Photon tunneling microscop

Commercially available photon tunneling microscopes have a lateral resolution of 160 nm but subnanometer vertical resolution. The nondestmctive, instantaneous 3-D viewing of a surface (no scanning) yields real-time imaging as one traverses a given sample. The sample must be a dielectric, but transparent polymer tepHcas of opaque samples can be studied. 

As the fine optical fiber can be inserted close to an object in water, the first applications of this instrument have been directed toward high resolution observation of tissue sections and living cells [167]. The associated photon tunneling microscope has been applied to polymer surfaces [168]. In principle all the contrast modes of normal optical microscopy can be used in the near-field and there may be other unique contrast mechanisms [169]. The light signal can be analyzed spectroscopically to give... 

Sharp S L, Warmack R J, Goudonnet J P, Lee I and Ferrell T L 1993 Spectroscopy and imaging using the photon scanning-tunnelling microscope Acc. Chem. Res. 26 377... 

Shen, Y. R., Swiatkiewicz, J., Winiarz, J., Markowicz, P, and Prasad, P. N. 2000. Second-harmonic and sum-frequency imaging of organic nanocrystals with photon scanning tunneling microscope. App/. Phys. Lett. 77 2946 8. 

In general, optically, electrically or chemically triggered switches would seem to be preferable to mechanically activated ones, as are photo-, electro- and chemo devices with respect to mechano devices and electronic or photonic computing with respect to mechanical computing. The ultimate in (nano)mechanical manipulation of a molecular device is represented by the realization of a bistable switch based on the motion of a single atom by means of the scanning tunnelling microscope [8.295] (see also Section 9.9). 

R. Berndt, R. Gaisch, J. K. Gimzewski, B. Reihl, R. R. Schlittler, W. D. Schneider and M. Tschudy, Photon-emission at molecular resolution induced by scanning tunneling microscope, Science 262, 1425 (1993). 

Nilius N, Ernst N, Freund HJ. Photon emission spectroscopy of individual oxide-supported silver clusters in a scanning tunneling microscope. Phys Rev I ett. 2000 84 3994-7. 

The last decade of the twentieth century has been revolutionary in the study of molecular electron transfer processes. For the preceding century scientists have investigated three types of such processes transfer between a donor and an acceptor species, transfer between two sites on the same molecule and transfer between a molecular species in solution and a metal or a semiconductor electrode. The main observable in such studies is the electron transfer rate, though in studies of photoinduced electron transfer processes the quantum yield, defined as the number of electrons transfeiTed per photon absorbed, is also a useful observable. The invention of the tunneling microscope and later experimental developments have now made it possible to investigate another manifestation of electron transfer electronic conduction by a molecule connecting two bulk metal or semiconductor electrodes. In this... 

In the first part of the chapter several methods used to observe morphology of polymer blends are presented. Various optical microscopic methods are reviewed, including such modem techniques as photon tunneling microscopy (PTM), scanning near-field optical microscopy (SNOM), phase measurement interference microscopy (PMIM), surface plasmon microscopy (SPM) and optical waveguide microscopy (OWM). Many of these methods have been developed to study surfaces and thin films. However, they can also be applied to polymer blend morphology. 

T Saiki, S Mononobe, M Ohtsu, N Saito, J Kusano. Tailoring a high-transmission hber probe for photon scanning tunneling microscope. Appl Phys Lett 68 2612-2614, 1996. 

Berndt R, Gaisch R, Gimzewski JK, Reihl B, Schlittler RR, Schneider WD and Tschudy M (1993) Photon emission at molecular resolution induced by a scanning tunnelling microscope. Science 262 1425-1427. 

Fig. 9.7 Setup of a PSTM (photon scanning tunneling microscope). Localized electromagnetic fields in the near field of the sample surface are detected with the help of a noncoated dielectric tip. Reprinted with permission from Rubahn (2004). Copyright 2004, B.G. Teubner Verlag.

However, photons are not actually reflected at the interface, but rather tunnel into the low-index material by optical tunneling. As a result, the reflected beam of fight is shifted along the interface by a small amount (Ax = 2Goos-Haenchen shift. This shift is ty pically small for fluid diagnostic applications (Ax < 1 pm) as compared to the field of view. A typical field of view for the magnification of microscope objectives is on the order of several hundred micrometers. 

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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