In situ characterization of alkali antimonide photocathodes

Alkali antimonide photocathodes are a prime candidate for use in high-brightness photoinjectors of free electron lasers and 4th generation light sources. These materials have complex growth kinetics - many methods exist for forming the compounds, each photocathode having different grain size, roughness, and crystalline texture. These parameters impact the performance of the cathodes, including quantum efficiency (QE), intrinsic emittance and lifetime. In situ analysis of the growth of these materials has allowed investigation of correlations between the growth parameters and the resulting cathode performance. This work explores the relationship between the crystallinity of the initial antimony film and the roughness of the final cathode. Two growth methods are compared - a traditional recipe which uses a crystalline initial antimony film and a yo-yo process which builds the cathode through an iterative process using sub-crystalline antimony layers. The traditional method provides exemplary QE (7.5% @ 532 nm), but an exceptionally rough surface. The yo-yo produces a somewhat lower final QE (4.9% @ 532 nm) but a much smoother surface, as observed by grazing incidence small angle x-ray scattering (GISAXS).