Department of Mechanical Engineering , Iowa State University , Ames , Iowa 50011 , United States.
Department of Mechanical Engineering & Mechanics , Lehigh University , Bethlehem , Pennsylvania 18015 , United States.
Langmuir. 2018 Mar 13;34(10):3326-3335. doi: 10.1021/acs.langmuir.7b03974. Epub 2018 Feb 27.
The thermal conductivity of the graphene-encapsulated MoS (graphene/MoS/graphene) van der Waals heterostructure is determined along the armchair and zigzag directions with different twist angles between the layers using molecular dynamics (MD) simulations. The differences in the predictions relative to those of the monolayers are analyzed using the phonon power spectrum and phonon lifetimes obtained by spectral energy density analysis. The thermal conductivity of the heterostructure is predominantly isotropic. The out-of-plane phonons of graphene are suppressed because of the interaction between the adjacent layers that results in the reduced phonon lifetime and thermal conductivity relative to monolayer graphene. The occurrence of an additional nonzero phonon branch at the Γ point in the phonon dispersion curves of the heterostructure corresponds to the breathing modes resulting from stacking of the layers in the heterostructure. The thermal sheet conductance of the heterostructure being an order of magnitude larger than that of monolayer MoS, this van der Waals material is potentially suitable for efficient thermal packaging of photoelectronic devices. The interfacial thermal conductance of the graphene/MoS bilayer as a function of the heat flow direction shows weak thermal rectification.
采用分子动力学（MD）模拟方法，沿扶手椅和锯齿方向，在不同层间扭转角下，确定了石墨烯封装的 MoS（石墨烯/MoS/石墨烯）范德华异质结构的热导率。利用声子能谱和谱能量密度分析得到的声子寿命，分析了相对单层预测的差异。异质结构的热导率主要是各向同性的。由于相邻层之间的相互作用，石墨烯的面外声子被抑制，导致声子寿命和热导率相对于单层石墨烯降低。在异质结构的声子色散曲线中，Γ 点处出现了一个额外的非零声子分支，这对应于异质结构中堆叠层的呼吸模式。由于异质结构的热面电导比单层 MoS 大一个数量级，这种范德华材料有望成为光电设备高效热封装的理想选择。作为热流方向函数的石墨烯/ MoS 双层界面热导呈现出较弱的热整流。
