Inelastic electron tunneling spectroscopy of an alkanedithiol self-assembled monolayer

Inelastic electron tunneling spectroscopy (IETS) of an alkanedithiol self-assembled monolayer (SAM) is investigated using a nanometer-scale device. The IETS spectrum of the octanedithiol device clearly shows vibrational signatures of an octanedithiolate, -SC8H16S-, bonded to gold electrodes. The pronounced IETS peaks correspond to vibrational modes perpendicular to the junction interface, which include the stretching modes of Au-S (at 33 mV) and C-C (at 133 mV) and the wagging mode of CH2 (at 158 mV). The observed peak intensities and peak widths are in good agreement with theoretical predictions.