Intensity studies of inelastic electron tunneling spectra

Inelastic electron tunneling spectroscopy (IETS) using metal-insulator-metal (MIM) tunnel junctions is an established technique for studying the vibrational modes of molecules adsorbed on metal surfaces. We are examining a new geometry for IETS in which the oxide layer of the MIM junction is replaced by an atomically thin gas film. "Clean" junctions in which the barrier is composed of pure neon exhibit Ohmic behavior except in the region near zero bias. When the neon barrier is doped with acetylene molecules, we observe peaks corresponding to the vibrational modes of these molecules. An analysis of the inelastic peak intensities indicates that dipole scattering is not the principle mechanism of the electron-molecule interaction in this geometry.