Optimized apertureless optical near-field probes with 15 nm optical resolution

Back-illuminated full body glass tips coated with a thin metal layer can be used as local probes for apertureless scanning near-field optical microscopy (SNOM). In order to achieve high spatial resolution, high electric field intensities and low background illumination, the thickness of the metal coating, angular illumination direction, and polarization have to be optimized. Optimal conditions have been calculated and experimentally verified for 10-15 nm thick aluminium and 15-25 nm thick silver layers. Upon imaging single dye molecules, characteristic single and double-peak patterns with peak widths down to 15 nm could be measured, exhibiting an optical resolution which exceeds the classical diffraction limit of Abbe significantly.