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We have investigated the efficiency and limits of polarization dependent
hard X-ray photoelectron spectroscopy (HAXPES) in order to establish how
well this method can be used to unravel quantitatively the contributions
of the orbitals forming the valence band of solids. By rotating the
energy analyzer rather than the polarization vector of the light using a
phase retarder, we obtained the advantage that the full polarization of
the light is available for the investigation. Using NiO, ZnO, and Cu2O
as examples for solid state materials, we established that the
polarization dependence is much larger than in photoemission experiments
utilizing ultra-violet or soft X-ray light. Yet we also have discovered
that the polarization dependence is less than complete on the basis of
atomic calculations, strongly suggesting that the trajectories of the
outgoing electrons are affected by appreciable side-scattering processes
even at these high kinetic energies. We have found in our experiment
that these can be effectively described as a directional spread of +/-
18 degrees of the photoelectrons. This knowledge allows us to identify,
for example, reliably the Ni 3d spectral weight of the NiO valence band
and at the same time to demonstrate the importance of the Ni 4s for the
chemical stability of the compound. (C) 2014 Elsevier B.V. All rights
reserved.
