Advanced Accelerator Research: Photocathode Sources

粒子加速器和光源是跨生物医学、生物学、化学和物理科学等许多学科进行科学发现的重要工具。具有改进发射特性的光电阴极对于某些下一代光源是理想的，例如基于自由电子激光（FEL）或能量回收直线加速器（ERL）技术的光源。它们也需要用于高分辨率显微镜工具，如动态透射电子显微镜（DTEM）设备。加速器也被工业用于各种制造任务。热离子阴极通常用于工业加速器，尽管光电阴极的光束特性在某些应用中更可取。一些例子是医疗放射加速器，电子束加工和焊接。光电阴极操作的成本和复杂性阻碍了其在工业上的应用。该奖项的目标是应用多学科研究方法来发现修改光电阴极表面以操纵发射特性的方法，使其操作成本更低，或者提高其性能。有了这个奖项，将进行使用薄膜沉积来系统地修改光发射表面特性的研究。具体而言，计划开发新型光电阴极，包括薄涂层等离子体阴极和薄外延多层MgO/Ag/MgO结构。通过在表面沉积薄层材料（如BaO），可以制造出坚固的、高量子效率的金属等离子体纳米结构阴极。目标是操纵光电阴极在可见光波段而不是紫外线波段工作，使该技术更容易用于工业应用。多层MgO/Ag/MgO结构中使用的MgO薄侧翼层改变了表面能带结构；发射特性随层厚有系统的变化。之前的研究可以继续进行，既要调查这些结构在加速器环境中的坚固性，也要更全面地确定性能如何取决于表面粗糙度等特性。

Particle accelerators and light sources are important tools for scientific discovery across many disciplines such as biomedical, biological, chemical, and physical sciences. Photocathodes with improved emission properties are desirable for certain next generation light sources, such as those based on Free Electron Laser (FEL) or Energy Recovery Linac (ERL) technologies. They are also needed for high-resolution microscopy tools such as Dynamic Transmission Electron Microscopy (DTEM) devices. Accelerators are also used by industry for a variety of manufacturing tasks. Thermionic cathodes are typically used for industrial accelerators, although the beam properties of photocathodes would in some applications be more desirable. Some examples are medical radiological accelerators, and electron beam machining and welding. The cost and complication of photocathode operation discourages their use in industry. A goal of this award is to apply a multidisciplinary research approach to discover methods to modify the photocathode surface to manipulate emission properties, making them cheaper to operate, or else improve their performance.With this award, an investigation of the use of thin film deposition to modify photo-emissive surface properties in a systematic way will be carried out. Specifically, development of novel photocathodes including plasmonic cathodes with thin coatings, and thin epitaxial multilayered MgO/Ag/MgO structures is planned. It may be possible to make robust, high quantum efficiency metallic plasmonic nanostructured cathodes by deposition of a thin layer of material such as BaO on the surface. The goal is to manipulate the photocathode to operate at visible, rather than ultra-violet wavelengths, making the technology more accessible for industrial applications. The thin flanking layers of MgO utilized in multilayered MgO/Ag/MgO structures modify the surface band structure; and emission properties vary systematically with layer thickness. Previous research can be continued, both to investigate how robust these structures are in an accelerator environment, and to determine more fully how performance depends on properties such as the surface roughness.