Electromagnetic modelling of the optical behaviour of silver nanospheres on dielectric substrates: The role of a silver buffer layer

Electromagnetic modelling is a fundamental tool to understand the localized surface plasmon resonances in metal nanoparticles and to provide a design strategy able to guide the development of complex plasmonic nanostructures. In this work we theoretically investigate the electromagnetic field enhancement of silver nanospheres on a SiO2 substrate with and without a thin Ag buffer interlayer. This plasmonic substrate can have promising applications for metal enhanced fluorescence. Calculations were performed within the Discrete Dipole Approximation (DDA) by discretizing the entire scatterer and an in-house written routine was used to calculate the near field distribution around the target and the corresponding local field enhancement factor (LFEF). We found that a silver layer increases the LFEF of a sphere by about 360%.