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Observation of an Electron Vortex Beam Created from a Self-Charging Rod

Electron vortex beams carry orbital angular momentum and have use in electron microscopy for characterizing the magnetic and chiral properties of materials [1, 2]. For these applications it is preferable to have a single isolated vortex beam to simplify the interpretation of scanning probe measurements. A ferromagnetic rod, which creates a spiral like phase shift for electrons passing near its free end when inserted into the beam path, has been shown to produce good quality single electron vortex beams and is well suited to these applications [3]. However, the production of the highest quality ferromagnetic rods requires well controlled lithography (typically around ±10 nm), along with process equipment capable of handling ferromagnetic materials. Further, the speed with which the magnetization direction of the ferromagnetic rod can be switched, is limited by the significant losses and response time of any macroscopic electromagnetic coil that is used to magnetize the rod. Thus, there is interest in electrostatic means of creating electron vortex beams, that could allow rapid switching of the handedness of the vortex beam, along with tuning of the orbital angular momentum.