层状二硫化钼研究进展

Recent progress of two-dimensional layered molybdenum disulfide

近年来,层状二硫化钼由于其特殊的类石墨烯结构和独特的物理化学性质已成为国内外研究的热点.本文综述了层状二硫化钼的物理结构、价带结构和光学性质;介绍了制备方法,包括生长制备和剥离制备.生长制备的原料包括四硫代钼酸铵((NH4)_2MoS_4)、钼(Mo)和三氧化钼(MoO_3)等.剥离制备包括微机械剥离、液相超声法、锂离子插层法和电化学锂离子插层法等.归纳了层状二硫化钼在场效应晶体管、传感器和存储方面的应用,展望了层状二硫化钼的研究前景.

Recently, two-dimensional（2D） layered molybdenum disulfide（Mo S_2） has attracted great attention because of its graphene-like structure and unique physical and chemical properties. In this paper, physical structure, band gap structure, and optical properties of Mo S_2 are summarized. Mo S_2 is semiconducting and composed of covalently bonded sheets held together by weak van der Waals force. In each Mo S_2 layer, a layer of molybdenum（Mo） atoms is sandwiched between two layers of sulfur（S） atoms. There are three types of Mo S_2 compounds, including 1T Mo S_2, _2H Mo S_2, and3 R Mo S_2. As the number of layers decreases, the bad gap becomes larger. The bad gap transforms from indirect to direct as Mo S_2 is thinned to a monolayer. Changes of band gap show a great potential in photoelectron. Preparation methods of 2D Mo S_2 are reviewed, including growth methods and exfoliation methods. Ammonium thiomolybdate（NH4）_2Mo S4, elemental molybdenum Mo and molybdenum trioxide Mo O3 are used to synthesize 2D Mo S_2 by growth methods.（NH4）_2Mo S4 is dissolved in a solution and then coated on a substrate.（NH4）_2Mo S4 is decomposed into Mo S_2 after annealing at a high temperature. Mo is evaporated onto a substrate, and then sulfurized into Mo S_2. Mo O3 is most used to synthesize Mo S_2 on different substrates by a chemical vapor deposition or plasma-enhanced chemical vapor deposition. Other precursors like Mo（CO）6, Mo S_2 and Mo Cl5 are also used for Mo S_2 growth. For the graphene-like structure, monolayer Mo S__2 can be exfoliated from bulk Mo S_2. Exfoliation methods include micromechanical exfoliation,liquid exfoliation, lithium-based intercalation and electrochemistry lithium-based intercalation. For micromechanical exfoliation, the efficiency is low and the sizes of Mo S_2 flakes are small. For liquid exfoliation, it is convenient for operation to obtain mass production, but the concentration of monolayer Mo S_2 is low. For lithium-based intercalation,the yield of monolayer Mo S_2 is high while it takes a long time and makes _2H Mo S_2 transform to 1T Mo S_2 in this process. For electrochemistry lithium-based intercalation, this method saves more time and achieves higher monolayer Mo S_2 yield, and annealing makes 1T Mo S_2 back to _2H Mo S_2. The applications of 2D Mo S_2 in field-effect transistors,sensors and memory are discussed. On-off ratio field effect transistor based on Mo S_2 has field-effect mobility of several hundred cm_2·V-1·s-1and on/off ratio of 108 theoretically.