Tracing electronic pathways in molecules by using inelastic tunneling spectroscopy

doi:10.1073/pnas.0704208104

Tracing electronic pathways in molecules by using inelastic tunneling spectroscopy

^†Department of Chemistry and Centre for Scientific Computing, University of Warwick, Coventry CV4 7AL, United Kingdom;
^‡National Institute of Standards and Technology, Gaithersburg, MD 20899;
^§Hewlett–Packard Laboratories, Palo Alto, CA 94304; and
^¶Department of Chemistry and Institute of Nanotechnology, Northwestern University, Evanston, IL 60208

Contributed by Mark A. Ratner, June 1, 2007 (received for review April 18, 2007)

Abstract

Using inelastic electron tunneling spectroscopy (IETS) to measure the vibronic structure of nonequilibrium molecular transport, aided by a quantitative interpretation scheme based on Green's 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. 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. Therefore, IETS measurements 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 the transport pathways and how they change with the geometry and placement of molecules in junctions.

Footnotes

^‖To whom correspondence should be addressed. E-mail: ratner{at}chem.northwestern.edu
Author contributions: A.T., R.D.v.Z., D.R.S., M.A.R., and J.G.K. designed research; A.T. and J.M.B. performed research; A.T. and L.B.P. contributed new reagents/analytic tools; A.T., J.M.B., L.B.P., M.A.R., and J.G.K. analyzed data; and A.T., M.A.R., and J.G.K. wrote the paper.
The authors declare no conflict of interest.
This article contains supporting information online at www.pnas.org/cgi/content/full/0704208104/DC1.
Abbreviations:

IET,

inelastic electron tunneling;

IETS,

IET spectroscopy.