Abstract
We investigate local electromagnetic field enhancements in oligomers of plasmonic nanospheres. We first evaluate via full-wave simulations the field between spheres in several oligomer systems: linear dimers, linear trimers, trimers 60°, trimers 90° and linear quadrumers. To gain a better understanding of the field enhancement values, we compare the results with local fields in a hexagonal close-packed (HCP) configuration with same structural dimensions. We then inter-relate the field enhancement values found via full-wave simulations to SERS enhancements of actual fabricated self-assembled oligomers. We find that linear oligomers provide the largest field enhancement values. Finally, we provide closed-form formulas for the prediction of the resonance frequency responsible for field enhancement in linear oligomers, namely dimers, trimers and quadrumers, modeling each nanosphere as a single electric dipole. These formulas provide with resonance values less than 7% shifted when compared to full-wave results even when the gap between spheres is only about one fifth of the radius, showing the powerfulness of dipolar approximations. The results shown in this paper demonstrate that ad hoc clusters of nanospheres can be designed and fabricated to obtain larger field enhancements than with the HCP structure and this may pave the way for the development of improved sensors for molecular spectroscopy.
Highlights
Metal nanoarchitectures, such as arrangements of nanosphere clusters with nm (
It is well known that the surface enhanced Raman scattering (SERS) enhancement is proportional to the fourth power of the field enhancement, we report in Fig. 7(b) the theoretical SERS enhancement calculated as (Ecl / E0)4 using the result computed via the finite element method (FEM)-based full-wave simulation in Fig. 4 pertaining to the linear oligomer configurations
In order to show that the single dipole approximation (SDA) model gains accuracy when the gap increases, we show in Table 3 similar results to Table 2 pertaining to linear clusters of nanospheres assuming a gap of 4 nm
Summary
Metal nanoarchitectures, such as arrangements of nanosphere clusters with nm (
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have