Demonstration of electron helical dichroism as a local probe of chirality

Abstract

We report observation of electron helical dichroism on a material with chiral structure. In analogy with circular dichroism, a common technique for molecular structural fingerprinting, we use a nanofabricated forked diffraction grating to prepare electron vortex beams with opposite orbital angular momenta incident upon metal nanoparticle clusters and post-select for a zero-orbital angular momentum final state. We observe a difference in the differential scattering probability for orbital angular momentum transfer from vortices with opposite handedness incident on chiral aluminum nanoparticle clusters at 3.5 $\pm$ 0.8 eV. We suggest that the observed electron helical dichroism is due to excitation of surface plasmon vortices. Electron helical dichroism enables chirality measurement with unprecedented spatial resolution over a broad range of energies.

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• Realization of electron vortices with large orbital angular momentum using miniature holograms fabricated by electron beam lithography
• Probing chirality with inelastic electron-light scattering
• Experimental Realisation of a π/2 Vortex Mode Converter for Electrons Using a Spherical Aberration Corrector
• Orbital angular momentum and energy loss characterization of plasmonic excitations in metallic nanostructures in TEM