Dr. Mark D. Ediger seminar
Seminar title: "Highly stable and anisotropic vapor-deposited glasses of organic semiconductors"
Abstract:
Glasses are generally regarded as disordered and the idea of “controlling” molecular packing in glasses is reasonably met with skepticism. However, as glasses are non-equilibrium materials, a vast array of amorphous structures are possible in principle. Physical vapor deposition (PVD) produces glasses with properties that cannot be achieved by other preparation routes, including high stability and controlled anisotropy. The exotic properties of PVD glasses can be explained by a surface equilibration mechanism: mobility near the free surface allows partial equilibration during deposition.
The active layers in commercial OLEDs are PVD glasses of organic semiconductors, and in order to connect with the device community, much of our current work involves organic semiconductors. For these systems, we have shown that highly stable glasses resist crystallization. We can control molecular orientation in both thick films, and the ~10 nm films used in OLEDS. Very recently, we have succeeded in measuring molecular orientation with sub-nm resolution at the interface between two vapor-deposited organic semiconductors. Molecular orientation is important for both charge transport and emission efficiency. These experiments utilize ellipsometry, grazing-incidence x-ray scattering, and polarized soft x-ray reflectivity.
Bio:
Mark Ediger received his Ph.D. from Stanford University in 1984 and moved to the University of Wisconsin-Madison as an assistant professor in the Department of Chemistry. He is currently the Hyuk Yu Professor of Chemistry at UW-Madison. His research is focused on organic glasses, both polymeric and low molecular weight materials. Current research projects include mobility induced in glasses by deformation and the formation of ultrastable and anisotropic glasses by physical vapor deposition. Ediger has served on advisory boards for Macromolecules, the Journal of Polymer Science B: Polymer Physics Edition, and the Journal of Chemical Physics, and is currently an Associate Editor for the Journal of Chemical Physics. He served as Chair of the Polymer Physics Gordon Conference in 2004 and Liquids Gordon Conference in 2013. He received the APS/DPOLY Dillon Medal in 1993 and the ACS Hildebrand Award in 2013, and the APS Polymer Physics Prize in 2015.
