Dissertation Defense – Gyuhyon (Eric) Lee
Dr. Zhitao Kang, Advisor, GTRI/MSE
Dr. Christopher Summers, Advisor, MSE
Dr. Naresh Thadhani, MSE
Dr. Meilin Liu, MSE
Dr. Brent Wagner, GTRI
"Design and Fabrication of Multilayer Structures in Dynamic Sensing and Transparent Nanocomposite Scintillators for High Energy Light Detection"
The development and exploitation of materials science, such as chemical synthesis, physical processes such as diffusion and transport, and the understanding of the thermodynamics that drives these processes are the foundation of new materials and material structures. For example, novel approaches in growth and processing techniques combined with an understanding of quantum effects have led to the development of quantum dots and nanoparticles with unique electronic and optoelectronic properties. Subsequently, new applications have emerged in the field of quantum dot electronics, energy storage systems, and optical communication devices.
In the present study, we have extended the principles of chemical synthesis to the solid phase regime to achieve the formation of nanoparticles of scintillating materials (BaGdF5 and GdF3) in different solid glass matrices to form novel transparent nanocomposite scintillators. Judicious manipulation of materials choice and thermal processing to drive diffusion and control solubility in the liquid-solid space has resulted in the selection of the robust host glass matrix and the high energy radiation absorbing material (aluminosilicate glass as the host for BaGdF5:Tb nanoparticles). These nanocomposite and similar material systems offer a new approach to achieve large area, low-cost and efficient scintillators. As a result, we have achieved 2.4 times improvement in light output under gamma-ray excitation. To further enhance efficiency, we have investigated technologies for patterning 2D photonic crystal structures into the surface of the scintillators to improve light out-coupling into a photomultiplier tube (PMT). The potential of this embodiment has been demonstrated and resulted in a completely different and new opportunity for dynamic load sensing.
During the investigation of 2D photonic crystal structures for dynamic loading sensing, it has become apparent that linearly deposited multilayer (1D photonic crystal) structures offer the best solution; therefore, optical microcavity (OMC) and distributed Bragg reflector (DBR) multilayer structures have been examined in greater detail. From a deeper understanding of the interplay between the optical and acoustic properties, highly sensitive devices (Ag/Al2O3/SiO2/Al2O3/Ag asymmetrical OMC (AOMC) and SiOx1/SiOx2 DBR structures) have been successfully developed and extensively characterized. At a relatively low applied shock pressure of ~4 GPa, both structures have exhibited spectral peak shifts of ~14-24 nm with response time <3 ns, limited only by the acoustic properties of the optically active material. These devices demonstrate the unique attributes of high sensitivity to shock pressure, ultra- fast response and with the additional potential for 2D imaging which can further widen the understanding of materials behavior under extreme conditions.