GENERATION OF SPIN POLARIZED ELECTRONS BY FIELD EMISSION

A pyramidal shaped GaAs (tip-GaAs) photocathodefor a polarized electron source (PES) was developed to improve beam brightness and negative electron affinity(NEA) lifetime by using field emission. The emission mechanism also enables the photocathodeto extract electrons from the positive electron affinity(PEA) surface, and relax the NEA lifetime problem. I-V characteristics of electrons extracted from tip-GaAs shows that the electron beam was extracted by field emission mechanism, because a linear dependence was obtained in Fowler-Nordheim (F-N) plot. Furthermore, a tip-GaAs cathode has succeeded in gcncration of spin polarized electron beam. The polarization degree of tipGaAs is about 34% at excitation photon energy of 1.63cV which is no less than that obtained by an NEA-GaAs cathode.