Irradiation-Driven Restructuring of UO₂ Thin Films: Amorphization and Crystallization.

Area of Science:

• Materials Science
• Nuclear Engineering
• Solid State Physics

Background:

• Understanding radiation-induced material transformations is crucial for nuclear applications.
• Thin film deposition techniques are essential for creating specialized targets.
• Actinide research requires robust and well-characterized materials.

Purpose of the Study:

• To investigate the irradiation-induced restructuring processes in thin uranium dioxide (UO2) films.
• To develop a method for preparing pure, robust, and uniform thin-film actinide targets.
• To explore nanoscale UO2 restructuring distinct from coarse-grained materials.

Main Methods:

• Combustion synthesis of UO2 films on aluminum substrates using uranyl nitrate-acetylacetone-2-methoxyethanol solutions.
• Thermal analysis for reaction initiation temperature and annealing.
• Ion irradiation (Ar2+) to induce atomic displacements and subsequent characterization using X-ray fluorescence (XRF), alpha-particle emission spectroscopy, X-ray photoelectron spectroscopy (XPS), high-resolution electron microscopy, and electron diffraction.

Main Results:

• Polycrystalline UO2 films with tunable thicknesses (35-260 nm) were successfully deposited.
• Films exhibited stability under irradiation, with no sputtering degradation or changes in stoichiometry.
• Early-stage irradiation led to complete amorphization and densification; prolonged irradiation induced surface crystallization and complete recrystallization into a highly crystalline film.

Conclusions:

• A novel radiation-induced restructuring pathway for nanoscale UO2 was identified, differing from bulk materials.
• The developed synthesis method yields high-quality thin UO2 films suitable for actinide targets.
• These findings contribute to stockpile stewardship and fundamental actinide research.