Transmission SNOM

Like conventional optical microscopy, the SNOM can be performed in transmission or in reflection. The most common method is the transmission SNOM in which a thin, transparent sample is excited by the tip (i.e., illumina-... 

Figure 11. SNOM and LELS. a) schematic SNOM experiment b) spectra following transmission enhancement via surface plasmon excitations, from [39] Copyright 1998 by the American Physical Society c) LELS simulation of a similar experiment for a fast (100 kV) electron.

Scanning near-field optical microscopy (SNOM) or near-field scanning optical microscopy (NSOM) Shear force microscopy (ShFM) Aperture SNOM (ASNOM) - Transmission ASNOM (T-ASNOM)... 

Scanning Near-Field Optical Microscopy (SNOM) Aperture SNOM (ASNOM) Collection ASNOM (C-ASNOM) Emission ASNOM (E-ASNOM) Evanescent Field SNOM (EF-SNOM) Nonaperture ASNOM (NA-SNOM) Shear Force Microscopy Transmission Mode (TSNOM) Reflection Mode Luminescence Mode... 

Figure 7.9. Types of the SNOM configurations, (a) Transmission coiiection mode. The tip is generaiiy metaiiized except for its nano-sized end. (b) Transmission iiiu-mination mode, (c) Refiection coiiection mode, (d) Photon scanning tunnei mode. The iiiumination beam is totaiiy refiected inside a substrate, (e) Duai iiiumination coiiection mode. It is a combination of (a) and (b). (f) Refiection illumination mode, it is an inverted photon tunnel mode (d) [53].

The first application of the SNOM for the MO studies happened in 1992 [62], when it was demonstrated that near-field MO observation can be obtained in the same manner as conventional far-field observation— that is, by using two cross-polarizers. Betzig et al. [62] visualized 100-nm magnetic domains and claimed spatial resolution of 30-50 nm. The possibility of MO domain imaging was confirmed in both the transmission regime (Faraday geometry) [63,64] and the reflection regime (Kerr microscopy) [65-67]. 

The other problem that arises during MO observation is that the SNOM resolution operating in transmission mode is limited not only by the size of the fiber-tip aperture but also by the thickness of the magnetic film [93-96]. 

The SNOM combines the possibilities of AFM and optical microscopy. On the one hand, it allows for probing of the surface and obtaining information on the topography. On the other hand, in aperture SNOM, the probe contains an aperture, and the sample can be illuminated locally (Fig. 5). The diameter of the aperture at the end of the probe is typically of the order of 50-100 nanometer, and therefore, the illuminating spot is not diffraction limited. Both transmission and tluorescence in combination with polarization provide appropriate contrast mechanisms. 

SD spinodal decomposition SEM scanning electron microscopy SNOM scanning near-field optical microscopy STED stimulated emission depletion SWNT single wall carbon nanotube TEM transmission electron microscopy... 

Fig. 24 SNOM images of a polymer network of PMMA with cross link density of 0.1%. (a) Shear force topographic image, (b) transmission image and (c) fluorescence image. The scale bar indicates 1 xm and the wavelength of the light source was 442 nm. Reprinted with permission of [82], copyright (2000) American Chemical Society...

SNOM can be applied in a range of modes including transmission, reflectance, and emission. Such techniques are likely to be coupled to electrochemical studies in the future. The spatial resolution of such imaging makes the possibility of interrogating potential control of single molecules a reality. 

The limitations Introduced by the minute aperture have meant that few papers have been published on the topic of aperture-based SNOM systems. However, Schnell et al. [3] recently reported how mid-infrared radiation could be focused Into a very small area through a tapered transmission line. Nanofocusing of 10.7 pm radiation was achieved by propagating a mid-infrared surface wave along a tapered two-wire transmission line. The spot diameter was compressed to 60 nm (A/150) at the taper apex. To the best of our knowledge, no nanoimaging results in which this approach has been applied have yet been reported. Most of the major advances in this field have been based on either photothermal (PT) spectroscopy or elastic scattering from a tip. In the remainder of this section, the early work that laid the foundations for some of the remarkable results that have been reported in the past decade will be described. 

We wrote earlier that the use of an aperture for SNOM was essentially precluded because of the extremely low transmission of narrow metalized glass fibers caused by the waveguide cutoff effect. Several workers recognized the potential of achieving better resolution by using a small scatterer instead of a small aperture [12-16] because an illuminated particle can exhibit enhanced optical fields in its neighborhood that is in turn modified by the presence of a sample. As a result of this near-field interaction, scattered light that is measured in the far field contains... 

Figure 12.16 Spectra of PMMA measured by (a) s-SNOM at a resolution of 6 cm" and (b) conventional transmission spectroscopy at a resolution of 4 cm". (Reprinted with permission from Ref. [30]. Copyright 2012, American Chemical Society.)...

Fig. 9.3 Imaging via near-field microscopy (a) SNOM in transmission (b) SNOM in reflection (c) PSTM.

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