Modification of the lattice thermal conductivity in silicon quantum wires due to spatial confinement of acoustic phonons

Khitun, Alexander; Balandin, Alexander A.; Wang, K.L.

doi:10.1006/spmi.1999.0772

Cited by 108 publications

(81 citation statements)

References 21 publications

(28 reference statements)

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“…24,25,26,27,28 The thermoelectric phenomenon can be utilized to harvest otherwise wasted thermal energy directly into electric power. To increase the thermoelectric efficiency, the thermal conductivity in NWs should be reduced, which can be realized through phonon confinement effects, 29,30,31,32 isotope doping, 33 surface roughness, 34,35,36 or non-planar (kinked) structures. 37 Shi et al suggested enhancing the thermoelectric efficiency through gallium doping, and the thermoelectric figure of merit was found to be increased by a factor of 2.5 at 4% gallium doping.…”

Section: Introductionmentioning

confidence: 99%

Polar surface effects on the thermal conductivity of ZnO nanowires: a shell-like surface reconstruction-induced preserving mechanism

2013

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We perform molecular dynamics (MD) simulations to investigate the effect of polar surfaces on the thermal transport in zinc oxide (ZnO) nanowires. We find that the thermal conductivity in nanowires with free polar (0001) surfaces is much higher than in nanowires that have been stabilized with reduced charges on the polar (0001) surfaces, and also hexagonal nanowires without any transverse polar surfaces, where the reduced charge model has been proposed as a promising stabilization mechanism for the (0001) polar surfaces for ZnO nanowires. From normal mode analysis, we show that the higher thermal conductivity is due to a shell-like reconstruction that occurs for the free polar surfaces. This shell-like reconstruction suppresses twisting motion in the nanowires such that the bending phonon modes are not scattered by the other phonon modes, and leads to substantially higher thermal conductivity in the ZnO nanowire with free polar surfaces. Furthermore, the autocorrelation function of the normal mode coordinate is utilized to extract the phonon lifetime, which leads to a concise explanation for the higher thermal conductivity in ZnO nanowires with free polar surfaces. Our work demonstrates that ZnO nanowires without polar surfaces, which exhibit low thermal conductivity, are more promising candidates for thermoelectric applications than nanowires with polar surfaces (and also high thermal conductivity).

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Section: Introductionmentioning

confidence: 99%

Polar surface effects on the thermal conductivity of ZnO nanowires: a shell-like surface reconstruction-induced preserving mechanism

2013

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“…Phonon confinement and subband quantization in nanostructures lead to modification of the phonon density of states (DOS) [5][6][7][8][9][10], electron -phonon scattering rates [10][11][12][13][14][15][16], optical response of the materials [17], and phonon relaxation via scattering on defects and in anharmonic Umklapp processes [5,[7][8][18][19][20]. It was predicted theoretically within the continuum approximation for phonons that the electron mobility can be increased in phonon engineered core-shell NWs or planar heterostructures via utilization of the barrier shell materials, which are acoustically harder than the core material [21][22].…”

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confidence: 99%

Thermal conductivity inhibition in phonon engineered core-shell cross-section modulated Si/Ge nanowires

Nika

Cocemasov

Crismari

et al. 2013

Applied Physics Letters

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We have shown theoretically that a combination of cross-section modulation and acoustic mismatch in the core-shell Si/Ge nanowires can lead to a drastic reduction of the thermal conductivity. Our calculations, which utilized two different models -five-parameter Bornvon Karman and six-parameter valence-force field -for the lattice vibrations, indicate that the room temperature thermal conductivity of Si/Ge cross-section modulated nanowires is almost three orders of magnitude lower than that of bulk Si. Thermal flux in the modulated nanowires is suppressed by an order of magnitude in comparison with generic Si nanowires.The effect is explained by modification of the phonon spectra in modulated nanowires leading to decrease of the phonon group velocities and localization of certain phonon modes in narrow or wide nanowire segments. The thermal conductivity inhibition is achieved in nanowires without additional surface roughness and, thus, potentially reducing degradation of the electron transport. Our results suggest that the acoustically mismatched cross-section modulated nanowires are promising candidates for thermoelectric applications.

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“…For example, theoretical studies [128,129] have suggested that, as the diameter of a Si nanowire becomes smaller than 20 nm, the phonon dispersion relation could be modified due to phonon confinement, such that the phonon group velocities would be significantly less than the bulk value. Molecular dynamics simulations [130] have shown that, for wires of nanometer diameter, the thermal conductivities could be 2 orders of magnitude smaller than that of bulk silicon [131].…”

Section: A Novel Thermoelectric Materialsmentioning

confidence: 99%

Optical Properties of Nanostructured Silicon

Chao

2011

Comprehensive Nanoscience and Technology

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Modification of the lattice thermal conductivity in silicon quantum wires due to spatial confinement of acoustic phonons

Cited by 108 publications

References 21 publications

Polar surface effects on the thermal conductivity of ZnO nanowires: a shell-like surface reconstruction-induced preserving mechanism

Polar surface effects on the thermal conductivity of ZnO nanowires: a shell-like surface reconstruction-induced preserving mechanism

Thermal conductivity inhibition in phonon engineered core-shell cross-section modulated Si/Ge nanowires

Optical Properties of Nanostructured Silicon

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