Molecule-superconductor structures

Chemical Sensors and Devices Based on Molecule—Superconductor Structures... 

Figure 2. Schematic illustration showing the steps that are required to prepare molecule/superconductor structures (A) hi the initial step, a MgO (100) substrate is cleaned, (B) then -KXX) A of YBa2Cu3(>7-5 is deposited by laser ablation. (C) A microbridge pattern is then created in the central portion of the film. (D) In the final step, the molecular layer is deposited over die microbridge junction.

In summary, methods have been devised to prepare a number of novel molecule/superconductor structures. The composite systems can be tailored for a variety of applications in which the superconductor and molecular components are chosen for a given purpose. In tMs chapter, the initial two examples of molecule/superconductor chemical sensor are reported. Future work will undoubtedly lead to a better understanding of molecule/sup conductor interactions which will foster further developments in the area of chemical sensors. 

These structures provide an excellent platform for the study of novel molecule-superconductor electron and energy transfer phenomena. 

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]. 

Calculations using the methods of non-relativistic quantum mechanics have now advanced to the point at which they can provide quantitative predictions of the structure and properties of atoms, their ions, molecules, and solids containing atoms from the first two rows of the Periodical Table. However, there is much evidence that relativistic effects grow in importance with the increase of atomic number, and the competition between relativistic and correlation effects dominates over the properties of materials from the first transition row onwards. This makes it obligatory to use methods based on relativistic quantum mechanics if one wishes to obtain even qualitatively realistic descriptions of the properties of systems containing heavy elements. Many of these dominate in materials being considered as new high-temperature superconductors. 

This spherical structure is composed of 60 carbon atoms covalently bonded together. Further spherical forms of carbon, bucky balls , containing 70, 72 and 84 carbon atoms have been identified and the discovery has led to a whole new branch of inorganic carbon chemistry. It is thought that this type of molecule exists in chimney soot. Chemists have suggested that due to the large surface area of the bucky balls they may have uses as catalysts (Chapter 7, p. 109). Also they may have uses as superconductors. 

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