Radial quasiballistic transport in time-domain thermoreflectance studied using Monte Carlo simulations

Abstract

Monte Carlo simulation of phonon transport in silicon including a realistic dispersion relation

Anisotropic failure of Fourier theory in time-domain thermoreflectance experiments

“…While this paper was under review, a paper was published by Ding et al 32 theoretically examining three-dimensional heattransfer in an Al/Si sample on timescales between 1 ps and 1 ns using the Boltzmann transport equation. Their model indicates that only J r , and not J z , is affected by a reduced spot size, consistent with our beam-offset measurements (Fig.…”

Nondiffusive thermal transport and prediction of the breakdown of Fourier’s law in nanograting experiments

“…However, due to a lack of well-accepted nondiffusive model, Fourier's law is currently still used in experimental data analysis of nanothermometries to extract ETC. Similar to hotspot-sizedependent ETC and thermal interface resistivity found in TDTR experiments, 11,12 the measured ETC and thermal interface resistivity in MG-X-ray experiments should also depend on the grating sizes. However, Fourier's law cannot determine the coupled ETC and thermal interface resistivity in MG-X-ray experiments simultaneously through data fitting to the thermal decay curves.…”

“…Given volumetric specific heat c and speed of sound c in Eq. (5) 5,11,12 demonstrates the breakdown of Fourier's law due to nondiffusive heat transfer, but none of these experiments at room temperature presents direct evidence of ballistic heat transfer. Therefore, the nondiffusive heat transfer characteristic length is a more appropriate name for Λ B than the ballistic transport length.…”

“…Among them, transient thermoreflectance (TTR), including time-domain thermoreflectance (TDTR) and frequency-domain thermoreflectance (FDTR), [7][8][9] is an established experimental technique contributing to the discovery of many nondiffusive heat transfer phenomena, such as frequency-dependent and hotspot-size-dependent effective thermal conductivity (ETC). [10][11][12] However, the presence of interface between the metal transducer layer and the interrogated sample makes it very complicated for experimental data analysis. To exclude the interface effects on a nanothermometry, a transient thermal grating (TTG) method was developed to measure the decay of thermal gratings without a metallic transducer layer.…”

“…15 An appropriate heat conduction model is indispensable for experimental data analysis in nanothermometry in order to extract parameters of interests from detected signals and to achieve a fundamental understanding of phonon-mediated heat transfer in nanostructures and across interfaces. The measured hotspot-size-dependent ETC 5,11,12 demonstrates that ETC is unsuitable to characterize nondiffusive heat transfer for at least three reasons: (1) ETC is defined within the framework of Fourier's law, but Fourier's law cannot describe nondiffusive heat transfer; (2) ETC is an artificial parameter rather than an inherent material thermal property because it depends on probing methods; and (3) The hotspot-size-and heating-frequency-dependent ETC makes the accurate measurement impossible. However, due to a lack of well-accepted nondiffusive model, Fourier's law is currently still used in experimental data analysis of nanothermometries to extract ETC.…”