<span style="FONT-FAMILY: 宋体">二维石墨烯</span>/h-BN<span style="FONT-FAMILY: 宋体">异质结构负热膨胀性质的理论研究</span>-中国材料进展

文章信息/Info

Title:: Theoretical study of negative thermal expansion in 2D graphene/h-BN heterostructure

关键词:: 石墨烯' target="_blank" rel="external"> FONT-FAMILY: 宋体">石墨烯; FONT-FAMILY: "; Calibri"; "; sans-serif"; ">h-BN ' target="_blank" rel="external"> FONT-FAMILY: 宋体">; 负热膨胀; 格林奈森参数; 范德瓦尔斯相互作用

摘要:: 二维材料由于存在着“膜效应”—即在垂直于薄膜方向的热涨落，使得沿着二维薄膜面内方向出现反常的负热膨胀现象。这种热效应对薄膜的稳定性及电子性质可产生重要影响。基于第一性原理计算和准谐近似，我们系统地研究了二维单层石墨烯、h-BN和石墨烯/h-BN异质结构的电子、声子以及热膨胀性质，计算了三种结构不同振动模式的格林奈森参数，讨论了引起这三种结构负热膨胀的振动模式。计算表明，由于垂直薄膜方向的热振动，石墨烯和h-BN在薄膜面内均具有较大的负热膨胀系数；它们形成的异质结构依靠弱的范德瓦尔斯相互作用结合在一起，这种层间弱相互作用对薄膜垂直方向的热振动产生影响，使得形成的异质结构的负膨胀系数介于石墨烯和h-BN之间。通过分析异质结构的振动模式，发现引起面内热收缩的ZA振动模式受到了层间范德瓦尔斯相互作用影响，导致异质结构的负热膨胀系数大于石墨烯而小于h-BN。我们的研究表明，可以在实验上通过范德瓦尔斯相互作用来改变层状结构材料的负热膨胀性质，从而提高薄膜材料结构和电子性质的热稳定性。

Abstract:: Two dimensional (2D) materials generally exhibit negative thermal expansion (NTE) along the in-plane directions due to the so called "membrane effect"，i.e. the thermal fluctuation in vertical direction. The thermal phenomenon may drastically impact the stability and electronic property of the low dimensional materials. Based on first-principles calculations and qusiharmonic approximation, electronic structures, phonon spectra and expansion property of the two dimensional materials: graphene, h-BN sheet and graphene/h-BN heterostructure are systematically studied. The mode grüneisen parameters are calculated and the vibrational modes which contribute to the NTE in the three systems are discussed. The calculated results show that both graphenen and h-BN exhibit pronounced NTE in the in-plane directions due to the vertical thermal vibration. The graphenen/h-BN heterostructure is formed through van der Waals (vdW) interaction between the monolayer graphene and the h-BN sheet and this weak interaction may influence the vertical thermal vibration of the monolayer graphene and the h-BN sheet, and consequently the thermal contraction of the heterostructure is significant smaller than that of the h-BN, but larger than the graphene. Our results indicate that NTE of the two dimensional materials can be altered through the vdW interactions in experiment and enhance the thermal stability of the stucture and electronic property.