Effect of a<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>SiO</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math>layer on the thermal transport properties of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mo>〈</mml:mo><mml:mn>100</mml:mn><mml:mo>〉</mml:mo><mml:mspace width="0.16em" /><mml:mi>Si</mml:mi></mml:mrow></mml:math>nanowires: A molecular dynamics study

Zushi, Tomofumi; Ohmori, Kenji; Yamada, Keiichi; Watanabe, Takanobu

doi:10.1103/physrevb.91.115308

Cited by 34 publications

(26 citation statements)

References 41 publications

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“…In the system with native oxide at the surfaces, the TA and LA modes show similar behavior as the pristine membrane, but, besides the TA and LA modes, numerous dispersion-less modes appear at random frequencies, es- pecially below 8 THz. A similar observation was made for SiO 2 coated SiNWs [57]. Such dispersionless modes are resonant modes due to the vibrations of the atoms in the amorphous SiO 2 layers.…”

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confidence: 77%

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Native surface oxide turns alloyed silicon membranes into nanophononic metamaterials with ultralow thermal conductivity

et al. 2017

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A detailed understanding of the relation between microscopic structure and phonon propagation at the nanoscale is essential to design materials with desired phononic and thermal properties. Here we uncover a new mechanism of phonon interaction in surface oxidized membranes, i.e., native oxide layers interact with phonons in ultra-thin silicon membranes through local resonances. The local resonances reduce the low frequency phonon group velocities and shorten their mean free path. This effect opens up a new strategy for ultralow thermal conductivity design as it complements the scattering mechanism which scatters higher frequency modes effectively. The combination of native oxide layer and alloying with germanium in concentration as small as 5% reduces the thermal conductivity of silicon membranes to 100 time lower than the bulk. In addition, the resonance mechanism produced by native oxide surface layers is particularly effective for thermal condutivity reduction even at very low temperatures, at which only low frequency modes are populated.Controlling terahertz vibrations and heat transport in nanostructures has a broad impact on several applications, such as thermal management in micro-and nano-electronics, renewable energies harvesting, sensing, biomedical imaging and information and communication technologies [1][2][3][4][5][6][7][8]. Significant efforts have been made to understand and engineer heat transport in nanoscale silicon due to its natural abundance and technological relevance [9][10][11][12]. In the past decade researchers explored strategies to obtain silicon based materials with low thermal conductivity (TC) and unaltered electronic transport coefficients, so to achieve high thermoelectric figure of merit and enable silicon-based thermoelectric technology [11][12][13][14][15][16][17][18].From the earlier studies it was recognized that lowdimensional silicon nanostructures, such as nanowires, thin films and nano membranes feature a largely reduced TC, up to 50 times lower than that of bulk at room temperature. TC reduction becomes more prominent with the reduction of the characteristic dimension of the nanostructures [19][20][21][22]. Theory and experiments consistently show that surface disorder and the presence of disordered material at surfaces play a major role in determining the TC of nanostructures [12,[23][24][25]. However, a comprehensive understanding of the physical mechanisms underlying so large TC reduction is lacking. The effect of surface roughness and surface disorder on phonons has been so far interpreted in terms of phonon scattering [26][27][28][29][30], but scattering would not account for mean free path reduction of long-wavelength low-frequency modes. Recent theoretical work demonstrated that surface nanostructures, such as nanopillars at the surface of thin films or nanowires, can efficiently reduce TC through resonances, a mechanism that is intrinsically different from scattering [31,32]. Surface resonances alter directly phonon dispersion relations by hybridizing with prop...

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confidence: 77%

“…To prove that the MFP reduction at low frequency is indeed due to random resonant modes, we obtained the effective phonon dispersion relations of pristine and surface oxidized Si membranes, computing the dynamical structure factor (DSF) in an EMD simulation [57]:…”

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confidence: 99%

Native surface oxide turns alloyed silicon membranes into nanophononic metamaterials with ultralow thermal conductivity

et al. 2017

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“…However, this value is not applicable at the nanoscale. [32][33][34][35][36] Recently, Hua and Cao studied the ballistic transport induced as some of the phonons directly fly from one boundary to another without scattering when the characteristic length is comparable to the phonon mean free path. 37 The ballistic transport causes deviations to the classical Fourier's law of heat conduction, for example, atomic geometry dependence of temperature jump and thermal conductivity.…”

Section: Introductionmentioning

confidence: 99%

Atomic density effects on temperature characteristics and thermal transport at grain boundaries through a proper bin size selection

