Dataset: A single-Crystal Alkali Antimonide Photocathodes: High Efficiency in the Ultrathin Limit

C. T. Parzyck, ^1,* A. Galdi, ^2,* J. K. Nangoi ,¹ W. J. I. DeBenedetti,³ J. Balajka ,³ B. D. Faeth,⁴ H. Paik,⁴ C. Hu, ¹ T. A. Arias ,¹ M. A. Hines ,³ D. G. Schlom ,^5,6,7 K. M. Shen, ^1,6 and J. M. Maxson^2
1Department of Physics, Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, New York 14853, USA
²Cornell Laboratory for Accelerator-Based Sciences and Education, Cornell University, Ithaca, New York 14853, USA
³Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, USA
⁴Platform for the Accelerated Realization, Analysis, and Discovery of Interface Materials (PARADIM), Cornell University, Ithaca, New York 14853, USA
⁵Department of Materials Science and Engineering, Cornell University, Ithaca, New York 14853, USA
⁶Kavli Institute at Cornell for Nanoscale Science, Cornell University, Ithaca, New York 14853, USA
⁷Leibniz-Institut für Kristallzüchtung, Max-Born-Straße 2, 12489 Berlin, Germany

The properties of photoemission electron sources determine the ultimate performance of a wide class of electron accelerators and photon detectors. To date, all high-efficiency visible-light photocathode materials are either polycrystalline or exhibit intrinsic surface disorder, both of which limit emitted electron beam brightness. In this Letter, we demonstrate the synthesis of epitaxial thin films of Cs₃Sb on 3C-SiC (001) using molecular-beam epitaxy. Films as thin as 4 nm have quantum efficiencies exceeding 2% at 532 nm. We also find that epitaxial films have an order of magnitude larger quantum efficiency at 650 nm than comparable polycrystalline films on Si. Additionally, these films permit angle-resolved photoemission spectroscopy measurements of the electronic structure, which are found to be in good agreement with theory. Epitaxial films open the door to dramatic brightness enhancements via increased efficiency near threshold, reduced surface disorder, and the possibility of engineering new photoemission functionality at the level of single atomic layers.