Improved robustness of sequentially deposited potassium cesium antimonide photocathodes achieved by increasing the potassium content towards theoretical stoichiometry

Journal Article · 23 January 2025 · Scientific Reports

DOI: https://doi.org/10.1038/s41598-025-87603-6 · OSTI ID:2564649

Guo, Lei ^[1]; Shiohara, Keisuke ^[1]; Yamaguchi, Hisato  ^[2]; Wang, Gaoxue  ^[2]; Okabe, Yuki ^[3]; Nakatake, Masashi ^[4]; Takakura, Shoichi ^[5]; Yamamoto, Masahiro ^[6]; Ogawa, Shuichi ^[3]; Takashima, Yoshifumi ^[1]

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1. Nagoya Univ. (Japan)
2. Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
3. Nihon Univ., Tokyo (Japan)
4. Aichi Science & Technology Foundation (Japan)
5. Nagoya Univ. (Japan); Aichi Science & Technology Foundation (Japan)
6. High Energy Accelerator Research Organization (KEK), Tsukuba (Japan)

Alkali antimonide semiconductor photocathodes are promising candidates for high-brightness electron sources for advanced accelerators, including free-electron lasers (FEL), due to their high quantum efficiency (QE), low emittance, and high temporal resolution. Two challenges with these photocathodes are (1) the lack of a universal deposition recipe to achieve crystal stoichiometries and (2) their high susceptibility to vacuum contamination, which restricts their operation pressure to ultrahigh vacuums and leads to a short lifetime and low extraction charge. To resolve these issues, it is essential to understand the elemental compositions of deposited photocathodes and correlate them to robustness. Here, we report depth profiles for potassium cesium antimonide photocathodes, which were investigated using synchrotron radiation x-ray photoelectron spectroscopy, and the robustness of those photocathodes. We prepared two types of photocathodes with different potassium contents via sequential thermal evaporation. Depth profiles revealed that the photocathodes with a potassium deficit had excess cesium at the surface, while the ratio of potassium and cesium to antimony decreased rapidly within the film. In contrast, the photocathodes with sufficient potassium had close to the theoretical stoichiometry of K₂CsSb at the surface and maintained that stoichiometry for over half the entire film thickness. Both photocathode types had a similar maximum QE at 532 nm; however, exposure to oxygen revealed that the photocathode with a crystalline stoichiometry of K₂CsSb maintained QE at one order of magnitude higher pressure compared to its potassium-deficit counterpart. These results highlight the importance of synthesizing potassium cesium antimonide photocathodes with sufficient potassium to achieve the theoretical crystalline stoichiometry for both high QE and improved robustness.

• Research Organization: Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
• Sponsoring Organization: Japan Society for the Promotion of Science (JSPS); USDOE Laboratory Directed Research and Development (LDRD) Program; USDOE Office of Science (SC), High Energy Physics (HEP)
• Grant/Contract Number: 89233218CNA000001
• OSTI ID: 2564649
• Report Number(s): LA-UR--25-20938
• Journal Information: Scientific Reports, Journal Name: Scientific Reports Journal Issue: 1 Vol. 15; ISSN 2045-2322
• Publisher: Nature Publishing GroupCopyright Statement
• Country of Publication: United States
• Language: English