Localized surface-plasmon resonances in periodic nondiffracting metallic nanoparticle and nanohole arrays

Abstract

We compare the optical response of periodic nondiffracting metallic nanoparticle and nanohole arrays. Experimental data from both structures show a pronounced minimum in their wavelength-dependent transmittance that, through numerical modeling, we identify as being due to the excitation of localized surface-plasmon resonances associated with the nanoparticles/nanoholes. Our main finding is that, while the optical response of the nanoparticle arrays is largely independent of interparticle separation, the response from nanohole arrays shows a marked dependence on interhole separation. We attribute this effect to coupling between localized surface-plasmon resonances mediated by the symmetric surface plasmon-polaritons associated with the metal film. Further numerical modeling supports this view. [4][5][6] applications that exploit the strongly localized electromagnetic fields associated with these resonant modes. Arrays of nanoparticles have in particular received considerable attention as advances in fabrication techniques allow finer control over structural dimensions. [7][8][9][10][11] It is also known that when metal nanoparticles are brought into close proximity to each other the modes they support may interact, or couple, so as to modify both the resonance shape and frequency of the LSPRs. 12,13 The properties of LSPRs associated with metallic nanoparticles can also be modified by the presence of a nearby metallic surface. 14,15 The extraordinary optical transmission properties of regular arrays of nanoholes in thin metal films were first reported by Ebbesen and co-workers. 16 Since then it has been demonstrated that under appropriate conditions single nanoholes in metallic films may support LSPRs in a manner analogous to that of nanoparticles. [17][18][19][20][21][22] The similarities between the LSPRs of nanoholes and nanodiscs were discussed by Haynes et al. 10 Indeed, Käll and co-workers 17 recently showed that for irregular arrays of such holes the LSPRs of the nanoholes are blueshifted as the hole density is increased, an effect attributed to coupling between LSPRs of neighboring holes. However, as far as we are aware, there has not yet been a comparison of interparticle/interhole coupling in periodic nondiffracting metallic nanoparticle/nanohole arrays.Here we present such a study and show that despite their similarities, these complementary structures show marked differences in their optical response. For the range of periods considered here, we find that the spectral position of the transmittance minimum associated with the nanohole arrays varies with the array period, an effect we attribute to strong LSPR coupling mediated by surface plasmon-polaritons ͑SPPs͒ supported by the intervening flat metallic film. For the complementary nanoparticle arrays there is little shift since SPPs are not supported by this structure. Results from numerical modeling help us identify the role of the symmetric ͑with respect to surface charge distributions 23 ͒ SPP mode supported by the metal film in causing this diffe...

Plasmoelectric potentials in metal nanostructures

“…Resonant absorption of light in the hole arrays results from the diffractive coupling of incident light to surface plasmon polaritons (SPP) propagating at the metal-dielectric interface (12,31). For the thin (18 nm) Au films used, SPPs on the Au-air and the Auglass interface are strongly coupled (32), giving rise to symmetric and anti-symmetric insulator-metal-insulator (IMI) SPP modes.…”

“…Due to the strong dispersion, the array pitches required to couple to the IMI SPP are much smaller than the free-space wavelength (e.g. 200 nm at = 600 nm) (31).…”

Plasmonic meta-atoms and metasurfaces

“…Instead of antennae one can also design metamaterials based on inverse structures, i.e. sub--wavelength apertures in a metallic sheet [19][20][21] and utilise Babinet's principle 22,23 or extraordinary transmission 24 based on surface--plasmon excitation.…”

Recent advances in plasmonic nanostructures for sensing: a review

“…Using such nanohole arrays etched into a gold metallic film, it has been shown that the LSPR can be easily tuned through the visible and NIR region of the electromagnetic spectrum simply by altering the interhole separation distance. 110,108 This tunability for a particular application of interest allows for dramatic increases in SPR sensitivity. 107,[118][119][120] Although the tunability of such nanoarrays in gold is limited to the NIR and longer wavelength region of the visible (i.e., ∼500 nm or greater), a variation of these nanoslit and nanohole arrays, known as nanotriangle arrays [see Fig.…”