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Mathematics and Natural Sciences

Eilaf Egap, PhD
ECAS: Chemistry
Design, Synthesis, and Properties of Radical Organic Semiconductors

Organic semiconductors are of significant interest for all-plastic complementary integrated circuits and for improving the efficiency of plastic solar cells. Indeed, the realization of simultaneous control of the molecular structure and spin properties would revolutionize the design of organic semiconductors and accelerate the emerging era of plastic electronics and optoelectronics for applications in information technologies and in renewable power sources. The PI and her group will generate new open-shell oligomer and polymer semiconductors, investigate their photophysics, structures and properties, and use computational chemistry to guide materials design. An important aspect of this project is the fundamental understanding of the structural and physical factors that controls photo-induced spin-alignment and spin-polarization in oligomer/polymer semiconductors and understanding and establishing design rules in modulating and predicting excited-states energy levels. This will be achieved by the synthesis of new materials, structural characterization, detailed characterization of the electronic structures, and excited-state dynamics and kinetics that includes steady-state optical absorption spectroscopy, ultrafast-transient absorption, steady-state and time-resolved photoluminescence spectroscopies, and computational chemistry. These studies will enable (1) a new archetype in materials design, (2) elucidate structural and physical factors that determines spin-polarization, excited-state energy levels in open-shell organic semiconductors, (3) determine how structural orientation and topology influences open-shell, closed-shell or hybrid states and spin-exchange, and (4) impact a range of technologies in flexible electronic devices with significantly reduced power consumption, improved sensitivity, and enhanced data and energy storage in low-cost and large-scale processability.

James Kindt, PhD and Eric Weeks, PhD
ECAS: Chemistry and Physics
Ordering transitions in monolayers of gravitationally confined microspheres: experimental and computational studies

When packed at high enough lateral densities, hard spheres confined to a plane undergo a transition to a hexagonally ordered state, in a process that has been studied for decades using theory and computation. Only recently have computer simulations on large systems been able to describe this transition unambiguously as a two-stage process: a discontinuous transition from a fluid to a liquid crystalline structure followed by a continuous transition to a 2d solid. In this collaborative project, an experimental realization of this idealized system will be studied: glass microspheres settled under the force of gravity into a monolayer on a glass surface and imaged dynamically in the Weeks lab. Computational studies using algorithms developed in the Kindt group will address the influences of "real-world" complications, including thermal fluctuations normal to the surface, the presence of a partially occupied second layer, and the non-uniformity of the microsphere sizes, on the experimentally observed structures. The dynamics of growth in the sizes of ordered domains and the influence of "dopant" spheres of a different size on these rates will be compared to theoretical models for grain coarsening. Finally, ordered structures arising from co-crystallization of two components with particular size ratios will be investigated, especially those with a 2:1 ratio that pack as arrays of squares rather than hexagonally. The ability to control domain size and packing symmetry of an initially deposited monolayer could be useful in creating templates to grow three-dimensionally ordered crystalline colloidal films with unusual structures or with fewer defects.