Near-field optical techniques

Addressing molecular switches remains a problem as well. The use of diffraction-limited focused light pulses provides a useful start, but subdiffraction optical techniques need to be improved and implemented to transfer information into and out of these molecular arrays. At present near-field optical techniques are relatively slow, so that although they provide better spatial resolution, the speed of information access is somewhat limited. 

Some of the most interesting recent work in the optical properties of nanoerystals involves the study of single nanoerystals rather than ensembles, using near-field optical techniques. These relatively new optical methods can... 

Near-field optical techniques are able to achieve resolutions beyond the diffraction limit (A/2) by exploiting the properties of evanescent waves, which are not restricted by the effects of diffraction. Evanescent waves are non-propagating components of electric fields, which decay rapidly with increasing distance from their source. 

Near-field optical techniques (evanescent waves and field enhancement), as well as TPAP, facilitate the manufacture of nano-objects. The light is confined in a nanometric volume which enables high luminous power densities even low reactivity PISs can woik in these conditions. For example, although they are not very efficient in usual film photopolymerization under conventional light excitations (see below), some polymethine dye/amine systems could appear as excellent candidates as NIR PISs in TPAP for the manufacture of microtips perfectly self-aUgned on the surface of vertical-cavity surface emitting lasers (VCSELs). 

Finally, in Chapter 11 some advanced techniques are briefly described fluorescence up-conversion, fluorescence microscopy (confocal excitation, two-photon excitation, near-field optics, fluorescence lifetime imaging), fluorescence correlation spectroscopy, and single-molecule fluorescence spectroscopy. 

Surface properties are important to the physical and chemical behavior of polymers. Similar to smaller molecules, polymer surface structures can be determined using a variety of techniques including AES, near-field optical microscopy, electron microscopy, SPM, SIMS, and certain IR and MS procedures. 

Single-Molecule Optical Microscopy 3.1. Near-field optical microscopy techniques... 

Betzig E and Trautman K, Near-Field Optics — Microscopy, Spectroscopy, and Surface Modification Beyond the Diffraction Limit , Science, 1992 257 189-195. Bard A J, Denault G, Lee C, Mandler D and Wipf D O, Scanning Electrochemical Microscopy A New Technique for the Characterization and Modification of Surfaces , Acc Chem Res, 1992 23 357. 

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... 

Among the various techniques, we shall only discuss STM, scanning force microscopy (SFM or AFM), and scanning near-field optical microscopy (SNOM or NSOM), as those can well be considered the most prominent members of the SPM family. Among the three, we shall further focus on SFM, as most of the work done on polymers has indeed made use of this method. However, a brief note on STM and SNOM seems appropriate. 

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