Generalization of the post-collision interaction effect from gas-phase to solid-state systems demonstrated in thiophene and its polymers

Abstract

We demonstrate experimentally and theoretically the presence of the post-collision interaction (PCI) effect in sulfur ${\mathrm{KL}}_{2,3}{\mathrm{L}}_{2,3}$ Auger electron spectra measured in the gas-phase thiophene and in solid-state organic polymers: polythiophene (PT) and poly(3-hexylthiophene-2,5-diyl), commonly known as P3HT. PCI manifests itself through a distortion and a blueshift of the normal Auger S ${\mathrm{KL}}_{2,3}{\mathrm{L}}_{2,3}$ spectrum when S $1s$ ionization occurs close to the ionization threshold. Our investigation shows that the PCI-induced shift of the Auger spectra is stronger in the solid-state polymers than in the gas-phase organic molecule. Theoretical modeling within the framework of the eikonal approximation provides good agreement with the experimental observations. In a solid medium, two effects influence the interaction between the photoelectron and the Auger electron. In detail, stronger PCI in the polymers is attributed to the photoelectron scattering in the solid, which overcompensates the polarization screening of electron charges which causes a reduction of the interaction. Our paper demonstrates the general nature of the PCI effect occurring in different media.