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 heterostructure by a scanning near-field optical microscope (SNOM) working in the external reflection mode and coupled with a Free Electron Laser (FEL). SNOM reflectivity images revealed features that were not present in the corresponding shear-force (topology) images and are due to localized lateral changes in the optical properties of the sample. The data indicate an optical spatial resolution well below the diffraction limit of ?/2 with most optical images having better lateral resolution than topographic images.