The recent discovery of vortex electron beams [1-3] has generated many interests and the new understanding may lead to applications in material characterization . The method of creating vortex electron beams using a forked aperture  is popular but has a drawback that electron vortex beams with different orders are produced side-by-side in the specimen plane. More recently a method of producing electron vortex using a spiral holographic aperture was demonstrated, with the advantage of being able to select a specific vortex beam in focus on the sample [5,6]. However, the spiral aperture is difficult to reproduce accurately because of many fine features and it is also mechanical fragile and the extra reinforcement bars were added in the mask for mechanical stability.
In this study, we propose and experimentally demonstrate a simple and versatile way of generating electron vortex beam carrying orbital angular momentum (OAM), using a chiral electron sieve illuminated by a plane electron wave. Fig. 1 (a) shows an electron sieve mask as viewed using a scanning transmission electron microscope. It consists of a number of spirals (5 in this case), each spiral consists of suitablly arranged holes in such a way that they produce a vortex beam approximate at a near field distance . Fig. 1(b) shows the resultant beam intesnity profile as the designated distance. This shows a characteristic donut shaped beam illumination characteristic of an electron vortex beam. The is confirmed by direct comparison of the intensity profile with the simulated result using Fresnel diffraction theory (Fig. 1(c)). The same simulation shows the phase structure at the center of the donut ring does contains a vortex structure of order 5.
For this particular electron sieve mask, the mask pattern can be compared with the spiral diffractive holographic grating structure produced by interference between the vortex beam and that of a spherical reference waves , showing comparable efficiency. However, it has the practical advantage of being much easier to produce and mechanically more robust than the normal binary diffractive grating. We will show that this is a practical example of a much rich set of electron sieves that we can generate to shape electron beams, many of which has no counter part in conventional holographic diffractive grating theory .
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To cite this abstract:Jun Yuan, Yuanjie Yang, Gnanavel Thirunavukkarasu, Mohamed Babiker; Chiral electron sieves for electron vortex beam generation. The 16th European Microscopy Congress, Lyon, France. https://emc-proceedings.com/abstract/chiral-electron-sieves-for-electron-vortex-beam-generation/. Accessed: December 5, 2022
EMC Abstracts - https://emc-proceedings.com/abstract/chiral-electron-sieves-for-electron-vortex-beam-generation/