Atomic-Scale Investigation of 2D Films and Flakes

Ever since the discovery of graphene, two-dimensional (2D) materials have captivated the scientific community. Their unique properties stem from their unusual combination of covalent and van der Waals bonding, as well as the fact that they can be as thin as a single atom and can be integrated into heterostructures or devices. Numerous properties of 2D materials have been demonstrated to depend on thickness, and because they are so thin, atomic-scale defects can play a very important role. This presentation will feature atomic-scale characterization of ultrathin 2D films grown via metal–organic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE), as well as bulk crystals that have been thinned via mechanical exfoliation. We will explore how grains in films have merged, drawing connections between how films are grown and the defects and defect arrays that result. We will also show examples of how features such as thickness and point defects can be readily identified using machine learning and discuss how key information can be extracted by multiple methods. We will focus on tungsten-based chalcogenides (e.g., WS₂, WTe₂) and then extend the discussion to other systems, including heterostructures.