ANL Photocathodes Growth and Characterization Facility

1. ANL Photocathodes Growth and Characterization Facility Kathleen Broughton Charles Kurtz Ernesto Indacochea Alexander Paramonov Klaus Attenkofer Photocathodes Group June 10, 2010

2. Outline • 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

3. The Vision of Photocathode Growth and Characterization Facility at ANL • 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) Transfer Process Accelerator APS III - V AFM, SEM Alkali Nano Technology Photoluminescence, Cathodoluminescence TEM, EBIC, XPS, SIMS, Auger Lehighton, Hall, ECV Cleaning

4. ANL Photocathode Growth / Characterization Modules – Alkali & III-V with Transfer Process Alkali Transfer III-V

5. Elements of a Photocathode Growth / Activation Module 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).

6. Wash U. MBE for Growth of Photocathode Layers D. Leopold, Advanced Photo-Cathode Material, LAPPD Psec Workshop VII, February 27, 2008.

7. ANL Growth / Activation Module Cryostat (4K – 900K) X,Y,Z Manipulation • 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 Structural / Electrical Characterization (LEED) Heating QE - Characterization Optional RHEED Evaporation

8. QE-Characterization Chamber Sample centered in chamber Temperature Range: 4K – 1050K Rotatable f & q • Optic • Work Function • Temperature dependent I-V curve * • Spectral dependency of I-V curves* • Transmittance, Reflectance, Absorbance • Function of wavelength, specular, off-specular • Quantum Efficiency QE (λ) • Dark Current D(T) • Ellipsometry • Thickness monitor • In situ on sample • Electrical • Triax / BNC Connector design • 1 GΩ+ Measurement • Measurements on Bulk and Surface • Resistivity (2 probe) • TCR (temperature coefficient of resistance) • Carrier Density • Activation Energy of dopants * * Correlated Measurements transmission reflection transmission I-V feedthroughs • Optional • Laser Characterization (Matth) K. Broughton, ANL Photocathodes Growth Chamber and Characterization Module, LAPPD Photocathodes Godparent Committee Review, February 26, 2010.

9. Sample Holder Mount 2” sample 10mm^2 sample • 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

10. Heating Unit • 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

11. Evaporator System • 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

12. Evaporator System Evaporator System • 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)

13. Conclusion • 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