Finite Element Method Simulations of the Near-Field Enhancement at the Vicinity of Fractal Rough Metallic Surfaces

Abstract

We report on (1) simulations of the influence of different surface morphologies on electromagnetic field enhancements at the rough surfaces of noble metals, and (2) the evaluations of the optimal conditions for the generation of a surface-enhanced Raman signal of absorbed species on a metallic substrate. All simulations were performed with a classical electrodynamics approach using the full set of Maxwell's equations that were solved with the three-dimensional finite element method (FEM). Two different classes of surfaces were modeled using fractals, representing dendritic and sponge-like structures. The simulations depict the high inhomogeneity of an enhanced electromagnetic field as that both a field enhancement and a field attenuation near the surface existed. While the dendritical fractals enhanced the local electromagnetic field, the sponge-like fractals significantly reduced the local electromagnetic field intensity. Moreover, the fractal orders of the fractal objects did not significantly alter the total enhancement, and the distribution of a near-field enhancement was essentially invariant to the changes in the angle of an incoming laser beam.