Joan Redwing is a professor of materials science and engineering at The Pennsylvania State University and serves as director of the 2D Crystal Consortium, an NSF Materials Innovation Platform (MIP) national user facility for the synthesis of 2D chalcogenides. Redwing received her PhD in chemical engineering from the University of Wisconsin-Madison in 1994, and worked at Advanced Technology Materials Inc. (ATMI) for five years prior to joining The Pennsylvania State University in 2000.
Redwing’s research focuses on crystal growth and epitaxy of electronic materials with an emphasis on thin-film and nanomaterial synthesis by metalorganic chemical vapor deposition (MOCVD). Her work has influenced a range of materials systems including group III-nitrides, MgB2 superconductors, Si/SiGe nanowires, and more recently, 2D layered chalcogenides.
Redwing currently serves as vice president of the American Association for Crystal Growth, is an associate editor for Journal of Crystal Growth, and a regional editor for 2D Materials. She is a Fellow of the Materials Research Society, the American Physical Society, and the American Association for the Advancement of Science. She is an author on over 300 publications in refereed journals and holds eight U.S. patents.
Epitaxial Growth and Properties of Atomically Thin Semiconductors – Moving Beyond Flakes
The field of two-dimensional (2D) materials began with the advent of graphene but has expanded to a wide class of materials that occur naturally as van der Waals crystals. Within this class of materials, transition metal dichalcogenides (TMDs) have attracted significant interest in condensed matter physics and next generation electronics and optoelectronics. At the monolayer limit, the semiconducting TMDs (e.g., MX2 where M = Mo,W and X = S,Se) exhibit direct band gaps within the visible range, large exciton binding energies and spin-valley polarization. Furthermore, TMD monolayers of different composition and twist angle can be stacked to form heterostructures and moiré superlattices with exotic properties.
The ability to fabricate TMD monolayers by exfoliation of bulk crystals using adhesive tape and stamps has made the field accessible to a wide range of researchers. However, current bulk crystals are limited in size and exfoliation of uniform monolayers is challenging, limiting developments in electronics and optoelectronic applications that require large area monolayers.
In this talk, I will discuss the prospects and challenges associated with the epitaxial growth of TMD monolayers and heterostructures for the development of wafer-scale 2D device technologies. Metalorganic chemical vapor deposition is highlighted as a promising approach which enables growth at high temperatures (>700oC) and large chalcogen overpressures which are needed to obtain stoichiometric epitaxial films. The unique aspects of van der Waals epitaxy of TMDs will be presented including the role of substrate defects, steps and surface passivation. Applications for TMD films in flexible electronics and optoelectronics, monolithic 3D integration and photonics will be reviewed.
Steven May, Drexel University
Probing Electronic Degrees of Freedom at Buried Interfaces in Quantum Heterostructures Using Resonant X-Ray Reflectivity
Prineha Narang, Harvard University
Predicting and Controlling the Electronic, Spin and Lattice Degrees of Freedom of Artificial Atoms in Solids