An individual mixed-valence molecule is a natural candidate to represent a bit of information. An electron on one charge center represents a binary “1” and on the other center represents a binary “0.” Such an approach, termed molecular quantum-dot cellular automata (QCA), constitutes the ultimate limit of device scaling: a single molecule is the smallest structure that can be designed by humans. To make computational structures requires that devices interact with other devices. In the field-effect transistor paradigm the basic device is a gated charge-controlled current switch and the device-device interaction is accomplished by using the current through one device to charge or discharge the gate on another device. This current flow is the source of the excessive power dissipation that has brought the semiconductor roadmap to its end. By contrast, mixed-valence molecules strongly couple to neighboring molecules Coulombically, without requiring current flow. Power dissipation can then be reduced to the fundamental constraints of thermodynamics, which require dissipating a minimum energy of kBT log(2) as heat only when a bit erasure occurs. It is possible to create mixed valence molecules that have three charge centers and so can represent a “null” state in addition to 1 and 0. This strategy permits clocked control of the computation to minimize errors and restore signal levels as information moves across the molecular array. Recent progress in synthesizing a neutral mixed valence zwitterion is very encouraging in this regard. The talk will describe the long-term vision for molecular QCA nanoelectronics, and several aspects of mixed-valence chemistry that will need to be explored. These include fundamentals of electron transfer dynamics, synthetic targets, theoretical methods, and single-molecule measurements.

Mixed-valence molecules could be the replacement for the transistor

253rd National Meeting (2017)

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