Near-field scanning optical measurements

Hayazawa, N Inouye, Y. and Kawata, S. (1999) Evanescent field excitation and measurement of dye fluorescence using a high N.A. objective lens in a metallic probe near-field scanning optical microscopy J. Microsc., 194, 472-476. 

Clancy, C. M. R. Krogmeier, J. R. Pawlak, A. Rozanowska, M. Sarna, T Dunn, R. C. Simon, J. D. Atomic Force Microscopy and Near-Field Scanning Optical Microscopy Measurements of Single Human Retinal Lipofuscin Granules. J. Phys. Chem. B 2000, 104, 12098-12101. 

Near-field scanning optical microscopy is a scanning probe technique that enables optical measurements to be conducted with very high spatial resolution [7-9]. NSOM overcomes the diffraction barrier that restricts the spatial resolution in conventional optical measurements and provides both optical and topographical information on samples with nanometric spatial resolution. 

L. K. Kapkiai, D. Moore-Nichols, J. Camell, J. R. Krogmeier and R. C. Dunn, Hybrid near-field scanning optical microscopy tips for live cell measurements, Appl. Phys. Lett., 84 (2004) 3750-3752. 

One interesting new Add in the area of optical spectroscopy is near-field scanning optical microscopy, a technique that allows for the imaging of surfaces down to sub-micron resolution and for the detection and characterization of single molecules [80,81] When applied to the study of surfaces, this approach is capable of identifying individual adsorbates, as in the case of oxazine molecules dispersed on a pol mier film, illustrated in figure Bl. 22,11 [82]. Absorption and emission spectra of individual molecules can be obtained with this technique as well, and time-dependent measurements can be used to follow the d5mamics of surface processes. 

Near-field scanning optical microscopes (NSOM or SNOM) are mainly used in fluorescence and VIS measurements. They provide optical images with spatial resolution less than the Abbe s limit of Ajl. The high lateral resolution is commonly achieved by using the optical near-field, e. g. in close vicinity of a very narrow fiber tip. Figure 5.16 illustrates the design of a near-field microscope. 

Kitts, C. C., and Vanden Bout, D. A. 2009. Near-field scanning optical microscopy measurements of fluorescent molecular probes binding to insuhn amyloid fibrils,/P/rys Chem B 113,12090-12095. 

As a technique complementary to AFM, near-field scanning optical microscopy (NSOM) studies have reported the nanoscale topographic and fluorescence features of poly(fluorene)s [156-158]. From the NSOM experiments, it is possible to quantify the film optical anisotropy on the local scale by measuring the polarization of the emitted light. The intensity of fluorescence is found to be the most when collected perpendicular to the fibril axis. Since the fluorescence is polarized along the conjugated backbone, this indicates that the ribbons are indeed composed of poly(fluorene) chains stacked orthogonal to the ribbon axis. 

In this chapter, we discuss the Langmuir deposition of ultrathin PDA fihns and the subsequent measurement of their structural, optical, and mechanical properties at the nanometer scale. By altering the head group functionality, we can choose between mono- and tri-layer PDA film structures. We then show that we can use the tip of an atomic force microscope (AFM) or a near field scanning optical microscope (NSOM) tip to locally convert the PDA from the blue form to the red form via applied stress. This represents the first time that mechanochromism has been observed at the nanometer scale. Dramatic structural changes are associated with this mechanochromic transition. 

Hollars, C. W. and R. C. Dunn (1997). "Submicron fluorescence, topology, and compliance measurements of phase-separated lipid monolayers using tapping-mode near-field scanning optical microscopy." Journal of Physical Chemistry B 101(33) 6313-6317. 

The scanning tunnelling microscope (STM) is the most suited, and the most developed of the various SPMs, to perform local spectroscopic measurements. Discussion of STM techniques will constitute the bulk of this article. It also has the most restricted range of accessible substrates in terms of conductivity and roughness. The atomic force microscope (AFM) has limited spectroscopic capabilities but can image a wider range of samples. The near-field scanning optical microscope (NSOM) has excellent spectroscopic, but limited spatial resolution. These latter two SPMs are discussed at the end of this article. 

The term SPM encompasses a family of surface-sensitive techniques, each based upon the interrogation at the nanometre level of a specific physical property by a sharp proximal probe. For example the original SPM, the STM measures local conductivity and the AFM local surface hardness. Figure 1 provides a summary of the operation of the most popular types of SPM. Extensive discussions on the operations of the various forms of SPMs can be found in numerous reviews of the subject. FFere we briefly highlight the three SPMs most readily applied to spectroscopic measurements, the STM, the AFM and the near-field scanning optical microscope (NSOM). 

Figure 5. A schematic of a near-field scanning opfical microscope, showing the primary components including the piezoelectric tip translator, the sample, the fiber optic probe, and the photodetector. The fiber is oscillated from side fo side and its oscillation measured in the photodetector to control the position of fhe fiber over the surface. The light leaving the end of the tip passes through the sample and is then collected in a typical microscope objective. The sample is scanned by moving it from side to side under the tip.

A wide variety of measurements can now be made on single molecules, including electrical (e.g. scanning tunnelling microscopy), magnetic (e.g. spin resonance), force (e.g. atomic force microscopy), optical (e.g. near-field and far-field fluorescence microscopies) and hybrid teclmiques. This contribution addresses only Arose teclmiques tliat are at least partially optical. Single-particle electrical and force measurements are discussed in tire sections on scanning probe microscopies (B1.19) and surface forces apparatus (B1.20). 

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