Qu Xilong, Gu Jinjie
Hunan Provincial Key Laboratory of Finance & Economics Big Data Science and Technology, School of Information Technology and Management, Hunan University of Finance and Economics Changsha 410205 P. R. China
RSC Adv. 2020 Jan 8;10(3):1243-1248. doi: 10.1039/c9ra08520c. eCollection 2020 Jan 7.
Due to the coupling of a superlattice's longitudinal periodicity to a nanowire's radial confinement, the phonon transport properties of superlattice nanowires (SLNWs) are expected to be radically different from those of pristine nanowires. In this work, we present the comparative investigation of phonon transport and thermal conductivity between diamond SLNWs and SiGe SLNWs by using molecular dynamics simulations. In the case of period length ∼ 25 Å, the thermal conductivities of diamond SLNWs and SiGe SLNWs both increase linearly with increasing the period number, which implies the wave-like coherent phonons dominate the heat transport of SLNWs. In the case of period length ∼ 103 Å, the thermal conductivity of SiGe SLNWs is length-independent with increasing the period number, indicating that the particle-like incoherent phonons in SiGe SLNWs control the heat transport, because the phonon-phonon scattering causes phonons to not retain their phases and the coherence is destroyed before the reflection at interfaces. However in diamond SLNWs the coherent phonons still dominate heat conduction and the thermal conductivity is length-dependent, because the mean free path of phonon-phonon scattering in diamond SLNWs is much longer. The spatial distribution of phonon localized modes further supports these opinions. These results are helpful not only to understand the coherent and incoherent phonon transport, but also to modulate the thermal conductivity of SLNWs.
由于超晶格的纵向周期性与纳米线的径向限制相互耦合，超晶格纳米线（SLNWs）的声子输运特性预计将与原始纳米线的特性截然不同。在这项工作中，我们通过分子动力学模拟对金刚石SLNWs和SiGe SLNWs之间的声子输运和热导率进行了对比研究。在周期长度约为25 Å的情况下，金刚石SLNWs和SiGe SLNWs的热导率均随周期数的增加而线性增加，这意味着波状相干声子主导了SLNWs的热输运。在周期长度约为103 Å的情况下，SiGe SLNWs的热导率随周期数的增加与长度无关，这表明SiGe SLNWs中的粒子状非相干声子控制了热输运，因为声子 - 声子散射导致声子无法保持其相位，并且在界面反射之前相干性就被破坏了。然而在金刚石SLNWs中，相干声子仍然主导热传导，并且热导率与长度有关，因为金刚石SLNWs中声子 - 声子散射的平均自由程要长得多。声子局域模的空间分布进一步支持了这些观点。这些结果不仅有助于理解相干和非相干声子输运，而且有助于调节SLNWs的热导率。
