1. 1 X-Ray Photoelectron Molecular By Amy Baker R. Steven Turley, David Allred, Matt Linford, Yi Lang, BYU Thin Special Thanks to R. Steven Turley, David Allred, Matt Linford, Yi Lang, BYU Thin

2. 2 Spectroscopy to Examine Composition and Liz Strein Films Group, Physics & Astronomy Department Funding, ORCA Mentoring Grant

3. 3 Why Extreme Ultraviolet? Thin Film or Multilayer Mirrors EUV Lithography Soft X-Ray Microscope Earth’s Magnetosphere in the EUV

4. 4 Why Thorium? High Reflectance in the EUV (10-100nm) High Reflectance in the EUV (10-100nm) Only one oxidation state: ThO 2 Only one oxidation state: ThO 2

5. 5 Will Thorium Work? The mirror’s surface will be oxidized. The mirror’s surface will be oxidized. At optical wavelengths, this oxidation is negligible. It is a major issue for our thin films, however. At optical wavelengths, this oxidation is negligible. It is a major issue for our thin films, however. We expect minimal oxidation We expect minimal oxidation

6. 6 Learn oxidation state of our thorium samples Learn oxidation state of our thorium samples Understand how composition changes with depth Understand how composition changes with depth Obtain an expression for oxidation as a function of depth Obtain an expression for oxidation as a function of depth Purposes of X-Ray Photoelectron Spectroscopy

7. 7 X-Ray Photoelectron Spectroscopy

8. 8 Einstein’s Photoelectric Effect When light shines on a metallic surface, atoms in the metal absorb quantized packets of light or photons and then eject electrons. When light shines on a metallic surface, atoms in the metal absorb quantized packets of light or photons and then eject electrons.

9. 9 How XPS works

10. 10 Electron Binding Energy O Th C

11. 11 Peak Shifts Thorium peaks on surface Thorium peaks on surface Thorium peaks after oxygen is gone Thorium peaks after oxygen is gone Change in peak shape due to oxygen bonding on the surface Change in peak shape due to oxygen bonding on the surface

12. 12 Depth Profiling Two methods Rastering: Rastering: Argon ions knock off individual atoms Argon ions knock off individual atoms Variable angle scans: Variable angle scans: More depth is obtained as x-ray gun and detector are moved towards incidence More depth is obtained as x-ray gun and detector are moved towards incidence

13. 13 Variable Angle Results Only penetrates about 100 Angstroms into the sample Only penetrates about 100 Angstroms into the sample This allows us to see surface contamination, but not composition with depth This allows us to see surface contamination, but not composition with depth

14. 14 Rastering Results

15. 15 Too Much Oxidation These samples were only a few hours old. These samples were only a few hours old. We need more uniformity. We need more uniformity. Solution: Make ThO 2 mirrors. Reflection is similar to Th and it should be more uniform. Solution: Make ThO 2 mirrors. Reflection is similar to Th and it should be more uniform.

16. 16 ThO 2 Results Fully oxidized thorium is uniform. Fully oxidized thorium is uniform. ThO 2 shows definite promise as a durable reflector in the EUV. ThO 2 shows definite promise as a durable reflector in the EUV.

17. 17 Other Results of Interest There was an increase in oxygen when the sample sat for more than 4 or 5 minutes in between sputtering/scans. There was an increase in oxygen when the sample sat for more than 4 or 5 minutes in between sputtering/scans. This was observed for 5 out of 5 samples that sat still between scans. This was observed for 5 out of 5 samples that sat still between scans.

18. 18 * * * * * indicates where the sample stood for more than 4 or 5 minutes in between scans

19. 19 What Could This Be? Hypothesis: This is likely due to preferential sputtering. Hypothesis: This is likely due to preferential sputtering. The argon ions will knock off oxygen atoms more readily than thorium. The argon ions will knock off oxygen atoms more readily than thorium. While sputtering, scans would show less O than actually exists. While sputtering, scans would show less O than actually exists.

20. 20 Future Research Shape of sputtered area may affect the sputtering rate. Shape of sputtered area may affect the sputtering rate. Finally: Make and measure optical Finally: Make and measure optical constants for thin films of other elements.

21. 21 Acknowledgements A special thanks to R. Steven Turley David Allred Matt Linford Yi Lang BYU Thin Films Group Physics & Astronomy Department Funding ORCA Mentoring Grant