Tunneling Spectroscopy for the Study of Adsorption and Reaction on Model Catalysts

Inelastic electron tunneling spectroscopy measures the vibrational modes of a small quantity of molecules that are included in or near the insulating layer of a metal-insulator-metal tunnel junction [l, 21. Figure 1 stows two metal electrodes separted by a thin insulating layer. If this layer is thin enough (of order 20 A) and if a voltage V is applied between the two electrodes, an electron current will flow from one electrode to the other. The maximum energy of the tunneling electrons will be of order eV. If there is a molecule in or near the insulating layer with a characteristic vibrational mode energy hv, this vibrational mode may or may not be excited by the tunneling electron. The most important factor turns out to be simply, does the tunneling electron have enough energy? In particular, is eV  hv?