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, −SC8 H16S−, 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.