Kathleen Broughton
Charles Kurtz
Ernesto Indacochea
Alexander Paramonov
Klaus Attenkofer
Photocathodes Group
June 10, 2010

 The Vision of Photocathode Growth and Characterization Facility at ANL
 ANL Photocathode Growth / Characterization Modules
 Elements of a Photocathode Growth / Activation Module
 Wash U. MBE for Growth of Photocathode Layers
 ANL Growth / Activation Module
 ANL III-V Photocathode Module
– Overall Design
– QE-Characterization Chamber
– Sample Holder Mount
– Optical Heating System
– Evaporator System
 Conclusion
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Alkali
Nano
Technology
Cleaning
Lehighton,
Hall, ECV
Transfer
Process
Photoluminescence,
Cathodoluminescence
III - V
Accelerator
APS
AFM, SEM
TEM, EBIC, XPS,
SIMS, Auger
 Goal: Single Facility for all Small
(up to d = 2”) Photocathode
Investigations
 Methodology to obtain: Utilization of existing lab infrastructure to
Develop upon new research technologies
 Facility Components:
– Cleaning
– Activation/Growth
– Characterization
 Utilization
– LAPPD collaboration (all partners)
– Accelerator community
– X-ray detector community
(APS/NSLS II)
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Alkali Transfer III-V
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Critical Element for High QE –
CLEANLINESS!
U. Weigel, et.al. “Cold intense electron beams from LN2-cooled GaAs-photocathodes”, Nuclear Instruments and Methods in Physics Research Section A . Vol. 536 pp. 323-328 (2005).
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D. Leopold, Advanced Photo-Cathode Material, LAPPD Psec Workshop VII, February 27, 2008.
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 New Design from prior Modules
– Vertical Manipulation
• 6’ X 2’ X 3’
– Compact and Efficient
• Heating, Quenching
• Activation
– Compatible for various types of activation materials (Cs, O, K, Sb etc.)
– Evaporator Transfer System to Clean Glove box for refilling activation materials
• Optical Analysis
– Transmission, reflection
• Electrical Analysis
– Monitor evaporator
– Conduct experiments on Samples
– Can Host Variety of Samples
• Size - Up to d = 2”
• Type - III-V or Alkali
– Designed to Transfer Samples to other Modules
Cryostat (4K – 900K )
X,Y,Z Manipulation
Structural / Electrical
Characterization
(LEED)
Heating
QE - Characterization
Optional RHEED
Evaporation
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 Optic reflection
Sample centered in chamber
Temperature Range: 4K – 1050K
Rotatable f
& q
– Work Function
• Temperature dependent I-V curve *
• Spectral dependency of I-V curves* transmission
– Transmittance, Reflectance, Absorbance
• Function of wavelength, specular, offspecular
• Quantum Efficiency QE (
λ)
• Dark Current D(T)
– Ellipsometry
• Thickness monitor
• In situ on sample
 Electrical transmission
 Optional
I-V feedthroughs
 Laser Characterization (Matth)
– Triax / BNC Connector design
• 1 G
Ω
+ Measurement
– Measurements on Bulk and Surface
• Resistivity (2 probe)
• TCR (temperature coefficient of resistance)
– Carrier Density
– Activation Energy of dopants *
K. Broughton, ANL Photocathodes Growth Chamber and Characterization Module, LAPPD Photocathodes Godparent Committee Review, February 26, 2010.
* Correlated Measurements
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 Multi-Functional
– Supports 10mm^2 to 2” sample size (WASH U)
– Adaptable from This Module to Material Science
Division for Further Analysis in Another Module
 Test Design
– Stainless Steel, Aluminum
– Used in Test Vacuum Chamber
– Worked properly first time!
 Actual Fabricated Design
– Sapphire, Tungsten
2” sample
10mm^2 sample
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 Capsulated Heater
– T reaches and maintains up to 750 ° C
– No direct contact between heating elements and sample
– Homogeneous heating
 Furnace – Black Body Radiator
– Optical Furnace
 Cooling Walls
– Absorb out gassing
– Minimize Thermal Mass
 Single Sample holder
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 Benefits of Custom 6-port Evaporator Design
– Variable evaporation distances
• Optimize Evaporation Materials released
– Variable evaporation Processes
• Yo-Yo evaporation
• Co-evaporation
– Various evaporator types
• High Temperature Evaporator (1600 C)
• E-beam Evaporator
• Magnetron
• RF Plasma Evaporator
– All evaporators are retractable
• Easy Load Transfer Process to replenish getters
• Replenish Getters in Glove Box to maintain cleanliness
– Can also coat electrodes (Cr-Ni) and conductive/insulating inter-layers between cathode and window (MgO)
– Minimize Coating Chamber
– Control Evaporation
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 Controlling Evaporation
– Power to Getter
– Temperature
– Ion release
Key
Plug (light green)
LN2 Cooling/Support Lines
(Aqua)
Signal (Red)
Guard (Blue)
Ground (Copper)
Insulator/Spacer (Yellow)
Shutter (green)
Getter (purple)
Getter/Power Holder (pink)
Thermocouple (dark green)
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 Innovative Photocathode Module
– Compact and Efficient
– Versatile and Adaptable
 Provides excellent Experimentation Opportunities
– Range of Instrumentation
– Range of Monitoring devices to vary experimentation
Please feel free to provide additional references and/or feedback – kbroughton@aps.anl.gov
– thank you!
Miss Broughton is a Supporter of the America COMPETES Act
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