  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. To do so, we have
developed a semi-classical approximation combining an azimuthal phase factor
and the dielectric formalism. Our results indicate that the vortex beam order
may be used to modify and control surface plasmon multipole excitation in
nanoparticles. In favorable cases, specific plasmon modes can even attain
enhancement factor of several orders of magnitude. Since, electron vortex beams
interact with particles mostly through interference effects due to azimuthal
symmetries, i.e. in the plane perpendicular to the electron beam, anisotropy
information (longitudinal and transversal) of the sample can be derived in EELS
studies by comparing non-vortex and vortex beam measurements.
