Plasmonic fanoholes: on the gradual transition from suppressed to enhanced optical transmission through nanohole arrays in metal films of increasing film thickness

Abstract

We study the evolution from suppressed to enhanced optical transmission through metal nanohole arrays with increasing film thickness. Due to Fano interferences, the plasmon resonances gradually shift from transmission dips for ultrathin films to peaks for thick films, accompanied by a Fano asymmetry parameter that increases with film thickness. For intermediate thicknesses, both peaks and dips in transmission are far from the plasmon resonances, and hence, also far from the spectral positions of maximum light absorption and nearfield enhancements. Calculations for various hole diameters and periodicities confirm the universality of our conclusions.

Optical properties of plasmonic nanopore arrays prepared by electron beam and colloidal lithography

“…3C) are possibly due to the weaker resonance strength and lower direct transmission for reduced pore area, which reduces the contribution of the hole resonance to the continuum background. 29 Finally, it should be noted that the scattering maximum for the CL pores with two gold lms appears very close to the transmission maximum (arrow in Fig. 3D).…”

“…23,24 However, such opaque lms are different because the surface plasmons at the two interfaces are decoupled. 29 In contrast, thinner lms ($50 nm or less) have hybridized modes with very different dispersion relations. Even though the effect of short-range vs. long-range ordering has been discussed also for nanohole arrays in semitransparent lms, 16,[18][19][20] previous work has (by necessity) altered the diameter and/or the surface density of apertures.…”

“…3E). We believe the picture of two spectral resonances with different properties can be made more generic: In recent theoretical work 29 we showed how the whole spectral feature of long-range ordered nanohole arrays can be interpreted as Fano interference between the broad transmission via single holes in a thin metal lm 32,33 and grating coupling to propagating surface plasmons. Similar behaviour can be expected also for CL arrays, albeit with less efficient grating coupling and correspondingly broader spectral features.…”

Hybrid Plasmonics for Energy Harvesting and Sensing of Radiation and Heat

“…[55] Nanoholes in optically thick metal films (a few hundreds of nanometers) strongly enhance the transmission of light, leading to extraordinary optical transmission which is not observed for the bare metal film. [22,56] However, this behavior is not valid for an optically thin metallic film with and without nanoholes. In thin semitransparent metallic films, transmission reduces by introducing nanoholes in the film.…”

“…In thin semitransparent metallic films, transmission reduces by introducing nanoholes in the film. [56] Figure 2-8a illustrates simulated cases of these conditions, for 10 nm and 200 nm thick silver films perforated with arrays of nanoholes. The transmission peak for the optically thick perforated silver film and the transmission dip for the optically thin perforated film represent the plasmonic resonance positions in each film.…”