Atomistic evidence of hydrodynamic heat transfer in nanowires

Universal Behavior of Highly Confined Heat Flow in Semiconductor Nanosystems: From Nanomeshes to Metalattices

“…The excellent fit quality further validates the use of hydrodynamic-like modeling to describe heat transport in highly confined nanosystems. The Poiseuille-like profiles obtained in MD are incompatible not only with the exponential profiles predicted by the Fuchs−Sondheimer approximation to the Boltzmann transport equation 11 but also with more general ballistic descriptions using the bulk MFP spectrum. 8 The viscosity fit with the steady-state GKE = / 2 GK follows the same scaling with porosity obtained from experiments using κ and K in eq 5.…”

“…Their presence might also reduce heat flux in the crystalline channels, which would result in an increased viscosity. 11,52 Moreover, we find that viscosity is independent of disorder in the nanostructured system; e.g., the periodically arranged 3D metalattices display the same viscosity as the randomly distributed pores in the nanowires. Hence, coherent interference effects previously reported in periodically structured silicon systems at very low temperatures 21,53 are negligible in the mainly room temperature experiments and simulations considered here.…”

“…Ballistic simulations predict a ray-like propagation of phonons in analogy with photons . This contrasts with recent molecular dynamics (MD) investigations of energy flow profiles in nanowires, which show a Poiseuille-like flow reminiscent of hydrodynamics. , These observations indicate the existence of a significant amount of phonon–phonon scattering and momentum diffusion at length scales much smaller than most of the bulk phonon MFPs, challenging the use of bulk phonon properties in nanoscale ballistic models. , While hydrodynamic effects are known to be enhanced at low temperatures or in 2D materials, where most phonon–phonon collisions conserve momentum, , increasing evidence suggests that they are also present at the nanoscale in semiconductors such as siliconeven at room temperature. − Therefore, a complete understanding of the breakdown of diffusive phonon transport in complex systems may require mesoscopic interpretations in analogy to fluid mechanics. Moreover, the degree to which heat dissipation through boundary scattering can be treated incoherently at the nanoscale remains unclear, since coherent effects modifying the phonon dispersion relations with respect to the bulk have been predicted and observed under some conditions. ,− These contradictions contribute to the lack of a unified description of heat transport in nanostructured semiconductors, especially at the smallest length scales and in emerging 3D phononic crystals …”

“…8 This contrasts with recent molecular dynamics (MD) investigations of energy flow profiles in nanowires, 9 which show a Poiseuille-like flow reminiscent of hydrodynamics. 10,11 These observations indicate the existence of a significant amount of phonon− phonon scattering and momentum diffusion at length scales much smaller than most of the bulk phonon MFPs, challenging the use of bulk phonon properties in nanoscale ballistic models. 12,13 While hydrodynamic effects are known to be enhanced at low temperatures or in 2D materials, where most phonon−phonon collisions conserve momentum, 14,15 increasing evidence suggests that they are also present at the nanoscale in semiconductors such as silicon�even at room temperature.…”

“…16,17,35,36 However, the predictive capabilities of this hydrodynamic-like approach are restricted to systems with dimensions sufficiently large compared to the average bulk phonon MFP, 37 since nanoscale confinement modifies the ab initio phonon properties used to determine the GKE coefficients. 10,11 This excludes the present metalattice and a broader class of nanostructured silicon materials.…”