Strain-mediated stability and electronic properties of WS2, Janus WSSe and WSe2 monolayers
Strain-mediated stability and electronic properties of WS2, Janus WSSe and WSe2 monolayers
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DOI：
10.1016/j.spmi.2018.07.039
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发表时间：
2018-10-01
影响因子：
3.1
通讯作者：
Pandey, Ravindra
中科院分区：
文献类型：
--
作者：
Chaurasiya, Rajneesh;Dixit, Ambesh;Pandey, Ravindra
单层过渡金属二硫化物（TMD）已被提议作为纳米级器件的下一代电子材料。我们使用密度泛函方法评估了 WS2、Janus WSSe 和 WSe2 单层在双轴拉伸和压缩应变下的热力学稳定性。无应变 WS2、WSSe 和 WSe2 单层的声子能带结构证实了它们的热力学稳定性。研究了这些单分子层在应变下的稳定性，并在高达 8% 拉伸应变的声学和光学模式下观察到声子软化。压缩应变下键长的减小导致面外变形，导致单分子层在压缩应变下不稳定。键长 W-S (Se) 和键角 W-S(Se)-W 对过渡金属 d 轨道和硫属 p 轨道之间介导电子特性的耦合强度表现出显着贡献。自旋轨道耦合对无应变单层的价带分裂表现出强烈的影响。价带中的自旋分裂随着拉伸应变的增加而增加，并随着压缩应变的增加而减少。有效质量和迁移率值为0.57m(e)、0.54m(e)、0.47m(e)；对于无应变的 WS2、WSSe 和 WSe2 单层，分别为 0.059、0.062、0.072 m(2)V(-1)s(-1)。钨 d(x2-y2) 轨道主要有助于压缩应变单层中的导带和价带电子态。相反，在拉伸应变下，钨 d(z2) 轨道有助于导带和价带电子态，导致这些单层中的直接带隙跃迁到间接带隙。我们观察到，与压缩应变相比，拉伸应变的影响更为敏感。
Monolayers of transition metal dichalcogenides (TMDs) have been proposed as the next generation electronic materials for nanoscale devices. We evaluated the thermodynamic stability of WS2, Janus WSSe and WSe2 monolayers under biaxial tensile and compressive strain using density functional approach. The phonon band structures of unstrained WS2, WSSe and WSe2 monolayers confirm their thermodynamic stability. The stability of these monolayers is investigated under strain and phonon softening is observed for acoustic and optical mode upto 8% tensile strain. The bond length reduction under compressive strain resulted in out of plane deformation, leading the instability of monolayers under compressive strain. The bond length W-S (Se) and bond angle W-S(Se)-W exhibit significant contribution in coupling strength between transition metal d-orbitals and chalcogen p-orbitals that mediated the electronic properties. The spin orbit coupling showed strong effect on splitting of the valence band for unstrained mono-layers. The spin splitting in valence band increases with increasing the tensile strain and decreases with increasing the compressive strain. The effective masses and mobility values are 0.57m(e), 0.54m(e), 0.47m(e); and 0.059, 0.062, 0.072 m(2)V(-1)s(-1) for unstrained WS2, WSSe and WSe2 monolayers, respectively. The tungsten d(x2-y2) orbitals are mainly contributing to the conduction and valence band electronic states in compressive strained monolayers. In contrast under tensile strain tungsten d(z2) orbitals contribute to conduction and valence band electronic states, causing the direct to indirect band gap transition in these monolayers. We observed that the impact of tensile strain is more sensitive as compared to that of compressive strain.