From Electronic Structure to Design Principles for Photocathodes: Cu-Ba Alloys

Developing the next generation of free-electron lasers (FELs) depends on lowering the work function and increasing the quantum efficiency of the photocathode material. However, rules for designing appropriate materials are difficult to discern from observations of structure-composition relationships. This study uses high-quality electronic-structure calculations and a simple physical model to develop design rules for metallic alloys. Interestingly, Cu-Ba alloys terminating in a plane of Ba atoms bear a significant surface dipole, low work function, and high quantum efficiency. These alloys could yield better photocathodes than conventional Cu, and thus better FEL performance.