L. A. Bumm, J. J. Arnold, T. D. Dunbar, D. L. Allara,* and P. S. Weiss,*
Submitted for publication.
Abstract
Electron transport through molecular frameworks is central to a wide range of chemical, physical, and biological processes. We demonstrate a means to measure electronically and to quantify electron transport through organic molecules and films. We show quantitative agreement with universal values of electron transport inferred in biological, electrochemical, photochemical, and related systems. Scanning tunneling microscopy (STM) was used to image adjacent chains and molecular terraces of different length alkanethiolates in an ordered self-assembled monolayer lattice on Au{111}. In STM transport measurements, both the driving force and the distance can be continuously varied. This allows independent electronic measurement of the molecular bridges through which electron transport takes place. The differences between the measured topography in STM and the physical heights of these molecules can be understood in terms of the transconductance through individual chains using a two-layer tunnel junction model.