Electric Directional Steering of Cathodoluminescence from Graphene-Based Hybrid Nanostructures

Controlling directional emission of nanophotonic radiation sources is fundamental to tailor radiation-matter interaction and to conceive highly efficient nanophotonic devices for on-chip wireless communication and information processing. Nanoantennas coupled to quantum emitters have proven to be very efficient radiation routers, while electrical control of unidirectional emission has been achieved through inelastic tunneling of electrons. Here we prove that the radiation emitted from the interaction of a high-energy electron with a graphene-nanoparticle composite has beams in directions that can be made to continuously span the full azimuthal circle even through small variations of the graphene Fermi energy. Emission directionality stems from the interference between the double-cone-shaped electron transition radiation and the nanoparticle dipolar diffraction radiation. Tunability is enabled since the composite hybrid plasmonic resonances and the graphene plasmon polariton phase drive the nanoparticle dipole moment, thus providing an effective electrical reorientation of the nanoantenna. The flexibility of our method provides a way to exploit graphene plasmon physics to conceive nanosources with ultrafast reconfigurability.