Light microscopy near field

These most interesting features raise important but difficult questions of characterization concerning composition, size, persistence length, shape, structure, etc. of the entities formed. To this end, an array of physicochemical methods is required and must be put to use, such as vapor phase osmometry, differential scanning calorimetry, electrospray mass spectrometry, NMR spectroscopy, gel permeation chromatography, light scattering, electron microscopy, near field microscopies, etc.). (For a relevant case, see Ref. 37.)... 

Nc.ar-Fi ld Scanning Optical Microscope.. The near-field scanning optical microscope (NSOM) should, strictiy speaking, be NSLM for near-field scanning light microscopy because "optical" includes electron optical as well as light optical and NSOM is a light microscope. 

A nano-light-source generated on the metallic nano-tip induces a variety of optical phenomena in a nano-volume. Hence, nano-analysis, nano-identification and nanoimaging are achieved by combining the near-field technique with many kinds of spectroscopy. The use of a metallic nano-tip applied to nanoscale spectroscopy, for example, Raman spectroscopy [9], two-photon fluorescence spectroscopy [13] and infrared absorption spectroscopy [14], was reported in 1999. We have incorporated Raman spectroscopy with tip-enhanced near-field microscopy for the direct observation of molecules. In this section, we will give a brief introduction to Raman spectroscopy and demonstrate our experimental nano-Raman spectroscopy and imaging results. Furthermore, we will describe the improvement of spatial resolution... 

With regard to the confinement and enhancement ability of a metallic nano-tip, we have proposed near-field Raman microscopy using a metallic nano-tip [9]. The metallic nano-tip is able to enhance not only the illuminating light but also the Raman scattered light [9, 15, 16]. Figure 2.5 illustrates our nano-Raman microscope that mainly comprises an inverted microscope for illumination and collection of Raman... 

Kottmann, J. P., Martin, O. J. F Smith, D. R. and Schultz, S. (2001) Non-regularly shaped plasmon resonant nanopartide as localized light source for near-field microscopy. J. Microsc., 202, 60-65. 

Nagahara, T., Imura, K. and Okamoto, H. (2004) Time-resolved scanning near-field optical microscopy with supercontinuum light pulses generated in microstructure fiber. Rev. Sci. Instrum., 75, 4528-4533. 

Atomic force microscopy (AFM) is a variant of STM and was introduced in 1986 by Binnig et al. (11). AFM belongs to a family of near-field microscopies and is capable of imaging a wide variety of specimens surface down to an atomic scale. The technique employs a probe (pyramidal tip) mounted at the end of a sensitive but rigid cantilever (see Fig. 2). The probe is drawn across the specimen under very light mechanical loading (1). Measurements of the probe s interaction with the sample s surface are accomplished with a laser beam reflected from the cantilever. 

Microscopic techniques, 70 428 Microscopists, role of, 76 467 Microscopy, 76 464-509, See also Atomic force microscopy (AFM) Electron microscopy Light microscopy Microscopes Scanning electron microscopy (SEM) Transmission electron microscopy (TEM) acronyms related to, 76 506-507 atomic force, 76 499-501 atom probe, 76 503 cathodoluminescence, 76 484 confocal, 76 483-484 electron, 76 487-495 in examining trace evidence, 72 99 field emission, 76 503 field ion, 76 503 fluorescence, 76 483 near-held scanning optical,... 

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). 

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. 

The third term is a damping term, which allows for the possibility that a wave is absorbed by the medium this is called the evanescent wave and the quantity a is also called the optical conductivity (at zero frequency it becomes the electrical conductivity). The evanescent wave is exploited in near-field scanning optical microscopy. If waves propagate along x, so that <)/ <)y = 0, d/dz = Q, then EX = HX = 0. Next, assume Ey(x,t)=f(x)exp(icot) = 0 and Ez(x,t)=g(x)exp(icot) = 0 that is, assume plane-polarized light with the E vector in the xy plane Then the differential equation to be solved is more simply... 

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. 

---