ANL Photocathodes Growth and Characterization

Facility

Kathleen BroughtonCharles Kurtz

Ernesto IndacocheaAlexander Paramonov

Klaus Attenkofer

Photocathodes GroupJune 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

NanoTechnolog

y

Accelerator

AFM, SEMLehighton, Hall, ECV

TEM, EBIC, XPS, SIMS, Auger

Transfer Process

APS

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

4

Alkali Transfer III-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. 323-328 (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, 2008.

6

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 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

Sample centered in chamberTemperature Range: 4K – 1050KRotatable f & q

OptionalLaser 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 – kbroughton@aps.anl.gov – thank you! Miss Broughton is a Supporter of the America COMPETES Act 13