Rugged bialkali photocathodes encapsulated with graphene and thin metal film

Lei Guo; Fangze Liu; Kazuki Koyama; Nolan Regis; Anna M Alexander; Gaoxue Wang; Jeffrey DeFazio; James A Valdez; Anju Poudel; Masahiro Yamamoto; Nathan A Moody; Yoshifumi Takashima; Hisato Yamaguchi

doi:10.1038/s41598-023-29374-6

Rugged bialkali photocathodes encapsulated with graphene and thin metal film

Sci Rep. 2023 Feb 10;13(1):2412. doi: 10.1038/s41598-023-29374-6.

Authors

Lei Guo^{1

2}, Fangze Liu³, Kazuki Koyama⁴, Nolan Regis⁵, Anna M Alexander⁵, Gaoxue Wang⁵, Jeffrey DeFazio⁶, James A Valdez⁵, Anju Poudel⁵, Masahiro Yamamoto⁷, Nathan A Moody⁵, Yoshifumi Takashima^{8

4}, Hisato Yamaguchi⁹

Affiliations

¹ Nagoya University Synchrotron Radiation Research Center (NUSR), Furo, Chikusa, Nagoya, Aichi, 464-8601, Japan. l.guo@nusr.nagoya-u.ac.jp.
² School of Engineering/Graduate School of Engineering, Nagoya University, Furo, Chikusa, Nagoya, Aichi, 464-8601, Japan. l.guo@nusr.nagoya-u.ac.jp.
³ Advanced Research Institute of Multidisciplinary Sciences, Beijing Institute of Technology, Beijing, 100081, China.
⁴ School of Engineering/Graduate School of Engineering, Nagoya University, Furo, Chikusa, Nagoya, Aichi, 464-8601, Japan.
⁵ Los Alamos National Laboratory (LANL), P.O. Box 1663, Los Alamos, NM, 87545, USA.
⁶ Photonis Defense Inc., 1000 New Holland Ave., Lancaster, PA, 17601, USA.
⁷ Innovation Center for Applied Superconducting Accelerators, High Energy Accelerator Research Organization (KEK), 1-1 Oho, Tsukuba, Ibaraki, 305-0801, Japan.
⁸ Nagoya University Synchrotron Radiation Research Center (NUSR), Furo, Chikusa, Nagoya, Aichi, 464-8601, Japan.
⁹ Los Alamos National Laboratory (LANL), P.O. Box 1663, Los Alamos, NM, 87545, USA. hyamaguchi@lanl.gov.

Abstract

Protection of free-electron sources has been technically challenging due to lack of materials that transmit electrons while preventing corrosive gas molecules. Two-dimensional materials uniquely possess both of required properties. Here, we report three orders of magnitude increase in active pressure and factor of two enhancement in the lifetime of high quantum efficiency (QE) bialkali photocathodes (cesium potassium antimonide (CsK₂Sb)) by encapsulating them in graphene and thin nickel (Ni) film. The photoelectrons were extracted through the graphene protection layer in a reflection mode, and we achieved QE of ~ 0.17% at ~ 3.4 eV, 1/e lifetime of 188 h with average current of 8.6 nA under continuous illumination, and no decrease of QE at the pressure of as high as ~ 1 × 10^-3 Pa. In comparison, the QE decreased drastically at 10^-6 Pa for bare, non-protected CsK₂Sb photocathodes and their 1/e lifetime under continuous illumination was ~ 48 h. We attributed the improvements to the gas impermeability and photoelectron transparency of graphene.