Abstract
Shear-force apertureless scanning near-field optical microscopy (SNOM) with very sharp uncoated tapered waveguides relies on the unexpected enhancement of reflection in the shear-force gap. It is the technique for obtaining chemical (materials) contrast in the optical image of “real world” surfaces that are rough and very rough without topographical artifacts, and it is by far less complicated than other SNOM techniques that can only be used for very flat surfaces. The experimental use of the new photophysical effect is described. The applications of the new technique are manifold. Important mechanistic questions in solid-state chemistry (oxidation, diazotization, photodimerization, surface hydration, hydrolysis) are answered with respect to simultaneous AFM (atomic force microscopy) and detailed crystal packing. Prehistoric petrified bacteria and concomitant pyrite inclusions are also investigated with local RAMAN SNOM. Polymer beads and unstained biological objects (rabbit heart, shrimp eye) allow for nanoscopic analysis of cell organelles. Similarly, human teeth and a cancerous tissue are analyzed. Bladder cancer tissue is clearly differentiated from healthy tissue without staining and this opens a new highly promising diagnostic tool for precancer diagnosis. Industrial applications are demonstrated at the corrosion behavior of dental alloys (withdrawal of a widely used alloy, harmless substitutes), improvement of paper glazing, behavior of blood bags upon storage, quality assessment of metal particle preparations for surface enhanced RAMAN spectroscopy, and determination of diffusion coefficient and light fastness in textile fiber dyeing. The latter applications include fluorescence SNOM. Local fluorescence SNOM is also used in the study of partly aggregating dye nanoparticles within resin/varnish preparations. Unexpected new insights are obtained in all of the various fields that cannot be obtained by other techniques.
Highlights
While most scanning near-field optical microscopy techniques (SNOM) [other acronyms are NSOM, PSTM, and STOM] are only suitable for very flat surfaces, an apertureless procedure in constant shear-force distance [1] is able to achieve artifact-free SNOM contrast on rough surfaces
The chemical nature of the material under the bright spot in Figure 11(b) has to be identified by near-field spectroscopy. This is possible by RAMAN SNOM due to the large enhancement factors that are obtained in the shearforce gap of about 5 nm between very sharp tip and surface, which enhances the local RAMAN intensity (Figure 12)
It could be shown that shear-force apertureless SNOM, which relies on our new photophysical effect of the strong enhancement of reflectivity in the shear-force gap under a sharp tip, is able to scan very rough “real world” samples in very different branches of the sciences without topographical artifacts
Summary
While most scanning near-field optical microscopy techniques (SNOM) [other acronyms are NSOM (near-field scanning optical microscopy), PSTM (photon scanning tunneling microscopy), and STOM (scanning tunneling optical microscopy)] are only suitable for very flat surfaces, an apertureless procedure in constant shear-force distance [1] is able to achieve artifact-free SNOM contrast on (very) rough surfaces. Our basic new and unexpected physical effect, which allows for the very good resolution despite an illuminated area of about 1 μm diameter, is the strongly enhanced reflection back into the very sharp fiber at shear-force distance [4, 5]. Blunt and broken tips do not provide the enhanced reflection back to the fiber in shear-force distance. These provide a series of possible artifacts that are recognized by the drop in recorded light intensity and by some characteristic features [6] that are apparent in many published images from the other SNOM techniques. Medicinal, and industrial applications of the unprecedented tool
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
