Assessing the Location of Surface Plasmons Over Nanotriangle and Nanohole Arrays of Different Size and Periodicity

Abstract

The increasing popularity of surface plasmon resonance (SPR) and surface enhanced Raman scattering (SERS) sensor design based on nanotriangle or nanohole arrays, and the possibility to manufacture substrates at the transition between these plasmonic substrates, makes them ideal candidates for the establishment of structure-property relationships. This work features near diffraction-limited Raman images and FDTD simulations of nanotriangle and nanohole arrays substrates, which clearly demonstrate that the localization of the hot spot on these SERS substrates is significantly influenced by the ratio of diameter/periodicity (D/P). The experimental and simulation data reveal that the hot spots are located around nanotriangles (D/P = 1), characteristic of localized SPR. Decreasing the D/P ratio to 0.75-0.7 led to the creation of nanohole arrays, which promoted the excitation of a propagating surface plasmon (SP) delocalized over the metal network. The optimal SERS intensity was consistently achieved at this transition from nanotriangles to nanoholes, for every periodicity (650 nm to 1.5 μm) and excitation wavelength (633 and 785 nm) investigated, despite the presence or absence of a plasmonic band near the laser excitation. Further decreasing the D/P ratio led to excitation of a localized SP located around the rim of nanohole arrays for D/P of 0.5-0.6, in agreement with previous reports. In addition, this manuscript provides the first evidence that the hot spots are positioned inside the hole for D/P of 0.4, with the center being the region of highest electric field and Raman intensity. The compelling experimental evidence and FDTD simulations offer an overall understanding of the plasmonic properties of nanohole arrays as SERS and SPR sensors, which is of significant value in advancing the diversity of applications from such surfaces.

Tuning the 3D plasmon field of nanohole arrays

“…In comparison, square arrays would only have 4 bands (90 symmetry) leading to more discontinuous excitation proles, which could be detrimental to broadband plasmon ltering. The bandwidth of the excitation prole increases for greater incident angles (covering a range from 575 to 900 nm at 10 ), which can reach the IR regions at relatively small incident angles (10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20). Thus, we report that precise control of the coloration and bandwidth of transmitted or absorbed light can simply be achieved by tuning the incident and rotation angles, an important concept for active plasmonic ltering.…”

“…SI4 †), which was previously found to maximize refractive index sensitivity. 13 The large periodicity of this substrate promotes NIR excitation, due to the high sensitivity of plasmonic sensors and transparent window of biouids in this spectral region.…”

“…Nanohole arrays recently attracted attention as a substrate for SERS. [29][30][31][32][33][34] We demonstrate enhanced SERS and plasmonic biosensing with the precise control of the resonance wavelength and tuneable eld penetration depth by changing the incident angle. These grating coupling conditions enable simple optimization to achieve higher sensitivity.…”

“…7 Nanohole arrays offer great promise for various applications, including theoretical investigation of light-surface plasmon interactions, 1 biosensing, 8,9 plasmon-enhanced photovoltaics, 10 spectro-electrochemistry, 11 and surface enhanced spectroscopy. 12,13 The optical properties of nanohole arrays are well understood for different hole diameters, 14 periodicities, 15 and metal compositions. 14 However, grating coupling conditions remain poorly characterized and uncertainty remains concerning the importance of symmetry (S, rotation symmetry of 60 for hexagonal arrays), incidence angle (q) and azimuthal rotation (f) for sensing and optical ltering.…”

Investigating the Optical Transmission Spectra of Plasmonic Spherical Nano-Hole Arrays

“…One of the most interesting plasmonic structures is metallic films perforated with periodic nano-hole arrays [7][8][9] that may lead to extraordinary transmission [10][11][12]. The extraordinary behaviors of the perforated metallic film are largely due to the presence of surface plasmons (SPs), which can be excited by illuminating the film using a Gaussian beam.…”