Near-field scanning optical microscopy NSOM

3 Near-field scanning optical microscopy (NSOM) 

The resolution of a conventional microcope is limited by the classical phenomena of interference and diffraction. The limit is approximately X/2, X being the wavelength. This limit can be overcome by using a sub-wavelength light source and by placing the sample very close to this source (i.e. in the near field). The relevant domain is near-field optics (as opposed to far-field conventional optics), which has been applied to microscopy, spectroscopy and optical sensors. In particular, nearfield scanning optical microscopy (N SOM) has proved to be a powerful tool in physical, chemical and life sciences (Dunn, 1999). 

The idea of near-field optics to bypass the diffraction limit was described in three visionary papers published by Synge in the period 1928-32. Synge s idea is illus- 

The systems that scan the piezos and record the image are similar to those used in atomic force microscopy. 

The NSOM tip is obtained by heating and pulling a single-mode optical fiber down to a fine point. A reflective metal coating (aluminum, silver or gold) is deposited by vacuum evaporative techniques in order to prevent light from escaping. 

6 Near-Field Scanning Optical Microscopy (NSOM) 

Teetsov and Vanden Bout [106-109] published a series of papers on NSOM studies of poly(9,9 -dialkylfluorene)s. In these papers they introduced a new procedure for 

McNeill et al. [113,114] studied the near-field photoluminescence of thin-fihn MEH-PPV induced by a voltage bias applied between the near-field probe and the substrate. The goal was to investigate the field-induced modulation of the local carrier density. The injected carriers recombined giving rise to photoluminescence measured by the NSOM probe. The images under applied bias showed a domain structure similar to those reported by other groups. This indicates that the inhomogeneous polymer structure affects the process both with and without an electric-field-induced carrier injection. 

Schaller et al. [115] used NSOM to collect local light emission from the surface of MEH-PPV polymer samples in contact with various solvents. The goal of this study was to identify various emissive interchain species present in annealed MEH-PPV films. The 

In addition to studies of nanoscale inhomogeneity of pristine semiconducting polymers, the NSOM technique and its variations were successfully used for imaging local nanoscale photocurrents and fluorescence emission produced by various polymer blends [119-124]. 

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For samples thicker than the depth of field, the images are blurred by out-of-focus fluorescence. Corrections using a computer are possible, but other techniques are generally preferred such as confocal microscopy and two-photon excitation microscopy. It is possible to overcome the optical diffraction limit in near-field scanning optical microscopy (NSOM). 

Near-field scanning optical microscopy (NSOM) allows an extension of optical microscopy to near that of electron microscopy. The central feature is the optical element that is similar. 

Brighter, tunable ultrafast light sources would benefit many of the areas discussed in the report, particularly infrared-terahertz (between visible light and radio waves) vibrational and dynamical imaging, near-field scanning optical microscopy (NSOM), and X-ray imaging. 

Schaller, R.D., L.F. Lee, J.C. Johnson, L.H. Haber, R.J. Saykally, J. Vieceli, I. Benjamin, T.-O. Nguyen, and B.J. Schwartz. 2002. The nature of interchain excitations in conjugated polymers Spatially varying interfacial solvatochromism of annealed MEH-PPV films studied by near-field scanning optical microscopy (NSOM). J. Phys. Chem. B 106 9496-9506. 

Near-Field Scanning Optical Microscopy (NSOM) is a technique which enables users to work with standard optical tools integrated with scanning probe microscopy (SPM). The integration of SPM and certain optical methods allows for the collection of optical information at resolutions well beyond the diffraction limit. 

E. Betzig, M. Isaacson, H. Barshatzky, A. Lewis and K. Lin, Near-field scanning optical microscopy (NSOM), Proc. SPIE, 897 (1988) 91-99. 

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

Figure 7.2. Schematic of operating principle of near-field scanning optical microscopy (NSOM). The resulting wavelength of light impinging on the sample ( 2) has a wavelength much smaller than the illuminating source, resulting in much higher resolution.

It should be noted that near-field scanning optical microscopy (NSOM) (discussed at the beginning of this chapter) is often grouped alongside other SPM techniques. However, for our discussion, we will focus on AFM and STM since these use physical probes to interrogate a surface, rather than focused light. 

Abashin M (2009) Near-field characterization of photonic nanodevices near-field scanning optical microscopy (NSOM) characterization of photonic nanodevices and nanoscale optical phenomena. Saarbriicken, Germany... 

Near-field scanning optical microscopy (NSOM) has been developed as a combination of scanning probe microscope and optical microscope in which the spatial resolution is determined by scanning probe microscope resolution while the signals detected are coming from several optical interactions. As a result, NSOM has achieved a higher spatial resolution than that of the classical optical microscopy that uses a conventional lens, which is strictly limited by the diffraction... 

Barbara, P. E, Adams, D. M., and O Connor, D. B. Characterization of organic thin film materials with near-field scanning optical microscopy (NSOM). Ann. Rev. Mater. Sci. 1999, 29, 433. 

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