The Enhancement Effect at Local Reflectance and Emission Back to Apertureless SNOM Tips in the Shear-Force Gap

摘要

Physical basics, technique, equipment, proper experimental conditions, and performance of aperturelessreflection back-to-the-fiber SNOM (Rayleigh, Raman, fluorescence) under shear-force control are reported. Thistechnique achieves optical resolutions of < 10 nm on flat surfaces and < 20 nm in the presence of topographies with verysharp tips (< 10 - 20 nm end radius). It works due to the large enhancement of the reflection to very sharp tapereduncoated tips in the shear-force gap. The dependence of preset vibration damping is linear with variations betweendifferent chemical entities. Thus, the optical contrast appears as chemical contrast in reflection or emission. Suchenhancement is however not obtained with blunt tips (> 30 nm end radius or broken). Typical images for all thinkablesituations show that topographical artifacts are excluded and that, unlike conventional aperture SNOM, precise sitecoincidence of optical contrast and chemical variation (often traceable in the topography) is obtained on planes, hills,slopes, depressions, and hidden geodes, even on very rough surfaces that give, however, no optical contrast if they arechemically uniform. Furthermore, positive and negative contrast on hills, slopes, and depressions is featured within thesame SNOM image each. Object sizes range from 30 nm in small scans to 25 μm in 40 μm wide scans. The versatiletechnique is therefore qualified for applications on real world samples without severe manipulations just as they occur inscience, technique, and medicine. The principal differences of apertureless SNOM with collection in the shear-force gapand conventional SNOM are worked out.