Comprehensive summary of the progress including crystal structures, fabrication methods, applications (especially for electronics) and functionalization of 2D-hBN from its discovery.

Two-dimensional (2D) materials play more and more important roles these days, due to their broad applications in many areas. Herein, we propose an optically-pumped terahertz (THz) modulator, based on Si-grown MoS₂ nanosheets. The broadband modulation effect has been proved by THz time domain spectroscopy and numerical simulation. The modulation depth of this Si-grown MoS₂ nanosheet can reach over 75% under the low pumping power of 0.24 W cm⁻², much deeper than that of bare silicon. By theoretical models and simulation, it is proved that the broadband modulation effect can be described as a free carrier absorption for THz waves in the Drude form. Importantly, by a catalyst mechanism in the Si-grown MoS₂, it is concluded that the MoS₂–Si heterostructure enables the MoS₂ to catalyze more carriers generated on the Si surface. This novel 2D material has a high effective modulation on THz waves under a low pumping power density, which affords it a promising potential in THz applications.

A Janus MoSSe monolayer, synthesized recently though the chemical vapor deposition method [A. Y. Lu, H. Zhu, J. Xiao, C. P. Chuu, Y. Han, M. H. Chiu, C. C. Cheng, C. W. Yang, K. H. Wei Y. Yang, Y. Wang, D. Sokaras, D. Nordlund, P. Yang, D. A. Muller, M. Y. Chou, X. Zhang and L. J. Li, Nat. Nanotechnol., 2017, 12, 744–749], has drawn considerable attention as a new two-dimensional (2D) material owing to its fascinating electronic and optical properties. In this study, based on first-principles calculations, we systematically explore for the first time the performance of Janus MoSSe monolayers as a channel material contacting with graphene to form van der Waals (vdW) heterostructures. Our calculations show that the intrinsic electronic properties of both the graphene and MoSSe monolayer are preserved well in our proposed two graphene/MoSSe heterostructures (i.e. G/SMoSe and G/SeMoS heterostructures), and n-type Schottky contacts with a small Schottky barrier height (SBH) are formed at their respective interfaces. An analytical model is presented for the barrier heights. Moreover, the n-type Schottky barrier at the G/SMoSe heterostructure interface can be reduced by increasing the interlayer distance and can even be changed to an Ohmic contact by applying a negative electric field. More interestingly, varying the interlayer distance or applying an external electric field can effectively modulate the Schottky barrier and the Schottky contact (n-type and p-type) of the G/SeMoS heterostructure interface. These theoretical findings not only provide insights into the fundamental properties of the graphene/MoSSe interfaces but also open the possibility of designing high-performance field-effect transistors (FETs) based on the graphene/MoSSe heterostructures.