![]() Liquid-phase exfoliation can also be used to produce monolayer to multi-layer MoS 2 in solution. While Scotch tape is generally used as the adhesive tape, PDMS stamps can also satisfactorily cleave MoS 2 if it is important to avoid contaminating the flakes with residual adhesive. The aforementioned scheme is good for graphene only. However, it can not be employed for a uniform 1-D layers because of weaker adhesion of MoS 2 to the substrate (either Si, glass or quartz). This facile method was first used by Konstantin Novoselov and Andre Geim to obtain graphene from graphite crystals. The crystal flakes can then be transferred from the adhesive film to a substrate. Micromechanical exfoliation, also pragmatically called " Scotch-tape exfoliation", involves using an adhesive material to repeatedly peel apart a layered crystal by overcoming the van der Waals forces. 2D MoS 2 can be produced by exfoliating bulk crystals to produce single-layer to few-layer flakes either through a dry, micromechanical process or through solution processing. The layer-dependent optoelectronic properties of MoS 2 have promoted much research in 2-dimensional MoS 2-based devices. While bulk MoS 2 in the 2H-phase is known to be an indirect-band gap semiconductor, monolayer MoS 2 has a direct band gap. Nanotube-like and buckyball-like molecules composed of MoSĢ are known. The 2H/1T-phase transition can be controlled via the incorporation of S vacancies. The 1T-phase can be stabilized through doping with electron donors such as rhenium, or converted back to the 2H-phase by microwave radiation. This phase has tetragonal symmetry and is metallic. ![]() Ī third, metastable crystalline phase known as 1T-MoS 2 was discovered by intercalating 2H-MoS 2 with alkali metals. ![]() Both the 2H- and 3R-phases are semiconducting. Each sulfur atom has pyramidal coordination and is bonded to three molybdenum atoms. In both of these structures, each molybdenum atom exists at the center of a trigonal prismatic coordination sphere and is covalently bonded to six sulfide ions. Bulk MoS 2 consists of stacked monolayers, which are held together by weak van der Waals interactions.Ĭrystalline MoS 2 exists in one of two phases, 2H-MoS 2 and 3R-MoS 2, where the "H" and the "R" indicate hexagonal and rhombohedral symmetry, respectively. These three strata form a monolayer of MoS 2. Crystalline phases Ģ have a layered structure, in which a plane of molybdenum atoms is sandwiched by planes of sulfide ions. Structure and physical properties Electron microscopy of antisites (a, Mo substitutes for S) and vacancies (b, missing S atoms) in a monolayer of molybdenum disulfide. Molybdenite ore is processed by flotation to give relatively pure MoSĢ also arises by thermal treatment of virtually all molybdenum compounds with hydrogen sulfide or elemental sulfur and can be produced by metathesis reactions from molybdenum pentachloride. MoS 2 is naturally found as either molybdenite, a crystalline mineral, or jordisite, a rare low temperature form of molybdenite. Bulk MoSĢ is a diamagnetic, indirect bandgap semiconductor similar to silicon, with a bandgap of 1.23 eV. It is widely used as a dry lubricant because of its low friction and robustness. In appearance and feel, molybdenum disulfide is similar to graphite. It is unaffected by dilute acids and oxygen. It is a silvery black solid that occurs as the mineral molybdenite, the principal ore for molybdenum. The compound is classified as a transition metal dichalcogenide. Molybdenum disulfide (or moly) is an inorganic compound composed of molybdenum and sulfur.
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