A reflection near-field scanning optical microscope technique for subwavelength resolution imaging of thin organic films

A dual mode near-field scanning optical microscopy (NSOM) technique, in which light is both emitted from and collected by a subwavelength aperture, is described and demonstrated. This dual mode configuration is capable of high contrast (via the refractive index) as well as high-resolution optical microscopy in reflection. The contrast in these images is shown to depend strongly on the interference of the light incident to and reflected from the sample surface. We show that with the dual mode configuration the topography induced contrast can be quantitatively separated from the true optical contrast resulting in a mapping of the refractive index of the sample. This separation has proven difficult, if not impossible, for other reflection NSOM geometries. To demonstrate the utility of this technique for thin organic films we present dual mode images of a nine-layer organic/inorganic self-assembled multilayer film on a silicon substrate.