Characterisation of multilayer mirror coatings

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Characterisation of multilayer mirror coatings

• Ian MacLaren

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IMSR0 imaging (undoped sample)
Layer widths were measured
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IMSR0 light layer EELS 500 eV

• O-K peak at 532 eV
• A slight pre-peak feature is seen to the left of
  the main edge
• The edge shape differs from that for SiO2 (see
  later) different bonding
• The layer is amorphous (diffraction patterns not
  yet developed)
• Seems to be an amorphous Al2O3 layer

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IMSR0 dark layer EELS 500 eV

• O-K edge clearly visible at 532 eV
• Very different edge shape to Al2O3 layer
  different bonding in this oxide
• No other edges found in range 0 2000 eV energy
  loss
• Basically pure, amorphous Ta2O5

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IMSR1 (doped 1)

• Both dark and light layers are amorphous
• Diffraction patterns to follow
• The dark layer shows some strong speckle contrast

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Dark layer EELS
Actually Ta N2,3 (not N K)

• Ti and O edges clearly seen
• O edge shape completely different to that in SiO2
• Completely different bonding (and this is no
  surprise)
• Similar to that in Ta2O5 layers in IMSR0
• Can quantify TiO ratio from this spectrum

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Ti quantification

• Quantifies to
• TiO 0.04 ? 0.006
• Assuming Ti present as TiO2 and Ta as Ta2O5
  estimate (8.5/1.2 ) Titania

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Map of TiO2 in first sample studied
Here, light layers are the doped Ta2O5 layers The
brighter the pixel, the more TiO2 is present