Molecular Electronics

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MOLECULAR ELECTRONICS

INTRODUCTION
Molecular electronics (sometimes called moletronics) is a branch of applied physics which aims at using molecules as passive (e.g. resistive wires) or active (e.g. transistors) electronic components. The concept of molecular electronics has aroused much excitement both in science fiction and among scientists due to the prospect of size reduction in electronics offered by such minute components. It is an enticing alternative to extend Moore's Law beyond the foreseen limits of small-scale conventional silicon integrated circuits.

Often molecular electronics is envisioned as the next step in device miniaturization. The importance of molecules in device applications stems not only from their electronic properties, but also from their ability to bind to one another, recognize each other, assemble into larger structures, and exhibit dynamical stereochemistry. As a result, molecular electronics is currently a very active research field

HISTORY
Study of charge transfer in molecules was advanced in the 1940s by Robert Mulliken and Albert Szent-Gyorgi in discussion of so-called "donor-acceptor" systems and developed the study of charge transfer and energy transfer in molecules. Likewise, a 1974 paper from Mark Ratner and Avi Aviram 1 illustrated a theoretical molecular rectifier. Later, Aviram detailed a single-molecule field-effect transistor in 1988. Further concepts were proposed by Forrest Carter of the Naval Research Laboratory, including single-molecule logic gates. Apart from the Aviram and Ratner proposal, molecular electronics received an initial boost from the experimental discovery of conducting polymers in the mid-seventies. Before this date, organic molecules (which form crystals or polymers) were considered insulating or at best weakly conducting semi-conductors. In 1974, McGinness, Corry, and Proctor reported the first molecular electronic device in the journal Science. As its active element, this voltage-controlled switch used melanin, an oxidized mixed polymer of polyacetylene, polypyrrole, and polyaniline. The "ON" state of this switch exhibited extremely high conductivity. This device is now in the Smithsonian's collection of historic electronic devices. As Hush notes, their material also showed negative differential resistance, "a hallmark of modern advances in molecular electronics". Melanin is also the first example of a "self-doped" organic semiconductor, though McGinness et al also looked at dopants such as diethyamine. A few years later, in 1977, Shirakawa, Heeger and MacDiarmid rediscovered the potential high conductivity of oxidized ("doped") polyacetylene, producing a passive highly-conductive form of polyacetylene. For this discovery and its subsequent development, they received the 2000 Nobel prize in physics. Subsequentely, chemists greatly improved the conductance of conjugated polymers. These findings opened the door to plastic electronics and optoelectronics, which are beginning to find extensive commercial application.

Molecular electronics comprises two related but separate sub disciplines: * molecular materials for electronics utilizes the properties of the molecules to affect the bulk properties of a material * molecular scale electronics focuses on single-molecule applications.

MOLECULAR SCALE ELECTRONICS
Molecular scale electronics, also called single molecule electronics, is a branch of nanotechnology that uses single molecules, or nanoscale collections of single molecules, as electronic components. Because single molecules constitute the smallest stable structures imaginable, this miniaturization is the ultimate goal for shrinking electrical circuits.

Fundamental concept
Conventional electronic devices are traditionally made from bulk materials. The bulk approach has inherent limitations in addition to becoming increasingly demanding and expensive....
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