In electron microscopes, electrons are hurled at a velocity near the speed of light at materials or nanoparticles, to learn about the shapes, morphologies and optical characteristics. In particular, in Energy Electron Loss Spectroscopy (EELS), the energies of electrons before, and after scattering off nanoparticles are compared to contruct the spectra, and detailed maps of their optical resonances.
In a new twist on this technology, here we explore how EELS can be upgraded by pre-shaping the electron into the so-called Vortex Electron Beams (VEBs). VEBs are made up of electrons with substantial orbital angular momentum, and thus behave like little magnetic probes. We show that this new property allows VEBs to resolve the electric of magnetic character of the detected optical modes of nanoparticles. Furthermore, we demonstrate that, unlike the conventional electron beams, VEBs can readily characterize the dichroism of nanoscale system!
Our paper has just been published in PRResearch:
https://journals.aps.org/prresearch/abstract/10.1103/PhysRevResearch.5.023192
Mikołaj K. Schmidt 