A progressive metal-semiconductor transition in two-faced Janus monolayer transition-metal chalcogenides

• Published in: Physical chemistry chemical physics : PCCP 2018-08, Vol.2 (32), p.21113-21118
• Main Authors: Guo, Yan-Dong, Zhang, Hong-Bo, Zeng, Hong-Li, Da, Hai-Xia, Yan, Xiao-Hong, Liu, Wen-Yue, Mou, Xin-Yi
• Format: Article
• Language: English
• Subjects: Asymmetry; Chalcogenides; Electronic properties; Electronic structure; First principles; Molybdenum compounds; Molybdenum oxides; Monolayers; Parents; Semiconductors; Tellurides
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c8cp02929f

Breaking the symmetry in the out-of-plane direction in two-dimensional materials to trigger distinctive electronic properties has long been predicted. Inspired by the recent progress in the experimental synthesis of a sandwiched S-Mo-Se structure (Janus SMoSe) at the monolayer limit [Zhang et al. , ACS Nano , 2017, 11 , 8192-8198], we investigate the transport and electronic structure of two-faced XMoY monolayers (X, Y = O, S, Se and Te) through first-principles calculations. It is found that all the monolayers are semiconductors except OMoTe, which is metallic. Interestingly, the "parents" of OMoTe (MoO 2 and MoTe 2 ) are both semiconductors. Further analysis shows that it is the out-of-plane asymmetry-induced strain that results in the metal-semiconductor transition between Janus OMoTe and its parents. By increasing the ratio of O atoms in one face of MoTe 2 , a progressive decreasing trend of the bandgap, as well as the transition to metallic, is found. In addition, a transition from the direct band gap semiconductor to the indirect one is also observed in the process. This could be used as an effective way to precisely control electronic structures, e.g. , the bandgap. Different from other methods, this method uses the intrinsic features of the material, which can persist without the need of additional equipment. Moreover, such a modulating method is expected to be extended to many other transition-metal chalcogenides, showing great application potential. The bandgap of two-faced monolayer O n /8 MoTe 2− n /8 decreases progressively as n increases from left to right, and finally converts to metallic.