Thermal conductivity of silicon nanowire by nonequilibrium molecular dynamics simulations

Wang, Shuai Chuang; Liang, Xin Gang; Xu, Xiang; Ohara, Taku

doi:10.1063/1.3063692

Cited by 105 publications

(88 citation statements)

References 13 publications

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“…1(a), is found to increase rapidly with nanowire length below ∼300 nm. This behavior is in agreement with the work of Wang et al 18 Thereafter, the thermal conductivity varies more slowly approaching asymptotically a constant value at lengths over 1200 nm. The slow increase above 300 nm implies that the NW is in the diffusive phonon transport regime.…”

Section: A Length Dependencesupporting

confidence: 81%

“…Hence, the obtained values only apply to the case of cross section of 9 × 9 unit cells, i.e. 3.5 × 3.5 nm 2 with (110) surface structure and temperature of 300 K. Since our cross section and surface orientation of the pure Si NW is different from previous studies, [18][19][20] no exact comparison can be made. For consistency with previous studies, we run one more case of pure Si NW with an exact cross section of 4 × 4 × 302 unit cells and (100) surface structure.…”

Section: A Length Dependencementioning

confidence: 93%

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Thermal conductivity reduction in core-shell nanowires

et al. 2011

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Nanostructuring of thermoelectric materials bears promise for manipulating physical parameters to improve the energy conversion efficiency of thermoelectrics. Using nonequilibrium molecular dynamics, we investigate how the thermal conductivity can be altered in core-shell nanocomposites of Si and Ge. By calculating the phonon vibrational density of states and performing normal mode analysis, we show that the thermal conductivity decreases when phonon-transport becomes diffusion-dominated and unveil a competition between modes from the various regions of the nanocomposite (core, interface, and shell). The effects of nanowire length, cross section, and temperature on thermal conductivity are explicitly considered. Surprisingly, the thermal conductivity variation with nanowire length is much weaker than in pure nanowires. Also, the thermal conductivity is almost independent of temperature in the wide region between 50 and 600 K, a direct result of confinement of the core by the shell. These results suggest that core-shell nanowires are promising structures for thermoelectrics.

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Section: A Length Dependencesupporting

confidence: 81%

Section: A Length Dependencementioning

confidence: 93%

Thermal conductivity reduction in core-shell nanowires

et al. 2011

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“…Numerous studies can be found in the literature regarding the thermal conductivity of Si NWs [3,4,5,6,7]. The effects of different scattering mechanisms, i.e.…”

Section: Introductionmentioning

confidence: 99%

Calculation of Confined Phonon Spectrum in Narrow Silicon Nanowires Using the Valence Force Field Method

Karamitaheri

Neophytou

Taheri

et al. 2013

Journal of Elec Materi

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We study the effect of confinement on the phonon properties of ultra-narrow silicon nanowires of side sizes of 1 10nm . We use the modified valence force field method to compute the phononic dispersion, and extract the density of states, the transmission function, the sound velocity, the ballistic thermal conductance and boundary scatteringlimited diffusive thermal conductivity. We find that the phononic dispersion and the ballistic thermal conductance are functions of the geometrical features of the structures, i.e. the transport orientation and confinement dimension. The phonon group velocity and thermal conductance can vary by a factor of two depending on the geometrical features of the channel. The <110> nanowire has the highest group velocity and thermal conductance, whereas the <111> the lowest. The <111> channel is thus the most suitable orientation for thermoelectric devices based on Si nanowires since it also has a large power factor. Our findings could be useful in the thermal transport design of siliconbased devices for thermoelectric and thermal management applications.

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“…(3) appears because a phonon travels on average half the distance between boundaries before being scattered. 23,24 It has been shown that this would be a good approximation for the Debye model at temperatures higher than 80 K for polycrystalline silicon. 25 The empirical parameters h f and h b define the probability of specular scattering at free surfaces and internal boundaries, respectively.…”

mentioning

confidence: 99%

Impact of internal crystalline boundaries on lattice thermal conductivity: Importance of boundary structure and spacing

Aghababaei

Anciaux

Molinari

2014

Applied Physics Letters

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The low thermal conductivity of nano-crystalline materials is commonly explained via diffusive scattering of phonons by internal boundaries. In this study, we have quantitatively studied phonon-crystalline boundaries scattering and its effect on the overall lattice thermal conductivity of crystalline bodies. Various types of crystalline boundaries such as stacking faults, twins, and grain boundaries have been considered in FCC crystalline structures. Accordingly, the specularity coefficient has been determined for different boundaries as the probability of the specular scattering across boundaries. Our results show that in the presence of internal boundaries, the lattice thermal conductivity can be characterized by two parameters: (1) boundary spacing and (2) boundary excess free volume. We show that the inverse of the lattice thermal conductivity depends linearly on a non-dimensional quantity which is the ratio of boundary excess free volume over boundary spacing. This shows that phonon scattering across crystalline boundaries is mainly a geometrically favorable process rather than an energetic one. Using the kinetic theory of phonon transport, we present a simple analytical model which can be used to evaluate the lattice thermal conductivity of nano-crystalline materials where the ratio can be considered as an average density of excess free volume. While this study is focused on FCC crystalline materials, where inter-atomic potentials and corresponding defect structures have been well studied in the past, the results would be quantitatively applicable for semiconductors in which heat transport is mainly due to phonon transport.

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Thermal conductivity of silicon nanowire by nonequilibrium molecular dynamics simulations

Cited by 105 publications

References 13 publications

Thermal conductivity reduction in core-shell nanowires

Thermal conductivity reduction in core-shell nanowires

Calculation of Confined Phonon Spectrum in Narrow Silicon Nanowires Using the Valence Force Field Method

Impact of internal crystalline boundaries on lattice thermal conductivity: Importance of boundary structure and spacing

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