Appl. Phys. Lett. 99, 203109 (2011)

Electron beams are typically plane waves. This means that the beam phase is identical for all points in a plane perpendicular to the beam direction. The phase of an electron vortex beam, on the other hand, describes a spiral. As a result, vortex beams carry orbital angular moment and magnetic moment, which leads to unique interactions with matter. Jo Verbeeck of the University of Antwerp and colleagues from Austria, the Netherlands and Canada have now demonstrated an electron vortex beam with a diameter of less than 1.2 Å.

Electron vortex beams were first created by passing a plane wave beam through a graphite film that spontaneously formed a spiral structure, and acted as a phase plate. This was difficult to reproduce and gave limited control over the resulting beam. Verbeeck and co-workers had improved on this approach by creating a vortex beam with a holographic mask inside a transmission electron microscope. However, the effective beam diameter was several micrometres.

Verbeek and colleagues have now reduced this beam diameter to atomic dimensions by placing a holographic mask in the condenser plane of a state-of-the-art microscope with double aberration correction. At 1.2 Å, the beam size is comparable to the size of the 2p orbital in a nitrogen atom (see image; left and right panels show the beam and the 2p orbital respectively, drawn approximately to scale). The tiny vortex beam may allow atomic-resolution mapping of magnetic states.