Transition Metal Dichalcogenides and Beyond: Synthesis,Properties, and Applications of Single- and Few-Layer Nanosheets.

In the wake of the discovery of the remarkable electronic and physicalproperties of graphene, a vibrant research area on two-dimensional(2D) layered materials has emerged during the past decade. Transitionmetal dichalcogenides (TMDs) represent an alternative group of 2Dlayered materials that differ from the semimetallic character of graphene.They exhibit diverse properties that depend on their composition andcan be semiconductors(e.g., MoS2, WS2), semimetals(e.g., WTe2, TiSe2), true metals(e.g., NbS2, VSe2), and superconductors(e.g., NbSe2, TaS2). The properties of TMDs can also be tailored accordingto the crystalline structure and the number and stacking sequenceof layers in their crystals and thin films. For example, 2H-MoS2is semiconducting, whereas 1T-MoS2is metallic. Bulk 2H-MoS2possessesan indirectband gap, but when 2H-MoS2is exfoliated into monolayers, it exhibits directelectronic and optical band gaps, which leads to enhanced photoluminescence.Therefore, it is important to learn to control the growth of 2D TMDstructures in order to exploit their properties in energy conversionand storage, catalysis, sensing, memory devices, and other applications. [ABSTRACT FROM AUTHOR]