Calculation of Electronic Lifetimes in Molecular Junctions

We study the electronic lifetimes in molecular junctions using the Keldysh nonequilibrium Green function (NEGF) model. It is found that two characteristic time scales which govern the electron tunneling phenomena. One is the electronic lifetime in which electronic energy in the molecular electronic state dissipates into the right/left electrode or vibrational mode, the other is the residence time due to virtual excitation of electrons between the two electrodes and the molecular electronic state. And using a set of the parameters which characterize the molecular junction, we show that the molecular vibrational frequency, the position of the electronic state of the molecule, the strength of electron-vibration coupling (via the electron-phonon interaction) and the distance between the molecule and the electrodes (via the molecule-electrode coupling) represent substantial contributions that affect the electronic lifetime in molecular junctions, as result all are represent important parameters to determine the nature and the mechanisms of electron transport in molecular junctions.