Scanning Transmission Electron Microscope (STEM) Characterization of Structures and Defects of Air-Stable Novel 2D van der Waals Magnets

van der Waals 2D magnetic materials have emerged as a novel platform that offer unique optoelectronic, magnetic, and quantum properties.¹ This low-dimensional spin system has vast potential in applications such as spintronics and nanoscale magnetic devices. Therefore, being able to engineer the structure and defects with respect to magnetic, optical, and electronic properties is critical. For example, an optically active single defect may have potential as a quantum emitter interacting with and embedded in the novel magnetic environment. Air-stable 2D van der Waals magnets are relatively unexplored making the study of such materials intriguing and helpful for both fundamental research and device design.<br/>Here, we exfoliate novel 2D magnets, specifically transition metal phosphorus trichalcogenides (MPX₃) in atmosphere down to mono- and few-layers and encapsulate them in hexagonal boron nitride (hBN). We image the structure of the 2D magnetic material in a scanning transmission electron microscope (STEM) with atomic resolution. We then modify the material using STEM electron probe patterning and/or controlled helium ion irradiation to create and explore different types of point defects, their local structure and concentration, and potential structural transitions arising from the defect introduction. Theoretical and computational modelling is performed to predict the structure and type of defects. Lastly, we relate the calculations to the results we obtain from STEM imaging to establish the fundamental properties of defects in these novel air-stable 2D magnetic materials as a basis for future control and application of magnetic and optical properties.<br/><br/><b>References </b><br/>1. Gibertini, M., Koperski, M., Morpurgo, A. F. <i>et al. </i>Magnetic 2D materials an heterostructures. <i>Nat. Nanotechnol. </i><b>14</b>, 408-129 (2019).