Construction and commissioning of a commercially viable high-brightness, ultra-fast, spin-polarized electron source using a novel GaAs nano-emitter cathode array.

An ultra-fast, polarized source for electron microscopy is not currently available from industry. Such a source would open the door to table top experiments of time-resolved dynamics of the out- of-equilibrium magnetic phases, which to date have mostly been investigated with large X-ray facilities. Novel magnetic phases could feasibly impact data storage and spin-based circuits for quantum information. Further, the spin-polarized electron beam itself is of fundamental interest to materials science—understanding the interplay of Coulomb repulsion and degeneracy pressure in the model system of a beam may help understand this interplay in quantum magnetic materials. In Phase I, we fabricated lithographically-defined GaAs photocathode nano-emitters with diameters down to 500 nm, having quantum efficiencies up to 1%, and spin polarization around 40%. In addition, we completed a full design (mechanical, electrostatic, vacuum, and optical features) of a compact dc electron source for use with these photocathodes. Detailed beam dynamics of beams generated from the source were performed, and the trade-offs between the beam brightness, energy spread, and bunch length were explored. Phase II will see the further development of these cathodes to allow ultra-short bunch generation (100’s of fs) and even smaller emission diameters (down to 200 nm), the construction of two dc guns (a first prototype, and a production unit), as well as a diagnostic beamline suite to characterize these sources. Our design is applicable to several forms of electron microscopy,, and our approach allows for robust operation while remaining flexible in terms of beam output (coherence, flux, and temporal resolution).