Electron energy loss spectra of NTCDA organic films

The electron energy loss (EEL) spectra of thin NTCDA films on the ZnO(0001) surface were measured. In the low-energy range (<60 eV), the EEL spectra (displaying the characteristic loss peaks at Eloss=4.0, 5.6, 12.5, and 14.5 eV) reflect the structure of transitions between the valence and conduction bands. As the primary electron energy increases, the dominating energy losses are due to the excitation of plasma oscillations at ħω1=6.5 eV (π plasmon) and ħω2=25 eV (π−σ plasmon).