Plasmonic Breathing and Edge Modes in Aluminum Nanotriangles

We use electron energy loss spectroscopy (EELS) to perform a comprehensive spectroscopy and mapping of the plasmonic modes sustained by aluminum nanotriangles. Behind the apparent simplicity of such structures, a rich variety of plasmonic modes is observed. Edge modes and pseudoradial breathing modes (pseudo-RBMs) are unveiled as they couple efficiently with the electron source. We propose analytical models confirmed by rigorous simulations to index both families of modes and describe their spatial symmetry. Edge modes could be indexed as nanoantenna modes, while pseudo-RBMs match triangular cavities ones. The dispersion relation of both modes is measured highlighting their different nature. Plasmonic resonances ranging from near-infrared (IR) to ultraviolet (UV) are obtained by varying the triangle sizes, and especially, we found pseudo-RBMs resonances in the UV region, making them interesting for UV applications.