Two-Dimensional Alloying Molybdenum Tin Disulfide Monolayers with Fast Photoresponse.

Elemental alloying in monolayer, two-dimensional (2D) transition metal dichalcogenides (TMDs) promises unprecedented ability to modulate their electronic structure leading to unique optoelectronic properties. MoS2 monolayer based photodetectors typically exhibit a high photoresponsivity but suffer from a low response time. Here we develop a new approach for Sn alloying in MoS2 monolayers based on the synergy of the customized chemical vapor deposition (CVD) and the effects of common salt (NaCl) to produce high-quality and large-size Mo1-xSnxS2 (x < 0.5) alloy monolayers. The composition difference results in different growth behaviors; Mo dominated alloys (x < 0.5) exhibit uniform and large size (up to 100 µm) triangular monolayers, while Sn-dominated alloys (x > 0.5) present multilayer grains. The Mo1-xSnxS2 (x < 0.5) based photodetectors and phototransistors exhibit a maximum responsitivity of 12 mA/W and a minimum response time of 20 ms, which is faster than most reported MoS2-based photodetectors. This work offers new perspectives for precision 2D alloy engineering to improve the optoelectronic performance of TMD-based photodetectors.

Controllable one-step growth of bilayer MoS2-WS2/WS2 heterostructures by chemical vapor deposition.

Heterostructures of two-dimensional (2D) transition metal dichalcogenides (TMDs) offer attractive prospects for practical applications by combining unique physical properties that are distinct from those of traditional structures. In this paper, we demonstrate a three-stage chemical vapor deposition method for the growth of bilayer MoS2-WS2/WS2 heterostructures with the bottom layers being the lateral MoS2-center/WS2-edge monolayer heterostructures and the top layers being the WS2 monolayers. The alternative growth of lateral and vertical heterostructures can be realized by adjusting both the temperature and the carrier gas flow direction. The combined effect of both reverse gas flow and higher growing temperature can promote the epitaxial growth of second layer on the activated nucleation centers of the first monolayer heterostructures. By using customized temperature profiles, single heterostructures including monolayer lateral MoS2-WS2 heterostructures and bilayer lateral WS2(2L)-MoS2(2L) heterostructures could also be obtained. Atomic force microscopy, photoluminescence and Raman mapping studies clearly reveal that these different heterostructure samples are highly uniform. These results thus provide a promising and efficient method for the synthesis of complex heterostructures based on different TMDs materials, which would greatly expand the heterostructure family and broaden their applications.