Molecular Electronics: Exploring the Limits of Small

Smaller circuits are faster, more power efficient, and require fewer materials to make, so electronics manufacturers constantly push to decrease the size of circuits. As a result, physicists and chemists are beginning to build circuits the size of molecules. In order to understand charge flow in molecular scale systems, it is ï¬rst important to understand what length scales deï¬ne the quantum regime so that moving charges can be modeled appropriately. The most basic equation for modeling quantum electron transport is the Landauer formula in which current depends on the transmission coefficient through a current carrying mode in a quantum dot or molecular wire, however, this model has limitations because it assumes collisionless (ballistic) transport, and therefore can only be applied for length scales less than the scattering length. As a result, Landauer theory is most useful for tunnel junctions in which charge transport is coherent and elastic. However, different types of molecular circuitry can have different charge transfer mechanisms, including thermally activating hopping and cotunneling. These charge transfer mechanisms will be considered in detail for molecular wires. In addition to new mechanisms for charge transport, molecular systems also offer possibilities for new types of switching based on conformational changes of the molecule from a redox reaction, light excitation, or the binding of another molecule. Molecular electronics has the potential to revolutionize nanoscience as physicists and chemists push on the very limits of how small we can make electronic devices