Phonon interference in crystalline and amorphous confined nanoscopic films

Liang, Zhi; Wilson, Thomas E.; Keblinski, Pawel

doi:10.1063/1.4976563

Cited by 10 publications

(10 citation statements)

References 46 publications

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“…As to the Si/a-SiO 2 interfaces, wave packet simulations have shown that for phonons of lower than 1 THz frequencies, their transmission coefficients at the interface are 0.98 and 0.95 for longitudinal and transverse phonon branches, respectively. , These results are comparable with the prediction from the acoustic mismatch model (AMM), which yields transmission coefficients for longitudinal and transverse phonons as 0.98 and 0.94, respectively . As such, in our model, we approximate the phonon transmission coefficient at the Si/a-SiO 2 interface as unity and combine its effects into the transmission through the vdW interface by adjusting the fitting parameter, K A in eq .…”

supporting

confidence: 67%

“…This difference, however, is not important if the penetration depth of thermal phonons in a-SiO 2 is approximately the same as the interatomic distance. We note that phonon transmission through Si/a-SiO 2 /Si sandwiched structures has been studied using wave packet simulations; 8,22 the results suggested that a large portion of phonons with frequencies up to 1.4 THz, which contribute more than 20% to the thermal conductivity of silicon, 23 could still ballistically penetrate through a 10 nm a-SiO 2 layer. However, no convincing experimental demonstration of this prediction has been reported.…”

mentioning

confidence: 95%

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Ballistic Phonon Penetration Depth in Amorphous Silicon Dioxide

et al. 2017

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Thermal transport in amorphous silicon dioxide (a-SiO) is traditionally treated as random walks of vibrations owing to its greatly disordered structure, which results in a mean free path (MFP) approximately the same as the interatomic distance. However, this picture has been debated constantly and in view of the ubiquitous existence of thin a-SiO layers in nanoelectronic devices, it is imperative to better understand this issue for precise thermal management of electronic devices. Different from the commonly used cross-plane measurement approaches, here we report on a study that explores the in-plane thermal conductivity of double silicon nanoribbons with a layer of a-SiO sandwiched in-between. Through comparing the thermal conductivity of the double ribbon samples with that of corresponding single ribbons, we show that thermal phonons can ballistically penetrate through a-SiO of up to 5 nm thick even at room temperature. Comprehensive examination of double ribbon samples with various oxide layer thicknesses and van der Waals bonding strengths allows for extraction of the average ballistic phonon penetration depth in a-SiO. With solid experimental data demonstrating ballistic phonon transport through a-SiO, this work should provide important insight into thermal management of electronic devices.

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confidence: 67%

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confidence: 95%

Ballistic Phonon Penetration Depth in Amorphous Silicon Dioxide

et al. 2017

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“…Yet, what is interesting to notice is that propagons can ballistically go through thin amorphous layers. This was recently demonstrated by Liang et al [48] for a-SiO 2 thin layers (4.6-9.2 nm) sandwiched between Si leads. In this work the governing criterion to check the propagative behavior of carriers is the Ioffe-Regel (IR) frequency that discriminates between propagons and diffusons.…”

Section: Figmentioning

confidence: 55%

“…In Ref. [48] the IR frequency of a-SiO 2 is about 1.4 THz, while for a-Si it is about 2 THz [49]. Thus, there are propagative modes on a more extended frequency range in amorphous silicon as compared to silicon dioxide.…”

Section: Figmentioning

confidence: 96%

Influence of amorphous layers on the thermal conductivity of phononic crystals

et al. 2018

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The impact of amorphous phases around the holes and at the upper and lower free surfaces on thermal transport in silicon phononic membranes is studied. By means of molecular dynamics and Monte Carlo simulations, we explore the impact of the amorphous phase (oxidation and amorphous silicon), surfaces roughness, and a series of geometric parameters on thermal transport. We show that the crystalline phase drives the phenomena; the two main parameters are (i) the crystalline fraction between two holes and (ii) the crystalline thickness of the membranes. We reveal the hierarchical impact of nanostructurations on the thermal conductivity, namely, from the most resistive to the less resistive: the creation of holes, the amorphous phase around them, and the amorphization of the membranes edges. The surfaces or interfaces perpendicular to the heat flow hinder the thermal conductivity to a much greater extent than those parallel to the heat flow.

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“…Liang et al that in the crystalline and amorphous sandwiched structures, phonon interference effect would exist if the thickness of the central amorphous silicon film were less than 5 nm 28 . A similar scale of phonon penetration depth was also observed in amorphous silicon dioxide 29 .…”

Section: (I)-(iv) It Was Reported Bymentioning

confidence: 99%

Probing thermal transport across amorphous region embedded in a single crystalline silicon nanowire

Zhao

Liu

Rath

et al. 2020

Sci Rep

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While numerous studies have been carried out to characterize heat transport behaviours in various crystalline silicon nanostructures, the corresponding characteristics of amorphous one-dimension system have not been well understood. in this study, we amorphize crystalline silicon by means of helium-ion irradiation, enabling the formation of a completely amorphous region of well-defined length along a single silicon nanowire. Heat conduction across both amorphous region and its crystalline/amorphous interface is characterized by an electron beam heating technique with high measurement spatial resolution. the measured thermal conductivity of the amorphous silicon nanowire appears length-independence with length ranging from ~30 nm to few hundreds nm, revealing the fully diffusons governed heat conduction. Moreover, unlike the size-dependent interfacial thermal conductance at the interface between two one-dimensional crystalline materials, here for the first time, we observe that the interface thermal conductance across the amorphous/crystalline silicon interface is nearly independent of the length of the amorphous region. this unusual independence is further supported by molecular dynamics (MD) simulation in our work. Our results provide experimental and theoretical insight into the nature of interaction between heat carriers in crystalline and amorphous nano-structures and shed new light to design innovative silicon nanowire based devices. While crystalline materials are commonly studied, studying the thermal properties of non-crystalline materials, including all kinds of inorganic, organic, biological materials and their hybrid structures, is equally important, as it can significantly enrich our knowledge of energy transport in non-periodic lattices. Moreover, emergent technologies, like new generations of wearable electronics and soft machines, often exploit non-crystalline materials 1-3. In such materials, the phonon picture fails for atoms arranged in a disordered fashion, where heat is carried in a random channel among series of independent oscillators 4-6. This uncorrelated oscillator picture could be attributed to Einstein, who in 1911 7 predicted the low thermal conductivity limit for a completely amorphous disordered material, namely the "amorphous limit", in which the interactions between random oscillators lead to heat conduction. Since then, this amorphous limit model has been debated in numerous studies, since the values of thermal conductivity of amorphous solids reported were much higher. For amorphous silicon, a ubiquitous component of modern electronic devices, the thermal conductivity based on the calculated amorphous limit is below 2 W/m•K 8. Recent studies have shown that the thermal conductivity of amorphous silicon could be much higher 9,10 and as high as 4-5 W/m•K has been claimed 11. The fact of much higher thermal conductivity than the amorphous limit prediction for amorphous silicon has spurred numerous theoretical calculations to understand how heat carriers transport in amorphous silico...

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Phonon interference in crystalline and amorphous confined nanoscopic films

Cited by 10 publications

References 46 publications

Ballistic Phonon Penetration Depth in Amorphous Silicon Dioxide

Ballistic Phonon Penetration Depth in Amorphous Silicon Dioxide

Influence of amorphous layers on the thermal conductivity of phononic crystals

Probing thermal transport across amorphous region embedded in a single crystalline silicon nanowire

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