DIRECT OBSERVATION OF LOCALIZED DIPOLAR EXCITATIONS ON ROUGH NANOSTRUCTURED SURFACES

Using a photon scanning tunneling microscope (operating alternatively at the wavelengths of 594 and 633 nm) with shear-force feedback we ima ge the topography of silver colloid fractals simultaneously with a nea r-field intensity distribution. We observe that near-field optical ima ges exhibit spatially localized (within 150-250 nm) intensity enhancem ent by one to two orders of magnitude. These bright light spots are fo und to be sensitive to the light wavelength, polarization, and angle o f incidence. We relate the observed phenomenon to the localization of resonant dipolar excitations in random nanostructured aggregates. [S01 63-1829(98)06941-0].