Experimental Evidence of Superdiffusive Thermal Transport in Si_0.4Ge_0.6 Thin Films

Abstract

Superdiffusive thermal transport represents a unique phenomenon in heat conduction, which is characterized by a size (L) dependence of thermal conductivity (κ) in the form of κ ∝ L β with a constant β between 0 and 1. Although superdiffusive thermal transport has been theoretically predicted for SiGe alloys, direct experimental evidence is still lacking. Here, we report on a systematic experimental study of the thickness-dependent thermal conductivity of Si0.4Ge0.6 thin films grown by molecular beam epitaxy. The cross-plane thermal conductivity of Si0.4Ge0.6 thin films spanning a thickness range from 20 to 1120 nm was measured in the temperature range 120–320 K via a differential three-omega method. Results show that the thermal conductivity follows a consistent κ ∝ t 0.26 power law with the film thickness (t) at different temperatures, providing direct experimental evidence that alloy-scattering dominated thermal transport in SiGe is superdiffusive.

Thickness‐Dependent Thermal Conductivity and Phonon Mean Free Path Distribution in Single‐Crystalline Barium Titanate

“…However, if the film thickness is smaller or comparable to the average phonon MFP, the thermal transport can be superdiffusive, as demonstrated in previous studies. [64,65] In our case, the average phonon MFP is below 10 nm, which is smaller than most of the films measured in our study. Thus, we do not observe any significant effect of super-diffusive phonon transport here.…”

Phononic thermal conduction and thermal regulation in low-dimensional micro-nano scale systems: Nonequilibrium statistical physics problems from chip heat dissipation

“…等 [24] 图 5 碳纳米管和氮化硼纳米管热阻随尺寸的变化关系 (a) 归一化的热阻随长度的变化关系, 插图为扫描电镜下悬空热桥法 的测试装置 [22] ; (b) 碳纳米管的归一化热阻随长度的变化关系(从热阻变化推断出热导率变化为 ) [22] ; (c) 氮化硼纳米管 的归一化热阻随长度的发散关系(从而得到 ) [22] Fig. 5.…”

“…2003年, Li和Wang [8] 利用分数维微分方程 描述的反常扩散现象, 建起了连接扩散与热传导之 图 6 NbSe 3 纳米线和Si 0.4 Ge 0.6 薄膜中的超扩散现象 (a) NbSe 3 纳米线材料体系中的超扩散声子热输运实验发现 [24] ; (b) Si 0.4 Ge 0.6…”

“…(a) Observation of superdiffusive phonon transport in NbSe 3 nanowire [24] ; (b) superdiffusive thermal transport in Si 0.4 Ge 0.6 thin films [25] .…”

Seeking non-Fourier heat transfer with ultrabroad band thermoreflectance spectroscopy

“…Such experimental measurements obtained with a classical TDTR setup 7 have enabled to highlight a superdiffusive regime but this kind of experiment has inherent drawbacks which complicate the analysis such as cumulative thermal effects or a limited acquisition time window. One new experimental evidence of superdiffusive transport was reported in 2022 16 . Nevertheless, the process described by the authors needs i) to grow more than 10 samples with thicknesses from 10 nm up to 1 µm, ii) to perform measurements from ambient temperature down to cryogenic.…”