Shifts and Dips in Inelastic Electron Tunneling Spectra Due to the Tunnel Junction Environment

摘要

In general, the tunnel junction environment has proved to be surprisingly benign; tunneling spectra of molecules included within tunnel junctions are similar to infrared and Raman spectra of molecules not covered by a metal electrode. Peak shifts have been typically less than the line width of the peaks and peak intensities have been comparable to infrared and Raman intensities. This report provides a different situation for tunnel junctions containing molecules absorbed on metal particles. Specifically, we find that different top metal electrodes give different tunneling spectra for CO on alumina supported iron and rhodium particles. Though metals with similar atomic radii give similar spectra, metals with dissimilar atomic radii can give qualitatively different spectra. We also find anomalies concerning intensities. Specifically for methyl isocyanide adsorbed on alumina supported rhodium particles, the strongest peak in the infrared spectrum, the NC- stretching mode, appears as a dip in the tunneling spectrum.