Fine tuning of plasmonic properties of monolayers of weakly interacting silver nanocubes on thin silicon films

Abstract

Plasmonic properties, such as refractive index sensitivity (RIS), surface enhancement of the Raman signal (SERS), fluorescence quenching, and photocatalytic activity, of monolayers of weakly interacting monodisperse silver nanocubes were qualitatively modified in a very well controlled manner by supporting them on thin silicon films with varying thickness. Such fine tunability is made possible by the strong dependence of the nanocube dipolar (D) and quadrupolar (Q) plasmon mode hybridization on the refractive index of the supporting substrate. By increasing the Si film thickness from zero to ~25 nm we were able to "shift" the D resonance mode by up to 200 nm for ~80 nm cubes without significantly affecting the Q mode. The silicon supported nanocubes showed a significant improvement in RIS via the Q mode with a figure of merit greater than 6.5 and about an order of magnitude enhancement of the SERS signal due to the stronger electric field created by the D mode. Such substrates also showed a ~10 times decrease in rhodamine 6G fluorescence as well as the rates of amorphous carbon formation. The study proposes a new way to design and engineer plasmonic nanostructures.

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.…”

Subradiant, Superradiant Plasmon Modes and Fano Resonance in a Multilayer Nanocylinder Array Standing on a Thin Metal Film

“…Metal nanoparticles [12][13][14][15][16][17] also show novel optical properties which strongly depend on their shapes, sizes, and compositions as well as the dielectric environments. Based on the theory of hybridized plasmon modes [18], complex nanostructures consisting of multilayer particles were also studied, including the most famous shell-core structures [19][20][21][22] and metal-dielectric-metal nanoparticles [20,[23][24][25].…”

Plasmonic properties of weakly interacting silver nanocubes on high refractive index substrates

“…However, we know from previous studies that the degree of separation between the hybrid D and Q modes is limited by the refractive index of the supporting substrate as well as the size of the silver nanocube being equal to roughly half of the edge length of the cube. 6 From this we can infer that the position of the D mode is further red shifted relative to the 20nm substrate. We see the continued trend in the shape of the reflection mode becoming even more asymmetric and tailing off even further towards the red part of the spectrum as well as a lack of any features in the spectrum that are situated in the area where the D mode is expected ( figure 5).…”

“…This range is determined by many factors including, cube size, substrate refractive index, and the refractive index of the surrounding medium. 6 The glass substrate has the lowest sensitivity for RIS sensing. This is primarily due to the small range that the hybrid plasmons are resolvable.…”

“…8 Additionally with the ever increasing ability to synthesize monodisperse metal nanoparticles of specific geometries 2 coupled with the ability to control the pattern and organization of these particles onto various substrates 1 has allowed for their properties to be studied in much greater detail leading to development of their use in applications including sensing 3 , IR 4 , photovoltaics 5 , and SERS enhancement. 6 Figure 1. Extinction spectra of silver nanocubes dispersed in ethanol (left), SEM-TED image of nanocubes (right) *anatoli_ianoul@carleton.ca; phone 1 613 520-2600; fax 1 613 520-3749…”