High-efficiency alkali antimonide photocathodes degrade with little oxidation, making them hard to characterize and test outside their growth chamber. In this proceeding, we report on the design and performance of the PHOtocathode Epitaxy and Beam Experiments (PHOEBE) laboratory at Cornell University, where the growth, characterization, and testing of alkali photocathodes in vacuum has been successfully integrated. The growth of photocathodes is characterized in-situ by measuring the QE and by looking at the photocathode’s reflection high energy electron diffraction (RHEED) pattern. Once the desired photocathode is obtained, it is moved to a storage chamber to collect spectral response data, after which it is moved to the cryogenic emittancediagnostic beamline via a vacuum suitcase. A rapid cathode exchange system in the diagnostic beam can efficiently transfer alkali-antimonide photocathodes to beamline operation with little QE loss. Using this beamline, the mean transverse energy of the photocathode can be measured at various photoexcitation wavelengths in the visible spectrum and sample temperatures within 20 - 300 K.

Molecular-beam epitaxy (MBE) growth with lattice-matched substrates can lead to the synthesis of single-crystal alkali antimonide photocathodes[1]. Single-crystal photocathodes are expected to have not only high quantum efficiencies (QE) but also low mean transverse energy since they are usually grown as thin films. In this proceeding, we report the synthesis of potassium antimonide photocathodes at the PHOtocathode Epitaxy Beam Experiments (PHOEBE) laboratory at Cornell via MBE by using a sequence of shuttered growth of different unit cells. These cathodes are characterized in terms of spectral response and crystalline structure. The RHEED pattern acquired while synthesizing these photocathodes indicates epitaxial growth occurring on both SiC and Si(100) substrates. Oxidation studies were also performed to better understand the robustness of these materials under non-ideal ultra-high vacuum (UHV) conditions.

A critical factor in determining the limit of the brightness of an electron beam is the mean transverse energy (MTE) of its source, which describes the spread in transverse momentum of electrons at the moment of emission from the source. To increase beam brightness, there has been much work in growing novel photocathodes with low MTE and high quantum efficiency (QE) near threshold photoemission excitation energies. Therefore, it is important to have a testing platform for accurately measuring the MTE of a cathode over a range of cryogenic temperatures and photoexcitation energies, with self-consistent results across multiple measurement techniques. Here, we will discuss the characterization and operation of the Cornell Cryo-MTE-Meter beamline which aims to fulfill these criteria for a robust photocathode testing platform.