Vibrational properties of perfluoropentacene thin film

We have studied the vibrational properties of perfluoropentacene (PFP) thin films on highly oriented pyrolytic graphite (HOPG) substrates by high-resolution electron energy loss spectroscopy (HREELS) and Raman spectroscopy. The HREELS spectra showed slight but clear increase in the vibrational energies with increasing film thickness as well as with decreasing temperature of the multilayer films. In the polarization-dependent Raman spectra of a multilayer film, the depolarization ratios of all detected vibrations with the Ag irreducible representation were found to be larger than 1, indicating that the molecular structure is distorted in the multilayer. Both results suggest that there is a fairly strong intermolecular interaction in PFP multilayer films.