Bi thin films as high-brightness photocathodes*

Photocathodes are integral components of a wide variety of x-ray and electron beam based tools, and the spatio-temporal resolution of these instruments is often limited by the intrinsic brightness of the electron beam when it is emitted from the source material. For photocathodes derived from epitaxial thin films, the band structure and surface termination can be engineered to enhance beam brightness for next generation electron sources. In this talk, we explore topological materials, particularly Dirac semimetals, as potential low mean transverse energy photocathodes. We discuss the synthesis of thin film Na₃Bi by molecular beam epitaxy. From our angle-resolved photoemission spectroscopy measurements, we extract the mean transverse energy and work function of our Na₃Bi films and compare our results to theoretical expectations.