Near field visualization

The highly localized electromagnetic fields of SERS active substrates have been studied for a number of years by various groups utilizing near-field visualization techniques. The groups of Martin Moskovits and Vladimir Shalaev investigated the electromagnetic field distribution of laser-excited optical modes of fractal clusters... 

In summary, it has been demonstrated that plasmon-mode wavefunctions of gold nanoparticles resonant with the incident light can be visualized by near-field transmission imaging. 

To summarize, we have shown here that enhanced electric-field distribution in metal nanoparticle assemblies can be visualized on the nanoscale by a near-field two-photon excitation imaging method. By combining this method and near-field Raman imaging, we have clearly demonstrated that hot spots in noble metal nanoparticle assemblies make a major contribution to surface enhanced Raman scattering. 

In this chapter, we have provided an overview of near-field imaging and spectroscopy of noble metal nanoparticles and assemblies. We have shown that plasmon-mode wavefunctions and enhanced optical fields of nanoparticle systems can be visualized. The basic knowledge about localized electric fields induced by the plasmons may lead to new innovative research areas beyond the conventional scope of materials. 

Methods of near-field, midfield and ensemble (global) imaging and real-time visualization have been developed for monitoring gas atomization of liquid metals.[327] The primary process sensors and monitors used include high-speed video and infrared imaging systems. The process monitors allowed continuous and detailed observations of the atomization process and enabled measurements of the key parameters necessary for adequate control and optimization of the process. The sensors provided the operators with real-time information on the temperature of nozzle tip, visual characteristics of atomization plume, and gas and metal flow rates. The images can be displayed in real time, offering the potential for more responsive process control. 

Once illustrated on a map of the industry s effluent plume, the ZPE can be seen visually as larger or smaller than the area of the plume defined by the isopleth for the 1% concentration of effluent (EC, 1999). A ZPE should be estimated for each test species and then illustrated on a site map. As well, it is possible to compare the zones of potential effect for sublethal tests with the locations of exposure areas (generally the near-field) that have been or are to be sampled for fish and benthic invertebrates. This comparison illustrates the relationship between the sublethal tests and potential industry related effects observed in field measurements of fish and benthic invertebrates. 

Microscopic visualization techniques have also been used to investigate mucus-polymer interactions. Transmission electron microscopy was used by Fiebrig et al., whereas different microscopical techniques were used by Lehr et al. for the visualization of mucoadhesive interfaces. Transmission electron microscopy in combination with near-field Fourier transform infrared microscopy (FTIR) has been shown to be suitable for investigating the adhesion-promoting effect of polyethyleneglycol added in a hydrogel. Moreover, scanning force microscopy may be a valuable approach to obtain information on mucoadhesion and specific adhesion phenomena. ... 

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. 

Typically, the temperature pattern in the burner near field is affected as shown in Figure 23.12 the upper half (flame mode) shows measured temperatures that clearly increase toward the burner nozzle (y -> 0,2 0), while the lower half (flameless mode) shows a profile increasing toward the combustion chamber temperature without forming temperature peaks. This confirms the visual observation of Figure 23.2 and has been checked with mathematical modeling, which confirms the overall outline as described in the next paragraph. 

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]. 

Abstract Plasmonic nanostructures exhibit unique optical properties, and fundamental studies of these structures are relevant to wide range of research areas, both fundamental and applied. Potential applications of the plasmonic nanostructures originate from their ability to confine (and sometimes propagate as well) optical fields in nanometer scales, and are closely related to the static and dynamic properties of plasmonic waves. In this chapter, visualization of wavefunctions and optical fields in plasmonic nanostructures using near-field linear and non-linear optical methods is described. 

Spatial resolution. In optics, to realize the ultimate resolution like that of STM, several breakthroughs may still be needed. However, wavefiinctions of elementary excitations such as excitons and plasmons can be visualized if a sufficiently high spatial resolution is achieved. Near-field optical microscopy is promising for this purpose. Wide special range and compatibility with dynamic measurements are the great advantages of optical methods and allow one to study materials properties from broad points of view. Here, the principles of visualization of wavefimctions using a near-field optical microscope will be briefly described in comparison with that of STM. 

STM detects elecflic currents due to tunnel electrons between the sample and the probe tip. Tunneling probability at the tip position is dependent on the overlap of electronic wavefiinctions between the sample and the tip. Because the wavefunction of the electron at the tip is localized on a single atom, STM visualizes the electronic local density-of-states (LDOS) of the sample at tip position T and energy E with atomic resolution [50,51]. Operation principles of a near-field optical microscope is similar to that of an STM [52,53]. Instead of using tunnel electrons as in an STM, a near-field optical microscope uses tunnel photons between the sample and the near-field probe tip and visualizes photonic LDOS at position V" and frequency co. In general, LDOS is defined by the following equation [54]. 

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