Infrared plasmons in long Cu nanorods: (a) maps of the different modes with n increasing from 1 to 10 for a Cu rod of length L = 3.15 μm, diameter D = 121.1 nm, and AR = L/D = 26 (see its ADF image on top). The number of nodes on each of these maps is equal to n + 1, in the middle of these rods there are visible peaks only for n is even; (b) plasmonic EELS spectra collected near the tip of Cu nanorods of different geometrical parameters L, D and AR. A spectrum collected in the middle of the rod displays only peaks of even number n, shown as a dashed plasmon spectrum (from Mkhitarian [141]).