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
Absorbance scans done with a Hitachi U-3010 spectrophotometer:
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
Instrument Parameters
Measurement Type: Wavelength Scan
Starting Wavelength: nm
Ending Wavelength: nm
Scan Speed: 300 nm/min
Sampling Interval: 1.00 nm
High Resolution
Path Length: 2.0 mm (window thickness 2.5 mm)

5. Absorbance of Substrate: 7980-2G Fused Silica,
Absorbance of Substrate: G Fused Silica
Absorbance
Wavelength

6. Absorbance of Substrate: Borofloat,
Absorbance of Substrate: Borofloat
Absorbance
Wavelength
Wavelength

7. Absorbance of Substrates,
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

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

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

12. Transmission Spectrum of
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;

13. Absorbance due to MgO peaks transitions across band gap
---- 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
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).

15. Absorbance due to MgO 1 5-7 eV peak predicted by band structure
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).

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?