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 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

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

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.

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

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

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.

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

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

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