SNOM microscopy

Of the methods described in this section, scaiming near-field optical microscopy (SNOM or NSOM) is tlie closest to being able to provide useful infonuation that is unobtainable by other means. Indeed, this teclmique has already been made available as a conunercial instmment. A detailed review of SNOM has been written by Pohl 11931. 

Durig U T, Pohl D W and Rohner F 1986 Near-field optical-scanning microscopy J. Appl. Phys. 59 3318 Pohl D W 1991 Scanning near-field optical microscopy (SNOM)/Icfr/. Opt. Electron. Microsc. 12 243... 

More recently, the method of scanning near-field optical microscopy (SNOM) has been applied to LB films of phospholipids and has revealed submicron-domain structures [55-59]. The method involves scanning a fiber-optic tip over a surface in much the same way an AFM tip is scanned over a surface. In principle, other optical experiments could be combined with the SNOM, snch as resonance energy transfer, time-resolved flnorescence, and surface plasmon resonance. It is likely that spectroscopic investigation of snbmicron domains in LB films nsing these principles will be pnrsned extensively. 

Scanning Near-field Optical Microscopy (SNOM)... 

Mechanistic investigations of gas-solid and solid-solid reactions as well as their proper engineering require identifiable crystal surfaces for atomic force microscopy (AFM) and scanning near-field optical microscopy (SNOM) [1,3, 13-15] in combination with X-ray diffraction data, which are the basis of crystal packing analyses [1,3,16-18]. 

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

Fig. 34. dPS volume fraction (J)dPS vs depth z for a 50/50 dPS/PBrxS mixture after annealing for different times at T=180 °C as revealed by TOF-FRES a tA=10 min, b tA=160 min, c tA= 6175 min). In the bottom part, a sketch of the domain structure is shown as revealed from the ion beam and scanning near field optical microscopy (SNOM) results (shaded areas dPS-rich domains white areas dPS-poor domains). From Straub et al. [153]... 

For overcoming the limit of light microscopy and further improvement in spatial resolution, the implementation of scaiuiing near-held microscopy (SNOM) by means of a local illumination probe is an interesting approach [33-35]. The method is based on the held enhancement in the cavity between a sharp metal dp and the sample. In combination with Raman spectroscopy, this scanning probe technique is called tip-enhanced Raman spectroscopy (TERS) and enables high-resolution spatial microscopy with a lateral resolution of 50 nm [35]. Bouhelier [36] has reviewed advances in this held. 

The combination of SERS and optical near held microscopy (SNOM) can be therefore an ideal technique to carry out real locally resolved Raman microscopy delivering both chemical and optical information. A similar alternative could be the combination of Raman spectroscopy and AFM. 

Among the various techniques, we shall only discuss STM, scanning force microscopy (SFM or AFM), and scanning near-field optical microscopy (SNOM or NSOM), as those can well be considered the most prominent members of the SPM family. Among the three, we shall further focus on SFM, as most of the work done on polymers has indeed made use of this method. However, a brief note on STM and SNOM seems appropriate. 

The aim of the present paper is to outline several important general properties of SVD basic functions that are relevant for resolution estimation and enhancement in near-field problems, including scanning near-field optical microscopy (SNOM). 

Pohl DW, Fischer UC, Durig UT. Scanning near-field optical microscopy (SNOM). J Microsc (Oxf) 1988 152 853-861. 

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... 

Ideally we would like to use different color tags in order to locate both proteins in a mixture. This requires optical microscopy below the diffraction limit and the use of near-field microscopy. SNOM can be used to visualize the displacement of tagged proteins by surfactants (Gunning et al., 2001) but, at present, the resolution achievable is only about 50 ran. This is not sufficient, at present, to visualize individual proteins in a mixture using different colored tags. Advances in SNOMs should lead to improved resolution and the imaging of mixed protein layers should become possible in the future. 

Deeper insight can be gained from a scanning near-field optical microscopy (SNOM) study by McNeill et al., who resolved the local photocurrent obtained on MDMO-PPV PCBM toluene cast blends [138]. The authors revealed that the photocurrent was considerably reduced on top of the small hUls caused by the PCBM clusters (Fig. 25), whereas it stayed nearly constant over the surface of chlorobenzene cast blends [ 138]. 

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