications

References 64 publications

Vibrational mean free paths and thermal conductivity of amorphous silicon from non-equilibrium molecular dynamics simulations

Vibrational mean free paths and thermal conductivity of amorphous silicon from non-equilibrium molecular dynamics simulations

Moiré Pattern Controlled Phonon Polarizer Based on Twisted Graphene

A Facile Strategy to Densify Aligned CNT Films with Significantly Enhanced Thermal Conductivity and Mechanical Strength

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