Barışık

Kim

2016

The Journal of Chemical Physics

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This study focuses on the proper characterization of temperature profiles across grain boundaries (GBs) in order to calculate the correct interfacial thermal resistance (ITR) and reveal the influence of GB geometries onto thermal transport. The solid-solid interfaces resulting from the orientation difference between the (001), (011), and (111) copper surfaces were investigated. Temperature discontinuities were observed at the boundary of grains due to the phonon mismatch, phonon backscattering, and atomic forces between dissimilar structures at the GBs. We observed that the temperature decreases gradually in the GB area rather than a sharp drop at the interface. As a result, three distinct temperature gradients developed at the GB which were different than the one observed in the bulk solid. This behavior extends a couple molecular diameters into both sides of the interface where we defined a thickness at GB based on the measured temperature profiles for characterization. Results showed dependence on the selection of the bin size used to average the temperature data from the molecular dynamics system. The bin size on the order of the crystal layer spacing was found to present an accurate temperature profile through the GB. We further calculated the GB thickness of various cases by using potential energy (PE) distributions which showed agreement with direct measurements from the temperature profile and validated the proper binning. The variation of grain crystal orientation developed different molecular densities which were characterized by the average atomic surface density (ASD) definition. Our results revealed that the ASD is the primary factor affecting the structural disorders and heat transfer at the solid-solid interfaces. Using a system in which the planes are highly close-packed can enhance the probability of interactions and the degree of overlap between vibrational density of states (VDOS) of atoms forming at interfaces, leading to a reduced ITR. Thus, an accurate understanding of thermal characteristics at the GB can be formulated by selecting a proper bin size. Published by AIP Publishing. [http://dx

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“…Analysis of the vibrational density of states showed that the amorphous coatings were significantly subdued in the high frequency regime compared to the crystalline layer and the entire frequency range was down-shifted, exhibiting a large vibrational mismatch between the crystalline and amorphous layers as seen in other simulations. 78,118 This should lead to strong phonon scattering at the crystalline/amorphous interface due to the appearance of new vibrational states. 78 Conversely, as amorphous silica shares more vibrational modes in common with a-Si than with c-Si, the introduction of surface modes is likely to have a much weaker effect on the thermal conductivity in the fully amorphous NTs.…”

Section: Elastic Softeningmentioning

confidence: 99%

“…78,118 This should lead to strong phonon scattering at the crystalline/amorphous interface due to the appearance of new vibrational states. 78 Conversely, as amorphous silica shares more vibrational modes in common with a-Si than with c-Si, the introduction of surface modes is likely to have a much weaker effect on the thermal conductivity in the fully amorphous NTs. Surface induced mechanical softening can have a strong effect on the properties of nanoparticles (NPs) as well and can directly affect the performance of devices incorporating them.…”

Section: Elastic Softeningmentioning

confidence: 99%

Thermal transport in Si and Ge nanostructures in the ‘confinement’ regime

et al. 2016

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Reducing semiconductor materials to sizes comparable to the characteristic lengths of phonons, such as the mean-free-path (MFP) and wavelength, has unveiled new physical phenomena and engineering capabilities for thermal energy management and conversion systems. These developments have been enabled by the increasing sophistication of chemical synthesis, microfabrication, and atomistic simulation techniques to understand the underlying mechanisms of phonon transport. Modifying thermal properties by scaling physical size is particularly effective for materials which have large phonon MFPs, such as crystalline Si and Ge. Through nanostructuring, materials that are traditionally good thermal conductors can become good candidates for applications requiring thermal insulation such as thermoelectrics. Precise understanding of nanoscale thermal transport in Si and Ge, the leading materials of the modern semiconductor industry, is increasingly important due to more stringent thermal conditions imposed by ever-increasing complexity and miniaturization of devices. Therefore this Minireview focuses on the recent theoretical and experimental developments related to reduced length effects on thermal transport of Si and Ge with varying size from hundreds to sub-10 nm ranges. Three thermal transport regimes - bulk-like, Casimir, and confinement - are emphasized to describe different governing mechanisms at corresponding length scales.

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Effect of aSiO2layer on the thermal transport properties of〈100〉Sinanowires: A molecular dynamics study

Cited by 34 publications

References 41 publications

Native surface oxide turns alloyed silicon membranes into nanophononic metamaterials with ultralow thermal conductivity

Native surface oxide turns alloyed silicon membranes into nanophononic metamaterials with ultralow thermal conductivity

Atomic density effects on temperature characteristics and thermal transport at grain boundaries through a proper bin size selection

Thermal transport in Si and Ge nanostructures in the ‘confinement’ regime

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