Reproducible measurement of single-molecule conductivity

A reliable method has been developed for making through-bond electrical con tacts to molecules. Current-voltage curves are quantized as integer multipl es of one fundamental curve, an observation used to identify single-molecul e contacts. The resistance of a single octanedithiol molecule was 900 +/- 5 0 megohms, based on measurements on more than 1000 single molecules. In con trast, nonbonded contacts to octanethiol monolayers were at least four orde rs of magnitude more resistive, less reproducible, and had a different volt age dependence, demonstrating that the measurement of intrinsic molecular p roperties requires chemically bonded contacts.