Adv. Mater. http://doi.org/fz9jgd (2012)

Light beams that have helical wavefronts were first developed and exploited in the 1990s and can be used to transfer angular momentum to particles and make them spin. Recently, twisted beams of electrons have also been created by passing electrons through a graphite film or a holographic mask. Jo Verbeeck and colleagues at the University of Antwerp have now shown that these electron vortex beams can be used to rotate gold nanoparticles.

The researchers used a holographic mask with an edge dislocation to generate a vortex beam in a transmission electron microscope. A left- or right-handed beam was then used to illuminate a single gold nanoparticle that had a diameter of 3 nm and was supported on a silicon nitride substrate. Owing to the transfer of angular momentum via elastic scattering, the nanoparticle can rotate clockwise or anticlockwise depending on the sign of the vortex beam.

Verbeeck and colleagues also show that the rotation can be used to examine the friction between the nanoparticle and the support, and were able to determine a rotational diffusion coefficient that was consistent with known theoretical values.