杰纳斯
单层
点反射
凝聚态物理
范德瓦尔斯力
对称性破坏
不对称
材料科学
偶极子
半导体
石墨烯
纳米技术
过渡金属
化学物理
化学
光电子学
物理
分子
有机化学
催化作用
量子力学
生物化学
作者
Ang Lu,Hanyu Zhu,Jun Xiao,Chih‐Piao Chuu,Yimo Han,Ming Hui Chiu,Chun Cheng,Chih Wen Yang,Kung‐Hwa Wei,Yiming Yang,Yuan Wang,Dimosthenis Sokaras,Dennis Nordlund,Peidong Yang,David A. Muller,M. Y. Chou,Xiang Zhang,Lain‐Jong Li
标识
DOI:10.1038/nnano.2017.100
摘要
Structural symmetry-breaking plays a crucial role in determining the electronic band structures of two-dimensional materials. Tremendous efforts have been devoted to breaking the in-plane symmetry of graphene with electric fields on AB-stacked bilayers or stacked van der Waals heterostructures. In contrast, transition metal dichalcogenide monolayers are semiconductors with intrinsic in-plane asymmetry, leading to direct electronic bandgaps, distinctive optical properties and great potential in optoelectronics. Apart from their in-plane inversion asymmetry, an additional degree of freedom allowing spin manipulation can be induced by breaking the out-of-plane mirror symmetry with external electric fields or, as theoretically proposed, with an asymmetric out-of-plane structural configuration. Here, we report a synthetic strategy to grow Janus monolayers of transition metal dichalcogenides breaking the out-of-plane structural symmetry. In particular, based on a MoS2 monolayer, we fully replace the top-layer S with Se atoms. We confirm the Janus structure of MoSSe directly by means of scanning transmission electron microscopy and energy-dependent X-ray photoelectron spectroscopy, and prove the existence of vertical dipoles by second harmonic generation and piezoresponse force microscopy measurements.
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