Inelastic Electron Tunneling Spectroscopy - STM-IETS

STM-IETS

Keeping the tip of a scanning tunneling microscope (STM) at fixed position over the surface and sweeping the bias voltage, one can record a I-V characteristic. This technique is called scanning tunneling spectroscopy (STS). The first derivative gives information about the local density of states (LDOS) of the substrate, assuming that the tip has a constant density of states. The second derivative gives information on vibrations of the adsorbate, exactly as in IETS. That is why this technique is commonly called STM-IETS. The role of the insulating oxide layer is played by the gap between the tip and the adsorbate.

Nowadays molecular transport junctions have been produced with one single molecule between two electrodes, possibly with an additional, gate electrode near the molecule. The advantage of this method in comparison with STM-IETS is that there is contact between both electrodes and the adsorbate, whereas in STM-IETS there is always a tunneling gap between the tip and the adsorbate. The disadvantage of this method is that it is experimentally very challenging to create and identify a junction with exactly one molecule between the electrodes.