Spectral Phonon Scattering from Sub-10 nm Surface Roughness Wavelengths in Metal-Assisted Chemically Etched Si Nanowires

Ghossoub, Marc G.; Valavala, Krishna; Seong, Myunghoon; Azeredo, Bruno; Hsu, Kuo Chin; Sadhu, Jyothi; Singh, Praveer; Sinha, Sanjiv

doi:10.1021/nl3047392

Cited by 63 publications

(38 citation statements)

References 28 publications

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“…For representative nanostructures, such as SiNWs, introduction of surface roughness is a commonly adopted method to reduce thermal conductivity. 35,[44][45][46][47][48][49][50][51] However, from the viewpoint of coherent models, this method (introduction of surface roughness) is believed to be a "negative" effect to reduce thermal conductivity of 2D PnCs, because it will destroy the coherence of phonons. In contrast, as demonstrated in our present work, phonon coherent transport is not the necessary condition to achieve ultra-low thermal conductivity in 2D PnCs.…”

Section: 40mentioning

confidence: 99%

Ultra-low thermal conductivity of two-dimensional phononic crystals in the incoherent regime

et al. 2018

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Two-dimensional silicon phononic crystals have attracted extensive research interest for thermoelectric applications due to their reproducible low thermal conductivity and sufficiently good electrical properties. For thermoelectric devices in high-temperature environment, the coherent phonon interference is strongly suppressed; therefore phonon transport in the incoherent regime is critically important for manipulating their thermal conductivity. On the basis of perturbation theory, we present herein a novel phonon scattering process from the perspective of bond order imperfections in the surface skin of nanostructures. We incorporate this strongly frequency-dependent scattering rate into the phonon Boltzmann transport equation and reproduce the ultra low thermal conductivity of holey silicon nanostructures. We reveal that the remarkable reduction of thermal conductivity originates not only from the impediment of low-frequency phonons by normal boundary scattering, but also from the severe suppression of high-frequency phonons by surface bond order imperfections scattering. Our theory not only reveals the role of the holey surface on the phonon transport, but also provide a computation tool for thermal conductivity modification in nanostructures through surface engineering.

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Section: 40mentioning

confidence: 99%

Ultra-low thermal conductivity of two-dimensional phononic crystals in the incoherent regime

et al. 2018

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“…In recent years, a number of advanced and sophisticated models of boundary scattering have been applied to the analysis of thermal transport in nanostructures [25][26][27][28][29][30][31][32][33][34][35]. Many of these studies involve detailed models of a rough surface or interface at the atomic level and use either lattice dynamics calculations based on Green's functions analysis [25][26][27][28][29] or molecular dynamics simulations [32][33][34][35].…”

Section: Introductionmentioning

confidence: 99%

Boundary scattering of phonons: Specularity of a randomly rough surface in the small-perturbation limit

Maznev

2015

Phys. Rev. B

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Scattering of normally incident longitudinal and transverse acoustic waves by a randomly rough surface of an elastically isotropic solid is analyzed within the small perturbation approach. In the limiting case of a large correlation length L compared with the acoustic wavelength, the The results indicate that thermal transport models using Ziman's formula are likely to overestimate the heat flux dissipation due to boundary scattering, whereas modeling interface roughness as atomic disorder is likely to underestimate scattering.

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“…4,5 In particular, the nanostructuring of silicon materials mediates phonon scattering and confinement, including reduction of thermal conductivity [6][7][8][9] and Si-based nanowire heterostructures have been employed as solar cell materials and nanoelectronic power sources. 10 Crystal sizes below the Bohr radius also results in light emission, and effective bandgap modification can influence absorbed thermopower in nanoscale silicon, and for photovoltaics.…”

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confidence: 99%

Quantum Confined Intense Red Luminescence from Large Area Monolithic Arrays of Mesoporous and Nanocrystal-Decorated Silicon Nanowires for Luminescent Devices

O’Dwyer

McSweeney

Collins

2015

ECS J. Solid State Sci. Technol.

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We report intense red luminescence from mesoporous n + -Si(100) nanowires (NWs) and nanocrystal-decorated p-Si NWs fabricated using electroless metal assisted chemical (MAC) etching. n + -Si NWs are composed of a labyrinthine network of silicon nanocrystals in a random mesoporous structure. p-type Si(100) NWs exhibit solid core structure, with a surface roughness that contains surfacebound nanocrystals. Both mesoporous n + -Si NWs and rough, solid p-Si NWs exhibit red luminescence at ∼1.7 and ∼1.8 eV, respectively. Time-resolved photoluminescence (PL) measurements indicated long (tens of μs) radiative recombination lifetimes. The red luminescence is visible with the naked eye and the red light is most intense from mesoporous n + -Si NWs, which exhibit a red-shift in the emission maximum to 1.76 eV at 100 K. The red PL from monolithic arrays of p-type NWs with nanocrystal-decorated rough surfaces is comparatively weak, but originates from the surface bound nanocrystals. Significant PL intensity increase is found during excitation for mesoporous NWs. X-ray photoelectron spectroscopy identifies a stoichiometric SiO 2 on the rough p-Si NWs with a SiO x species at the NW surface. No distinct oxide is found on the mesoporous NWs. The analysis confirms that long life-time PL emission arises from quantum confinement from internal nanoscale crystallites, and oxidized surface-bound crystallites, on n + -and p-Si NWs respectively. Recent advancements in the growth and formation of semiconducting nanostructures, particularly group 14 metalloid semiconductors such as silicon and germanium have shown how quantum effects can be engineered and controlled 1-3 to modify thermal and optical properties. 4,5 In particular, the nanostructuring of silicon materials mediates phonon scattering and confinement, including reduction of thermal conductivity 6-9 and Si-based nanowire heterostructures have been employed as solar cell materials and nanoelectronic power sources.10 Crystal sizes below the Bohr radius also results in light emission, and effective bandgap modification can influence absorbed thermopower in nanoscale silicon, and for photovoltaics.11 In photovoltaics, polycrystalline silicon comprises more than 90% of the PV cell production. The efficiency is limited to ∼33-35%, with most of the power converted to heat via phonon emission.12 Recent developments in nanoscale silicon crystals that provide multiple exciton generation events (at energies greater than twice the bandgap) per incident photon may improve efficiencies. 13Porous semiconductors and clusters of quantum dots, particularly of silicon, have also been the subject of intense research recently for Li-ion batteries [14][15][16] water oxidation 17 and electroluminescent devices 18 and those exhibiting optical gain, 19-21 and a range of (bio)sensors. 22,23 Since the discovery of visible light emission in porous silicon [24][25][26] that in the main, arose from quantum confinement effects, porous silicon has had some usefulness for nanoelectronic devices, 27 and field ef...

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Spectral Phonon Scattering from Sub-10 nm Surface Roughness Wavelengths in Metal-Assisted Chemically Etched Si Nanowires

Cited by 63 publications

References 28 publications

Ultra-low thermal conductivity of two-dimensional phononic crystals in the incoherent regime

Ultra-low thermal conductivity of two-dimensional phononic crystals in the incoherent regime

Boundary scattering of phonons: Specularity of a randomly rough surface in the small-perturbation limit

Quantum Confined Intense Red Luminescence from Large Area Monolithic Arrays of Mesoporous and Nanocrystal-Decorated Silicon Nanowires for Luminescent Devices

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