npj: 李登峰教授等重要发现—2D材料的极高热导和反常应力效应

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诸如石墨烯、过渡金属二硫化物、六方氮化硼和黑色磷烯等原子级薄二维（2D）材料，可为各种应用领域提供巨大的机会，包括纳米电子学、光电子学、可再生能源和散热等，因而在基础科学和工程应用领域激起了广泛兴趣，人们正热切盼望能在不久的将来应用这些材料实现原子级薄器件。

但随着运行速度的快速提高和集成密度的提高，集成纳米级器件的功耗也会迅速攀升、性能也会下降。因而基于2D材料的器件在受限体积中的局部加热便会成为重要问题。显然，充分揭示2D材料的热导机理、提高操纵2D材料热性能成为其应用的关键。固体中的热能由声子和电子共同携带，但在大多数2D材料中，电子对热导的贡献要远小于声子。那么，是否存在一种2D材料同时具有高电子热导和高声子热导？元素周期表中硼与碳相邻，是否存在一种由硼构成的2D材料比石墨烯更高的热导？

来自重庆邮电大学的李登峰教授课题组和新加坡高性能计算研究院张刚教授课题组，基于第一性原理和非平衡格林函数法，研究了类石墨烯型氢化硼烯（hydrogenated graphene-likeborophene）的弹道热输运性质，给出了声子和电子对热导的贡献，发现类石墨烯型氢化硼烯具有高的声子热导和电子热导，声子热导为4.07nWK^-1nm^-2，与石墨烯(4.1nWK^-1nm^-2)相近；电子热导几乎是石墨烯的10倍，从而类石墨烯型氢化硼烯总的热导是石墨烯的2倍，是目前报道的热导最大的材料。另外，他们研究了类石墨烯型氢化硼烯热输运性质的应变效应，在费米面上，沿扶手椅方向的拉伸应变会产生更高的电子态密度，从而有效地将更多的电子态引入，导致电子热导的增加，且在此方向增加的电子热导弥补了声子热导的减小，从而总热导随拉伸应变的增加而增加。相反，在锯齿形方向施加16%的应变时会产生带隙，从而完全“关闭”电子通道，导致电子热导为零。这与扶手椅方向的应变效应相反。

该文近期发表于npj Computational Materials 5: 47 (2019)，英文标题与摘要如下，点击左下角“阅读原文”可以自由获取论文PDF。

Orbitally driven giant thermal conductance associated with abnormal strain dependence in hydrogenated graphene-like borophene

Jia He, Dengfeng Li*, Yan Ying, Chunbao Feng, Junjie He, Chengyong Zhong, Hangbo Zhou,Ping Zhou, Gang Zhang*

Heat energy in solids is carried by phonons and electrons. However, in most two-dimensional (2D) materials, the contribution from electrons to total thermal conduction is much lower than that for phonons. In this work, through first-principles calculations combined with non-equilibrium Green’s function theory, we studied electron and phonon thermal conductance in recently synthesized 2D hydrogen boride. The hexagonal boron network with bridging hydrogen atoms is suggested to exhibit comparable lattice thermal conductance (4.07 nWK⁻¹ nm⁻² ) as graphene (4.1 nWK⁻¹ nm⁻² ), and similar electron thermal conductance (3.6 nWK⁻¹ nm⁻²), which is almost ten times that of graphene. As a result, total thermal conductance of 2D hydrogen boride is about two-fold of graphene, being the highest value in all known 2D materials. Moreover, tensile strain along the armchair direction leads to an increase in carrier density, signifificantly increasing electron thermal conductance. The increase in electron thermal conductance offsets the reduction in phonon thermal conductance, contributing to an abnormal increase in thermal conductance. We demonstrate that the high electron density governs extraordinarily high thermal conductance in 2D hydrogen boride, distinctive among 2D materials.

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