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P-DOPED STRONTIUM TITANATE GROWN USING TWO TARGET PULSED LASER DEPOSITION FOR THIN FILM SOLAR CELLS
Title
P-DOPED STRONTIUM TITANATE GROWN USING TWO TARGET PULSED LASER DEPOSITION FOR THIN FILM SOLAR CELLS
Creator
Man, Hamdi
Date
2015, 2015-12
Description
Thin-film solar cells made of Mg-doped SrTiO3 (STO) p-type absorbers are promising candidates for clean energy generation. This material shows...
Show moreThin-film solar cells made of Mg-doped SrTiO3 (STO) p-type absorbers are promising candidates for clean energy generation. This material shows p-type conductivity and also demonstrates reasonable absorption of light. In addition, p-type SrTiO3 can be deposited as thin films so that the cost can be lower than the competing methods. In this work, Mg:SrTiO3 (Mg:STO) thin-films were synthesized and analyzed in order to observe their potential to be employed as the base semiconductor in photovoltaic applications. Mg:STO thin-films were grown with pulsed laser deposition (PLD) using a frequency quadrupled Yttrium Aluminum Garnet (YAG) laser and with a substrate that was heated by back surface absorption of infrared (IR) laser light. The samples were characterized using X-ray photoelectron spectroscopy (XPS) and it was observed that Mg atoms were incorporated in the STO films. Reflection high energy electron diffraction (RHEED) spectroscopy proved that the thin films were polycrystalline. Calculations showed that the lattice constant of Mg:STO/SSF is slightly greater than that of STO/SSF, therefore, the conservation of the characteristic ring pattern for STO suggests of doping by substitution, which is consistent with the examples in literature. Kelvin Probe work function measurements indicated that the work function of the films were 4.167 eV after annealing. EDS spectroscopy showed that Mg was present in the thin films.
M.S. in Physics, December 2015
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Physicochemical Characterization of the SiC Barrier Layer of Irradiated TRISO Fuel
Title
Physicochemical Characterization of the SiC Barrier Layer of Irradiated TRISO Fuel
Creator
Seibert, Rachel
Date
2018
Description
Tristructural-isotropic (TRISO) nuclear fuel is designed to be an inherently safe microencapsulated fuel for use in advanced nuclear reactors...
Show moreTristructural-isotropic (TRISO) nuclear fuel is designed to be an inherently safe microencapsulated fuel for use in advanced nuclear reactors. TRISO fuel is comprised of an uranium-carbide/uranium-oxide mixed kernel, surrounded subsequently by a porous carbon buffer layer, pyrolytic carbon, silicon carbide, and pyrolytic carbon. The silicon carbide layer acts as both the structural backbone and the main barrier to non-gaseous fission product release from the kernel. During operation, fission products are known to release from intact fuel (silver) and to locally corrode the silicon carbide layer (palladium). Release of silver can pose a threat to safety and maintenance workers due to plate-out on reactor components, while palladium corrosion leads the possibility of failure of the SiC layer. An understanding of the silver release mechanism, the diffusion of palladium and fuel kernel components, and their possible correlation is necessary to understand envelopes for safe operation using these fuels.This work focuses on analysis of the reactivity of silver, palladium, and fissile inventory with silicon carbide to determine potential mechanisms and interactions. Irradiated TRISO particles and model thin film cubic silicon carbide (3C-SiC) surfaces were studied to compare and understand the reaction mechanisms of these fission products. Analysis on both systems involved X-ray Absorption Fine Structure Spectroscopy (XAFS) measurements to determine the local atomic structure of the bulk material and electron microscopy studies to observe the microstructure and fission product location. Additionally, x-ray photoelectron spectroscopy (XPS) was used to study the fundamental surface science of silver and palladium in the 3C-SiC thin films. From the comparative studies in this work, the interaction of silver, palladium, and fuel kernel products has been observed. Palladium silicides are preferentially formed, but silver remains metallic and diffuses through both bulk SiC, through material defects, and through grain boundary diffusion. Uranium preferentially forms carbides with increasing temperature. Plutonium primarily forms silicides, but with short carbon bonds. All fission products and fissile inventory were observed to be segregated along grain boundaries in the SiC. This work did not measure a single release mechanism, but suggests multiple mechanisms work together simultaneously. It also presents the first evidence of uranium carbide formation at elevated temperatures and of silver as a metal in irradiated TRISO fuel, to the best of the author's knowledge.
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