Electronic excitation spectrum of doped organic thin films investigated using electron energy-loss spectroscopy

Highlights: • Determination of electronic excitation spectra of picene and chrysene single crystals. • Observation of a series of singlet excitons for both materials. • Excitons are localized. • Successful potassium intercalation of both materials. • Observation of a plasmon around 1.5 eV with negative dispersion for doped picene and chrysene. - Abstract: The electronic excitation spectra of undoped, and potassium as well as calcium doped phenanthrene-type hydrocarbons have been investigated using electron energy-loss spectroscopy (EELS) in transmission. In the undoped materials, the lowest energy excitations are excitons with a relatively high binding energy. These excitons also are rather localized as revealed by their vanishing dispersion. Upon doping, new low energy excitation features appear in the former gaps of the materials under investigation. In K₃picene and K₃chrysene they are characterized by a negative dispersion while in Ca₃picene they are dispersionless.