Vortex Beams opens new possibilities for electron microscopy

Vortex beams render completely new possibilities for electron microscopy. A method of producing extremely intense vortex beams has been discovered at the Vienna University of Technology (TU Vienna).

Nowadays, electron microscopes are an essential tool, especially in the field of materials science. At TU Vienna, electron beams are being created that possess an inner rotation; these vortex beams cannot only be used to display objects, but to investigate material-specific properties with minute precision. A new breakthrough in research now allows scientists to produce much more intense vortex beams than ever before.

In a tornado, the individual air particles do not necessarily rotate on their own axis, but the air suction overall creates a powerful rotation. The rotating electron beams that have been generated at TU Vienna behave in a very similar manner. Vortex beams can only be explained in terms of quantum physics: the electrons behave like a wave, and this quantum wave can rotate like a tornado or a water current behind a ship's propeller.

After the vortex beam gains angular momentum, it can also transfer this angular momentum to the object that it collides. The angular momentum of the electrons in a solid object is closely linked to its magnetic properties. For materials science it is therefore a huge advantage to be able to make statements regarding angular momentum conditions based on these new electron beams.

Peter Schattschneider and Michael Stöger-Pollach (USTEM, TU Vienna) have been working together with a research group from Antwerp on creating the most intense, clean and controllable vortex beams possible in a transmission electron microscope. The first successes were achieved two years ago: at the time, the electron beam was shot through a minuscule grid mask, whereby it split into three partial beams: one turning right, one turning left and one beam that did not rotate.

Now, a new, much more powerful method has been developed: researchers use a screen, half of which is covered by a layer of silicon nitride. This layer is so thin that the electrons can penetrate it with hardly any absorption, however they can be suitably phase-shifted. After focusing using a specially adapted astigmatic lens, an individual vortex beam is obtained.

 

More exotic applications of vortex beams are also conceivable: in principle, it is possible to set all kinds of objects in rotation, even individual molecules using these beams, which possess angular momentum. Vortex beams could therefore also open new doors in nanotechnology.