Abstract
Crystalline uranium oxide thin films were deposited in an unbalanced magnetron sputtering system by sputtering from a depleted uranium target in an Ar + O 2 mixture using middle frequency pulsed dc magnetron sputtering. The substrate temperature was constantly maintained at 500 °C. Different uranium oxide phases (including UO 2-x , UO 2 , U 3 O 7 and U 3 O 8 ) were obtained by controlling the percentage of the O 2 flow rate to the total gas flow rate (fO 2 ) in the chamber. The crystal structure of the films was characterized using X-ray diffraction and the microstructure of the films was studied using transmission electron microscopy and atom probe tomography. When the fO 2 was below 10%, the film contains a mixture of metallic uranium and UO 2-x phases. As the fO 2 was controlled in the range of 10-13%, UO 2 films with a (2 2 0) preferential orientation were obtained. The oxide phase rapidly changed to a mixture of U 3 O 7 and U 3 O 8 as the fO 2 was increased to the range of 15-18%. Further increasing the fO 2 to 20% and above, polycrystalline U 3 O 8 thin films with a (0 0 1) preferential orientation were formed. The hardness and Young's modulus of the uranium oxide films were evaluated using nanoindentation. The film containing a single UO 2 phase exhibited the maximum hardness of 14.3 GPa and a Young's modulus of 195 GPa. The UO 2 thin film also exhibited good thermal stability in that no phase change was observed after annealing at 600 °C in vacuum for 104 h.
Original language | English |
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Pages (from-to) | 475-480 |
Number of pages | 6 |
Journal | Applied Surface Science |
Volume | 301 |
DOIs | |
State | Published - 15 May 2014 |
Externally published | Yes |
Keywords
- Annealing
- Hardness
- Pulsed dc magnetron sputtering
- Thin films
- Uranium oxide
ASJC Scopus subject areas
- Condensed Matter Physics
- Surfaces and Interfaces
- Surfaces, Coatings and Films