Agradecimentos: We are very grateful to M. Kociak for discussions on electron energy loss spectroscopy and the physics of surface plasmons. D.U. thanks the Brazilian Agencies FAPESP (Grant No. 2014/01045-0) and CNPq (Grant No. 302767/2012-6) for financial support. C.D. acknowledges funding from the ERC under Grant No. 259619 PHOTO EM Ver menos

Abstract: We have theoretically studied how the azimuthal phase structure of an electron vortex beam excites surface plasmons on metal particles of different geometries as observed in electron energy loss spectroscopy (EELS). We have developed a semiclassical approximation combining a ring-shaped beam and the dielectric formalism. Our results indicate that for the case of total orbital angular momentum transfer, we can manipulate surface plasmon multipole excitation and even attain an enhancement factor of several orders of magnitude. Since electron vortex beams interact with particles mostly through effects due to azimuthal symmetry, i.e., in the plane perpendicular to the electron beam, anisotropy information (longitudinal and transversal) of the sample may be derived in EELS studies by comparing nonvortex and vortex beam measurements Ver menos