Electron transfer and vibrational modes in a finite molecular chain

Abstract

A statistical quantum discrete model for a molecular bridge between metallic electrodes is proposed. A theory of conduction is developed on the assumption that the main contribution to the electron transfer is due to nonequilibrium-populated electron-affinity states of the molecule. It is shown that the field-induced modification of the states of the bridge molecule, together with the Coulomb blockade effect, leads to suppression of the electron transfer. Relations are obtained for the electron–vibron interaction, and the contribution of atomic vibrations to the conductance of the chain is discussed. The current–voltage characteristics of molecular bridges are calculated for different positions of the spectrum of the molecule with respect to the levels of the chemical potentials of the electrodes. Explanations are given for the stepped and asymmetric character of the current–voltage characteristic observed experimentally and for the fractional charging of the bridge molecule.