Reflectivity Measurements of Oxide Layers on Glass

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Reflectivity Measurements of Oxide Layers on Glass
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Reflectivity Measurements of Oxide Layers on Glass

• Contents
• Applications
• Principle
• Instrumentation
• Evaluation
• Examples
• Conclusions

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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.

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Principle (1)

• Below ?c beam penetrates only few nm
• Above ?c penetration depth increases sharply

n1 1
?
n2
d
n3
? 2
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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

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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, 7orders of
  reflectivity magnitude
• Coupled q-2q scan

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Principle (4)
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Instrumentation (1)
Oxide layers on glass

• Philips
• XPert PRO
• Materials
• Research
• Diffractometer

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Instrumentation (2)

• X-ray tube Cu anode, LFF, 40 kV/40 mA
• PDS beam width lt0.04º 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

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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

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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
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Example 1 Polished BK7 borosilicate glass

• Reflectivity recorded over 7 orders of magnitude
• Excellent fit agreement
• Thin layers are determinable

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Example 2Ion plated (IP) and reactive
evaporated (RE) TiO2 on glass

• Density IP gt RE
• Roughness RE gt IP

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Example 3 Coated float glass (1)
Good visibility of oscillations up to high
angles
7 decades dynamic range
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Example 3 Coated float glass (2)

• High 2? measurements -gt 10º over 7 decades
  dynamic range possible
• Good visibility of oscillations up to high
  angles requires interface roughness lt 3-4 Å
• High quality measurement allows fit of complex
  multi-layer structures

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

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

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Conclusion

• X-ray reflectivity is a powerful technique for
  measuring parameters of thin layers
• High quality data can be recorded with the XPert
  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