Mathieu Kemp

Electron conduction in molecular wires. I. A scattering formalism

We extend a model originally intended for the description of the scanning tunneling microscope (STM) current in molecular imaging of one‐dimensional systems, to encompass the more general process of electron transfer between two reservoirs of states. In the STM problem, the reservoirs are naturally associated with the metal density of states of the electrodes. In the molecular electron transfer problem, the identification of the reservoirs with the Franck–Condon weighted density of vibrational states allows a number of fruitful connections with the theory of nonadiabatic electron transfer (ET) in molecules to be established. In this article, we present an exact procedure, based on Lowdin’s partitioning technique, to determine the Green’s function and the T matrix, relevant to the transport process. We obtain compact expressions for the conductance and the density of states in the limit of small applied voltage and low temperature, and discuss the important case where the molecular wire is described by a t...

Electron conduction in molecular wires. II. Application to scanning tunneling microscopy

We use scattering methods to calculate the conductance of molecular wires. We show that three kinds of wire length dependences of the conductance arise: the decay can be exponential, polynomial, or very slow, depending on whether the reservoir Fermi level lies far from, in, or at the edge of the molecular energy band. We use the formalism to discuss simple models of tip‐induced pressure and of imaging in scanning tunneling microscopy (STM), and point out a paradoxical situation in which the current can decrease with increased tip pressure. We also consider the connection of this formalism with the conventional theory of intramolecular, nonadiabatic electron transfer (ET).

Molecular Wires: Charge Transport, Mechanisms, and Control

ABSTRACT: By molecular wires, one generally means molecular structures that transmit a signal between two termini. We discuss some theoretical models and analysis for electronically conductive molecular wires in which a single molecule conducts charge between two electrodes. This situation resembles both intramolecular non‐adiabatic electron transfer, in which electronic tunneling between donor and acceptor is seen, and mesoscopic quantum transport.

Molecular electronics: Disordered molecular wires

We present results for the effect of diagonal disorder on the conductance of molecular wires, using a simple one‐dimensional tight‐binding picture. We show that diagonal disorder affects three aspects of the conductance: (i) It produces large conductance fluctuations from wire to wire. (ii) It reduces the conductance in situations where the transfer would be resonant, and enhances the conductance when transfer is nonresonant. (iii) It gives near‐exponential conductance decays with wire length.

Molecular wire interconnects: Chemical structural control, resonant tunneling and length dependence

Molecular wires have several promising features, that would appear to make them ideal for advanced interconnects in nanoscale electronic devices. We discuss several aspects of the linear and nonlinear conductance of molecular wire interconnects. Topics include energy dependence of molecular conductance, resonant tunneling behavior, control of conductance by molecular structure and geometry, length dependence including the tunneling regime energetics. Design rules using molecular interconnects will differ substantially from those with more standard, lithographically structured silicon interconnects. In particular, the dissipation mechanisms will differ, both tunneling and ballistic regimes should be available, coulomb blockade and staircase behavior will be observed (but under differing conditions) and fabrication of gate electrodes is a challenge.

A new model of low-temperature photoluminescence in amorphous semiconductors

Abstract Recent low-temperature a-Si:H photoluminescence shows the presence of two peaks in the lifetime distribution, and a G−0.5 dependence of the efficiency on the generation rate. These results cannot be explained by existing models of amorphous semiconductor photoluminescence. The reason for the discrepancy is that every model predicts diffusive motion of the photogenerated pairs. It is shown how the inclusion of the Coulomb interaction between photocarriers, of spin selection effects, and of Auger recombination, gives better agreement of theory with experiment.