Single molecule electronic circuits

Keywords Intramolecular kirchhoff laws Molecular electronics Molecular logic gates Single molecule electronic circuits Quantum hamiltonian computing... 

The next step is to estimate how long a molecule can stay in its vibrational excited state during a single electric pulse. A conventional electronic circuit carmot generate a short pulse like 10 ps, so that the use of electric pulses longer than 100 ps is more... 

The time has come to make a quantum leap, both figuratively and literally. Short-term solutions may exploit organic semiconductors [31-33] and semiconductor quantum heterostructures [34, 35]. A long-term solution will be provided by molecular electronics [36-40] in which single molecules are employed as integrated circuits [41, 42]. 

A second essential part of any electrical circuit is a switch, a device that can he turned ON to allow the flow of current or OFF to stop that flow. The simplest imaginable switch would consist of a single molecule that could assume two conformations, one that permits the flow of electrons (ON) and one that prevents such a flow (OFF). 

A third part of an electric circuit is a rectifier, a device that allows the flow of electrons in only one direction. As early as 1974, two researchers, Ari Avram at the IBM Thomas J. Watson Research Center and Mark A. Ratner at Northwestern University, suggested the possibility that single molecules might he constructed that would operate as rectifiers. Some 23 years later, that goal was achieved by a team of researchers at the University of Alabama at Tuscaloosa led by Robert M. Metzger. 

The origin of molecular electronics can be traced back to 1974, when Aviram and Ratner suggested that a single molecule could perform as a cuiTent rectifier. The paradigm of molecular electronicis that typical functions of electronic devices can be emulated by individual molecules or by suitable assemblies thereof (supramolec-ular systems). The ultimate objective of this research field is the construction of electronic circuits (and computers) from molecules, in a bottom-up approach. 

Different approaches to bridge the size gap between conventionally fabricated circuit elements and truly atomic scale components have been discussed. These indude the use of electron transport through single molecules, the concept of molecular rectification, and the design of atomic relays or molecular shuttles. Today, the approach that receives the most attention among the different concepts of futuristic drcuit design is drcuitry based on single-electron transistors. 

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