Revealing the Three-Dimensional Orientation and Interplay between Plasmons and Interband Transitions for Single Gold Bipyramids by Photoluminescence Excitation Pattern Imaging

Abstract

Gold bipyramids (AuBPs) attract significant attention due to the large enhancement of the electric field around their sharp tips and well-defined tunability of their plasmon resonances. Excitation patterns of single AuBPs are recorded using raster-scanning confocal microscopy combined with radially and azimuthally polarized laser beams. Photoluminescence spectra (PL) and excitation patterns of the same AuBPs are acquired with three different excitation wavelengths. The isotropic excitation patterns suggest that the AuBPs are mainly excited by interband transitions with 488/530 nm radiation, while excitation patterns created with a 633 nm laser exhibit a double-lobed shape that indicates a single-dipole excitation process associated with the longitudinal plasmon resonance mode. We are able to determine the three-dimensional orientation of single AuBPs nonperturbatively by comparing experimental patterns with theoretical simulations. The asymmetric patterns show that the AuBPs are lying on the substrate with an out-of-plane tilt angle of around 10−15°.

Mode-Specific Coupling of Nanoparticle-on-Mirror Cavities with Cylindrical Vector Beams

“…In particular, if the excitation frequency ω 0 is close to resonance with a longitudinal antenna mode, then K z (ω 0 ) ≫ K xy (ω 0 ) and the Raman signal will be strongest when the sample position r matches a maximum of I bg z ( r , ϵ); conversely, if ω 0 is close to resonance with a transverse antenna mode, then K z (ω 0 ) ≪ K xy (ω 0 ) and the Raman signal will be strongest when the sample position r matches a maximum of I bg xy ( r , ϵ). This discussion allows us to interpret the experimental confocal Raman maps by connecting them to the near-field distribution of the focused excitation beam and the transverse vs longitudinal nature of the antenna mode that is associated with each plasmonic gap mode.…”

Pump-Selective Spectral Shaping of the Ultrafast Response in Plasmonic Nanostars

“…Special interest has been given to geometries featuring spikes, tips, and edges such as, e.g., bi-pyramids, cones, or star-shaped nanoparticles (s-NPs): in the sharpest regions, light excitation produces electromagnetic hot spots where radiation is highly confined and extreme field enhancements can be attained. Because of these intense near fields induced at their hot spots, spiky nanostructures show enhanced sensitivity to their local environment and, as such, have gained great attention, e.g., in surface-enhanced Raman spectroscopy, − biochemical sensing and applications, − and surface chemistry. − …”