GaAs-based photoemission sources of spin-polarized electrons: A composite GaAs-coated W nanotip and plasmonic planar GaAs emitters

We have recently demonstrated ultrafast multi-photon photoemission of spin-polarized electrons from GaAs shards using a 20 kV Mott gold-target electron polarimeter. Both the yield and polarization of the emitted electron pulses were characterized. Scanning electron microscopy of these photocathodes revealed  random nanostructures at the photoemitting surfaces. To achieve well-defined point-like nanotips with significant spatial coherence properties, we are now investigating the deposition of thin layers of GaAs on electrochemically etched W nanotip needles using molecular beam epitaxy. We report progress made on this study as well as on the development of GaAs tips fabricated by focused ion beam milling. Additionally, simulation results of several plasmonic nanostructures in planar film geometry are presented that demonstrate local field enhancement due to surface plasmon excitation. The excited plasmons are expected to increase both the photoemission yield and the order [1], when compared with a flat film at modest fs laser oscillator powers. The structures include arrays of nanoholes [2], and noble metal islands and nanoscale patterns on flat GaAs substrates.  

[1] S. Keramati, et al., New J. Phys. 22, 083069 (2020).

[2] R. K. Li, et al., Phys. Rev. Lett. 110, 074801 (2013).