Colloquium Series: Joan Redwing (Penn State)

Join us for another event in the 2018-2019 Colloquium Series as APS welcomes Joan Redwing, Ph.D. to present on her recent research. Dr. Redwing is currently a Professor of Materials Science and Engineering, Chemical Engineering, and Electrical Engineering at Penn State. Her group’s “research is carried out in a collaborative, interdisciplinary environment that spans several academic disciplines including Materials Science and Engineering, Electrical Engineering and Chemical Engineering.”

Epitaxy of 2D Materials: Challenges and New Approaches

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 the substrate, 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 demonstrated the formation of ultra-thin GaNx 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.