SNOM

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. 

While the spatial resolution in classical microscopy is limited to approximately X/2, where X is the optical wavelength (tlie so-called Abbe Limit [194], -0.2 pm with visible light), SNOM breaks through this barrier by monitoring the evanescent waves (of high spatial frequency) which arise following interaction with an... 

Figure Bl.19.38. Schematic of a scaimmg near-field optical microscope (SNOM). (Taken from [196]. figure 2.)...

Pohl D W 1991 Soanning near-field optioal miorosoopy (SNOM) Advances/n Optical and Electron Microscopy yo 12, ed R Barer and V E Cosslett (London Aoademio)... 

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. 

Figure4.1 Block diagram ofa SNOM apparatus (a), SEM images of a cantilever-type SNOM probe (b) and the aperture at the tip end (c).

Figure4.2 Fluorescence SNOM image ofa single Rhodamine 6G molecule. Panel (b) indicates the cross-section profile for the dashed line in panel (a).

Figure 4.3 shows the fluorescence SNOM images of single PMMA-Pe chains embedded in the unlabeled PMMA matrix. In the SNOM image, each PMMA-Pe chain was observed as an isolated fluorescent spot. The molecular weight of each chain can be estimated from the integrated fluorescence intensity [19], and Figure 4.3... 

Figure 4.3 SNOM images of the single PMMA-Pe chains in an ultra-thin film. The scanned area is 1.4 x 1.4 lm for each image. The molecular weight (M) and the value of for each chain were...

Figure 4.4 Histogram of the lateral chain dimension for the PMMA-Pe chains in ultra-thin films with thickness 15, 50, and 80 nm.The PMMAchains with a molecularweightof4 x 10 were selected in the SNOM images and analyzed to construct the histogram. Reproduced with permission from The Society of Polymer Science, Japan.

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

SNOM Scanning near-field optical microscopy (see NSOM)... 

The achievable spatial resolution in an FTIR-SNOM imaging experiment will, however, be poorer than that cited above because of different technical problems. Spatial resolutions in the range between 100 nm and several micrometers have... 

Raman microscopy provides a spatial resolution slightly better than IR, and no sample preparation is necessary in many cases. It has advantages with special types of substances (e.g., systems containing conjugated double bonds, oriented systems, amorphous and crystalline carbon, oxides). SNOM techniques (with spatial resolution below 1 pm) have been more popular with Raman than with IR, so far, but as yet are not routinely practiced. 

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