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Janus monolayers of transition metal dichalcogenides

2017; Nature Portfolio; Volume: 12; Issue: 8 Linguagem: Inglês

10.1038/nnano.2017.100

1748-3395

Ang‐Yu Lu, Hanyu Zhu, Jun Xiao, Chih‐Piao Chuu, Yimo Han, Ming‐Hui Chiu, Chia-Chin 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,

Quantum Dots Synthesis And Properties

A novel synthetic approach makes it possible to grow MoS2 monolayers where S is fully replaced with Se atoms only in the top layer. 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 bilayers1,2 or stacked van der Waals heterostructures3,4. 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 optoelectronics5,6. 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 fields7,8 or, as theoretically proposed, with an asymmetric out-of-plane structural configuration9. 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.