Diverse anisotropy of phonon transport in two-dimensional IV-VI compounds: A first-principles study
Diverse anisotropy of phonon transport in two-dimensional IV-VI compounds: A first-principles study
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发表时间：
2016-02
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通讯作者：
G. Qin;Zhenzhen Qin;W. Fang;Li-chuan Zhang;Shengying Yue;Qing-Bo Yan;Ming Hu;G. Su
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作者：
G. Qin;Zhenzhen Qin;W. Fang;Li-chuan Zhang;Shengying Yue;Qing-Bo Yan;Ming Hu;G. Su
石墨烯以外的新型二维（2D）材料，包括层状和非层状材料及其异质结构，由于其在纳米电子学、光电子学和清洁能源等领域的应用前景，目前正引起人们越来越多的关注，其中热输运性质是基本物理参数之一。本文采用基于第一性原理的方法，通过求解Boltzmann输运方程，系统地研究了二维正交晶系Ⅳ-Ⅵ族化合物$GeS$，$GeSe$，$SnS$和$SnSe$的声子输运性质.尽管有类似的起皱四种单层化合物均具有类似磷烯的沿着扶手椅方向的铰链结构，在群速度、杨氏模量和晶格热导率等方面表现出不同的各向异性（$\kappa$）等，尤其是，单层$GeS$的$\kappa$沿沿着Z字形和扶手椅方向的各向异性最强，而单层$SnS$和$SnSe$尽管它们的结构特征相似，但声子输运几乎各向同性。通过对频率相关的$\kappa$和平均声子群速度的分析，我们发现，声子色散中的各向异性主要来自于差距以下的声子模。差距越大，各向异性越强。从差距两侧声子模之间的耦合解释了这一机制，并通过声子散射通道得到进一步证实。我们进一步表明，反映成键特性的电子局域函数（ELF）的各向异性行为是各向异性性质的物理根源。我们的研究提供了基本的理解具有铰链状结构的二维化合物的各向异性声子输运性质，并将有助于在新兴技术中的进一步调制和应用。
New class two-dimensional (2D) materials beyond graphene, including layered and non-layered, and their heterostructures, are currently attracting increasing interest due to their promising applications in nanoelectronics, optoelectronics and clean energy, where thermal transport property is one of the fundamental physical parameters. In this paper, we systematically investigated the phonon transport properties of 2D orthorhombic IV-VI compounds of $GeS$, $GeSe$, $SnS$ and $SnSe$ by solving the Boltzmann transport equation (BTE) based on first-principles calculations. Despite the similar puckered (hinge-like) structure along the armchair direction as phosphorene, the four monolayer compounds possess diverse anisotropic properties in many aspects, such as group velocity, Young's modulus and lattice thermal conductivity ($\kappa$), etc. Especially, the $\kappa$ along the zigzag and armchair directions of monolayer $GeS$ shows the strongest anisotropy while monolayer $SnS$ and $SnSe$ shows an almost isotropy in phonon transport, despite the similar characteristics of their structures. Based on the analysis of the frequency dependent $\kappa$ and average phonon group velocity, we find that, the anisotropy mainly arises from the phonon modes below the gap in the phonon dispersions. The larger the gap, the stronger the anisotropy. This mechanism is explained from the coupling between the phonon modes on both sides of the gap and is further confirmed by the phonon scattering channels. We further show that the anisotropic behavior of the electron localization functions (ELF) reflecting the bonding characteristics is the physical origin of the anisotropic properties. Our study offers fundamental understanding of the anisotropic phonon transport properties of 2D compounds with hinge-like structure, and would be helpful for further modulation and applications in emerging technologies.