Plasmonic resonances in diffractive arrays of gold nanoantennas: near and far field effects

Abstract

We examine the excitation of plasmonic resonances in arrays of periodically arranged gold nanoparticles placed in a uniform refractive index environment. Under a proper periodicity of the nanoparticle lattice, such nanoantenna arrays are known to exhibit narrow resonances with asymmetric Fano-type spectral line shape in transmission and reflection spectra having much better resonance quality compared to the single nanoparticle case. Using numerical simulations, we first identify two distinct regimes of lattice response, associated with two-characteristic states of the spectra: Rayleigh anomaly and lattice plasmon mode. The evolution of the electric field pattern is rigorously studied for these two states revealing different configurations of optical forces: the first regime is characterized by the concentration of electric field between the nanoparticles, yielding to almost complete transparency of the array, whereas the second regime is characterized by the concentration of electric field on the nanoparticles and a strong plasmon-related absorption/scattering. We present electric field distributions for different spectral positions of Rayleigh anomaly with respect to the single nanoparticle resonance and optimize lattice parameters in order to maximize the enhancement of electric field on the nanoparticles. Finally, by employing collective plasmon excitations, we explore possibilities for electric field enhancement in the region between the nanoparticles. The presented results are of importance for the field enhanced spectroscopy as well as for plasmonic bio and chemical sensing.

Vivid, full-color aluminum plasmonic pixels

“…Prism coupling creates an evanescent wave owing to total internal reflection at the PI-air interface, strongly reducing interfacial background scattering, but does not occur at the substrate-PI interface. Although diffractive coupling in nanostructure arrays typically is studied using normal incidence (18,(31)(32)(33), it can also be achieved using the off-normal angles of incidence used here (28,(34)(35)(36)(37). Images were obtained by mounting a digital single-lens reflex (DSLR) camera into the eyepiece of the microscope; spectra were obtained by directing the signal toward a CCD camera attached to a spectrograph.…”

Understanding and controlling plasmon-induced convection

“…This effect arises from the near-field diffraction of the incident light by the grating formed by the nanoantenna array [26][27][28][29] . When the incident light matches the critical grating period…”

“…Þ is the refractive index of the ITO (water) and y inc is the incident angle, incident light switches from evanescent to propagating, is diffracted parallel to the transverse plane, and results in a grating resonance, also known as the Rayleigh anomaly 26,28 . Here, G c B515, 590 and 650 nm for l OR , l NR and l R , respectively.…”

“…To this end, our work provides insight into the physics of plasmonic arrays by showing that diffractive effects enable elements outside of the excited region of the input field to participate in the heating process, thereby increasing maximum temperature and enhancing fluid velocities 26 . The experimental observation of these convection velocities are in fair agreement with theoretical predictions; however, discrepancies exist due, in part, to differences in the optical properties of the actual and simulated ITO films and the polycrystalline nature of the structures.…”

Overcoming the adverse effects of substrate on the waveguiding properties of plasmonic nanoparticle chains

“…[1][2][3][4][5][6][7][8][9][10] The useful feature of the physical objects mentioned above is their capacity to support very narrow non-Lorentzian resonances 11 that are not broadened by Ohmic losses but very sensitive to the chemical environment. These spectral lines have been observed experimentally.…”