二维IV-VI化合物中声子输运各向异性的比较研究
Diverse anisotropy of phonon transport in two-dimensional IV-VI compounds: A comparative study
摘要：
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计算的Boltzmann输运方程（BTE），系统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.尽管有类似的起皱由于四种单层化合物具有与磷烯一样的沿扶手椅方向的铰链状结构，在声子群速度、杨氏模量和晶格热导率等方面具有不同的各向异性（$κ$）等。特别地，单层$GeS$的Z字形和扶手椅方向的$κ$显示出最强的各向异性，而单层$SnS$和$SnSe$显示出最强的各向异性。声子输运几乎各向同性。全面研究了各种各向异性的起源，并详细讨论了其机制。在有限的尺寸下，通过纳米结构化可以有效地降低$κ$，并有效地调节其各向异性，这将扩大其在纳米热电和热管理领域的应用。我们的研究为二维材料的各向异性声子输运性质提供了基础性的认识，对于进一步研究、调制和应用新兴技术具有重要意义。
英文摘要：
New classes 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 group 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 phonon group velocity, Young's modulus and lattice thermal conductivity ($κ$), etc. Especially, the $κ$ 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. The origin of the diverse anisotropy is fully studied and the underlying mechanism is discussed in detail. With limited size, the $κ$ could be effectively lowered, and the anisotropy could be effectively modulated by nanostructuring, which would extend the applications in nanoscale thermoelectrics and thermal management. Our study offers fundamental understanding of the anisotropic phonon transport properties of 2D materials, and would be of significance for further study, modulation and aplications in emerging technologies.
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