Modal analysis of the thermal conductivity of nanowires: examining unique thermal transport features

Samaraweera, Nalaka; Larkin, Jason M.; Chan, Kin L; Mithraratne, Kumar

doi:10.1088/1361-648x/aabe54

Cited by 5 publications

(1 citation statement)

References 58 publications

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“…Argon, modeled in 6-12 Lenard-Jones (LJ) interatomic potential, is chosen as the base fluid, and a modified LJ potential having a higher energy depth is chosen to model the solid nanowires in the nanofluid. This method of using a fictitious material to predict the thermal properties reduces the computational demand, thus allowing us to obtain a better understanding on the fundamental mechanisms in the system [52,53]. The crystal structure and the atomic mass of the modified LJ material are taken to be equal to copper (Cu) and, therefore, will be referred to as copper from here onwards.…”

Section: Molecular Dynamics Methodsmentioning

confidence: 99%

Microscopic thermal characteristics of parallelly arranged nanowires in a liquid: the role of interface thermal resistance, solid-like liquid layer, and the restricted phonon transport

et al. 2023

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Nanofluids based on extended nanostructures, such as nanowires, have been demonstrated improved thermal conductivities (κ). However, the lack of a complete understanding at the microscopic level hinders the development of such nanofluids towards practical applications. We aim to provide it by investigating how the interface thermal resistance (Rb), ballistic phonon transport, and the solid-like liquid layer affect the heat conduction in nanowire based nanofluids. By employing Non-Equilibrium Molecular Dynamics (NEMD), it is found that the heat conduction in the parallelly arranged liquid and the nanowires exhibit a coupled thermal behavior owing to the Rb. This contradicts the predictions of the classical parallel heat conduction model, therefore, a novel model is proposed taking this coupled behavior into account. Using this model, it is shown that the high κ of the solid phase has a limited contribution to the effective κ of nanofluids having short nanowires due to the dominant Rb effect. For the case of long nanowires, however, the individual nanowire κ becomes a vital parameter defining the effective κ. Further, NEMD calculations reveal that the κ of suspended nanowires in a liquid is markedly reduced, questioning the validity of classical effective medium theories which use the bulk parameters. This reduction is attributed to surface atoms’ restricted vibrational freedom and the nanowire’s phonon-boundary scattering. By substituting this reduced κ of the solid phase into the new mathematical model, the theoretical predictions align closely with the NEMD calculations, exhibiting deviations below 10%. The sole contribution from the solid-like liquid layer to the κ enhancement lies between 20-30% in the nanofluids presently considered. Therefore, the findings of this study highlight the important roles played by the identified microscopic thermal characteristics in defining the effective κ for nanofluids based on nanowires.

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Section: Molecular Dynamics Methodsmentioning

confidence: 99%

Microscopic thermal characteristics of parallelly arranged nanowires in a liquid: the role of interface thermal resistance, solid-like liquid layer, and the restricted phonon transport

et al. 2023

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Reduced thermal conductivity of Si/Ge random layer nanowires: A comparative study against superlattice counterparts

Samaraweera

Larkin²,

Chan

et al. 2018

Journal of Applied Physics

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Si/Ge nanowires are considered to be promising candidates as efficient thermoelectric materials due to their remarkable thermal insulating performance over bulk counterparts. In this study, thermal insulating performance of Si/Ge nanowires of randomly organized layer thickness, called random layer nanowires (RLNWs), is systematically investigated and compared against superlattice nanowires (SLNWs).The thermal conductivity (TC) of these structures is evaluated via non-equilibrium molecular dynamic simulations, and more informative insight is gained by normal mode decomposition and lattice dynamics calculations. It is demonstrated that the modes in random layer structures, in general, exhibit similar characteristics except the degree of localization to the corresponding superlattice counterparts by comparing the mode spectral energy densities, relaxation times, density of states, and participation ratios. For all physical and geometrical conditions investigated here, RLNWs show improved thermal insulating performance over corresponding SLNWs. More importantly, a RLNW of low mean layer thickness attains even lower TC than the corresponding Si/Ge alloy nanowire indicating the effectiveness of the random layer arrangements. An anomalous trend in TC of RLNWs (larger than the bulk counterpart) is observed at higher cross-sectional widths, and it is explained as a competing effect of phonon localization and wall scattering. Moreover, it is illustrated that the effectiveness of thermal insulating performance of RLNW depends on the fraction of coherent phonons that exist and how effectively those phonons are subject to localization under different cases.

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Ultra-low thermal conductivity of nanoparticle chains: A nanoparticle based structure for thermoelectric applications

Henadeera

Samaraweera

Ranasinghe

et al. 2021

Journal of Applied Physics

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Nanostructured semiconductors are promising candidates for thermoelectric materials owing to their superior thermal insulating properties over their bulk counterparts. In this study, a one-dimensional, crystalline nanostructure synthesized by sintering Si nanoparticles, called Nano Particle Chain (NPC) structures, is proposed. The structure is systematically analyzed for its thermal transport properties and compared with the nanowire counterparts. Both classical molecular dynamics and lattice dynamics tools were employed to evaluate lattice thermal conductivity (k) and to perform phonon mode level decomposition. A marked reduction in the phonon relaxation time of the NPC structure was observed indicating possible effects of phonon-boundary/constriction scatterings. This has resulted in a two-order reduction in k in NPC structures over bulk Si. Further, one order reduction of k of NPC structures was attained with respect to a nanowire of the same constriction size, indicating the effectiveness of the mismatch of particle and constriction diameters as an efficient thermal suppression mechanism. With the addition of a second material of different mass, the NPC structures can be further diversified to core/shell configurations. It was also identified that a non-monotonic variation of k exists, with a minimum in core/shell NPC structures. This effect is materialized by using a Ge-like fictitious material to coat the original Si nanoparticles, owing to competing effects of two phonon suppression mechanisms. Moreover, these core/shell NPC structures are compared with previously reported diameter modulated core/shell nanowire structures [E. Blandre et al., Phys. Rev. B, 91, 115404 (2015)] to highlight their capability to enhance the thermoelectric performance over conventional one-dimensional nanostructure configurations.

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Modal analysis of the thermal conductivity of nanowires: examining unique thermal transport features

Cited by 5 publications

References 58 publications

Microscopic thermal characteristics of parallelly arranged nanowires in a liquid: the role of interface thermal resistance, solid-like liquid layer, and the restricted phonon transport

Microscopic thermal characteristics of parallelly arranged nanowires in a liquid: the role of interface thermal resistance, solid-like liquid layer, and the restricted phonon transport

Reduced thermal conductivity of Si/Ge random layer nanowires: A comparative study against superlattice counterparts

Ultra-low thermal conductivity of nanoparticle chains: A nanoparticle based structure for thermoelectric applications

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