Observation and resonant x-ray optical interpretation of multi-atom resonant photoemission effects in O 1s emission from NiO

TL;DR

This study investigates multi-atom resonant photoemission effects in NiO using experimental measurements and theoretical modeling, revealing how incidence angle and polarization influence the observed resonances and their agreement with optical calculations.

Contribution

It provides a detailed analysis of the angular and polarization dependence of MARPE effects in NiO and validates resonant x-ray optical calculations against experimental data.

Findings

Strong MARPE effects at grazing incidence that diminish with angle

Resonant x-ray optical calculations accurately predict observed effects

Polarization changes significantly enhance MARPE effects in NiO

Abstract

We present experimental and theoretical results for the variation of the O 1s intensity from a NiO(001) surface as the excitation energy is varied through the Ni 2p1/2,3/2 absorption resonances, and as the incidence angle of the radiation is varied from grazing to larger values. For grazing incidence, a strong multi-atom resonant photoemission (MARPE) effect is seen on the O 1s intensity as the Ni 2p resonances are crossed, but its magnitude decreases rapidly as the incidence angle is increased. Resonant x-ray optical (RXRO) calculations are found to predict these effects very well, although the experimental effects are found to decrease at higher incidence angles faster than those in theory. The potential influence of photoelectron diffraction effects on such measurements are also considered, including experimental data with azimuthal-angle variation and corresponding multiple-scattering-diffraction calculations, but we conclude that they do not vary beyond what is expected on the basis of the change in photoelectron kinetic energy. Varying from linear polarization to circular polarization is found to enhance these effects in NiO considerably, although the reasons are not clear. We also discuss the relationship of these measurements to other related interatomic resonance experiments and theoretical developments, and make some suggestions for future studies in this area.