Chemical contrast in scanning near-field optical microscopy

Repeatable and stable scanning near-held optical microscopy (SNOM) images are obtained under shear-force control if uncoated, i.e. cold and sharp, tapered fiber tips are used, True chemical contrast is seen for the first time on organic crystals due to the different near-held reflectivities of different chemical species on partly oxidized anthracene. The topography spans a Z-range of 500 nm. The surface roughness is tolerable and the sites of reaction can be related to crystal structure data, A submicroscopic local resolution of 18 nm has been obtained for chemical contrast, discriminating different chemical species even with poorly reflecting organics on rough crystal surfaces. Thus, reflection-back-to-the-fiber SNOM will find wide applications for both transparent and opaque samples. All drawbacks with blunt and hat metal-coated tips at a <10 nm distance from the surface in previous SNOM setups are overcome. (C) 1997 John Wiley & Sons, Ltd.