Abstract
We demonstrate the information on molecular vibrational modes via the second derivative (d2IB/dV2) of the ballistic electron emission spectroscopy (BEES) current. The proposed methoddoes not create huge fields as in the case of conventional derivative spectroscopy andmaintains a zero bias across the device. BEES studies carried out on three different types oflarge polycyclic aromatic hydrocarbon (PAH) molecular layers show that thed2IB/dV2 spectra consist of uniformly spaced peaks corresponding to vibronic excitations. The peakspacing is found to be identical for molecules within the same PAH family though theBEES onset voltage varies for different molecules. In addition, injection into a particularorbital appears to correspond to a specific vibrational mode as the manifestation of thesymmetry principle.
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