Investigations of Novel Sources of Spin-polarized Electrons

Using a pulsed laser, we investigated the spin-polarization of electrons emitted from bulk GaAs, Ti and Pd chiral nanostructures, and electro-chemically thinned GaAs. Standard sources of spin-polarized electrons from GaAs can have polarizations of approximately 30%, while state-of-the-art spin-polarized electron sources using GaAs cathodes can have as high as 85% spin polarization. Drawbacks for these sources are that they require constant upkeep, have strict vacuum requirements, and are very difficult to learn how to use. For these reasons, we investigated new methods through a different emission process and different materials to see if we could measure a spin-polarization from these electron sources. For the bulk GaAs, we found that the amount of emission that is obtained for a laser pulse decreases due to an electron population in the conduction band state caused by an earlier laser pulse. We refer to this as subadditivity and developed a model that would describe the emission of the electrons and showed us that the emission of the electrons is fast, i.e. comparable to the duration of a laser pulse. After measuring the spin-polarization of the electrons from bulk GaAs, we found that it is spin-polarized, so this may be the first fast, spin-polarized source of electrons with a polarization of approximately 13%. Measurements of the other materials yielded no spin-polarization but brought up further questions that may be investigated in the future. Photoemitted electrons from a chiral surface reconstruction of Si were also investigated to find out if there is a polarization of emitted electrons using the APE beamline at the Elettra Sincrotrone facility