Effect of the second metal electrode on vibrational spectra in inelastic-electron-tunneling spectroscopy

Inelastic-electron-tunneling-spectroscopy experiments on the peak positions and bandwidths of the hydroxyl and deuteroxyl stretch bands for three different oxides and four different top metals are described. The bandwidths and peak positions depend on the top metal electrodes used. Two possible mechanisms for this effect, hydrogen bonding between the hydroxyl ions and the metal atoms, and an image-dipole model, are discussed. Order-of-magnitude estimates are made for the simple image-dipole model and compared with experiment.