Title: "Understanding Disorder and Electronic Phenomena in Metastable, and Intercalated TMDs"

Daniel Rhodes, Assistant Professor, Materials Science and Engineering

University of Wisconsin-Madison

Host: Kirill Kovnir

Abstract: For much of the last decade, understanding of the disorder in transition metal dichalcogenides has focused heavily on identifying the origin of point defects and grain boundaries. However, in addition to the point-defect-type disorder in stable semiconducting TMDs, there can also be substantial stacking disorder. This is particularly true in intercalated TMDs, which have gained in popularity in recent years. Solving out the layer stacking in weakly bonded materials can be incredibly tedious to the inherent disorder present in these kinds of materials. As a result, typically utilized characterization techniques may not be sufficient for determining the real, average stacking order present in a given crystal. In the first half of this talk, I will discuss how structural heterogeneity captured by single-crystal X-ray diffraction (SCXRD) and scanning transmission electron microscopy (STEM) can elude the routine characterization techniques of powder X-ray diffraction, Raman spectroscopy, and electronic transport measurements in SnxTaSe2. I will also comment on the unusual trend in electronic properties that we observe with as a function of Sn concentration in these compounds. In the second half, I will talk about another intercalated system (in this case K-intercalated), the metastable 2M-WSe2 and WS2 TMDs, the latter of which has been suggested as a topological superconductor candidate. I will discuss both the chemistry of de-intercalating these compounds to realize these metastable structures and the unique electronic phenomena we can obtain from them in both the bulk and few-layer limit.

Bio: Dr. Daniel A. Rhodes is an Assistant Professor of Materials Science and Engineering at the University of Wisconsin–Madison, where he has served since January 2020. His research focuses on the processing, synthesis, and characterization of novel 2D and bulk quantum materials, with particular interest in correlated electronic phases, superconductivity, and multiferroic phenomena. [rhodeslab....r.wisc.edu], [engineering.wisc.edu]

He earned his Ph.D. in Physics from Florida State University, conducting research at the National High Magnetic Field Laboratory on topological and superconducting single crystals. He later completed a postdoctoral appointment at Columbia University with the Columbia Nano Initiative, where he expanded his work on 2D materials. [rhodeslab....r.wisc.edu], [orcid.org]

At UW–Madison, Dr. Rhodes’ group investigates quantum materials, 2D heterostructures, crystal growth, nanofabrication, and magnetotransport phenomena, combining experimental methods to uncover correlated states and defect-driven behavior in emerging materials systems.