טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentToroker Maytal
SubjectNew Rate Expressions: Formulation and Applications to
Electron Transfer Processes
DepartmentDepartment of Chemistry
Supervisor Professor Uri Peskin
Full Thesis textFull thesis text - English Version


Abstract

The field of molecular electronics is based on the notion that an electronic device may be comprised of a molecule. Molecular bridges between electronic sites/reservoirs have special transport properties where the rate/frequency of charge transport is determined by the structure of the bridge. This work is devoted for modeling electronic dynamics within molecular bridges and for developing theoretical methods for calculating current through such bridges.

Part of the work is thus dedicated to studies of bound molecular systems that have more than a single acceptor where the central question was the ability to control the direction of the electron. Conditions for site directing the electron to a specific acceptor were obtained by a reduction scheme based on a perturbation theory, valid in the deep tunneling regime. Our study showed that site directing an electron to an acceptor can be achieved by changing the electronic properties of the molecular bridge or by electronic-nuclear coupling. The contact between the molecular bridge and the donor/acceptor sites was pointed as the most effective place for controlling the dynamics. 

The other part of the work is devoted to studies of open electronic systems, where the molecular bridge is coupled to electrons reservoirs, leading eventually to a steady flux of electrons passing through the bridge.

A linear relation was formulated between the current in a molecular junction and the widths of resonance states. This intuitive relation breaks down for strong molecule-lead coupling where the transport rate becomes dominated by direct scattering between the electrodes continua.

Bound states on the other hand are molecular bridge states which do not contribute to the transmission. A condition for obtaining a bound state in the continuum was established in terms of the projection operator formalism, demonstrating again the importance of the contact region.

Landauer-type expression for the current was generalized to include electronic-nuclear coupling at the molecule-electrodes contacts, showing that the current can be calculated at a compact subspace that does not include the molecule-electrode interactions.

The close analogy between rate process of electron transport through molecular junctions and the thermal reaction rate of chemical reactions, led us to the formulation of new time-dependent approaches based on correlation functions that have been advanced for calculating rates of chemical reactions. We developed a theory, termed the flux averaging method, for direct calculations of thermal resonant tunneling rates, circumventing the problem of long time-delays due to population of resonance states.