Reflectivity Measurements of Oxide Layers on Glass

1. Reflectivity Measurements of Oxide Layers on Glass

2. Reflectivity Measurements of Oxide Layers on Glass Contents: • Applications • Principle • Instrumentation • Evaluation • Examples • Conclusions

3. Applications X-ray reflectivity : Measurement to determine • Layer thickness ( 0.5 - 1%) • Density ( 1 - 2%) • Interface roughness, etc. of • Glass coatings • Semiconductors • Magnetic or optical media, etc.

4. Principle (1) • Below c beam penetrates only few nm • Above c penetration depth increases sharply n1= 1  n2 d n3 2

5. Principle (2) • Partial reflection at each layer interface • Interference of reflected beams creates oscillations in reflectivity curves n1= 1  n2 d n3 2 • Permits surface/layer analysis

6. Principle (3) Oxide layers on glass Grazing incidence X-ray reflectivity (GIXR): • Sample reflectivity measured around critical angle of total reflection c • Measurement over 4 - 5º  range, 7+orders of reflectivity magnitude • Coupled q-2q scan

7. Principle (4)

8. Instrumentation (1) Oxide layers on glass Philips X’Pert PRO Materials Research Diffractometer

9. Instrumentation (2) • X-ray tube Cu anode, LFF, 40 kV/40 mA • PDS beam width <0.04º 2 • Alignment accuracy ± 0.001 º (in w) • Attenuator automatic at high intensities • PRS/PASS coupled (50-100mm) • Monochromator graphite • Soller slits 0.04 rad

10. Evaluation Oxide layers on glass • GIXA software simulates and fits experimental data • User inputs estimates of instrumental resolution, sample parameters • Calculate simulated curve, compare with collected data • Manual/automatic fit

11. Application examples Measurement of oxide layers on glass surfaces to monitor changes in glass melt and surface corrosion during production Acknowledgement: Dr. O. Anderson, SCHOTT GLAS, Germany

12. Example 1: Polished BK7 borosilicate glass • Reflectivity recorded over 7 orders of magnitude • Excellent fit agreement • Thin layers are determinable

13. Example 2:Ion plated (IP) and reactive evaporated (RE) TiO2 on glass • Density: IP > RE • Roughness: RE > IP

14. Example 3: Coated float glass (1) Good visibility of oscillations up to high angles 7 decades dynamic range

15. Example 3: Coated float glass (2) • High 2 measurements -> 10º over 7 decades dynamic range possible • Good visibility of oscillations up to high angles requires interface roughness < 3-4 Å • High quality measurement allows fit of complex multi-layer structures

16. Example 4: Multi-layer coated soda-lime glass (anti-reflection coating)

17. Example 4 • Fit requires good knowledge of approximate parameters • Good fit quality visible in fine structure of oscillations

18. Conclusion • X-ray reflectivity is a powerful technique for measuring parameters of thin layers • High quality data can be recorded with the X’Pert PRO X-ray diffraction system (Large dynamic range / up to high 2-angles) • Even thin layers and interface layers are determinable • Allows fit of complex multi-layer structures