Near-field interactions

The main characteristic of the SPM is a sharp probe tip that scans a sample surface. The tip must remain in very close proximity to the surface because the SPM uses near-field interactions between the tip and a sample surface for examination. This near-field characteristic eliminates the resolution limit associated with optical and electron microscopy as discussed in the previous chapters, because their resolution is limited by the far-field interactions between light or electron waves and specimens. Diffraction of light or electron waves associated with far-field interactions limit their resolution to wavelength scales. The near-field interactions in a SPM, however, enable us to obtain a true image of surface atoms. Images of atoms can be obtained by an SPM because it can accurately measure the surface atom profiles in the vertical and lateral directions. The lateral and vertical resolutions of an SPM can be better than 0.1 nm, particularly the vertical resolution. The lateral range of an SPM measurement is up to about 100 /xm, and its vertical range is up to about 10 /xm. However, the SPM must operate in a... 

While SPM offers unique advantages for surface measurement in terms of simplicity and high resolution, it also has its unique problems of image artifacts caused by near-field interactions between tip and sample. The artifacts in imaging may originate from the tip, the scanner, vibrations and/or image processing. Typical artifacts as introduced from several sources are briefly described in this section. 

Nanophotonics, proposed by the author in 1993 [1-3], is a novel optical technology that utilizes the optical near-field. The optical near-field is the dressed photons that mediate the interaction between nanometric particles located in close proximity to each other. Nanophotonics allows the realization of qualitative innovations in photonic devices, fabrication techniques, and systems by utilizing novel functions and phenomena enabled by optical near-field interactions that would otherwise be impossible if only conventional propagating light were used. In this sense, the principles and concepts of nanophotonics are completely different from those of conventional wave-optical technology, encompassing photonic crystals, plasmon-ics, metamaterials, and silicon photonics. This review describes these differences and shows examples of such qualitative innovations. 

Abstract To implement innovative nanometric optical processing systems as probe-free nanophotonic systems, it is necessary to exploit the unique atbibutes of nanometer-scale optical near-field interactions in a completely parallel fashion. This chapter is devoted to describing basic concepts necessary for two-dimensional parallel processing of light-matter interactions on the nanometer scale to realize probe-free nanophotonic systems. Additionally, the concepts and some demonstrations of the hierarchy inherent in nanophotonics, based on the hierarchy between optical near- and far-fields, are described as practical applications of optical near-field interactions. 

This idea is one of the most effective solutions to utilize multiple nanometric components without impairing the spatial parallelism or the superior speed of optical signals. The key to this idea is how to determine the arrangement of nanometric components that generates the intended optical near-field interactions. This can be achieved by precisely designing and fabricating nanostructures, such as shapes, layouts, compositions, and so on, that can induce arbitrary optical near-field interactions [21,22]. Moreover, protocols for the broadcast control and the narrowcast retrieval must be appropriately defined. 

There are several physical implementation methods that can achieve such a transform using optical near-field interactions. One is based on optical excitation transfer between quantum dots via optical near-field interactions [23, 24]. For instance, assume two cubic quantum dots whose side lengths L are a and -Jla, which we call QDa and QDb, respectively. 

Fig. 2.2 A quadrupole-dipole transform in the transition from the (2,1,1) level to the (1,1,1) level in QDb- Such a transform is unachievable without the optical near-field interactions between QDa and QDb, which allow the (2,1,1) level in QDb to be populated with excitons...

Fig. 2.3 Schematic diagram of nanophotonic matching system. The function is based on a quadrupole-dipole transform via optical near-fleld interactions, tind it is achieved through shape-engineered nanostructures and their associated optical near-field interactions...

Fig. 2.7 (a) Horizontal and vertical misalignments between Shape A and Shape B denoted by Ax and Ay, and (b), (c), their relations to conversion efficiency, (d) Schematic cross-sectional profiles of samples with different gaps. The thickness of the Si02 gap layer between the first and second layers was set in three steps, (e) The conversion efficiency decreased as the gap increased. The result validates the principle of the quadrupole-dipole transform that requires optical near-field interactions between closely arranged nanostructures... 

These mechanisms indicate that such nanophotonic codes embedded in holograms could also exploit these polarization and structural dependences, not only for retrieving near-mode information via optical near-field interactions. For instance, we could facilitate near-mode information retrieval using suitable input light polarization and environmental structures. 

In many-body assemblies of nanoparticles, a number of inter-particle near-field interactions are involved and may give further unique properties. Many-particle assemblies have been paid much attention in relation to the development of the... 

We can see the hierarchy of optical near-fields and far-fields because optical near-field interactions are distinguishable with propagating light. This characteristic feature has led to hierarchical optical system designs, such as nanophotonic hierarchical holograms (Tate et al., 2008), where independent functions are associated with both optical near- and far-fields in the same device. Figure 3 shows the basic concept of the hierarchical hologram. 

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