window coating absorbance spectra

Window Coating Absorbance Spectra

Lisa Pawlowicz17 August 2010

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

2

Window Coatings

.098” Fused Silica

45 Å In2O3 (ITO)

50 Å MgO1.22” diameter

• Windows cut by Oswald Siegmund at SSL• Coatings applied by Joe Libera at Argonne

• coatings applied to one side but (likely) diffused onto both

45 Å In2O3 (ITO)50 Å MgO

.098” Borofloat(Sn doped on one side)

OR

3

Absorbance Spectrum Scans

A - absorbanceI0 – intensity of incident lightI – intensity of transmitted lightα – attenuation coefficientx – optical path length

(thickness)T - transmission

Measuring absolute absorbance: no scaling factor

Instrument ParametersMeasurement Type: Wavelength ScanStarting Wavelength: 800.00 nmEnding Wavelength: 200.00 nmScan Speed: 300 nm/minSampling Interval: 1.00 nmHigh ResolutionPath Length: 2.0 mm (window thickness 2.5 mm)

Absorbance scans done with a Hitachi U-3010 spectrophotometer:

http://home.uevora.pt/~filmflc/GQS_Equipment_eng.htm4

200 300 400 500 600 700 800nm

FS

0.0250.0260.0270.0280.0290.0300.0310.0320.0330.0340.0350.0360.0370.0380.0390.0400.0410.0420.043

Abs

Absorbance of Substrate: 7980-2G Fused Silica

Wavelength

,

http://rmico.com/technical-notes/transmission-curves

Absorbance

5

Absorbance of Substrate: Borofloat

200 300 400 500 600 700 800nm

B33.5

-0.5

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

Abs Absorbance

Wavelength

,

http://www.pgo-online.com/intl/katalog/curves/boro_kurve.html

Wavelength

6

400 500 600 700 800nm

0.025

0.026

0.027

0.028

0.029

0.030

0.031

0.032

0.033

0.034

Abs

Absorbance of Substrates

Absorbance

Wavelength

,

---- Fused Silica---- Borofloat

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

7

Absorbance due to ITO

400 500 600 700 800nm

0.000

0.005

0.010

0.015

0.020

0.025

0.030

0.035

Abs

Absorbance

Wavelength

---- Fused Silica (orientation #1)---- Fused Silica (orientation #2)---- Borofloat

8

Multiple orientations of fused silica due to orientation dependent absorbance of coated window

Absorbance due to ITO

Conclusions: • ITO absorbance independent of substrate

Transmission

http://www.evaporatedcoatings.com/eci-949ar-ITOar.htm

• no industry standard for ITO coatings

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Absorbance due to MgO

200 300 400 500 600 700 800nm

-0.010

-0.005

0.000

0.005

0.010

0.015

0.020

0.025

0.030

0.035

0.040

0.045

0.050

0.055

0.060

0.065Abs

Absorbance

Wavelength


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300 400 500 600 700 800nm

0.000

0.005

0.010

0.015

0.020

Abs

Absorbance

Wavelength


11


Transmission

Transmission Spectrum of

1 nm thick MgO

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.

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23456eV

0.000

0.005

0.010

0.015

0.020

0.025

0.030

0.035

0.040

0.045

0.050

0.055

0.060

0.065Abs

Absorbance

Energy

---- Fused Silica (orientation #1)---- Fused Silica (orientation #2)

peaks transitions across band gap

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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

• 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

1

EC

EF

EV

e-

Glass MgO Photocathode

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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

• 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

1

EC

EF

EV

e-

Glass MgO Photocathode

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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

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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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window coating absorbance spectra

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