Optimizing the electric field around solid and core–shell alloy nanostructures for near-field applications

Abstract

The near electric field enhancement around plasmonic nanoparticles (NPs) is very important for applications like surface enhanced spectroscopies, plasmonic dye-sensitized solar cells and plasmon-enhanced OLEDs, where the interactions occur close to the surface of the NPs. In this work we have calculated the near-field enhancement around solid and core-shell alloy NPs as a function of their geometrical parameters and composition. We have found that the field enhancement is lower in the AuxAg1-x alloys with respect to pure Ag NPs, but it is still high enough for most near-field applications. The higher order modes have a stronger influence over the near-field due to a sharper spatial decay of the near electric field with the increase of the order of multipolar modes. For the same reason, in AuxAg1-x@SiO2 core-shell structures, the quadrupolar mode is dominant around the core, whereas the dipolar mode is predominant around the shell. The LSPR modes can have different behaviours in the near- and the far-field, particularly for larger particles with high Ag contents, which indicates that caution must be exercised for designing plasmonic nanostructures for near-field applications, as the variations of the LSPR in the near-field cannot be inferred from those observed in the far-field. These results have important implications for the application of gold-silver alloy NPs in surface enhanced spectroscopies and in the fabrication of plasmon-based optoelectronic devices, like dye-sensitized solar cells and plasmon-enhanced organic light-emitting diodes.

Near-Electric-Field Tuned Plasmonic Au@SiO2 and Ag@SiO2 Nanoparticles for Efficient Utilization in Luminescence Enhancement and Surface-Enhanced Spectroscopy

“…26a To compare their results with our calculations, we extended the NEF calculation to an NP with R C = 60 nm and t S = 4 nm, resulting in E S−MI /E 0 = 6.1, for which the estimated Raman signal enhancement was 448 (approximate enhancement factor = |E| 4 /|E 0 | 4 ). 24 This enhancement factor is about three times larger than the one computed for an NP with R C = 22.5 nm and t S = 4 nm, which is 1677, but eight times lower than the value reported by Tian et al However, a direct comparison between the experimental result obtained by Tian et al and our theoretical estimation is not possible because they placed the composite NPs over a silver surface, which increases the intensity of the NEF due to the secondary hotspots generated between the NPs and the metal surface. Additionally, the NPs used by Tian et al were of quasi spherical shape with sharp edges, which also increase the intensity of the metal-core hotspots.…”

Size controlled green synthesis of gold nanoparticles using Coffea arabica seed extract and their catalytic performance in 4-nitrophenol reduction

“…With the advancement of nanotechnology, noble metal nanostructures have received great attention in recent times due to their promising contribution in the elds of plasmonics, catalysis, photocatalysis and renewable energy. [1][2][3][4][5] Consequently, the technology or methods of their fabrication have been rened to produce shape, size and geometry-controlled nanostructures to accommodate different applications. While the application of noble metal nanostructures in plasmonic devices has been well established, the performance of noble metals supported over semiconductors and dielectric matrices has been exploited successfully in catalytic and photocatalytic reactions, 3,6,7 alongside other optoelectronic applications.…”

Understanding the ion-induced elongation of silver nanoparticles embedded in silica

“…The LSPR properties (i.e., position, intensity and linewidth) are very flexible and can be controlled by a number of parameters, such as shape, size, geometrical configuration and composition 4–6 . Hence, applications of the plasmonic NPs are equally diverse and cover a large number of areas, like photonics 7 , surface enhanced spectroscopies 8, 9 , biological imaging 10 , catalysis 11 , chemical and biological sensing 12–14 , cancer treatment 15, 16 and energy production 17, 18 .…”