Nanoscopic functional device

Eirst-principles simulation has been carried out to simulate the transient current through a series of molecular and nanoscopic electronic devices, based on the AWBL approximation for Qq, and EDA for exchange-correlation functional. Figure 2.1 depicts a carbon nanotube based electronic device. The device is a (5, 5)... 

There have been some impressive, relatively recent examples of molecular rectification. Compound 11.52 has proved to be an extremely efficient molecular rectifier, able to actually function as a rectification device by intramolecular tunnelling either as a monolayers or multilayer macroscopic film or on a nanoscopic level.51 Switchable rectification has been demonstrated for a related dye shown in Figure 11.36. The electrical asymmetry can be chemically switched, off and then back on, by treatment with acid and base, respectively. Protonation disrupts the intramolecular charge-transfer axis, destroying the rectification effect.52 Recent calculations, however, suggest that there may be relatively unpromising theoretical limits on the rectification possible by a single molecule.53... 

The examples represented here have demonstrated our increasing ability to design and to manipulate ever larger supramolecular systems and merge concepts from supramolecular and polymer chemistry. Yet we are still far Irom approaching the perfection and versatility and, most important, the functionality of biomolecules and their superstructures. Like in biology, macromolecules and the competition between macromolecular order and disorder will play a dominant role in the preparation of functional molecular devices and nanoscopic objects. 

Given the ability of nanochemistry to provide functional materials of practical utility in the near future, the elaborative quantum-chemical calculations of clusters are of significant value because interesting individual molecules or small clusters can be developed as viable functional materials and devices. The prediction of properties of nanomaterials, from a nanoscopic determination of the properties of individual atoms, molecules, or clusters, is based on molecular interactions (with ion/atom/molecule/ electron/photon) and the resulting molecular structures (clustering/aggregation by self-assembly and self-synthesis process). In this context, we have carried out detailed... 

Much remains to be learned before the true rational design of functional PDAs can be realized, as either the transducer of chemical and biological colorimetric sensors or the molecular tenqrlate of functional conqrosites and devices witii structural control ranging fix>m nanoscopic to microscopic levels. In this ch ter, we will discuss the design and prepmation of mono-functional (amphiphilic) and bis-functional (bolaanqrhiphilic) PDAs that adopt exotic... 

In order to get die discussion of specific problems under way, I returned to an issue that was discussed after one of the morning lectures given that in our drive towards miniaturization we may eventually be able to build nanoscopic devices in which individual molecules perform functions that are currendy performed by the elements of microelectronic or optoelectronic circuits or additional functions that we are presendy not able to perform, how shall we address the individual molecules and connect them to the outside world At times, this has been declared inqxissible, and much criticism has been leveled at the whole so far non-existent field of molecular electronics as a result. 

Tremendous interest has arisen in recent years regarding die issues of chain mobility and glass transition at polymer surfaces (1-4). Keddie et al used ellipsometric measurements of thermal expansivity to study Tg of polystyrene on silicon as a function of film thickness (1). The observed Tg asymptotically approached the bulk value of 100 C as thickness was increased, but for thinner films lO s of nm), Tg was significantly depressed. Clearly, such effects are of critical importance in the application of ultrathin polymer films as lubricants and protective coatings in magnetic data storage devices and micromechanical systems (5). Until recently, however, direct mechanical measurements of polymer behavior at the nanoscopic scale (which is necessary for mechanical analysis of ultrathin films) and at elevated temperatures has not been possible. 

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