1. Characterization Update Ageing Studies
Slade J. Jokela

2. Discussion on Ageing Multiple causes of ageing are apparent
Fast component (decreased gain, short-lived)
I think this is most likely water, hydroxyls
Maybe some other surface-adsorbed species containing oxygen
Plot of work done at SSL (O. Siegmund, J. McPhate, A. Tremsin)
Two slower components
Increase in gain after the initial rapid decrease
Overall decrease in gain that wins out

3. Discussion on Ageing Fast component is “revived” upon air exposure
Studies from SSL
Indicates to me that it is plentiful, but weakly adsorbed
H2O, CO2
OH¯ or CO

4. What could cause Ageing?
Surface composition
Electron stimulated desorption
Electron stimulated migration
Interstitial atoms or atoms in grain boundaries
Surface morphology
Electrons could also induce changes in structure
I know high energy electrons can, not sure about electrons in the 100eV or less range.

5. What tools are available
Center for Nanoscale Materials (CNM)
Two Potentially Useful Instruments
Variable-temperature, UHV, AFM/STM
In High Demand
Scanning Tunneling Spectroscopy
Resistive and e-beam heating
Gas dosing (may be useful for photocathode tests)
LEED/Auger Module

6. What tools are available
Scanning probe/scanning electron microscopy
Four-point contact measurement
Very little demand for this instrument
May be useful for electrical characterization
Has limited functionality as STM
Vibration is the limiting factor
SEM – Normally used for 4-point probe positioning
Gemini column for scanning Auger microscopy
Additional LEED/Auger module
Resistive heater

7. Details LEED module on each instrument
Can be configured to emit low-energy electron beam for sample exposure in small area
Used to test SEY
STM/AFM/SEM/LEED may be used to detect differences in morphology
Scanning Auger can be used to measure surface composition across electron-exposed region.

8. Details What could we study? Initial studies will be on sample coupons
Non-reactive photocathodes
Later studies may include cleaved MCPs
Vacuum transfer system would allow activated photocathodes
The 2nd system mentioned may have its sample prep. module moved to another system, giving us the opportunity to add vacuum transfer capabilities at that time

9. Details
Full details of these systems can be found at:
What to do with the information we learn
Structural and chemical/compositional changes may be able to be induced in order to accelerate the scrubbing treatment
Annealing schedule
Examine other processes available in ALD to eliminate remnant precursor molecules

10. CNM Proposal CNM Proposal is due Friday, March 4th
Have discussed some of these details with Anton at SSL
Have discussed scope of project with Nathan Guisinger at CNM