Tunnel Near-Field Optical Microscopy: TNOM-2

Light emitted from the aperture of a near-field optical probe in close vicinity to a dielectric object propagates in classically ``forbidden'' as well as ``allowed'' directions; the two zones are separated by the critical angle for total internal reflection. The new ``TNOM'' technique makes use of the forbidden radiation, in contrast to standard SNOM-NSOM, which records only the allowed light. A new interferometric shear (friction) force detector allows very small-amplitude tip vibrations, which helped improve the resolution. Scan images obtained with allowed and forbidden light are complementary to some extent; the latter, however, provide high contrast and resolution even in situations in which standard SNOM/NSOM shows little or no contrast. Several examples of images with a resolution of less than or equal to 50 nm are presented. The influence of topography on image formation is analyzed and discussed.