Date of Graduation

7-2021

Document Type

Thesis

Degree Name

Master of Science in Microelectronics-Photonics (MS)

Degree Level

Graduate

Department

Microelectronics-Photonics

Advisor/Mentor

Arun Nair

Committee Member

Paul Millett

Second Committee Member

Rick Wise

Third Committee Member

Jingyi Chen

Keywords

Bilayer, Irradiation, Molecular Dynamics, Radiation, Radiation Damage, Silicon-Gold

Abstract

Irradiation from sources such as nuclear reactors bombard materials with neutrons and heavy ions. The primary consequence of this irradiation is the displacement of atoms from their atomic structure. As the structure becomes damaged, the mechanical properties can change. Eventually, this can result in a failure due to embrittlement. This type of damage is hard to detect and can result in sudden, unexpected failure. Therefore, focusing on managing the consequences of irradiation has been a heavily researched topic. To manage irradiation, the focus is primarily to manage the voids and interstitials that appear during irradiation. Grain boundaries and amorphous regions are known to be good sinks for both. This research focuses on computational modeling of bilayer silicon-gold to analyze the difference between a crystalline-crystalline silicon-gold boundary (the pristine model) and an amorphous silicon-gold boundary (the amorphous model). As the whole system is pristine gold and silicon, this allows focus only on the boundary and the ability of either boundary to individually assist in managing the effects of irradiation. Silicon-gold material system was chosen for this study as amorphous silicon is known to be a good sink for voids and interstitials. Silicon and gold are immiscible and, therefore, are not expected to form compounds and have limited solubility. For comparison, a pristine gold computational model of similar size was also chosen. To accomplish this task, molecular dynamics simulations were used to irradiate each system. Following irradiation, biaxial and uniaxial compression and tension yield simulations were performed for all samples to obtain yield stresses for each direction and analyze the yield strength of the system at different levels of radiation damage. Results showed a sudden, significant loss in yield surface at early damage levels in all models. There was also the appearance and rapid growth of an amorphous layer in the pristine model, as well as a slower growth of an amorphous layer in the amorphous model. Overall, this study advances the understanding of crystalline-crystalline and amorphous boundaries and their absorption of point defects such as voids and interstitials in silicon-gold bilayer structures.

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