Revealing Nanostructures through Plasmon Polarimetry

Abstract

Polarized optical dark-field spectroscopy is shown to be a versatile noninvasive probe of plasmonic structures that trap light to the nanoscale. Clear spectral polarization splittings are found to be directly related to the asymmetric morphology of nanocavities formed between faceted gold nanoparticles and an underlying gold substrate. Both experiment and simulation show the influence of geometry on the coupled system, with spectral shifts Δλ = 3 nm from single atoms. Analytical models allow us to identify the split resonances as transverse cavity modes, tightly confined to the nanogap. The direct correlation of resonance splitting with atomistic morphology allows mapping of subnanometre structures, which is crucial for progress in extreme nano-optics involving chemistry, nanophotonics, and quantum devices.

Advances in optoplasmonic sensors – combining optical nano/microcavities and photonic crystals with plasmonic nanostructures and nanoparticles

“…Controlled surface chemistry for the active part of a sensor can create remarkable properties, such as it serving as an internal standard in SERS or creating defined spacing between numerous plasmonic particles or a substrate and particle [51,58,60]. Figure 5B shows tunnel junctions in Ag nanocube dimers obtained by defined particle spacing from surface functionalisations.…”

Ideal Dimers of Gold Nanospheres for Precision Plasmonics: Synthesis and Characterization at the Single‐Particle Level for Identification of Higher Order Modes

“…For predicting the properties of AuNP dimers, computer simulations usually employ a pair of gold spheres separated by a constant gap distance . In contrast to theory, the experimental realization of such an ideal dimer of spheres is challenging because of structural inhomogeneities: (i) uncontrolled gap distance at the scale of Ångströms; (ii) AuNPs prepared by conventional reduction chemistry are faceted, nonspherical nanocrystals; and (iii) multiple gap morphologies, i.e., different configurations of the opposing crystal facets in the gap region . The combination of all these structural inhomogeneities leads to plasmonic inhomogeneities of the corresponding dimers.…”

“…The second issue, the nonperfect sphericity at the monomer level, has been solved in pioneering colloidal chemistry work using chemical etching yielding a smooth metal surface (Figure S2, Supporting Information) . The third issue, gap morphology, has recently been recognized as a decisive factor influencing the plasmonic properties of dimers or model system of dimers such as a particle on a mirror . However, it is currently not possible to experimentally control either gap morphology or to eliminate the influence of gap morphology in metal nanoparticle dimers.…”

Effect of Film Thickness on the Far- and Near-Field Optical Response of Nanoparticle-on-Film Systems

“…21,23 On the other hand, multiple groups have investigated the physical mechanisms in generating these localized fields in simpler, nanoparticle-on-a-film (NPoF) systems, where the optical properties of noble-metal nanoparticles near a metal film are measured and modeled. 4,5,26−38 From these studies, it is clear that the localization and field strength in the plasmonic gap are heavily dependent on the nanoparticle and film composition, 4,26,27,32 the nanoparticle size and shape, 15,28,39 the polarization/incident angle of excitation, 4,15,20 and plasmonic gap distance. 4,5,15,[29][30][31][32][33][34][35][36]40 Studies that best quantify these dependencies are single-particle NPoF studies, in which spectral broadening due to ensemble averaging is removed and the spectral properties of the individual nanoparticles are compared to theory.…”