Bialkali Cathode Process Program Process samples to optimize QE and bandpass K2CsSb cathodes Small sample test runs, 1.22” Substrate material tests Fused silica and B33 No ITO/Al2O3 ALD underlayers 5th run(s) in small tank used to process Bialkali cathodes (1.22”). Can now deposit 4 simultaneous samples/1 cathode shoot, cover area ~4” wide. 1

Run #5 test Bialkali Cathodes. New geometry, Cathode too thin Longer bakeout & thicker Lower temp / higher Alkali vapor pressure 1st deposition 2nd deposition 3rd deposition Getting the optimal conditions and geometry sorted out Results suggest some cathode area non-uniformities

Cathode/Substrate Plans Can do more tweaking to optimize depositions need to rotate samples to see if non-uniformity is in the deposition geometry or is just the sample type Now have new samples with ITO/Al2O3 ALD underlayers Will use new substrates for next run(s) after we deposit inconel evaporated borders New larger cathode/seal tank is close to being ready, will switch tanks and commission as soon as tooling is done The sensitivity of the activated photocathode is considerably higher, with a quantum efficiency of as high as 37% at about 450 Å and a sensitivity cut off energy of about 6.2 eV. The observed decrease of sensitivity at 988 and 520 Å (and probably not observed at ~670 Å) is likely to correspond to 2xEgap+Eaff,, 4xEgap+Eaff,, and 3xEgap+Eaff,, respectively. A much better spectral continuity of the illumination source is required in order to study the UV absorption fine structure.