Molecular electronics organic superconductors conducting

The neutral insulator TMTSF, which shows field-effect conduction with /Th — 0.2 cm s (Nam et al, 2003), when transformed into a Bechgaard salt also becomes superconducting, but at lower temperatures. In this case the perfect segregation of organic and inorganic molecular planes leads to confined electronic systems, which in the normal state are quasi ID. Organic superconductors based on the BEDT-TTF molecule represent the case of pure 2D electronic systems. 

Achievements in the field of organic conductors and superconductors have promoted the development of the field of molecular electronics as well. The latter is a nascent field of research, suggesting the use of organic molecules with the tunability of their electronic structure, instead of conventional inorganic microelectronics. It has been suggested that molecular electronic devices could utilize a variety of optoelectronic and conductivity phenomena of organic substances at the nanometer level. Whereas the conductivity and superconductivity of organic metals is a result of bulk electrical behavior of lower-dimensional systems, molecular electronics deals... 

The optical properties of conducting polymers are important to the development of an understanding of the basic electronic structure of the material. These and other problems were described in various books and review papers [90-93]. Raman spectroscopy is also an ideal tool for predicting many important electronic properties of molecular materials, organic conductors, and superconductors as well as for understanding their different physical properties, since it is a nondestructive tool, which can be used in situ and with spatial resolution as good as 1 xm. 

In principle, molecules can be either passive or active electronic components, either singly or in parallel as a one-molecule-thick monolayer array. This may lead to electronic devices with dimensions of 1-3 nm. Unimolecular electronics (UE) or molecular electronics sensu stricto, or molecular-scale electronics evolved from studies of organic crystalline metals, superconductors, and conducting polymers the idea is to exploit the electronic energy levels of a single molecule, and most importantly its HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital), which can be tuned, or modified by incorporation of electron-donating... 

All metals conduct electricity on account of the mobility of the electrons that bind the atoms together. Ionic, molecular, and network solids are typically electrical insulators or semiconductors (see Sections 3.f3 and 3.14), but there are notable exceptions, such as high-temperature superconductors, which are ionic or ceramic solids (see Box 5.2), and there is currently considerable interest in the electrical conductivity ol some organic polymers (see Box 19.1). 

The prospective applications ofmolecular assemblies seem so wide that their limits are difficult to set. The sizes of electronic devices in the computer industry are close to their lower limits. One simply cannot fit many more electronic elements into a cell since the walls between the elements in the cell would become too thin to insulate them effectively. Thus further miniaturization of today s devices will soon be virtually impossible. Therefore, another approach from bottom up was proposed. It consists in the creation of electronic devices of the size of a single molecule or of a well-defined molecular aggregate. This is an enormous technological task and only the first steps in this direction have been taken. In the future, organic compounds and supramolecular complexes will serve as conductors, as well as semi- and superconductors, since they can be easily obtained with sufficient, controllable purity and their properties can be fine tuned by minor adjustments of their structures. For instance, the charge-transfer complex of tetrathiafulvalene 21 with tetramethylquinodimethane 22 exhibits room- temperature conductivity [30] close to that of metals. Therefore it could be called an organic metal. Several systems which could serve as molecular devices have been proposed. One example of such a system which can also act as a sensor consists of a basic solution of phenolophthalein dye 10b with P-cyciodextrin 11. The purple solution of the dye not only loses its colour upon the complexation but the colour comes back when the solution is heated [31]. 

Having identified methods to deposit conductive polymer and molecular metal systems onto cuprate superconductor structures without damage to either material, it becomes important now to consider the electronic interactions that occur when the two conductors are in contact with one another. Of particular importance is the interaction that occurs between the polymer-derived charge carriers and the superconducting Cooper pairs. Important background information related to this area can be obtained from the well-documented behavior of the more classical metal/superconductor and semicon-ductor/superconductor systems. Thus, prior to considering experimental data and theoretical treatments for organic conductor proximity effects, we review previous studies of proximity effects in the more classical systems. 

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