Electromagnetic field enhancement in TERS configurations

We use three-dimensional finite-difference time domain (3D-FDTD) simulations to investigate the field enhancement properties of tip-enhanced Raman scattering (TIERS) in order to find optimal geometric parameters of the metal tip and the metal substrate under certain excitation wavelengths with side illumination. The simulation results show that plasmon coupling effects between the metal tip and the metal substrate play the key role in TIERS enhancement, and the enhancement drops dramatically as the distance between the tip and the substrate increases. The spatial resolution of TIERS is mainly dependent on the radius of curvature of the tip end. A sharp tip with a small radius can dramatically increase the spatial resolution of TERS. Increasing the tip-substrate distance or changing the metallic substrate into a dielectric substrate lowers the spatial resolution. The TERS enhancement dependence on the incident angle and polarization, the size of tip, as well as the composition of the substrate is also discussed in detail. Copyright (C) 2009 John Wiley & Sons, Ltd.