Figure 1. SEM image of an ordered array of silver vertical nanotubes, with a given length (height h varied between 0.85 μm and 7.5 μm) and inter-antenna distance (pitch p varied between 2 μm and 9.5 μm).

IR broadband illumination (impinging angle θ = 25°, TM-polarization) triggers LSPRs on the longitudinal axis; inset: magnified view of a 3D hollow nanocylinder. Inner cavity and outer diameter (80 nm and 140 nm respectively) are kept constant in all specimen.