npj: 极高热导奇材—类石墨烯型氢化硼烯

Original npj 知社学术圈 2021-06-13

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在固体中，热能不仅由声子携带，而且由电子携带，因为电子同样在温度梯度的存在下流动。然而，在2D材料中，这两个热载流子对总热传导的贡献是不同的。在诸如MoS₂ 和黑磷的2D半导体中，声子主导热传导。尽管由石墨烯代表的第IV族2D材料，是主导Dirac费米子的无带隙半金属，吸足了眼球，但费米级的低载流子浓度限制了电热导。如单层锡原子（Stanene）在室温下表现出与声子相当的电热导性。然而，其晶格（电子）热导率仅为约的10％。那么，是否存在一种二维材料同时具有高的电子热导和声子热导？元素周期表中硼与碳相邻，是否存在一种由硼构成的二维材料比石墨烯有更高的热导？

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，共同研究了类石墨烯型氢化硼烯（hydrogenated graphene-like borophene）的弹道热输运性质，给出了声子和电子对热导的贡献。他们发现类石墨烯型氢化硼烯竟然同时具有高的声子热导和电子热导，声子热导为4.07 nWWK^-1nm^-2，与石墨烯的(4.1 nWK^-1nm^-2)相近，而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，是目前报道的所有二维材料中热导最大的材料。他们对该材料热输运性质的应变效应研究显示，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，出现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，出现电子热导为零，与扶手椅方向的应变效应恰好相反。

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^-1nm^-2 ) as graphene (4.1 nWK^-1nm^-2 ), and similar electron thermal conductance (3.6 nWK^-1nm^-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.