Metal Plasmonic Nanostructures Functionalized by Atomic Layer Deposition of 2A Metal-Oxides for Robust High-Quantum-Efficiency Ultrafast Photocathodes
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AbstractHigh quantum efficiency (QE) photocathodes are central for efficient photoinjectors and ultra-fast electron microscopes. Current high QE photo cathode materials like GaAs, alkali-tellurides and alkali-antimonides require ultra-high vacuum and even then have a short life time. Moreover, most of these materials require an ultraviolet light source to operate. Photoemission using a light source in the visible can be accomplished with Cs:GaAs; however this cathode has a slow response time. We propose a principally new engineered photocathode which is robust, high QE efficient, operates in visible wavelengths, and has a & lt;100 fs response time. Such a cathode would preserve the current benefits of high QE photocathodes and address future challenges in the field of scientific accelerators as well as aiming at additional commercial applications such as ultrafast microscopy and detection systems. We propose to fabricate a plasmonic base substrate (Au or Ag nanoparticles or nanowires) functionalized by atomic layer deposition (ALD) of MgO and BaO (known as 2A metal oxides) of only few atomic monolayers to lower the work function. The work function is lowered to enable photoemission with visible photons. The plasmonic resonance of the noble metal nanoparticles can be tuned to provide efficient light absorption hence improving the quantum efficiency of the system. Finally, the cathode consists simply of noble metal nanoparticles under a robust oxide coating and is expected to have a long lifetime. In Phase I we will fabricate the proposed cathode in two steps: synthesis of a plasmonic base structure, followed by atomic layer deposition of the functional layer. The cathode then will be characterized by measuring its quantum efficiency, lifetime in terms of vacuum/atmospheric poisoning, and the thermal emittance will be estimated. Applications and benefits: Robust, high quantum efficiency, extended lifetime, ultrafast photocathodes operating at visible wavelengths will significantly improve the beam quality of the photoinjectors for current and future light sources. Besides applications in basic science, the long life of the cathode material and the ability to use a visible laser means that photoinjectors will find a variety of applications in electron microscopy and vacuum electronics. Medical therapy and diagnostic systems will be able to make use of the high quality electron beams generated in a high QE photo-injector without sacrificing the average current.
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