Addressing Single Molecules

In a CITS experiment the current control is released and the I-V characteristics at the particular pixel are recorded. This added information represents a three-dimensional data set of current-voltage characteristics as a function of the x, y spatial position on the image and can be displayed as a 3D map of current at a particular location at a particular voltage. At certain bias voltages, the current 

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Finally, tlie ability to optically address single molecules is enabling some beautiful experiments in quantum optics. The non-Poissonian photon arrival time distributions expected tlieoretically for single molecules have been observed directly, botli antibunching at short times [112] and bunching on longer time scales [6, 112 and 113]. The fluorescence excitation spectra of single molecules bound to spherical microcavities have been examined as a probe... 

Many of the most interesting current developments in electronic spectroscopy are addressed in special chapters of their own in this encyclopedia. The reader is referred especially to sections B2.1 on ultrafast spectroscopy. Cl.5 on single molecule spectroscopy, C3.2 on electron transfer, and C3.3 on energy transfer. Additional topics on electronic spectroscopy will also be found in many other chapters. 

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). 

The simulation of molecules in solution can be broken down into two categories. The first is a list of elfects that are not defined for a single molecule, such as diffusion rates. These types of effects require modeling the bulk liquid as discussed in Chapters 7 and 39. The other type of effect is a solvation effect, which is a change in the molecular behavior due to the presence of a solvent. This chapter addresses this second type of effect. 

Moreover, tunneling spectra from single molecules can be obtained (see below). Thus, tunneling spectroscopy is an excellent tool to address fundamental questions about the molecular layer or single molecule in a molecular electronic device. 

Three- and four-terminal systems have yet to be addressed either as single molecules or as nanometer-sized bundles. This situation stems from the fact that it is far easier to bring two probes into close proximity than it is to bring three probes into near contact. Macroscopic leads are akin to basket-... 

Electrochemical reactions may be carried out at any scale from the smallest to the largest and progress in nanotechnology has made it possible to address electron transfer at the single molecule level [26, 27]. Conversions at the laboratory scale are well established and have been addressed by numerous authors [1, 2] and, at the industrial scale, more than 50 electrochemical processes have reached a respectable level with the reductive hydrodimeri-sation of acrylonitrile to adiponitrile topping the list with an annual production of about 300 000 tons [28],... 

Key questions ahead of us concern new concepts for addressing individual molecular switches and the construction of more complex systems which incorporate several switchable functions. Advances in scanning - probe techniques and single molecule spectroscopy as well as supramolecular chemistry will play an important role in this endeavor. 

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