Architectures in Molecular Electronics

The first approach to molecular computing is based on quantum cellular automata (QCA) and related electrostatic information transfers. This method relies on electrostatic field repulsions to transport information throughout the circuitry. One major benefit of the QCA or electrostatics approach is that heat dissipation is less of an issue because only a few or fractions of an electron are used for each bit of information in classical solid-state devices. 

The second approach is based on the massively parallel solid-state Teramac computer developed at Hewlett-Packard (HP) and involves building a similarly massively parallel computing device using molecular electronics- 

Heath discovered that hexane solutions of Ag nanoparticles, passivated with octanethiol, formed spontaneous patterns on the surface of water when the hexane was evaporated, and has prepared superlattices of quantum dots. Lieber has investigated the energy gaps in metallic single-walled carbon nanotubes and has used an atomic-force microscope to mechanically bend SWNT in order to create quantum dots less than 100 nm in length. He found that most metallic SWNT are not true metals, and that by bending the SWNT, a defect was produced that had a resistance of 10 to 100 kfl. Placing two defects less than 100 nm apart produced the quantum dots. 

Therefore, even though this author has been a vocal proponent of the methodology due to its minimal heat dissipation features, it is his opinion that the QCA and electrostatics computing methods will not be commercially viable 

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The opportunities to develop new structures for computing, quantum computation, and spintronics—together with other areas in molecular electronics—raise important issues about the role of computation in the chemical sciences (Chapter 6). In order for chemical scientists to play a major role in converting clever new ideas for computational devices into full-fledged computers, they will have to become increasingly competent in the architectures, algorithms, and protocols that are necessary for reliable computation. 

A frontier area in molecular electronics is the coupling of functional molecules with the appropriate input-output device architecture. 

A wide range of optically interesting bronze materials such as LiFe Fe F6 have been described.Although architecturally and magnetically of interest, typical resistivity is high at room temperature, 10 2 cm. The factors that influence the rates of intramolecular electron transfer in solids have been discussed by Hendrickson. Intramolecular electron transfer in this area is being intensely examined for possible application in molecular electronics. 

Cyclodextrin complexes are the only group of supramolecular entities that have reached the stage of significant commercialization [1], In the author s opinion, they will only be surpassed in the future by carbon nanotubes when the latter s usage in molecular electronics is realized, allowing the bottom-up approach in computer architecture to be realized. 

A major barrier to understanding fundamental relationships between molecular architecture, electronic structure, and charge transport in molecular metals derives from our inability to introduce poten-... 

An excihng new scientific direction emerged in the 1980s and 1990s for exploring molecular sieves as advanced solid state materials. In a 1989 review, Ozin et al. [88] speculated that zeolites (molecular sieves) as microporous molecular electronic materials with nanometer dimension window, channel and cavity architecture represent a new fronher of solid state chemistry with great opportunihes for innovahve research and development . The applicahons described or envisioned included molecular electronics, quantum dots/chains, zeolite electrodes, batteries, non-linear ophcal materials and chemical sensors. More recently there have been significant research reports on the use of zeolites as low k dielectric materials for microprocessors [89]. 

Despite many studies having been reported regarding the reactivity of Ir—NHC complexes, it seems that the catalytic properties of these materials have not yet been fuUy explored. Studies on the reactivity, and the access to new molecular architectures in which the metal in highly electron-rich, envisage a wide set of appUcations in homogeneous catalysis. It is noteworthy to point out that Ir—NHcs offer a clear advantage over other metal complexes in processes implying C—H activations, as observed by the number of intramolecular versions of this process that have been reported and fully studied. 

Since 2004 [183], graphene research has evolved from a heavily theoretical and fundamental field into a variety of research areas [301]. Its electrical, magnetic, physical-mechanical, and chemical properties position it as the most promising material for molecular electronic and optoelectronic applications, possibly replacing the currently used silicon and metal oxide based devices. Nonetheless, further research is essential in order to control easily such properties and construct devices with specific and novel architectures to explore in depth all of these exciting properties, as well as to achieve the synthesis of large-scale, size- and layer-count controlled graphene. 

It should also be recalled that a full electrochemical, as well as spectroscopic and photophysical, characterization of complex systems such as rotaxanes and catenanes requires the comparison with the behavior of the separated molecular components (ring and thread for rotaxanes and constituting rings in the case of catenanes), or suitable model compounds. As it will appear clearly from the examples reported in the following, this comparison is of fundamental importance to evidence how and to which extent the molecular and supramolecular architecture influences the electronic properties of the component units. An appropriate experimental and theoretical approach comprises the use of several techniques that, as far as electrochemistry is concerned, include cyclic voltammetry, steady-state voltammetry, chronoampero-metry, coulometry, impedance spectroscopy, and spectra- and photoelectrochemistry. 

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