Apertureless SNOM

In September 2000, Hayazawa and coworkers reported the next study on apertureless SNOM using a silver-coated cantilever and a dye-coated silver film on a glass slide [137]. The dye was rhodamine 6g (Rh-6g). A 40-fold enhancement of Raman scattering was observed with a 4 8-nm laser excitation an enhancement of fluorescence was also noticed (see Fig. 10.16) [137]. The authors observed bleaching behavior for rhodamine 6g, but did not mention whether or not the bleaching rate was tip-enhanced. Instead, they pretreated this system with 20-min illumination until a stationary state was reached. 

Foundation of apertureless SNOM with near-field collection... 

Copenhagen, for apertureless SNOM of real-world, rough samples is depicted in Figure 4. Ventilation of the laser is via the flexible tubing. It is even possible to support the laser with a book. Parts 2 and 3 in Figure 3 and the AFM are hanging on the three elastic ropes for vibration protection. 

The basic requirement for apertureless SNOM is the reflectance enhancement in the shear-force gap. The studied material strongly influences the efficiency of the shear-force damping (100 x d/do where d is the set amplitude and do the free amplitude of vibration). Thus, for example, 50% damping will be obtained at different distances on different materials, and the reflectance enhancement factor F (F = I/Iq where I is the total intensity and 7o the far-field background intensity) depends on the distance. Fortunately, there are numerous material properties, such as refraction index, gloss, crystal packing, water layer, and distance, that influence the value of F. The far-field intensity lo should... 

The scanning of nanoparticles with shear-force AFM and simultaneous apertureless SNOM is an easy task. The nanoparticle suspension is spread and dried on a microscope slide without further treatment and scanned as usual. Scanning in water is also possible, but the sensitivity under water... 

Figure 17 Simultaneous shear-force AFM (a) (10 im, z-range 300 nm) and (c) (z-range 1.6(im) and apertureless SNOM (b, d) of an abraded dental nickel alloy (a) and (b) before, (c) and (d) after the electrochemical standard leaching test.

AFM tips (diameter <50nm metalized with silver) on transparent samples were illuminated by a focused laser beam from below through the support and the sample to reach a 30 times increase of the scattered Raman light. This apertureless scatter SERS SNOM succeeded also with an etched gold wire in shear-force distance with 40-fold increase of the Raman signal, but this shifted the Raman lines with respect to those in the bulk Raman spectra. Nanopipette probes for apertureless SERS SNOM with gold or silver particles held in the aperture are also available. However, none of these elaborate techniques approaches the capabilities and versatility of the easiest apertureless SNOM with sharp pulled tips and enhanced internal reflection (Figure lb). 

Subsurface structures in silicon were also studied using apertureless s-SNOM in the IR range. Lahrech et al. have shown successfully that implanted boron lines in silicon can be detected with a lateral resolution of -400 mn, even in the absence of any topographical contrast [47]. Knoll and Keilmann have performed near-field... 

Figure 10 Simultaneous shear-force AFM (a, a ) and apertureless fluorescence SNOM (b, b ) of dye nanoparticles in polyvidone resin showing angular aggregation by the difference in shape of topographic and optical image both in the top views (a, b) and in the surface-views (a, b ). ...

Figure 15 AFM topographies (5 pm) on (001) of phthalimide at room temperature (a) fresh from acetone (b) after two days in air at relative humidity of 50-60% (c) after 16 h storage in an atmosphere of almost saturated water vapor at room temperature (d) simultaneous apertureless shear-force SNOM (488 nm) with dark optical contrast precisely at the island site.

A new approach in cancer prediagnosis is SNOM monitoring of the chemical change of healthy into cancerous tissue at the subcellular level. Apertureless shear-force SNOM provides a rapid prediagnostic tool for early cancer recognition with very rough dried cold-cuts (cut at -10 °C) of unstained human bladder tissue. A safe differentiation with AFM is not possible (Figure 18a and b) in this case however, SNOM provides characteristic differences. While the healthy tissue provides no distinct chemical contrast at... 

Figure 18 Shear-force AFM topographies (25 and 20 xm, z-range 1 xm) of (a) healthy bladder tissue and (b) cancerous bladder tissue (a ) and (b ) are the corresponding apertureless shear-force SNOM images, where only (b ) shows characteristic bright plate-like and dark ribbon-like contrast.

The spectrum (Figure 19c) required only a short Raman collection, because shear-force controlled apertureless internal reflection Raman SNOM also creates the characteristic enhancement of the Raman reflection back to the sharp tapered fiber. Further, resonant Raman SNOM spectra of silicon (519.7 cm ) under an old (5 nm) or a freshly grown silica layer, and nomesonant Raman SNOM of these layers (500 cm ) as well as of gallium nitride (nonresonant El (TO) and E2 Raman modes at 560.8 and 570.4 cm ) on alumina (subtraction of the Raman response of support and fiber) with the shear-force apertureless technique (using 488 nm light) at total collection times of <10 min have been reported in Ref. 25. 

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