Molecular Electronics: Theory and Device Prospects

Abstract

Understanding current flow through molecular conductors involves simulating the contact surface physics, the molecular chemistry, the device electrostatics, and the quantum kinetics of nonequilibrium transport, along with more sophisticated processes such as scattering and many-body effects. We summarize our current theoretical understanding of transport through such nanoscale devices. Our approach is based on self-consistently combining the nonequilibrium Green's function (NEGF) formulation of transport with an electronic structure calculation of the molecule. We identify the essential ingredients that go into such a simulation. While experimental data for many of the inputs required for quantitative simulation are still evolving, the general framework laid down in this treatment should still be applicable. We use these concepts to examine a few prototype molecular devices, such as wires, transistors, and resonant-tunneling diodes.

Coulomb blockade in molecular quantum dots

“…1 is associated with kinetic energy, while the second term is the electrostatic energy stored in the capacitor formed by the conducting level and the electrodes [4]. The electrostatic energy term can be obtained from the relation Q 2 /(2C) by noting that Q = e(N − N eq ) denotes an amount of charge stored in the mentioned capacitor (N eq being the equilibrium number of electrons occupying the particular energy level) and taking into account charging energy defined as U = e 2 /(2C).…”

“…Molecular-scale electronic devices are of growing interest among scientists and engineers due to their potential in becoming active components for future nanocircuits, namely: interconnects, switches, diodes, transistors, dielectrics, photovoltaics, memories and others [1][2][3][4]. Recent advances in experimental techniques has made it possible to fabricate such junctions, composed of single molecules (or molecular layers) attached to two (or more) electrodes [5][6][7][8][9][10][11].…”

Kinetic control of the current through a single molecule

“…During recent years a number of different experiments have been described demonstrating strong nonlinear current-voltage (I-V) characteristics of single organic molecules attached to nanoelectrodes [1][2][3][4][5][6][7][8][9][10]. These nonlinear I-V characteristics are connected with such specific effects like current rectification and negative resistance.…”

“…This descriptions of the electron transmission through a single molecule reproduces the experimental findings rather satisfactory if the molecule is covalently linked to the leads (which is the case for some types of break junctions [18]). An agreement between measured data and calculations based on the Landauer approach is less satisfactory, however, for a weak (noncovalent) molecule-lead coupling [10]. The alternative of Landauer approach could be achieved in using the nonequilibrium Green function approach [19,20].…”

Lindblad equation and its semiclassical limit of the Anderson-Holstein model

“…Multi-level open quantum systems have received much attention due to their wide applications and intriguing phenomena [1][2][3]. One of the simplest models is perhaps the Anderson-Holstein model, a two-level open quantum system [4].…”