Guo Lei, Shiohara Keisuke, Yamaguchi Hisato, Wang Gaoxue, Okabe Yuki, Nakatake Masashi, Takakura Shoichi, Yamamoto Masahiro, Ogawa Shuichi, Takashima Yoshifumi
Nagoya University, Furo, Chikusa, Nagoya, Aichi, 464-8601, Japan.
Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, NM 87545, USA.
Sci Rep. 2025 Jan 23;15(1):2900. doi: 10.1038/s41598-025-87603-6.
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 KCsSb 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 KCsSb 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.
碱金属锑化物半导体光阴极因其高量子效率（QE）、低发射度和高时间分辨率，有望成为包括自由电子激光器（FEL）在内的先进加速器的高亮度电子源。这些光阴极面临的两个挑战是：（1）缺乏实现晶体化学计量比的通用沉积方法；（2）它们对真空污染高度敏感，这将其工作压力限制在超高真空，导致寿命短和提取电荷量低。为了解决这些问题，了解沉积光阴极的元素组成并将它们与稳健性相关联至关重要。在这里，我们报告了使用同步辐射X射线光电子能谱研究的锑化铯钾光阴极的深度分布以及这些光阴极的稳健性。我们通过顺序热蒸发制备了两种不同钾含量的光阴极。深度分布表明，钾含量不足的光阴极表面有过量的铯，而膜内钾和铯与锑的比例迅速下降。相比之下，钾含量充足的光阴极表面接近KCsSb的理论化学计量比，并在整个膜厚度的一半以上保持该化学计量比。两种类型的光阴极在532nm处具有相似的最大量子效率；然而，暴露于氧气表明，晶体化学计量比为KCsSb的光阴极在比其钾含量不足的对应物高一个数量级的压力下仍保持量子效率。这些结果突出了合成具有足够钾的锑化铯钾光阴极以实现高量子效率和提高稳健性的理论晶体化学计量比的重要性。
