MechE PhD Prospectus Defense - Joseph J. Quigley IV
- Starts: 10:00 am on Friday, September 28, 2018
- Ends: 2:00 pm on Friday, September 28, 2018
TITLE: ADVANCED PERIODIC BOUNDARY CONDITION MODELING FOR CRYSTALLINE AND AMORPHOUS CONFIGURATIONS OF π-CONJUGATED SYSTEMS. COMMITTEE: Prof. Harold Park (ME/MSE) (Advisor) Prof. Srikanth Gopalan (ME/MSE) Prof. Sahar Sharifzadeh (ECE/MSE) Dr. Yongwoo Shin (Samsung Research America) ABSTRACT: The usefulness of organic electronic materials has seen great growth and potential for the performance and engineered designable materials using pi-conjugated systems. In particular, organic optoelectronic materials serve as low cost, structurally flexible, easily formed and readily adherent to many substrate options for devices such as: Organic Light-Emitting Diodes (OLEDs), Organic Field Effect Transistors (OFETs), Organic Solar Cells, Organic Photovoltaics (OSCs, OPVs), Organic Photoconductive Film (OPFs), Organic Photorefractive Devices (OPDs), and many other electronic devices. Potential applications could include pervasive incorporation into consumer products replacing inorganic crystal materials as well as new smart product concepts. Meanwhile, in manufacturing with the best of processes there continues to exist levels of in situ defects, such as incorporate unintentional structure defects as well as the surfaces and interfaces of heterogeneous materials, and variation from the original material design intent. Therefore, investigation of defects on organic electronic systems are attracting research interests. The research reported and planned here investigates defects, including surfaces and interfaces of heterogeneous systems of pentacene of different crystal configurations. This research reports a novel periodic boundary condition (PBC) approach that can model various defects with the atomistic simulation. As for this research, the electronic structure and geometry optimization method was completed with adapted Su- Schrieffer-Heeger (aSSH) Hamiltonian which is a model that successfully captures the pi-electron localization in organic electronic materials. For the practical application, this investigation included the crystal configurations of pentacene which have been widely studied in various applications such as: OLEDs for use in digital displays; OFET for switching functions and transistors; OPVs for low cost, flexible and light weight power generation devices; OPF for high resolution digital imaging with CMOS image sensors; and, OPDs for high-density holographic storage. This research includes the six organic crystal configurations of pentacene which have been reported: Brick Layer, Herringbone-90°, 1D Co-Facial-45°, Slip Stack, 1D Co-Facial-0° (π-Stack) and Herringbone-45°. Their geometric configurations as well as electronic structure variations were studied with the modeling of bulk material and satisfying the Bloch condition to the solution. It is shown that the Herringbone-45° structure is the most stable configuration, while 1D Co-Facial-0° (π-Stack), Slip Stack, 1D Co-Facial-45°, Herringbone-90°, and Brick Layer, presents 0.0082 eV/f.u., 0.0255 eV/f.u., 0.1742 eV/f.u., 0.2247 eV/f.u., and 0.3193 eV/f.u. higher than Herringbone-45°, respectively. During the research several additional configurations have been discovered as possible organic crystal structures. Future research will focus on investigating various structural defects of pentacene with the new PBC method including principally the various defects that covers missing or extra pentacene molecule in crystal systems, dislocations, and interfaces. This novel PBC approach that has been completed thus far will be extended to an interface in one direction to indicate the free surface of a semi-finite solid. This approach will enable the study of the surface energy of crystalline pentacene, which can be an alternate solution of the traditional slab-vacuum model.
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