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Characterization Update Ageing Studies

Characterization Update Ageing Studies. Slade J. Jokela. 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.

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Characterization Update Ageing Studies

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  1. Characterization UpdateAgeing 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: http://nano.anl.gov/facilities/proximal_probes.html • 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

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