An Experimental Study of the Line Shape of Orbital Mediated Tunneling Bands Seen in Inelastic Electron Tunneling Spectroscopy

The line shape of inelastic transitions seen in inelastic electron tunneling spectroscopy (IETS) performed on metal−insulator−adsorbate−metal junctions is well understood. Recently, there have been reports of quasi-elastic processes leading to strong wide bands in what heretofore had been called IETS. It is demonstrated that these quasi-elastic ionizations, known as orbital mediated tunneling (OMT) bands, are actually differential in nature. However, because of the steeply rising elastic background in IETS, and because of the asymmetric shape of these bands, they often give the appearance of simple peaks. It is experimentally shown that the position and width of these false peaks can be used to reasonably estimate the actual maximum in the density of states associated with the orbital mediated transition.