Nonequilibrium electron dynamics under energetic ions or electrons irradiation

Focused ion and electron beams are indispensable tools for characterizing material properties and modifying structures with nanoscale precision. These experimental successes push the theoretical development of the underlying interaction between the incident projectiles with the materials beyond the analytical models. Real-time time-dependent functional theory provides a unified and parameter-free framework to investigate the elusive fundamental physics governing the electronic response of materials under energetic ion or electron irradiation. Insights gained from such simulation can then inform ion or electron microscopy and nanoscale patterning techniques. This thesis investigates the secondary electron emission characteristics of cold and hot graphene under proton irradiation. A detailed analysis of the time evolution and kinetic energy distribution of emitted electrons reveals that elevating the graphene lattice temperature leads to a noticeable increase in the secondary electron yield. Based on the experience of the proton-irradiated graphene, this thesis further irradiates the graphene with an electron. After a detailed validation of the implementation of the quantum mechanical wave packet, we analyze the differences in momentum distribution evolution, kinetic energy loss, and secondary electron emission characteristics when simulating the incident electron as either a classical point charge or a quantum wave packet. This comprehensive analysis not only provides an estimation of the secondary electrons that might be difficult to measure for the 2D materials directly but also critical insights into the energy regimes where quantum mechanical effects are significant, i.e., under what energy can we describe the incident electron as a classical point charge. Finally, this thesis explores the nonadiabatic forces experienced by ions in an insulating MgO slab under proton irradiation. By calculating these forces directly from the interatomic potential perturbed by the excited electrons, we gain insights into the initial stages of defect formation mediated by electronic excitations. Collectively, this thesis establishes a predictive approach for studying electron dynamics in 2D and thin film materials triggered by energetic ion and electron irradiation. The findings provide quantitative implications for interpreting experimental results and optimizing focused ion and electron beam techniques across various applications, including nanoscale imaging, materials characterization, and device fabrication.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Materials Science & Engr

Grantor

University of Illinois Urbana-Champaign

Year dc:date

2025

Author dc:creator

• Yao, Yifan

Contributors dc:contributor

• Schleife, André
• Bellon, Pascal
• Perry, Nicola
• Ertekin, Elif

• First-principles Simulations
• Nonequilibrium Electron Dynamics

Statement dc:rights

• Copyright 2025 Yifan Yao

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/129999

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F129999