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Window Coating Absorbance Spectra

Explore absorbance due to MgO and In2O3 coatings on substrates, evaluating orientation-dependent effects. Investigate peaks in MgO absorbance spectrum for potential impacts. Necessary spectroscopic tests for quality assurance.

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Window Coating Absorbance Spectra

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  1. Window Coating Absorbance Spectra Lisa Pawlowicz 17 August 2010

  2. Overview • Materials and Methods • Absorbance of Substrates • Absorbance due to In2O3 (ITO) • Absorbance due to MgO • Topics for Further Investigation

  3. Window Coatings 1.22” diameter 50 Å MgO 45 Å In2O3 (ITO) .098” Borofloat (Sn doped on one side) .098” Fused Silica OR 45 Å In2O3 (ITO) 50 Å MgO • Windows cut by Oswald Siegmund at SSL • Coatings applied by Joe Libera at Argonne • coatings applied to one side but (likely) diffused onto both

  4. Absorbance Spectrum Scans A - absorbance I0 – intensity of incident light I – intensity of transmitted light α – attenuation coefficient x – optical path length (thickness) T - transmission • Measuring absolute absorbance: no scaling factor Absorbance scans done with a Hitachi U-3010 spectrophotometer: Instrument Parameters Measurement Type: Wavelength Scan Starting Wavelength: 800.00 nm Ending Wavelength: 200.00 nm Scan Speed: 300 nm/min Sampling Interval: 1.00 nm High Resolution Path Length: 2.0 mm (window thickness 2.5 mm) http://home.uevora.pt/~filmflc/GQS_Equipment_eng.htm

  5. , Absorbance of Substrate: 7980-2G Fused Silica Absorbance Wavelength http://rmico.com/technical-notes/transmission-curves

  6. , Absorbance of Substrate: Borofloat Absorbance Wavelength Wavelength http://www.pgo-online.com/intl/katalog/curves/boro_kurve.html

  7. , Absorbance of Substrates ---- Fused Silica ---- Borofloat Absorbance Wavelength • Conclusions: • caution required in UV range (Borofloat particularly a poor choice for wavelengths < 350 nm) • otherwise these substrates acceptable for the purposes of the LAPPD

  8. Absorbance due to ITO Multiple orientations of fused silica due to orientation dependent absorbance of coated window ---- Fused Silica (orientation #1) ---- Fused Silica (orientation #2) ---- Borofloat Absorbance Wavelength

  9. Absorbance due to ITO Transmission • no industry standard for ITO coatings • Conclusions: • ITO absorbance independent of substrate http://www.evaporatedcoatings.com/eci-949ar-ITOar.htm

  10. Absorbance due to MgO ---- Fused Silica (orientation #1) ---- Fused Silica (orientation #2) ---- Borofloat Absorbance Wavelength

  11. Absorbance due to MgO ---- Fused Silica (orientation #1) ---- Fused Silica (orientation #2) ---- Borofloat Absorbance Wavelength

  12. Absorbance due to MgO Transmission Spectrum of 1 nm thick MgO Transmission Bhattacharya, P., Das, R. R., and Katiyara, R. S. (2003). “Fabrication of stable wide-band-gap ZnOÕMgO multilayer thin films.” Applied Physics Letters, 83; 10. 2010-2012.

  13. Absorbance due to MgO ---- Fused Silica (orientation #1) ---- Fused Silica (orientation #2) peaks transitions across band gap Absorbance Energy

  14. Absorbance due to MgO 1 • 5-7 eV peak predicted by band structure • 2.75 eV peak • caused by interaction with substrate? ITO? • could enable unwanted interactions between conduction bands of adjacent layers e- EC EF EV Glass MgO Photocathode 1 Leone, R.M. (2006). Wide band gap engineering of magnesium oxide-zinc oxide II-VI semiconductors (Master’s dissertation, Northern Arizona University, 2006). http://www.physics.arizona.edu/~leone/dox/leone_thesis.pdf

  15. Absorbance due to MgO 1 • 5-7 eV peak predicted by band structure • 2.75 eV peak • caused by interaction with substrate? ITO? • could enable unwanted interactions between conduction bands of adjacent layers EC EF EV e- Glass MgO Photocathode 1 Leone, R.M. (2006). Wide band gap engineering of magnesium oxide-zinc oxide II-VI semiconductors (Master’s dissertation, Northern Arizona University, 2006). http://www.physics.arizona.edu/~leone/dox/leone_thesis.pdf

  16. Absorbance due to MgO • Conclusions: • MgO absorbance doesn’t match literature • MgO absorbance shows some dependence on substrate • Orientation dependence  implies uneven coating • Spectroscopic measurements necessary to ensure quality of samples • Interactions between layers could cause complications

  17. Topics for Further Investigation • Why is there a 2.75 eV peak in the MgO absorbance spectrum? • How do the 5 eV and 2.75 eV peaks in the MgO absorbance spectrum affect MgO’s functionality? • How would tempering the different materials affect their absorbance spectra? • How do absorbance spectra differ between batches of windows and films?

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