Date on Master's Thesis/Doctoral Dissertation

12-2024

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Mechanical Engineering

Degree Program

Mechanical Engineering, PhD

Committee Chair

Narayanan, Badri

Committee Co-Chair (if applicable)

Yu, Ming

Committee Member

Yu, Ming

Committee Member

Wang, Hui

Committee Member

Bhatia, Bikram

Author's Keywords

Reax; ZBL; sputtering; annealing; bombardment; void

Abstract

Controlled introduction of defects in phosphorene using high-energy ion beams offers a promising route to design novel high-performance materials for energy technologies. However, this potential remains underexplored due to a lack of fundamental understanding of the atomic-scale mechanisms governing the production, accumulation, and temporal evolution of defects during ion irradiation. Here, we employ a combination of classical and ab initio molecular dynamics simulations to elucidate the effects of ion energy, angle of incidence, noble gas ion size/mass, and fluence on (a) defect generation (i.e., point defects, topological imperfections, voids), (b) atomic-scale mechanisms of defect formation and re-arrangement, and (c) defect relaxation during annealing. Using ReaxFF simulations, we systematically investigate defect formation and identify the intricate coupling between ion beam parameters, including energy, size, and incidence angle. Noble gas ions (e.g., He, Ne, Ar, Kr, Xe) in the nuclear stopping regime induce a diverse range of structural transformations, from localized point defects (mono-, di-, and multi-vacancies with areasŲ) to extended features such as line defects and voids. The occurrence of defects closely follows the sputtering yield trends, reflecting their vi dependence on the energy transfer processes during irradiation. Intermediate energy ranges consistently produce high-quality nanopores at angles (40o, 60o) that promote collisional cascades, while grazing incidence (80o) at high energies favors the development of forked and linear defects. The ReaxFF framework enables precise modeling of atomistic mechanisms, including bond formation, rotation, angle bending, and dihedral twisting, that govern defect construction and reorganization under ion irradiation. Ion fluence further dictates the nature of defect accumulation and annealing behavior. At low fluence (1.43 × 10¹³ ions/cm²) leads to the formation of large nanopores (5–10 nm) that coalesce into 3D networks of P-centered tetrahedra. Thermal rippling, bond reorganization, and cooperative dihedral movements are pivotal in the annealing pathways. These findings establish ion-beam engineering as a powerful tool to precisely tailor phosphorene's properties, unlocking its potential for applications in nanoelectronics, optoelectronics, batteries, gas separation, and neuromorphic computing.

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