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

TL;DR

This study uses electron energy-loss spectroscopy to analyze how doping affects the electronic excitation spectra of phenantrene-type hydrocarbons, revealing new low-energy excitations and their dispersion characteristics.

Contribution

It provides new insights into the doping-induced changes in excitation spectra and dispersion behavior in organic thin films using EELS.

Findings

Doped materials exhibit new low-energy excitation features.

Excitons in undoped materials are highly localized with high binding energy.

Doping alters dispersion properties of excitations, showing negative dispersion or dispersionless behavior.

Abstract

The electronic excitation spectra of undoped, and potassium as well as calcium doped phenantrene-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 K$_3$picene and K$_3$chrysene they are characterized by a negative dispersion while in Ca$_3$picene they are dispersionless.