EFTEM study of surface plasmon resonances in silver nanoholes

Using energy-filtering transmission electron microscopy we observe localized plasmon resonances in nanoholes of silver. We find two resonances that are typical for single, isolated holes. A comparison with calculations based on the discrete dipole approximation shows that these are dipolar and quadrupolar resonances. In case of the close vicinity of holes we observe modes at lower energies that are ascribed to coupling effects between holes. We propose a hybridization scheme for the case of three collinear holes.