(3) Zeeman-like spin splitting is nearly intact by a vertical electric field in ML MoS 2 but it becomes tunable in BL MoS 2 because top and bottom MoS 2 feel different electric potentials 16. By contrast, inversion symmetric BL MoS 2 is not a VHI, but it can be transformed into a VHI with a tunable valley magnetic moment by a vertical electric field, which destroys the inversion symmetry 5. (2) ML MoS 2 is inversion asymmetric and serves as an ideal valley Hall insulator (VHI) 1. Correspondingly, photoluminescence is dramatically enhanced in ML MoS 2 6, 20. They show quite interesting differences and make up a pair of complementary materials: (1) ML MoS 2 has a larger direct band gap, while BL MoS 2 possesses a smaller indirect band gap due to the strong interlayer coupling. Very recently, wafer-scale high performance 2D MoS 2 FETs have been fabricated in batch mode, paving the way towards atomically thin integrated circuitry 19. A variety of prototype devices based on 2D MoS 2 have been fabricated, such as field-effect transistors (FETs) 7, 8, 9, inverters 10, fully integrated circuits 11, sensors 12, photoelectronic devices 13, phototransistors 14, 15, spintronic devices 16, and valleytronic devices 17, 18. Owing to their excellent properties, two-dimensional (2D) molybdenum disulfide MoS 2 has attracted much recent attention 1, 2, 3, 4, 5, 6. BL MoS 2-metal contacts generally have a reduced SBH than ML MoS 2-metal contacts due to the interlayer coupling and thus have a higher electron injection efficiency. By contrast, an ab initio quantum transport device simulation better reproduces the observed SBH in 2D MoS 2-Sc interface and highlights the importance of a higher level theoretical approach beyond the energy band calculation in the interface study. The extensively adopted energy band calculation scheme fails to reproduce the observed SBHs in 2D MoS 2-Sc interface. A comparison between the calculated and observed Schottky barrier heights (SBHs) suggests that many-electron effects are strongly suppressed in channel 2D MoS 2 due to a charge transfer. We provide a comprehensive ab initio study of the interfacial properties of a series of monolayer (ML) and bilayer (BL) MoS 2-metal contacts (metal = Sc, Ti, Ag, Pt, Ni, and Au). Although many prototype devices based on two-dimensional (2D) MoS 2 have been fabricated and wafer scale growth of 2D MoS 2 has been realized, the fundamental nature of 2D MoS 2-metal contacts has not been well understood yet.
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