Molybdenum disulfide (MoS 2 ) with excellent properties has been widely reported in recent years. However, it is a great challenge to achieve p-type conductivity in MoS 2 because of its native stubborn n-type conductivity. Substitutional transition metal doping has been proved to be an effective approach to tune their intrinsic properties and enhance device performance. Herein, we report the growth of Nb-doping large-area monolayer MoS 2 by a one-step salt-assisted chemical vapor deposition method. Electrical measurements indicate that Nb doping suppresses ntype conductivity in MoS 2 and shows an ambipolar transport behavior after annealing under the sulfur atmosphere, which highlights the p-type doping effect via Nb, corresponding to the density functional theory calculations with Fermi-level shifting to valence band maximum. This work provides a promising approach of two-dimensional materials in electronic and optoelectronic applications.

Black phosphorus, a promising two-dimensional material to be widely used in many areas of electronics and optoelectronics, can be prepared traditionally by high pressure or fast low-pressure transport routes. However, there lacks a general understanding of the growth mechanism and it often suffers from poor yield and high cost. In this paper, we developed a facile method to synthesize large-scale black phosphorus micro-ribbons, significantly decreasing its cost and increasing its yield, and then it can commercially produce black phosphorus. The growth process of black phosphorus micro-ribbons has been investigated systematically and its growth mechanism has been speculated, which opens up the possible opportunity to directly grow black phosphorus micro-belts even few-layered nanobelts by adjusting the growth conditions. In addition, ribbon-like few-layered black phosphorus with large area can be easily exfoliated from the grown micro-ribbons because of their smooth and large area of the cleavage plane. The ribbon-like few-layered phosphorus is beneficial to investigate the anisotropic properties of black phosphorus.

We introduce a metal-assisted exfoliation method to produce few-layer black phosphorus with the lateral size larger than 50 μm and the area 100 times larger than those exfoliated using the normal "scotch-tape" technique. Using a field effect transistor it was found the hole mobility is 68.6 cm V s and the current on/off ratio can reach about 2 × 10.

The growth of high-quality black phosphorus crystals is very important to further study the physical properties of two-dimensional black phosphorus exfoliated from bulk crystals. Herein, we designed a series of experiments to fully understand the growth of black phosphorus crystals and then explore the roles of metals (or alloys) and I elements in its growth process. Finally, we developed a general approach to grow black phosphorus in high yield with high quality and low cost. The work introduced here sheds light on the growth mechanism of black phosphorus crystals and opens up the possibility of the growth of black phosphorus thin film.