1 LAPPD Team meeting 6/10/2010 Ossy Siegmund, Experimental Astrophysics Group, Space Sciences...

1LAPPD Team meeting 6/10/2010

Ossy Siegmund, Experimental Astrophysics Group,

Space Sciences Laboratory,

U. California at Berkeley

Bialkali Photocathode Development

GALEX M31


LAPD Photocathode MilestonesLAPD Photocathode Milestones

• Systematic characterization of Photo-electron Emission (PE) properties of materials for photocathode development.

• Demonstration of an operational 8”-square photo-cathode with a viable path to QE ≥ 15% for wavelengths between 300 and 450 nm.

Associated Milestones - Dependencies:-

• Demonstration of the window-to-body seal solution.

• Design and costing of the vacuum-transfer/assembly facility for the 8”-square MCP module.


Cathode Bandpass and WindowsCathode Bandpass and Windows

Acceptable cutoff range

Typical window transmission curvesNominal Cherenkov emissionspectrum compared with bialkali


100 200 300 400 500 600 700 800

0,1

1

10

100

Na-K-Sb:Cs (S-20)

Wavelength [nm]

Cs3Sb (S-11)

Na2KSb

Rb2CsSb

K2Cs-Sb6*109Ohm/square

2*106Ohm/square

Bi-Alkali Cathode Characteristics

QE and resistivity for various bialkaliswe will use K2CsSb & Na2KSb

Lyashenko, Chicago 7/09

Cathode Noise vs Temp


Photocathode Configuration Photocathode Configuration

Numerous processes affect the QE

Bialkali is a few 100Å thick,and is compatiblewith depositionas semitransparenton the window,but is very difficultto achieve as anopaque cathode on the MCPsurface.


Work Flow Program for Bialkali Cathode Development


Bialkali Photocathode QEBialkali Photocathode QE

Examples of SSL bialkali photocathode depositions with different wavelength optimizations (on fiber optics). PeakQEs 15% to 20% using Na2KSb.

0

0.2

0.4

0.6

0.8

1

1.2

350 400 450 500 550 600 650

AST (t)AST (d)STL02 (d)Cherenkov

Wavelength (nm)High efficiency Bialkali cathodes at Photonis. Clear room for improvementover standard bialkalis. Need to Establish enhancement techniques.

Schyns, Clermont 2010


B33/B270 General Parameters

B33 Composition

Refractive index

@400nm

B33 1.47

Air ~1.0

Water ~1.32

The cathode substrate, window or window coating, affects the photocathode performance. Quartz, fiber optics, 7056 glass are common. Borofloat B33 Borosilicate is not, and also has Tin diffused into one side from the float process, so we we need to test this. B270 is a soda-lime Crown glass and should be OK.

Standard AR coating is bad for LAPD - most likely don’t needAR coating for water/B33 interface


Compatibility and Transmittance of Windows

B33 Transmittance is typicalfor borosilicate glasses

B270 Transmittance isonly slightly worse than B33

Both materials have similar mechanical properties, strength,hardness, etc, BUT the thermal coeff’ts are not, 0.003”/100Cfor B33 and 0.008”/100C for B270 - not clear that this is an issue.

3.25 x 10-6/K

8.8 x 10-6/K

Thermal

Thermal


Conductive Layer Properties for Windows

Braem, NIMA 2003

ITO is a possibility for the conductive underlayer,BUT - it might affect the cathode QE! So we can alsotry metal conductor stripes as we did for GALEX.


Small Tube and Cathode Process Tank System

Small window cathode development, 33mm samples- Process samples to optimize QE and bandpass

-Na2KSb, K2CsSb cathodes- Use several substrate materials, SiO2, verify B33/B270- Test precursor/ITO/conductor underlayer for cathodes

Large size window cathode study, 8” windows.- Study source alkali design for large cathodes- Develop techniques to make larger area uniform QE- Optimize cathode QE levels- Test metal/ITO conductor underlayer for cathodes- Test metalization and sealing techniques


33mm Cathode Test Samples

We have cut up one B33 and one B270 window to make 30ea 1.3”test samples each, also have 18ea fused silica as control samples.

Inconel annular electrodes were evaporated just as they would be for In seals

13LAPPD Team meeting 6/10/2010 13

Tube Lab, 33mm sample test/process station.

Small tank used to process alkali cathodes (33mm) and tubes of small area. Can take 4 samples/run. 1st run done, making mods for 2nd run.- Small sample test runs- Substrate material tests


0

2

4

6

8

10

12

350 400 450 500 550 600 650 700

Quartz, NaKSbB33-1, NaKSbB33-2, NaKSbB270, KCsSb

Wavelength (nm)

Initial Bialkali Trials on 33mm Sample Substrates

Trying to set up process parameters for comparative tests and optimizations.

Used quartz, B33 and B270 sequential depositions in one pumpdown.

Short process / thin cathode-ended up too blue / low QE.

-Had problems with K channels that precluded optimal process, mostly on

later depositions.

Initial cathode trials,

Process order

Plan for next run-Fix alkali dispensers, retool window holders-shoot all substrates in one go at same time-Add extra cycles to push peak redder-higher QE


Cathode Process Test Tank Systemreplacement for 33mm chamber

Larger 16” flange tank, can take full size windows (8.7”) to test-Quantum efficiency-QE Uniformity-Seal tests


Evaporator design modifications to Evaporator design modifications to accommodate 8.7” windowsaccommodate 8.7” windows

Design done for NiCr/Cu evaporation tooling for 8.7” windows

Currently OK to 5” Rotation stage for 8.7” windows


Window Seal Development and Window Seal Development and Cathode Test “Diodes”Cathode Test “Diodes”

3” window test article on metal frame with Indium seal

Will metalize 8.7”window and produce an Will metalize 8.7”window and produce an Indium seal on a frame to test leak Indium seal on a frame to test leak

tightness of the seal.tightness of the seal.

3” ceramic body with strip anode, and metal frame with Indium seal


8” Tube and Cathode Process Tank System

UHV 18” processChamber:-Initial use for cathode and seal development.Eventually use for complete tubeprocess task.

B33/B2708.66” windows- large area cathodes- uniformity tests- QE optimization


8” Tube and Cathode Process Tank System

Large window cathode development, 8.66” square

- Implement alkali source design for large cathode areas- Develop wet cleaning and plasma cleaning processes- Establish metalization scheme- Test metal/ITO conductor underlayer for 8” cathodes- Implement AR coatings/treatment on both surfaces- Develop techniques to make 8” area uniform QE- Optimize cathode QE levels- Trial seals on 8.66” “frames”

- Then

- Make LAPD 8” tubes

1 LAPPD Team meeting 6/10/2010 Ossy Siegmund, Experimental Astrophysics Group, Space Sciences...

Documents

Transcript of 1 LAPPD Team meeting 6/10/2010 Ossy Siegmund, Experimental Astrophysics Group, Space Sciences...