Investigations of the interference of surface plasmons on rough silver surface by scanning plasmon near-field microscope

A scanning plasmon near-field microscope with gold and silver tips, operati ng in tapping mode of atomic force microscope is used to measure the distri bution of the near-field intensity of surface plasmons on rough silver surf aces. Using the fast Fourier transformation of near-field images, it is sho wn that the distribution of the near-field intensity on the surface is the result of the interference between scattering plasmons and the initial plas mon beam. Multiple scattering effects such as backscattering enhancement of surface plasmons are also observed. It is shown that a nonuniformity in th e registration of the scattered light leads to some artifacts in near-field images. Several registration modes of the light signal are considered and it is shown that recording the light signal at the second harmonic of the t apping frequency one can pick out the signal associated with an electromagn etic (em) resonance in a tip-surface (sphere-plane) structure. Possible imp lementations of this em resonance for studies of local permittivities and l ocal nonlinear susceptibilities of intermediate media between the tip and s urface with a subtip resolution are discussed. (C) 2001 Elsevier Science B. V. All rights reserved.