Tuning the Electronic Properties of Semiconducting Transition Metal Dichalcogenides by Applying Mechanical Strains
Tuning the Electronic Properties of Semiconducting Transition Metal Dichalcogenides by Applying Mechanical Strains
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DOI：
10.1021/nn301320r
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发表时间：
2012-06-01
期刊：
影响因子：
17.1
通讯作者：
Shenoy, Vivek B.
中科院分区：
文献类型：
--
作者：
Johari, Priya;Shenoy, Vivek B.
半导体过渡金属二硫属化物（TMD）正在成为石墨烯的潜在替代品。与石墨烯一样，TMD 的单层可以使用机械或化学方法轻松剥离，并且它们的性能也可以调整。同时，半导体TMD（MX2；M = Mo、W，X = S、Se、Te）比石墨烯具有优势，因为它们表现出的带隙大小适合光电器件的应用。通过从头算模拟，我们证明了可以通过施加机械应变来广泛调整该带隙。虽然石墨烯的电子特性几乎不受拉伸应变的影响，但我们发现 TMD 对拉伸应变和剪切应变都很敏感。此外，与石墨烯相比，改变TMD的带隙所需的应变量要小得多。我们的结果表明，机械应变降低了半导体 TMD 的带隙，导致直接带隙到间接带隙以及半导体到金属的转变。然而，这些转变很大程度上取决于所施加的应变的类型和硫族化物原子的类型。较重的多族化物的扩散性质需要相对较大的拉伸和较小的剪切应变（当单层在 y 方向膨胀并在 x 方向压缩时）以获得直接到间接带隙转变。此外，我们的结果表明，约 10% 的均匀双轴拉伸应变会导致所有半导体 TMD 中的半导体到金属的转变，而通过纯剪切应变，这种转变只能通过分别在 y 和 x 方向上扩展和压缩 MTe2 单层来实现。我们的结果通过说明应变对从 MS2 到 MSe2 再到 MTe2 的重大影响，强调了拉伸应变和纯剪切应变在调节 TMD 电子特性方面的重要性。
Semiconducting transition metal dichalcogenides (TMDs) are emerging as the potential alternatives to graphene. As in the case of graphene, the monolayer of TMDs can easily be exfoliated using mechanical or chemical methods, and their properties can also be tuned. At the same time, semiconducting TMDs (MX2; M = Mo, W and X = S, Se, Te) possess an advantage over graphene in that they exhibit a band gap whose magnitude is appropriate for applications in the opto-electronic devices. Using ab initio simulations, we demonstrate that this band gap can be widely tuned by applying mechanical strains. While the electronic properties of graphene remain almost unaffected by tensile strains, we find TMDs to be sensitive to both tensile and shear strains. Moreover, compared to that of graphene, a much smaller amount of strain is required to vary the band gap of TMDs. Our results suggest that mechanical strains reduce the band gap of semiconducting TMDs causing an direct-to-indirect band gap and a semiconductor-to-metal transition. These transitions, however, significantly depend on the type of applied strain and the type of chalcogenide atoms. The diffuse nature of heavier dolcogenides require relatively more tensile and less shear strain (when the monolayer is expanded in y-direction and compressed in x-direction) to attain a direct-to-indirect band gap transition. In addition, our results demonstrate that the homogeneous biaxial tensile strain of around 10% leads to semiconductor-to-metal transition in all semiconducting TMDs, while through pure shear strain this transition can only be achieved by expanding and compressing the monolayer of MTe2 in the y- and x-directions, respectively. Our results highlight the importance of tensile and pure shear strains in tuning the electronic properties of TMDs by illustrating a substantial impact of the strain on going from MS2 to MSe2 to MTe2.