Chemical contrast observed at a III-V heterostructure by scanning near-field optical microscopy

We observed chemical contrast with subwavelength resolution on a III-V hete rostructure by a scanning near-field optical microscope (SNOM) working in t he external reflection mode and coupled with a Free Electron Laser (FEL). S NOM reflectivity images revealed features that were not present in the corr esponding shear-force (topology) images and are due to localized lateral ch anges in the optical properties of the sample. The data indicate an optical spatial resolution well below the diffraction limit of lambda/2 with most optical images having better lateral resolution than topographic images.