Nature 467, 301–304 (2010)

Twisted laser beams with wavefronts that spiral around their axis of travel are routinely used to trap and manipulate microscopic particles such as cells. Earlier this year, Masaya Uchida and Akira Tonomura of the RIKEN Institute in Japan showed that electron beams could also be made to twist by passing them through a spiral stack of graphite thin films. However, these vortex beams of electrons were difficult to reproduce reliably. Jo Verbeeck and colleagues at the University of Antwerp and Vienna University of Technology have now shown that such beams can be readily generated in conventional electron microscopes with the help of holograms.

In a similar approach to that previously applied in optics, the Belgian–Austrian team used computer-generated holograms to design a 'mask' that, when placed in the path of an electron beam, would convert a plane wave into vortex beams. The mask, which has a specific grid-like pattern with micrometre-sized gaps, was then constructed from a 100-nm-thick sheet of platinum using a focused ion beam.

Verbeeck and colleagues illustrate the capabilities of their electron vortex beams by using them to probe the magnetic properties of a thin layer of iron. Moreover, they suggest that the beams could prove particularly useful in analysing and manipulating nanoscale materials.