Ion Beam Synthesis and Irradiation for Si-Based Photonic Materials and Nuclear Waste Management

This thesis describes investigations of material synthesis and interactions of radiation with materials using ion beam techniques, with applications in Si photonics and in nuclear waste management. Advances in electronics and telecommunications drive the need for Si-based optical materials (group IV alloys) with tunable bandgaps, and for strategies to overcome fabrication challenges. Ion implantation and annealing were used to incorporate Ge and Sn into Si (2.5 – 10 × 10¹⁶ Ge/cm²; 5 ×10¹⁴ – 4 × 10¹⁶ Sn/cm², 0 – 800 °C annealing temperatures), producing SixGe1−x−ySny layers with tunable bandgaps ranging from 0.45 to 1.1 eV. Significant increase in optical absorption coefficients (×10⁴ cm⁻¹ for λ > 1100 nm) were observed, compared to c-Si. Sn segregation was observed at temperatures ≥ 600 °C for Sn doses > 1 × 10¹⁶ Sn/cm². Doses of Sn ≤ 1 × 10¹⁶ Sn/cm² lead to substitutional incorporation of Sn above the solid solubility limit, with minimal Sn segregation, and enhances Si absorption at wavelengths above 1100 nm. These results suggest a route for Sn incorporation into Si-based optical materials for use in near infrared detectors and other active photonic devices. Demand for sustainable energy has heightened interest in nuclear power and, with it, the need for long-term nuclear waste containment strategies. Ion beam irradiation was used to investigate the effects of alpha radiation on UO₂ under both solid and aqueous conditions, to simulate long-term radiation exposure under deep geological repository conditions. Alpha irradiation of UO₂ in the solid phase increased the fraction of U in the U(IV) state (surface reduction), while aqueous conditions promoted surface oxidation, with increased U(VI) compared to unirradiated UO₂. These findings suggest that prolonged exposure of used fuel to residual alpha radiation within a sealed used fuel container poses no additional safety concerns as long as containment remains intact.

Name thesis:degree_name

Ph D

Discipline thesis:degree_discipline

Physics

Grantor dc:publisher

The University of Western Ontario

Year dc:date.issued

2025

Author dc:creator

• Ekeruche, Chinenye Uchenna

Advisors dc:contributor.advisor

• Goncharova, Lyudmila V.
• Simpson, Peter J.

• Ion implantation
• Rutherford backscattering spectrometry (RBS)
• group IV semiconductors
• SiGeSn
• near-infrared (NIR) detectors
• Si photonics
• uranium dioxide (UO2)
• alpha radiation
• x-ray photoelectron spectroscopy (XPS)
• uranium oxidation states.

Statement dc:rights

• Attribution 4.0 International

Language dc:language.iso

en

Handle dc:identifier.uri

https://hdl.handle.net/20.500.14721/38426

OAI identifier oai:identifier

oai:uwo.scholaris.ca:20.500.14721/38426