Molecular beam epitaxial growth of Sodium Antimonide photocathodes

Cornell University has been working on developing techniques to grow single crystal photocathodes for electron sources using the Molecular Beam Epitaxy (MBE) technique. As a result, the first single crystal Cs3Sb photocathode was produced, which has shown high quantum efficiency and is expected to have a low Mean Transverse Energy (MTE). Now, other alkali materials are being explored. In this work, we report the epitaxial growth of Na-Sb photocathodes at the PHOtocathode Epitaxy Beam Experiments (PHOEBE) laboratory at Cornell University, employing a sequence of shuttered growth steps to form distinct unit cells. The photocathodes were characterized by Quantum Efficiency (QE) measurements and Reflection High-Energy Electron Diffraction (RHEED) patterns collected during growth. The RHEED streaky pattern shows angle dependence, confirming their single crystal structure. Notably, these Na-Sb photocathodes exhibited a QE exceeding 1% at 400 nm, which is much higher than previous reports on this compound. The possible reasons for this discrepancy are discussed.