Using inelastic electron tunneling spectroscopy (IETS) to measure the vibronic structure of non-equilibrium molecular transport, aided by a quantitative interpretation scheme based on non-equilibrium Greens function/density functional theory methods, we are able to characterize the actual pathways that the electrons traverse when moving through a molecule in a molecular transport junction. The pathways idea has been present in physical organic chemistry for years in connection with reaction mechanisms, and has been widely used in the interpretation of electron tunneling pathways in proteins, but no distinct observations have been made. We show that the IETS observations directly index electron tunneling pathways along the given normal coordinates of the molecule. One can then interpret the maxima in the IETS spectrum in terms of the specific paths that the electrons follow, as they traverse the molecular junction. IETS measurements therefore not only prove (by the appearance of molecular vibrational frequencies in the spectrum) that the tunneling charges in fact pass through the molecule, but also can be used to determine just what the transport pathways are, and how they change with the geometry and placement of molecules in junctions.
Citation: Proceedings of the National Academy of Sciences of the United States of America
Pub Type: Journals
molecular electronics, nanotechnology