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

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 2

The Vision of Photocathode Growth and Characterization Facility at ANL 3  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) Cleaning Nano Technology AcceleratorAFM, SEM Lehighton, Hall, ECV TEM, EBIC, XPS, SIMS, Auger Transfer Process APS Photoluminescence, Cathodoluminescence

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

Elements of a Photocathode Growth / Activation Module 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 (2005). 5 Critical Element for High QE – CLEANLINESS!

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

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

QE-Characterization Chamber 8  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 G Ω + 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 Sample centered in chamber Temperature Range: 4K – 1050K Rotatable f & q  Optional  Laser Characterization (Matth) K. Broughton, ANL Photocathodes Growth Chamber and Characterization Module, LAPPD Photocathodes Godparent Committee Review, February 26, 2010.

Sample Holder Mount  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 9 2” sample 10mm^2 sample

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 10

 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 Evaporator System 11

Evaporator System  Controlling Evaporation –Power to Getter –Temperature –Ion release 12 Evaporator System 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)

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 – – thank Miss Broughton is a Supporter of the America COMPETES Act 13