Plasmonic nanostructures in aperture-less scanning near-field optical microscopy (aSNOM)

Apertureless scanning near-field optical microscopy offers superb spatial resolution, but interpreting the recoreded signal can still be a challenge. Especially images of eigenmodes in plasmonic nanostructures are very often obscured by concurrent scattering from the tip and/or coupling effects in hte tip sample system. We show here how the use of orthogonal polarizations in excitation and detection affords us with an elegant method to map near-fields of plasmonic eignenmodes and other optical phenomenta. We demonstrated with a variety of samples possible applications of this cross-polarization scheme, such as verification of functional nanooptical structures, systematic studies of localized and propagating plasmonic eignenmodes, and their susceptibility to disturbance from structural defects. (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim