Study and Characterization of Nano-structured Electron Sources Using Photoemission Electron Microscope

Photoinjectors, renowned for producing electron beams of unparalleled brightness, are pivotal to numerous high-impact scientific endeavors, including free electron lasers, ultrafast electron diffraction and microscopy experiments, and inverse Compton scattering x-ray sources. Among the critical components of the photoinjector, the photocathode plays a central role, as its quantum efficiency, mean transverse energy, response time, electron energy spread of emitted electrons, and lifetime/robustness collectively determine the quality of the electron bunch generated for the aforementioned applications. Notably, a Photoemission Electron Microscope emerges as a standout instrument capable of simultaneously measuring these parameters. This study marks the inaugural utilization of PEEM as a tool for characterizing nanostructured electron sources developed for nextgeneration accelerator applications.Chapter two discusses characterization techniques using photoemission electron microscope. In this chapter, the various capabilities of PEEM which includes imaging in real space, k-space and measuring the kinetic energy distribution of the emitted photoelectrons was discussed. Chapter three presents a detailed investigation and photoemission characterization of nitrogen-incorporated ultrananocrystalline diamond, (N)UNCD, a novel semiconductor photocathode which has garnered attention for its potential application in photoinjectors aimed at high peak current extraction. Chapter four presents a detailed photoemission characterization measurements from low electron affinity cesium antimonide (Cs3Sb) photocathode films. In this work, for the first time, thermal limit mean transverse energy from Cs3Sb photocathode was demonstrated. Chapter five presents non-linear photoemission studies from the (N)UNCD pyramid tip cathode. In this work for the first time, the photoemission electron energy spectra from the (N)UNCD pyramid tip cathode was measured. In Chapter six using plasmonic Archimedean spiral photocathode, an emission spot (σx) of ∼50 nm rms resulting in a record low emittance of less than 40 pm-rad - at least an order of magnitude smaller compared to the best of the Åmittance previously demonstrated from a geometrically flat photocathode was demonstrated. Lastly, in Chapter seven, using PEEM, a new mode, ‘evanescent mode’ photoemission from novel photonics integrated cathodes was demonstrated. Photoemission confined in the transverse direction as small as 1 μm using a nanofabricated Si3N4 waveguide under a ∼5 nm thick Cs3Sb photoemissive film was demonstrated. This work demonstrates a proof of principle feasibility of such photonics-integrated photocathodes and paves the way to integrate the advances in the field of photonics and nanofabrication with photocathodes to develop next-generation high-brightness electron sources for various accelerator applications.