Dutoi Group @ University of the Pacific


Excitonic Coupled Cluster	X-ray Photoelectron Background	Time-resolved X-ray Spectroscopy	Ultrafast Electron Dynamics

One elementary open problem in the electronic structure theory of solids is the source of extra background electrons in x-ray photoelectron spectroscopy. Removal of this background component is phenomenologically understood, and it must be done for compositional analysis. However, its contribution to the total electron flux is not accounted for by direct cross-sections, and its shape is not accounted for by energy losses as electrons traverse the solid. In collaboration with an experimental group, we proposed an interesting many-body effect by which some of the total flux can be accounted for by a kind of intensity borrowing from a deeper core polarization; energy losses to the valence from this transient local oscillator give an unusual background shape. This hypothesis is supported well by the experiments of our collaborators. We are now working on an approach to semi-quantitative (trend-predictive) simulation.

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25. Intensity Modulation of the Shirley Background of the Cr 3p spectra with Photon Energies around the Cr 2p Edge

A. Herrera-Gomez, D. Cabrera-German, A. D. Dutoi, M. Vazquez-Lepe, S. Aguirre-Tostado, P. Pianetta, D. Nordlund, O. Cortazar-Martinez, A. Torres-Ochoa, O. Ceballos-Sanchez and L. Gomez-Muñoz [Surf. Interface Anal. 50 246 (2018)]

The background in X-ray photoelectron spectroscopy data originates, partially, from inelastically scattered photoelectrons. In fact, the current theoretical methods for calculating the background intensity are based on electron energy losses. However, a critical part of the experimental signal, which is known as the Shirley background, cannot be described within the current formalisms. This suggests that the Shirley electrons are not associated with energy losses of photoelectrons and must originate from a different photoexcitation phenomenon with a cross section of its own. We propose a mechanism based on core channeling as the physical origin of the Shirley signal.