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Electronic correlations in inner-shell ionized molecules can be probed via Auger spectroscopy. After a high-energy photon ionizes the atomic core shell close to ionization threshold, a slow photoelectron leaves the atom, not without interacting with the ionic field. Decay may take place via emission of an Auger electron, with which the photoelectron may interact. This Coulombic interaction between the three parties is known as post-collision interaction (PCI). From a classical perspective, PCI occurs due to an energy exchange between the ejected Auger electron, photoelectron and the remaining ion. PCI visibly affects photoelectron and Auger spectra in two characteristic ways: the energy distribution represented by the lineshape, becomes distorted, and the position of the lines in the energy spectrum may shift considerably $^1$.
PCI has been extensively studied in gaseous systems, such as argon $^2$ and carbonyl sulfide (OCS) $^3$. However, little is known on manifestation of PCI in solid systems. Using the HAXPES experimental end-station installed at the GALAXIES beamline of the SOLEIL French synchrotron facility $^4$, we measured high-resolution KLL Auger spectra at photon energies between 0 and 200 eV above the sulfur 1s ionization threshold of an aromatic thiophene molecule in the gas phase, and the thiophene-based π-conjugated polymer poly(3-hexylthiophene-2,5-diyl), known as P3HT, prepared as a film.
A stronger PCI shift was observed in P3HT compared to thiophene, which can be tentatively explained by the screening of the photoelectron field in P3HT, considering the dielectric constant of the polymer and the photoelectron retardation within the polymer.
$^1$ Kuchiev et al. https://doi.org/10.1070/PU1989v032n07ABEH002731
$^2$ Guillemin et al. http://dx.doi.org/10.1103/PhysRevA.92.012503
$^3$ Bomme et al. https://doi.org/10.1088/0953-4075/46/21/215101
$^4$ Céolin et al. http://dx.doi.org/10.1016/j.elspec.2013.01.006
