Differentiating Polymorphs in Molybdenum Disulfide via Electron Microscopy

• Published in: Advanced materials (Weinheim) Vol. 30; no. 47; pp. e1802397 - n/a
• Main Authors: Zhao, Xiaoxu, Ning, Shoucong, Fu, Wei, Pennycook, Stephen J., Loh, Kian Ping
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 01.11.2018
• Subjects: atomic edges; Atomic structure; Catalysis; Chemical vapor deposition; Epitaxial growth; Magnetic properties; Microscopy; Molecular beam epitaxy; Molybdenum; Molybdenum disulfide; Optical properties; Organic chemistry; phase engineering; phase identification; Polytypes; Scanning electron microscopy; Scanning transmission electron microscopy; Spatial resolution; Transmission electron microscopy; atomic edges; molybdenum disulfide; phase engineering; phase identification; scanning transmission electron microscopy
• ISSN: 0935-9648; 1521-4095; 1521-4095
• DOI: 10.1002/adma.201802397

The presence of rich polymorphs and stacking polytypes in molybdenum disulfide (MoS2) endows it with a diverse range of electrical, catalytic, optical, and magnetic properties. This has stimulated a lot of interest in the unique properties associated with each polymorph. Most techniques used for polymorph identification in MoS2 are macroscopic techniques that sample averaged properties due to their limited spatial resolution. A reliable way of differentiating the atomic structure of different polymorphs is needed in order to understand their growth dynamics and establish the correlation between structure and properties. Herein, the use of electron microscopy for identifying the atomic structures of several important polymorphs in MoS2, some of which are the subjects of mistaken assignment in the literature, is discussed. In particular, scanning transmission electron microscopy‐annular dark field imaging has emerged as the most effective and reliable approach for identifying the different phases in MoS2 and other 2D materials because its images can be directly correlated to the atomic structures. Examples of the identification of polymorphs grown under different conditions in molecular beam epitaxy or chemical vapor deposition, for example, 3R, 1T, 1T′‐phases, and 1T′‐edges, are presented, including their atomic structures, fascinating properties, growth methods, and corresponding thermodynamic stabilities. The presence of rich polymorphs and stacking polytypes in molybdenum disulfide (MoS2) endows it with a diverse range of properties. This has stimulated great interest in the unique properties associated with each polymorph. The use of electron microscopy for identifying the atomic structures of several important polymorphs in MoS2 is discussed and the correlation between structure and properties is established.