Local Dielectric Constants of Molecular Layers
M. Nikiforov, S. Kehr, T. Park, P. Milde, U. Zerwech, C. Loppacher, L. Eng, M. Therien, N. Engheta, D. Bonnell
The idealized system of an atomically flat metallic surface (HOPG) and an organic monolayer composed of porphyrin, is used to demonstrate how the dielectric function and associated properties of thin films can be accessed with a scanning probe technique. The junction of a metallic tip and surface is illuminated with a laser and the light scattering in the near field is detected. The theoretical analysis and numerical modeling, as well as experimental data, demonstrate that higher harmonic scattering can be used to extract the dielectric properties of materials with tens of nms spatial resolution. The 3d harmonic provides the best lateral resolution (~ 50 nm) and dielectric constant contrast for porphyrin molecules film HOPG, and the intensity of scattered s-polarized light is 100 times higher than that of p-polarized light for this configuration.