Near-field study on the transition from localized to propagating plasmons on 2D nano-triangles

In this manuscript we report on a near field study of two-dimensional plasmonic gold nano-triangles using electron energy loss spectroscopy in combination with scanning transmission electron microscopy, as well as discontinuous Galerkin time-domain computations. With increasing nano-triangle size, we observe a transition from localized surface plasmons on small nano-triangles to non-resonant propagating surface plasmon polaritons on large nano-triangles. Furthermore we demonstrate that nano-triangles with a groove cut can support localized as well as propagating plasmons in the same energy range.