1. Thorium Oxide Thin Films as EUV Reflectors Jed Johnson Dr. David D. Allred Brigham Young University

2. Reflectors in EUV range EUV range is about 50- 1500Å EUV range is about 50- 1500Å General Challenges: General Challenges: - multilayers required - absorption - high vacuum needed Applications Applications - XUV lithography - Soft x-ray microscopy - Astronomy Complex index of refraction: Complex index of refraction: ñ=n+ik

3. Delta =1-n vs. Beta (absorption) 30.4 nm (41 eV) 30.4 nm (41 eV)

4. Periodic table

5. Thorium vs. Uranium Thorium (11.7 g/cm^3) is less dense than uranium (19.1 g/cm^3). Thorium (11.7 g/cm^3) is less dense than uranium (19.1 g/cm^3). In the EUV and Soft x-ray, uranium is in theory more reflective than thorium because of its density. In the EUV and Soft x-ray, uranium is in theory more reflective than thorium because of its density.

6. Reflectivity vs. energy (eV)

7. But the mirror’s surface will be oxidized. Both uranium and thorium oxidize easily at room temperature. Both uranium and thorium oxidize easily at room temperature. The image mirror used UO2 as its top layer. The image mirror used UO2 as its top layer. 4 Å in 5 min, tens of nm in week. 4 Å in 5 min, tens of nm in week. EUV at low angle only see top few nm. EUV at low angle only see top few nm.

8. The 2 Dioxides are Similar! Thin films usually start oxidizing when exposed to “air.” Thin films usually start oxidizing when exposed to “air.” The density, lattice structure, and therefore reflectivity of an element are altered by oxidation. The density, lattice structure, and therefore reflectivity of an element are altered by oxidation.

9. Which oxide is better? Oxidation occurs at room temperature for both uranium and thorium. Oxidation occurs at room temperature for both uranium and thorium. Uranium, however, has many oxidation states (UO 2, U 2 O 5, UO 3 etc.). As long as there is unoxidized U nearby, most oxidation stops at UO 2. But eventually, they could oxidize towards UO 3. Uranium, however, has many oxidation states (UO 2, U 2 O 5, UO 3 etc.). As long as there is unoxidized U nearby, most oxidation stops at UO 2. But eventually, they could oxidize towards UO 3. This has lower density! This has lower density!

10. The reflectance of UO 3 is lower than UO 2

11. Advantages of Thorium Oxide Rock stable: highest known melting point of any oxide. Rock stable: highest known melting point of any oxide. Only one oxidation state, ThO2. We know what we have! Only one oxidation state, ThO2. We know what we have!

12. Project Challenges Thorium metal acquisition Thorium metal acquisition Thorium Oxide sputtering target production Thorium Oxide sputtering target production Long distances to analysis equipment Long distances to analysis equipment