Liu Fangze, Guo Lei, DeFazio Jeffrey, Pavlenko Vitaly, Yamamoto Masahiro, Moody Nathan A, Yamaguchi Hisato
Los Alamos National Laboratory, P.O. Box 1663, Los Alamos, New Mexico 87545, United States.
Advanced Research Institute of Multidisciplinary Sciences, Beijing Institute of Technology, Beijing 100081, China.
ACS Appl Mater Interfaces. 2022 Jan 12;14(1):1710-1717. doi: 10.1021/acsami.1c19393. Epub 2021 Dec 22.
Photocathodes are essential components for various applications requiring photon-to-free-electron conversion, for example, high-sensitivity photodetectors and electron injectors for free-electron lasers. Alkali antimonide thin films are widely used as photocathode materials owing to their high quantum efficiency (QE) in the visible spectral range; however, their lifetime can be limited even in ultrahigh vacuum due to their high reactivity to residual gases and sensitivity to ion back-bombardment in these applications. An ambitious technical challenge is to extend the lifetime of bialkali photocathodes by coating them with suitable materials that can isolate the photocathode films from residual gases while still maintaining their highly emissive properties. We propose the use of graphene, an atomically thin two-dimensional material with gas impermeability, as a promising candidate for this purpose. Here, we report that high-quality bialkali antimonide can be grown on a two-layer (2L) suspended graphene substrate with a peak QE of 15%. More importantly, by comparing the photoemission through varying layers of graphene, we demonstrate that photoelectrons can transmit through few-layer graphene with a maximum QE of over 0.7% at 4.5 eV for 2L graphene, corresponding to a transmission efficiency of 5%. These results demonstrate important progress toward fully encapsulated bialkali photocathodes having both high QEs and long lifetimes using atomically thin protection layers.
光电阴极是各种需要将光子转换为自由电子的应用中的关键组件，例如高灵敏度光电探测器和自由电子激光器的电子注入器。碱金属锑化物薄膜由于在可见光谱范围内具有高量子效率（QE）而被广泛用作光电阴极材料；然而，由于它们对残余气体的高反应性以及在这些应用中对离子背轰击的敏感性，即使在超高真空中它们的寿命也可能受到限制。一个艰巨的技术挑战是通过用合适的材料涂覆双碱光电阴极来延长其寿命，这些材料可以将光电阴极薄膜与残余气体隔离开，同时仍保持其高发射特性。我们提议使用石墨烯，一种具有气体不渗透性的原子级薄二维材料，作为实现这一目的的有前途的候选材料。在此，我们报告高质量的双碱锑化物可以生长在双层（2L）悬浮石墨烯衬底上，峰值量子效率为15%。更重要的是，通过比较不同层数石墨烯的光发射，我们证明光电子可以透过几层石墨烯，对于2L石墨烯，在4.5 eV时最大量子效率超过0.7%，对应于5%的传输效率。这些结果表明，在使用原子级薄保护层制备具有高量子效率和长寿命的完全封装双碱光电阴极方面取得了重要进展。
