High Order Gap Modes of Film-Coupled Nanospheres

Abstract

Tailoring coupled plasmonic structures is an alternative way to obtain new optical properties of plasmonic materials. Recently, film-coupled nanoparticle systems with high stability and controllability have been used to probe the ultimate limits of field enhancement/confinement and near-field interaction with other quantum emitters. When the gap between particles and films is below a few nanometers, induced high order (HO) gap modes become significant. In this report, we investigate these HO modes associated with the system of a gold nanosphere positioned above a gold film, separated by a nanometer scale spacer layer.The shift in far-field scattering profile under different excitation conditions and collection wavelengths indicates the influence of HO modes and the results are compared to the corresponding simulations. In addition, the far-field scattering spectra/patterns by multipole expansion and the near-field distributions by FEM, both calculated with dielectric function of the low damping factor are utilized to resolve the individual HO modes. These findings not only identify the HO gap modes but also clarify their excitation conditions and far-field/near-field scattered field distribution. The effect of HO modes should be taken into account when the interaction between the gap field and quantum emitters nearby is investigated for active plasmonic devices.

Limits of the Effective Medium Theory in Particle Amplified Surface Plasmon Resonance Spectroscopy Biosensors

“…Figure 12 shows the near-field surrounding a 10 nm-AuNP over a 2 nm thick SiO 2 layer at the wavelengths of 633 nm and 783 nm. In this case, we observe that the interaction decreases with the wavelength, in accordance with [39].…”

“…Vice versa, for the same value of h SiO2 , δσ decreases for higher excitation wavelengths. These general tendencies in the behavior of δσ can be explained with the set-up of the dipolar interaction between the single isolated AuNP and the thin Au layer constituting the Au/SiO 2 sensing platform [7,39], coherently with the results reported in Figure 11 and Figure 12. In our calculation for the 10 nm sized AuNPs, we observed that δσ is maintained below 10% for all the excitation wavelengths considered, when the SiO 2 thickness is higher than 20 nm.…”

“…In this case, we consider a value of σ low enough to disregard the dipole-dipole interaction between the AuNPs, and a nanoparticle size small enough to validate the quasi-static regime [16]. The intensity of the electromagnetic field at the SiO 2 /Au interface clearly shows the onset of AuNP-Au thin film for very small values of h SiO2 [7,17,39].…”

“…The AuNP-Au thin film interaction is also dependent on the wavelength [7,13,17,39]. Figure 12 shows the near-field surrounding a 10 nm-AuNP over a 2 nm thick SiO 2 layer at the wavelengths of 633 nm and 783 nm.…”

Enhancing the Interaction between High-Refractive Index Nanoparticles and Gold Film Substrates Based on Oblique Incidence Excitation

“…The scattering signal was acquired with the use of a customized microscope (modified Olympus BX51) equipped with confocal apertures, a monochromator (Andor SR303i), and an EMCCD (Andor iXon 888). 16 The scattering spectra of nanoparticles were excited by white light from a 150 W xenon lamp and collected by the objective lens. Spectrum normalization was performed as per the following expressionHere, S NP-film represents the scattering signal obtained from the area containing only one nanoparticle, and S film represents the background signal obtained from the area without the nanoparticle on the same sample.…”