Plasmonic Metasurfaces with Tunable Gap and Collective Surface Plasmon Resonance Modes

Abstract

Optical properties of a plasmonic metasurface made of a monolayer of gold nanoparticles in close proximity to an aluminum thin film were studied numerically and experimentally. Extinction spectra of the plasmonic metasurface were studied as functions of the thickness of a dielectric spacer between the monolayer of gold nanoparticles and the aluminum film in the visible wavelength range. The goal was to understand the excitation of a collective surface plasmon resonance (SPR) mode and a gap plasmon mode as well as their dependence on the spacer thickness, nanoparticles spacing, and their size. By using finite-difference-time-domain (FDTD) calculations, we find that the SPR extinction peak first red-shifts and then splits into two peaks. The first extinction peak is associated with the collective SPR mode of the monolayer, and it shifts to shorter wavelengths as the spacer layer decreases. As the spacer layer decreases from 35 to 7.5 nm, the second peak gradually appears in the extinction spectra of the metasurface. We assign the second peak to the gap mode. The gap mode first appears at around 620 nm or greater, and it shifts to larger wavelength for larger nanoparticle spacing and size. The FDTD simulations are confirmed by an experimental examination of the dispersion curves of a similar multilayer system. The computational results match the experimental results and confirm the excitation of the two modes.

Plasmonic Coupled Modes in a Metal–Dielectric Periodic Nanostructure

“…Consequently, there is a strong field enhancement and confinement in the dielectric region of the gap. GSP modes [ 28 , 29 , 30 , 31 ] exhibit broad resonances that are minimally affected by the array periodicity. This behavior arises due to the enhanced near-field coupling between the metal film and the nanoblocks when the gap thickness is much smaller than the wavelength of the incident light.…”

“…However, achieving precise control of hybridized plasmonic resonances is challenging due to the relatively high number of parameters involved in an SLR-coupled system [ 25 , 26 , 27 ]. In this context, gap surface plasmon metasurfaces (GSPMs) [ 28 , 29 , 30 , 31 ] based on metal–insulator–metal (MIM) nanostructures [ 32 , 33 , 34 , 35 ] have exhibited strong broadband absorption of multi-spectral coverage. The thickness of the dielectric function of the sandwiched material closely correlates with such absorption [ 36 ], and this geometry has also shown excellent performance in optical phase, amplitude, and polarization manipulation of reflected fields [ 37 ].…”

Laser-Induced Periodic Ag Surface Structure with Au Nanorods Plasmonic Nanocavity Metasurface for Strong Enhancement of Adenosine Nucleotide Label-Free Photoluminescence Imaging

“…Some approaches have been elaborated to achieve an increase in the total quantum yield of fluorophores, namely, by its placing in close vicinity with metal nanostructures. , The nanoscale metal structures could increase the excitation efficiency due to the enhancement of electromagnetic (EM) field near the metal surface caused by the excitation of surface plasmon resonance (SPR). It has been shown that SPR excitation provides an increase in the radiative emission rate and, as a consequence, quantum yield of fluorophores .…”

“…In particular, in NPOM structures, metal NPs are located in close vicinity to metal substrate–mirror. NPOM structures with metal NPs support a new collective plasmonic mode, the so-called gap mode, emerging due to the hybridization of the plasmonic mode of metal NP layer and the propagating surface plasmon polariton (SPP) of the metal substrate. ,,− At the excitation of the plasmonic gap mode, the EM field is squeezed into a very thin gap between the NP layer and the metal film, causing a strong field enhancement in the nanogap, i.e., the generation of hot spots. Moreover, the cavities containing nonspherical NPs with sharp edges should provide a higher signal enhancement for some processes than the cavities with spherical NPs.…”

Controlling light with light in silver-nanospheres and gold-nanorods colloids

“…Exploitation of LSP allows one to amplify, concentrate and manipulate light at the nanoscale, overcoming the optical diffraction limit and improving spatial resolution and sensitivity of optical probes (Novotny and Hecht, 2006). Besides the fundamental interest on the individual NPs properties, research has been dedicated also to the synthesis of new supramolecules containing metal NPs that act as optical antennas (Bharadwaj et al, 2009;Novotny and Hecht, 2006), synthesis and characterization of metaldielectric photonic nanocomposites (de Araújo and Kassab, 2016;Kassab and de Araújo, 2019), as well as fabrication of metamaterials based on metal nanostructures (Lee et al, 2014;Chen et al, 2016;Menezes et al, 2019;Yeshchenko et al, 2019). Surface-enhanced Raman spectroscopy, enhanced photoluminescence, biosensing, photovoltaic cells and thermotherapy are examples of very active areas in many laboratories (see for example: Qin and Bischof, 2012;Saha et al, 2012;Pareek et al, 2017).…”