Correlating structure and function - in situ x-ray analysis of high QE alkali-antimonide photocathodes

Alkali antimonide photocathodes have high quantum efficiency and low emittance when illuminated by visible light, and are thought to be well suited for use in highbrightness photoinjectors for 4th generation light sources. Here we report on the growth of multi-alkali K₂CsSb cathodes on [100] silicon substrates measured using in situ x-ray scattering. Correlations between cathode structure, growth parameters and the resulting quantum efficiency (QE) are also explored. The best cathodes in this study have a QE at 532 nm in excess of 6% and are structurally textured K₂CsSb with grain sizes in excess of 20 nm. In an attempt to reduce the complexity of the current growth methodology, we are also making alkali antimonides in parallel via the reaction of bulk materials in an inert environment. This approach has the advantage that the desired stoichiometry can be obtained exactly. Initial diffraction results from prepared bulk materials are promising and show the formation of well reacted K₃Sb. In the future, we intend to transfer this material to smooth thin photocathode films by either sputtering or pulsed laser deposition.