Control of Surface Plasmon Excitation in Metallic Slit Nanostructures in a Wet Environment

We report a modification of the electromagnetic field distribution associated with a surface plasmon polariton excited on a metal slit array in the vicinity of liquid. By successful operation of a Near-field Scanning Optical Microscope (NSOM) in both dry and wet environments, we found that near-field distribution showed a considerable change from a clear double-periodic distribution (spatial oscillation of electromagnetic field having the period half of that of slit array), which is a signature of surface plasmon excitation, to a single periodic distribution, which denotes that the surface plasmon polariton no longer exists. A simulation performed based on a partial wave expansion combined with a surface impedance boundary conditions show that such change of electromagnetic field distribution are explained by a change of surface plasmon resonance, associated with the change of dielectric constant of the surrounding media