PhD, University of Cincinnati, 2018, Arts and Sciences: Physics

Organic materials have proved very useful for many devices, ranging from organic light emitting diodes (OLED) to waveguiding structures. One such organic material is tris(8-hydroxyquinoline)aluminum (Alq3), whose high emission efficiency and electron mobility make it ideal for efficient high-quality OLED displays. However, a complete picture of the exciton dynamics responsible for Alq3 fluorescence is still up for debate. With a better understanding of these dynamics we will have the potential to make OLEDs even more efficient than those capable today. For this reason, the singlet exciton lifetime of Alq3 films is investigated using time-integrated (TI-) and time-resolved photoluminescence (TR-PL) measurements for temperatures between 20 and 300 K. By adjusting the laser excitation pulse repetition and energy fluence, the dynamics of bimolecular quenching processes between singlets and triplets can be observed. Furthermore, the quasi-amorphous structure of Alq3 creates local traps, which not only account for an increase in singlet and triplet annihilation rates, but also explains the decrease in PL efficiency above 180 K, where singlets can be thermally freed from their traps and recaptured by non-radiative centers. In addition to their emission properties, organic materials make ideal waveguides insofar that they can be better integrated into opto-electronic computing devices because of their ability to be deposited on various substrates without the need of lattice matching, unlike traditional crystalline semiconductors. As will be shown, the inclusion of magnetic layers within an organic waveguide allows the structure to act as an optical mode switch. In order to create such a device with efficient mode conversion, there must be perfect index matching (PIM) between transverse electric (TE) and transverse magnetic (TM) waveguide polarizations. Thus, several Alq3 – perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) multilayer waveguides are fabricated an (open full item for complete abstract)

Committee: Hans Peter Wagner Ph.D. (Committee Chair); Philip Argyres Ph.D. (Committee Member); Carlos Bolech Ph.D. (Committee Member); Leigh Smith Ph.D. (Committee Member) Subjects: Condensation

Master of Science in Civil Engineering, University of Toledo, 2014, Civil Engineering

The use of Lamb waves to investigate damage in thin metal plates is investigated. This study is necessary to have a thorough understanding of Lamb wave propagation characteristics, its dispersion phenomena, its behavior when scattered from minor flaws, and its ability to detect damages. Nowadays, there is a growing interest to use Lamb waves for damage detection techniques. A literature review of Lamb waves and other types of waves pertinent to their use in damage detection mechanisms is presented. Dispersion curves for aluminum plates are studied for symmetric and anti-symmetric modes. Detailed comparison between the different modes, and the merits and demerits of these wave modes which help to select an appropriate mode for use in damage detection is also explained. Different types of damage have been detected experimentally using a pitch-catch method and are verified by using Waveform Revealer and finite element software, Pzflex. Based on selected fundamental Lamb wave modes, damage inflicted by drilling a through-thickness hole in an aluminum plate has been detected experimentally using a pitch-catch method by applying mode conversion phenomena and is verified by using Waveform Revealer. Moreover, different sizes of through-thickness holes and cracks in an aluminum plate have been detected by running simulations in Pzflex and using changes in time of flight and amplitude of the wave as parameters. Based on the experimental and simulation results, it is concluded in this paper that Lamb waves are sensitive to cracks and holes in thin aluminum plates, and that these types of defects can be detected by techniques using Lamb waves.

Committee: Douglas Nims Dr. (Advisor); Brian Randolph Dr. (Committee Member); Daniel Georgiev Dr. (Committee Member) Subjects: Engineering