Experimental study of relative intensities in inelastic electron-tunneling spectra

Publisher Website
Google Scholar
Abstract
This paper is devoted to an experimental study of relative intensities in inelastic electron tunneling spectra of organic molecules. The theoretical framework is given by the first theory of tunneling intensities, the theory of Scalapino and Marcus. We compare the predictions of this theory with our experimental data and find evidence for an important disagreement: the difference between the predicted and observed relative intensities in the spectrum of a given molecule may be as large as one order of magnitude. This leads us to consider the influence of the counterelectrode of the junctions of tunneling intensities: we find that the intensity of a given peak is strongly attenuated when the distance of the associated radical of the counterelectrode increases provided that the associated dipole is perpendicular to the insulator-electrode interface. This effect only partially resolves the discrepancy. This brings us to re-examine the theory of Scalapino and Marcus. We try, on the basis of an alternative derivation of the results of this theory, to understand to what extent it can be applied to the interpretation of the spectra. We are able to justify the theory for the case of an infraredlike interaction with a dipole perpendicular to the interface. This treatment is not adapted to the other cases of interest (parallel dipole or Raman-like interaction). An explanation of the observed disagreement could appear in an appropriate treatment of these situations.