Pozzi Giulio, Lu Peng-Han, Tavabi Amir H, Duchamp Martial, Dunin-Borkowski Rafal E
Department of Physics and Astronomy, University of Bologna, Viale B. Pichat 6/2, 40127 Bologna, Italy; Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons and Peter Grünberg Institute, Forschungszentrum Jülich, 52425 Jülich, Germany.
Ernst Ruska-Centre for Microscopy and Spectroscopy with Electrons and Peter Grünberg Institute, Forschungszentrum Jülich, 52425 Jülich, Germany.
Ultramicroscopy. 2017 Oct;181:191-196. doi: 10.1016/j.ultramic.2017.06.001. Epub 2017 Jun 2.
It has recently been shown that an electron vortex beam can be generated by the magnetic field surrounding the tip of a dipole-like magnet. This approach can be described using the magnetic Aharonov-Bohm effect and is associated with the fact that the end of a long magnetic rod can be treated approximately as a magnetic monopole. However, it is difficult to vary the magnetisation of the rod in such a setup and the electron beam vorticity is fixed for a given tip shape. Here, we show how a similar behaviour, which has the advantage of easy tuneability, can be achieved by making use of the electrostatic Aharonov-Bohm effect associated with an electrostatic dipole line. We highlight the analogies between the magnetic and electrostatic cases and use simulations of in-focus, Fresnel and Fraunhofer images to show that a device based on two parallel, oppositely charged lines that each have a constant charge density can be used to generate a tuneable electron vortex beam. We assess the effect of using a dipole line that has a finite length and show that if the charge densities on the two lines are different then an additional biprism-like effect is superimposed on the electron-optical phase.
最近的研究表明，偶极子状磁体尖端周围的磁场可以产生电子涡旋束。这种方法可以用磁阿哈罗诺夫 - 玻姆效应来描述，并且与长磁棒的末端可以近似视为磁单极子这一事实相关。然而，在这样的装置中很难改变磁棒的磁化强度，并且对于给定的尖端形状，电子束的涡度是固定的。在这里，我们展示了如何利用与静电偶极线相关的静电阿哈罗诺夫 - 玻姆效应来实现具有易于调谐优点的类似行为。我们强调了磁和静电情况之间的类比，并使用聚焦、菲涅耳和夫琅禾费图像的模拟来表明，基于两条平行且带相反电荷、每条具有恒定电荷密度的线的装置可用于产生可调谐的电子涡旋束。我们评估了使用有限长度偶极线的效果，并表明如果两条线上的电荷密度不同，那么一种额外的类似双棱镜的效应会叠加在电子光学相位上。
