Plasmonic Properties of Silver Trimers with Trigonal Symmetry Fabricated by Electron-Beam Lithography

Abstract

We investigate the dipolar plasmon modes of nanoparticle trimers formed by three equal silver disks of diameter D = 100 nm located on the vertexes of an equilateral triangle. Samples were fabricated by electron-beam lithography and studied experimentally by dark-field spectroscopy. The results are found to be in good agreement with electrodynamical simulations based on the discrete dipole approximation (DDA). Similar to nanoparticle dimers, the trimer system exhibits two hybridized dipole resonances to the red and to the blue of the single particle resonance. However, the far-field spectra are polarization-insensitive for light incident normal to the plane of the trimer, and the peak shifts, which occur as the edge-to-edge distance d between the particles decrease, are smaller than for dimers. Moreover, we find that the dipolar displacement patterns are well described by linear combinations of bonding and antibonding symmetry adapted coordinates obtained through symmetry analysis based on the ideal D 3h point-group.

Collective plasmon modes in a compositionally asymmetric nanoparticle dimer

“…1 The electromagnetic field surrounding a metallic nanoparticle that has been excited near the plasmon resonance can extend for a considerable distance, and a compelling analogy therefore exists between the plasmon resonance of individual nanoparticles and the wave functions of simple atoms. Similar to the roles of atoms in molecules and solids, metal nanoparticles can assemble to create a diverse range of new plasmonic nanoclusters, 2 including dimers, 3 trimers, 4 quadrumers 5 and tetramers, 6 etc. 7 Each type of plasmonic nanocluster exhibits its own unique set of collective plasmon modes.…”

The surface plasmon modes of self-assembled gold nanocrystals

“…3a) under two typical polarization cases: p-polarization and s-polarization. In the s-polarization case (k perpendicular to the substrate plane), the 2D equilateral trimer exhibits D 3h symmetry and should display one in-plane electric dipolar bonding mode at lower energy than the triply degenerate single-particle plasmon mode 29 . This collective mode is predicted to possess a strong net dipole moment and will couple efficiently to the incident radiation.…”

EFTEM study of surface plasmon resonances in silver nanoholes

“…The low-energy resonances 1 and 2 show approximately trigonal symmetry. For a discussion of plasmon resonances in such structures we refer to the paper of Alegret et al [33]. Here we concentrate more closely on the linear 3-hole resonance 3 which is shown enlarged in Fig.…”