The spectrum of two-dimensional (2D) materials "beyond graphene" has been continually expanding driven by the compelling properties of monolayer films compared to their bulk counterparts. Device applications, however, require the ability to deposit single crystal 2D films over large areas necessitating the use of epitaxy techniques to control film orientation. Our studies have primarily focused on the epitaxial growth of layered transition metal dichalcogenide (TMD) films, including WSe2, WS2 and MoS2, by gas source chemical vapor deposition (CVD) on sapphire, hexagonal boron nitride and other single crystal substrates. Gas source CVD provides excellent control of the precursor partial pressure enabling control over nucleation density, lateral growth rate and film composition for the layer-by-layer growth of 2D films and heterostructures. Our studies are aimed at understanding the fundamental growth mechanisms of layered TMDs including the role of precursor chemistry, gas phase and surface diffusion and 2D crystal edge termination on monolayer growth. In addition to layered chalcogenide epitaxy, we are also investigating unconventional approaches to 2D materials synthesis including intercalation and chemical conversion within the van der Waals gap of epitaxial graphene formed on SiC. Using this approach, we recently demonstrated the formation of ultra-thin Ga2N3, a direct gap semiconductor with a bandgap energy in the range of 4.8-4.9 eV. Prospects for using graphene-encapsulated growth for the synthesis of other 2D materials will also be discussed.
Joan M. Redwing received her Ph.D. in Chemical Engineering from the University of Wisconsin-Madison in 1994. After working as a research engineer at Advanced Technology Materials Inc., she joined the faculty of the Department of Materials Science and Engineering at Penn State University in 1999. She currently serves as director of the 2D Crystal Consortium, an NSF-supported Materials Innovation Platform. Her research focuses on understanding fundamental mechanisms of crystal growth and epitaxy of electronic materials, with a particular emphasis on thin film and nanomaterial synthesis by chemical vapor deposition. Dr. Redwing currently serves as vice president of the American Association for Crystal Growth and is an associate editor for the Journal of Crystal Growth. She is a fellow of the Materials Research Society, the American Physical Society and the American Association for the Advancement of Science and is a senior member of IEEE. She is an author or co-author on over 270 publications in refereed journals and holds 8 U.S. patents.